ORIGINAL ARTICLE: HEPATOLOGY
AND
NUTRITION
Effect of Fat- and Carbohydrate-Rich Diets on Metabolism and Running Performance in Trained Adolescent Boys
Patricia Guimaraes Couto, yHessel Marani Lima, zRuda Pinheiro Soares, Romulo Bertuzzi, z Fernando Roberto De-Oliveira, and yAdriano Eduardo Lima-Silva
ABSTRACT Objectives: A randomized crossover trial was designed to analyze the impact of a short-term, isoenergetic fat-rich or carbohydrate (CHO)-rich diet on substrate oxidation rates during submaximal exercise and on performance in a 10,000-m running time trial in trained, mid- to late-pubertal boys. Methods: An incremental test was performed to determine the peak oxygen uptake (VO2peak). After 2 days on a fat-rich (24.2% 0.8% CHO, 60.4% 0.3% fat, and 15.5% 1.0% protein), CHO-rich (69.3% 1.2% CHO, 15.9% 2.1% fat, and 15.1% 1.1% protein), or habitual (56.1% 7.0% CHO, 27.5% 4.9% fat, and 16.5% 4.0% protein) diet, 19 trained adolescent boys (15.2 1.5 years) performed a 10-minute constant run at 65% VO2peak to determine the respiratory exchange ratio (RER) during exercise and 10,000-m running on an outdoor track. Results: During the constant run, the RER and CHO contribution to energy expenditure were lower, and fat contribution higher, in the fat-rich diet than in the CHO-rich diet (P < 0.05), but the results were not different from those of the habitual diet. Performance in the 10,000-m run after consuming CHO- and fat-rich diets was similar to performance after a habitual diet (50.0 7.0, 51.9 8.3, and 50.9 7.4 minutes, respectively), but consuming a CHO-rich diet enhanced performance compared with that after a fat-rich diet (P ¼ 0.03). Conclusions: These findings indicate that a CHO-rich diet provides additional benefits to 10,000-m running performance in trained adolescent boys compared with a fat-rich diet. Key Words: aerobic exercise, children, dietary manipulation, running, substrate oxidation
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t has been widely reported that young boys have a larger oxidative capacity and oxidize greater amounts of fat throughout a wide range of exercise intensities when compared with adults (1,2). Oxidative capacity and fat oxidation amount are inversely Received January 10, 2014; accepted April 30, 2014. From the Endurance Performance Research Group, School of Physical Education and Sport, University of Sa˜o Paulo, Sa˜o Paulo, the ySport Science Research Group, Department of Physical Education and Sports Science (CAV), Federal University of Pernambuco and Federal University of Alagoas, Alagoas, and the zHuman Movement Studies Group, Physical Education Department, Federal University of Lavras, Lavras, Brazil. Address correspondence and reprint requests to Patricia Guimaraes Couto, Endurance Performance Research Group, School of Physical Education and Sport, University of Sa˜o Paulo, Prof Mello de Morais Ave, 65, Sa˜o Paulo 05508-030, Brazil (e-mail: [email protected]). The authors report no conflicts of interest. Copyright # 2014 by European Society for Pediatric Gastroenterology, Hepatology, and Nutrition and North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition DOI: 10.1097/MPG.0000000000000427
related to maturation and reduce progressively with the growth (1–4). When exogenous (orally ingested) carbohydrate (CHO) is consumed either before or during exercise, children and adolescent boys (ages 9–17 years) have considerably higher oxidation rates of exogenous CHO when compared with adult men, which lead to a greater contribution to the total energy expended from this source (4–6). Therefore, young boys have a well-developed capacity to oxidize both fat and CHO during exercise, but CHO is preferably selected when exogenous CHO is provided at a sufficient rate. Although it has been demonstrated that exogenous CHO ingestion increases CHO oxidation in young boys, previous studies investigating the effects of exogenous CHO on performance have produced conflicting results. For example, Hendelman et al (7) have found that preexercise CHO snacks (fig or candy bar) had no effect on respiratory gases, heart rate, blood glucose, and lactate concentrations measured during 75 minutes of cycling at 60% VO2max or on performance during high-intensity exercise (2500-m cycling time trial) in 14- to 16-year-old adolescent boys. In contrast, Riddell et al (8) showed a delayed time to exhaustion at 90% of maximal power output after young boys (age ranging from 10 to 14 years and Tanner stage from 2 to 4) had ingested glucose plus fructose solution or only glucose at 15-minute intervals during a previous 90-minute exercise at 55% VO2max compared with placebo ingestion. It is difficult to compare these results because they included different timing of feedings and forms of CHO. It should also be noted that these studies used a high (>90% VO2max) exercise intensity, whereas CHO ingestion may be more closely associated with performance when the exercise duration is 45 minutes or longer (9,10). Although it has been shown that short-term diet manipulation (from 1 to 3 days) increases CHO oxidation and benefits performance in adults (10,11), its effects on both substrate oxidation and performance in young boys remain unknown. In adults, it has been largely demonstrated that a short-term CHO-rich diet (70%–80% of CHO) elevates preexercise liver and muscle glycogen contents and increases muscle glycogen utilization during exercise, resulting in improved endurance performance (10,11). In contrast, a short-term fat-rich diet (60%–70% of fat) markedly increases fat oxidation and reduces CHO utilization during exercise (12). It also appears that a short-term fat-rich diet impairs performance in adults (13). Nevertheless, although largely investigated in adults, the effect of shortterm diet manipulation on exercise performance in young boys has not been investigated. Instead, studies in the present literature using young people (9–17 years) have examined the effect of acute preexercise CHO ingestion (4–8), which could provoke different metabolic and physiological alterations than short-term diet manipulation. Thus, it is unclear whether dietary intervention would be beneficial or harmful to performance in young boys. Therefore, the purpose of the present study was to investigate the influence of short-term CHO- and fat-rich diets on substrate oxidation during submaximal exercise and on running performance
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in a prolonged, high-intensity exercise in trained, mid- to latepubertal boys. Based on results from studies investigating the effects of CHO- and fat-rich diets in adults (10,11,13), we hypothesized that a short-term CHO-rich diet would increase CHO oxidation and performance and that a short-term fat-rich diet would have the opposite effect.
METHODS Participants A total of 20 adolescent boys (15.2 1.5 years) volunteered to participate in the present study. All of the participants were physically active, had been engaged in daily athletic training program for 2.5 years (general athletic training program), and were familiar with running on an athletics track. Their characteristics are summarized in Table 1. The present study was conducted according to the guidelines in the Declaration of Helsinki, and all procedures involving participants were approved by the ethics committee of the Federal University of Alagoas. Written informed consent was obtained from all of their guardians. Because of a muscle injury, the data from 1 participant were excluded from the statistical analysis. Thus, the statistical analysis was performed for the remaining 19 boys who completed all trials.
Design Each participant visited the laboratory to be measured for height, body mass, body fat, and pubertal stages. Body fat was estimated from triceps and subscapular skinfold thickness (14). The pubertal status of the boys was self-assessed and based on pubic hair development according to Tanner (15), a method that has proven valid and reproducible among boys (16). Based on this information, the participants were set as prepubertal if the pubic hair was classified as 1, early pubertal if it was 2, and mid- to late pubertal if the pubic hair ranged from 3 to 5 (6). All 20 adolescent boys enrolled in the present study were classified as mid- to late pubertal (Table 1). Thereafter, each subject participated in 3 experimental trials performed 7 to 14 days apart, in a randomized and repeatedmeasures crossover design. The experimental trials were identical, except for meal composition 48 hours before each trial (habitual, CHO-, or fat-rich diet).
Initial Testing To become familiar with the testing procedures, each participant performed a familiarization run on a treadmill (Explorer
ProAction, BH Fitness, Vitoria-Gasteiz, Spain). This allowed them to experience different exercise stages, increasing speed and breathing into the metabolic mouthpiece. A total of 48 hours after the familiarization session, peak oxygen uptake (VO2peak) was determined during a progressive exercise test until exhaustion. The test began at 8 km/h for 4 minutes, and the speed was increased by 1 km/h every 1 minute. The incline was set at 3% during the entire test. Measurements of the oxygen uptake (VO2), carbon dioxide output (VCO2), respiratory exchange ratio (RER), and pulmonary ventilation (VE) were made continuously every 10 seconds using open-circuit spirometry (PowerLab 4/30, ADInstruments, Bella Vista, Australia). The participants received verbal encouragement throughout the test. VO2peak was calculated from the average of the values in the last 30 seconds of the incremental test. The highest speed achieved during the test was recorded as Speedmax. When participants were not able to complete the last stage, the Speedmax was calculated using the following equation (17): TLIS Speedmax ¼ LCS þ 60 where LCS is the speed in the last complete stage, TLIS is the time in seconds sustained on the last incomplete stage, and 60 is the length of each stage in seconds.
Assessment and Dietary Manipulation Participants registered all of the foods consumed for 4 days (type, amount, and hour) using a food diary. After determining the subjects’ daily energy consumption from their food diaries, the individual isoenergetic CHO- and fat-rich diets were prepared and monitored by a dietitian from our laboratory. Participants followed a standardized fat-rich diet (25% CHO, 60% lipids, and 15% protein), CHO-rich diet (70% CHO, 15% lipids, and 15% protein), or replication of their habitual diet for 48 hours before the experimental trials. All foods were prepackaged before being offered to the participants. The diets were isoenergetic in accordance with the reported habitual diet of each participant. Training schedule was recuperative during the 48 hours of diet manipulation (low intensity, without running bouts or lower limb training). The training schedule was recorded and then replicated in the 48 hours before each subsequent experimental test session. During all of the experimental periods, participants trained and ate all of their meals at the university center under the supervision of a researcher from our laboratory who was not directly involved in the present study.
Experimental Trials TABLE 1. Participants’ characteristics
Age, y Height, m Body mass, kg Body fat, % Pubertal status Speedmax, km/h VO2peak, L/min VO2peak, mL kg1 min1 HRmax, bpm
Mean
SEM
15.2 1.71 59.9 14.0 4 16.6 3.6 61.8 208
0.3 0.02 3.5 0.8 3–5 0.3 0.2 2.7 2
HRmax ¼ maximal heart rate reached during the incremental test; SEM ¼ standard error of the mean; Speedmax ¼ maximal speed reached during the incremental test; VO2peak ¼ peak oxygen uptake. Pubertal status is reported as the median and range.
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After each diet period, the participants performed an experimental trial. All of the tests were performed at the same time of day, in the afternoon. Participants remained lying for 5 minutes and then performed a constant steady-state run for 10 minutes at a speed requiring 65% of their predicted VO2peak to estimate substrate utilization (18). Gas exchange measurements were obtained at 10second intervals throughout the test using standard open-circuit spirometry techniques (PowerLab 4/30), and a metabolic software program calculated the averages of VO2, VCO2, RER, and VE (LabChart 7 Pro, ADInstruments). The average of the last 2 minutes of rest and exercise data was used for further analysis. The CHO and fat oxidation rates were calculated using nonprotein stoichiometric equations (19) and expressed relative to total energy expenditure. Protein energy contribution was assumed to be negligible (20). Each subject then individually completed a 10,000-m running performance test on an outdoor 400-m track. They were instructed to
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finish the race as quickly as possible and encouraged during the entire event by a laboratory staff member who was unaware of the objectives of the study. No feedback about time was provided to participants until the end of the study.
Statistical Analysis The data are presented as mean standard error of the mean, unless otherwise noted. The Shapiro-Wilk test was used to check normality. Diet nutrient composition data were non-normally distributed, and the Friedman test was used. Pairwise comparisons were made with a Wilcoxon matched-pairs test with a Bonferroni adjustment. The effects of maturation and age on dependent variables were analyzed using analysis of covariance, but no such effects were detected. The time and mean speed during the 10,000-m running race and VO2, VCO2, RER, VE, and fat and CHO oxidation at 65% VO2peak were then compared across the experimental categories using 1-way repeated-measures analyses of variance (21). The Mauchly test was used to determine sphericity. If any violation of the assumptions of sphericity was found, the degrees of freedom were corrected using Greenhouse-Geisser or Huynh-Feldt epsilon correction factors where appropriate. The Tukey honest significant difference post hoc test was used to identify significant differences when analysis of variance yielded a significant F-ratio. Polynomial contrasts were also used to test any trend in the treatment means. For all statistical comparisons, the significance level was set at P < 0.05 (2-sided). Analyses were performed using Statistical Package for the Social Sciences software version 13.0 (SPSS, Chicago, IL).
RESULTS Diet The performed diet in the 3 experimental conditions is displayed in Table 2. The percentage of CHO intake during the 2-day dietary intervention was significantly lower in the fat-rich diet (24.2% 0.8%) than in the CHO-rich diet (69.3% 1.2%) and the habitual diet (56.1% 7.0%). The habitual diet also provided a lower percentage of CHO than the CHO-rich diet (P ¼ 0.0001). In contrast, the percentage of dietary fat intake was significantly
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higher in the fat-rich diet (60.4% 0.3%) than either the CHOrich diet (15.9% 2.1%) or the habitual diet (27.5% 4.9%). The habitual diet also provided a higher percentage of fat intake than the CHO-rich diet (P ¼ 0.0001). Similar results were found when expressed in absolute values (kilojoules). The protein intake across the diets was similar in both absolute and relative terms. No differences were found in total energy intake among the diets (P ¼ 0.14).
Ventilatory and Metabolic Responses During Submaximal Exercise No differences in VO2, VCO2, VE, and total energy expenditure were found among the diets during rest or during submaximal exercise (Table 3). The RER values in rest and exercise were lower in the fat-rich diet than in the CHO-rich diet (P ¼ 0.01 and 0.02, respectively); RER in neither the fat-rich nor the CHO-rich diets differed from the habitual diet (Table 3). Similarly, the CHO contribution during exercise was significantly lower after consuming the fat-rich diet when compared with the CHO-rich diet (P ¼ 0.01). On the contrary, fat contribution was significantly higher after consuming the fat-rich diet when compared with the CHO-rich diet (P ¼ 0.01). Total energy contributions from CHO and fat were similar when both CHO- and fat-rich diets were compared with the habitual diet (Table 3).
10,000-m Running Performance The 10,000-m running times after the fat-rich, habitual, and CHO-rich diets averaged 51.9 8.3, 50.9 7.4, and 50.0 7.0 minutes, respectively. The 10,000-m run times were significantly faster under the CHO-rich diet condition than under the fat-rich diet condition (P ¼ 0.03). No significant differences were found between the fat-rich and habitual diets (P ¼ 0.35) or between the CHO-rich and habitual diets (P ¼ 0.46) (Fig. 1). A linear trend toward the times was observed in the 10-km run; times were 1.9% longer after the fat-rich diet and 1.7% shorter after the CHO-rich diet, when compared with those after the habitual diet (P ¼ 0.03). Similar results were found for the average speeds.
TABLE 2. Nutrient composition of the study diets Diet condition Fat rich
Energy intake, kJ/day CHO, kJ Fat, kJ Protein, kJ CHO, % Fat, % Protein, % CHO, kJ kg1 day1 Fat, kJ kg1 day1 Protein, kJ kg1 day1
Habitual
CHO rich
Mean
SEM
Mean
SEM
Mean
SEM
9851 2410 ,y 5944 ,y 1502 24.2 ,y 60.7 ,y 15.5 41.9 ,y 103.6 ,y 26.3
732 199 441 92 0.9 0.3 1.0 3.8 8.7 2.0
9537 5244y,z 2758y,z 1526 56.0y,z 27.5y,z 16.5 91.6y,z 47.7y,z 26.6
776 454 227 125 7.2 5.0 4.1 8.9 4.9 2.5
9924 6839 ,z 1607 ,z 1476 69.3 ,z 16.1 ,z 15.1 119.3 ,z 28.3 ,z 25.8
725 512 130 94 1.2 2.2 1.1 10.1 2.8 2.0
CHO ¼ carbohydrate. Significantly different from the habitual diet. y Significantly different from the CHO-rich diet. z Significantly different from the fat-rich diet.
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TABLE 3. Rest and exercise cardiorespiratory and metabolic variables under the experimental conditions Fat-rich diet Rest
VO2, L/min VCO2, L/min RER, units VE, L/min Total energy expenditure, kJ Fat, % energy expenditure CHO, % energy expenditure
Habitual diet
Exercise
Rest
CHO-rich diet
Exercise
Rest
Exercise
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
0.42 0.31 0.75 10.9 8.3 66.5 33.5
0.06 0.04 0.02 1.4 1.2 7.7 7.7
2.43 1.85 0.76 55.5 437.7 77.5 22.5
0.15 0.12 0.01 3.3 29.1 2.2 2.2
0.45 0.36 0.78 12.5 9.0 44.3 55.7
0.06 0.05 0.03 1.4 1.1 9.9 9.9
2.55 1.97 0.77 58.2 436.9 74.0 26.0
0.16 0.10 0.01 3.4 26.1 2.4 2.4
0.42 0.35 0.83 11.5 7.8 50.7 49.3
0.05 0.04 0.01 1.1 1.1 6.6 6.6
2.61 2.07 0.79y 60.1 448.6 66.1y 33.9y
0.15 0.13 0.01 2.6 21.3 2.5 2.5
CHO ¼ carbohydrate; RER ¼ respiratory exchange ratio; SEM ¼ standard error of the mean; VE ¼ pulmonary ventilation; VCO2 ¼ carbon dioxide output; VO2 ¼ oxygen uptake. Significantly different from the fat-rich diet at rest. y Significantly different from the fat-rich diet during exercise.
DISCUSSION The main purpose of the present study was to investigate the influence of short-term CHO- and fat-rich diets on substrate oxidation and running performance during a 10,000-m running trial in trained, mid- to late-pubertal boys. To analyze the effect of altering the dietary CHO and fat intake on the CHO and fat contributions to the energy expenditure during a submaximal exercise and on running performance during a 10,000-m running race, 2 extreme profiles of diet composition (CHO- and fat-rich) were analyzed in the present study. We found that the CHO-rich diet increased CHO energy contribution compared with the fat-rich diet during submaximal exercise, whereas the fat-rich diet increased fat energy contribution compared with the CHO-rich diet. In addition, although performance in a 10,000-m running trial was unchanged when compared with the habitual diet, the CHO-rich diet resulted in an improved performance when compared with the fat-rich diet. In the present study, the CHO-rich diet provided a significantly higher CHO content than the fat-rich and habitual diets. On the contrary, the fat-rich diet had a higher fat content than either the CHOrich or habitual diet. Nonetheless, we successfully produced 3 representative diet conditions on an ‘‘increasing continuum’’ for the CHO content in each diet (24%, 56%, and 69% of CHO for the fatrich, habitual, and CHO-rich diets, respectively), with a corresponding ‘‘decreasing continuum’’ of the fat contents (60.7%, 27.5%, and 16.1%, respectively). In addition, the diets were isoenergetic (habitual 9537 776 kJ/day, CHO-rich diet 9924 725 kJ/day, and 54.0
Time (min)
53.0
*
52.0 51.0 50.0 49.0 48.0 Fat rich
Habitual
CHO rich
FIGURE 1. Running times for the 10,000-m running performance after the fat-rich, habitual, and CHO-rich diets. () CHO-rich diet is significantly lower than the fat-rich diet.
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fat-rich diet 9851 732 kJ/day; P ¼ 0.14). Therefore, manipulation of the diet enabled us to successfully verify the effect of different CHO and fat contents in the diet on both substrate contributions to the energy expenditure and exercise performance in adolescent boys. During constant running at moderate intensity (65% VO2peak), we found that the percentage of fat contribution to total energy expenditure was significantly higher after the fat-rich diet compared with that after the CHO-rich diet, but both were not different from that after the habitual diet. Previous studies showed that prepubertal and early pubertal boys are able to maintain high rates of fat oxidation during submaximal exercise (3,6), and that this higher relative contribution from fat persisted even when exogenous CHO was consumed during the exercise (4). This higher relative contribution from fat reduces progressively as maturation (1–4). In the present study, we have evaluated mid- to late-pubertal adolescent boys who must have had a reduced influence of the maturation on substrate oxidation. Despite the fact that advanced pubertal development is associated with a decrease in fat oxidation rate during exercise (2,3,6), it is noteworthy that our participants were trained and engaged in a regular training program, showing an elevated VO2peak (62 mL kg1 min1), which is higher than that predicted for a normal population of boys of the same age. It has been demonstrated that trained boys demonstrated an enhanced fat oxidation rate during submaximal exercise when compared with untrained boys (22). Therefore, the engagement in a training program seems to preserve the elevated fat oxidation rate during submaximal exercise observed in prepubertal and early pubertal boys, taking into account that our adolescent boys were able to maintain an elevated fat oxidation rate, mainly when they consumed a diet rich in fat. The mechanism controlling a higher fat oxidation with a high-fat diet in adolescent boys is unclear, but it may be attributed to the decreased release of liver-derived glucose into the circulation, a greater provision of nonesterified fatty acids, a larger reliance on intramyocellular lipids for oxidation, and extended fatty acid transport into mitochondria (23,24). CHO energy contribution was similar after short-term CHOrich and habitual diets. When compared with the fat-rich diet, increased CHO contribution to energy expenditure was observed after the CHO-rich diet. In addition, CHO contribution increased proportional to the CHO content in the diet. Our findings are partially consistent with the results from previous studies in adults, in which elevated CHO availability resulted in a greater CHO contribution (9–11) and also consistent with findings in boys ages 9 to 17 years, in which CHO ingestion increased CHO oxidation and led to a greater contribution to the total energy expended (4,6,8). It
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Guimaraes Couto et al has also been suggested that additional dietary CHO intakes may compensate for naturally lower CHO reserve in young boys (24). Results of the present study suggest that a 2-day, CHO-rich diet is sufficient to increase CHO contribution during exercise compared with an isoenergetic fat-rich diet. Hence, it seems that CHO and fat contributions seem to alter according to the main substrate provided by diet in trained, mid- to late-pubertal boys. It is noteworthy that CHO oxidation rates during neither the CHO-rich diet nor the fat-rich diet were different from those during the habitual diet. This suggests that an alteration in CHO oxidation rate is observed only when the extremes in a continuous of CHO diet content are compared. Although neither the CHO-rich nor the fat-rich diet affected the performance times in 10,000-m running trial compared with the habitual diet, the participants’ performance did improve after consuming a CHO-rich diet compared with performance after a fat-rich diet. It is worth noting that there was a linear trend showing that faster times were a function of an increase in the amount of dietary CHO consumed (1 minute faster in a CHO-rich diet and 1 minute slower in a fat-rich diet, both compared with a habitual diet). To the best of our knowledge, the present study is the first one showing that performance after a short-term CHO-rich diet is improved in trained, mid- to late-pubertal boys when compared with a fat-rich diet (1.9 minutes faster). In the same direction, although using younger boys than in the present study, Riddell et al (8) found that acute CHO ingestion (glucose or glucose plus fructose) during a previous exercise (90 minutes at 55% VO2max) increased exercise capacity during a subsequent cycling bout at 90% of maximal power output in 10- to 14-year-old boys, when compared with placebo. Although CHO ingestion has beneficial effects on performance, the mechanisms for this improvement are not fully understood (25). It should also be noted that although running times were 1.7% shorter after the CHO-rich diet compared those after the habitual diet, this was not statistically significant, so the performance benefits of this diet are only present when compared with a fat-rich diet. The fact that we also found similar performance among subjects consuming the fat-rich and habitual diets was somewhat surprising. In adults, a short-term high-fat diet actually impairs performance as a result of the inability for fat oxidation replenishment at the same rate as the energy requirement from high-intensity exercise (7). This conflicting result may have been because of greater fat contribution in youths compared with that in adults (1–4). Some studies have suggested that young boys have reduced muscle glycogen content and reduced release of hepatic-derived glucose than do adults (2,24,26). Youth seem to counterbalance the negative effects of reduced CHO availability by their increased transport of and higher oxidation rate for free fatty acids (14,23). It seems to be supported by the elevated fat contribution during the submaximal exercise in trained adolescent boys found in the present study (Table 3), when compared with data reported in the literature for adults (3). Because our participants were trained, mid- to latepubertal boys, it could be argued that performance may not have been affected after a short fat-rich diet period when compared with the habitual diet because participants in the present study already have a well-developed capacity to oxidize fat during exercise because of their conditioning level, which may sufficiently replenish the energy they require. When compared with a CHO-rich diet, performance was significantly diminished in subjects consuming a fat-rich diet, suggesting that increasing additional exogenous CHO may play a larger role in performance improvement than fat intake does. On the contrary, the potential harmfulness of the fat-rich diet is not clear when compared with a habitual diet, so its negative biological effect on performance is only apparent when compared with a CHO-rich diet.
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The present study has some limitations. It should be mentioned that participants of the present study were adolescent boys in mid- to late-puberty stages. Several studies showed a greater fat oxidation in prepubertal boys than in postpuberty stages (2). Therefore, differences in the performance between the diets may have been larger if prepubertal boys had been recruited. Furthermore, we assessed CHO and fat contributions in single-exercise intensity. Considering that many factors could influence fat and CHO oxidation rate such as intensity, duration, and mode of exercise, and habitual physical activity and aerobic capacity, it would have been difficult to cover all of these factors in a single study. In conclusion, the results of the present investigation demonstrated that a CHO-rich diet increases the CHO contribution to energy expenditure during a submaximal exercise, whereas a fat-rich diet increases fat contribution in trained, mid- to late-pubertal boys. Although neither the fat-rich nor the CHO-rich diet affected the 10,000-m running performance when compared with the habitual diet, increasing CHO intake with a short-term CHO-rich diet results in increased performance when compared with a fat-rich diet. Acknowledgments: The authors thank the participants for their enthusiastic participation throughout the study. The authors also thank Carla C. de Souza and Pedro Bigardi for technical assistance. P.G.C. is grateful to Coordination for the Improvement of Higher Education Personnel, Ministry of Education, Brazil, for the scholarship.
REFERENCES 1. Tonson A, Ratel S, Le Fur Y, et al. Muscle energetics changes throughout maturation: a quantitative 31P-MRS analysis. J Appl Physiol 2010; 109:1769–78. 2. Riddell MC, Jamnik VK, Iscoe KE, et al. Fat oxidation rate and the exercise intensity that elicits maximal fat oxidation decreases with pubertal status in young male subjects. J Appl Physiol 2008;105:742–8. 3. Stephens BR, Cole AS, Mahon AD. The influence of biological maturation on fat and carbohydrate metabolism during exercise in males. Int J Sport Nutr Exerc Metab 2006;16:166–79. 4. Timmons BW, Bar-Or O, Riddell MC. Oxidation rate of exogenous carbohydrate during exercise is higher in boys than in men. J Appl Physiol 2003;94:278–84. 5. Riddell MC, Bar-Or O, Schwarcz HP, et al. Substrate utilization in boys during exercise with (13C)-glucose ingestion. Eur J Appl Physiol 2000;83:441–8. 6. Timmons BW, Bar-Or O, Riddell MC. Influence of age and pubertal status on substrate utilization during exercise with and without carbohydrate intake in healthy boys. Appl Physiol Nutr Metab 2007;32:416– 25. 7. Hendelman DL, Ornstein K, Debold EP, et al. Preexercise feeding in untrained adolescent boys does not affect responses to endurance exercise or performance. Int J Sport Nutr 1997;7:207–18. 8. Riddell MC, Bar-Or O, Wilk B, et al. Substrate utilization during exercise with glucose and glucose plus fructose ingestion in boys ages 10–14 yr. J Appl Physiol 2001;90:903–11. 9. Jeukendrup A, Brouns F, Wagenmakers AJM, et al. Carbohydrateelectrolyte feedings improve 1 h time trial cycling performance. Int J Sports Med 1997;18:125–9. 10. Jeukendrup AE, Jentjens R. Oxidation of carbohydrate feedings during prolonged exercise: current thoughts, guidelines and directions for future research. Sports Med 2000;29:407–24. 11. Bergstrom J, Hermansen L, Hultman E, et al. Diet, muscle glycogen and physical performance. Acta Paediatr Scand 1967;71:140–50. 12. Phinney SD, Bistrianb BR, Evansc WJ, et al. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism 1983;32:769–76. 13. Burke LM, Hawley JA. Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. Med Sci Sports Exerc 2002;34:1492–8.
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Effect of Fat-/Carbohydrate-Rich Diets in Trained Adolescent Boys
14. Slaughter MH, Lohman TG, Boileau RA, et al. Skinfold equations for estimation of body fatness in children and youth. Hum Biol 1988; 60:709–23. 15. Tanner JM. Growth at Adolescence. Oxford, UK: Blackwell Scientific; 1962. 16. Matsudo SM, Matsudo VK. Self-assessment and physician assessment of sexual maturation in Brazilian boys and girls: concordance and reproducibility. Am J Hum Biol 1994;6:451–5. 17. Kuipers H, Verstappen FTJ, Keizer HA, et al. Variability of aerobic performance in the laboratory and its physiological correlates. Int J Sports Med 1985;6:197–201. 18. Boisseau N, Delamarche P. Metabolic and hormonal responses to exercise in children and adolescents. Sports Med 2000;30:405–22. 19. Pe´ronnet F, Massicotte D. Table of nonprotein respiratory quotient: an update. Can J Sport Sci 1991;16:23–9.
20. Jeukendrup AE, Saris WHM, Wagenmakers AJM. Fat metabolism during exercise: a review—part I: fatty acid mobilization and muscle metabolism. Int J Sports Med 1998;19:231–44. 21. Field A. Discovering Statistics With SPSS. 2nd ed. London: Sage Publications; 2005. 22. Duncan GE, Howley ET. Metabolic and perceptual responses to shortterm cycle training in children. Pediatr Exerc Sci 1998;10:110–22. 23. Aucouturier J, Baker JS, Duche´ P. Fat and carbohydrate metabolism during submaximal exercise in children. Sports Med 2008;38:213–38. 24. Riddell MC. The endocrine response and substrate utilization during exercise in children and adolescents. J Appl Physiol 2008;105:725–33. 25. Karelis AD, Smith JW, Passe DH, et al. Carbohydrate administration and exercise performance. What are the potential mechanisms involved? Sports Med 2010;40:747–63. 26. Eriksson B, Saltin B. Muscle metabolism during exercise in boys aged 11 to 16 years compared to adults. Acta Paediatr Belg 1974;28:257–65.
Dewees on Colic William Dewees (1768–1841) wrote the first truly comprehensive and authoritative American pediatric work in 1826, A Treatise of the Physical and Medical Treatment of Children. There were 8 editions of this popular, straightforward, and practical guide to child care. Of colic he wrote: Owing to improper feeding, or the peculiar quality of the mother’s milk, or perhaps in some instances to the particular constitution of the child, it becomes liable to severe attacks of pain in the bowels, which continue for several hours, with great suffering to the poor infant. . .the child may be seized at any time of the day . . .perhaps diarrhea, with green stools, is produced, or it may not have too many evacuations, but they are evidently the remains of ill-digested food. . . its little abdomen becomes swoln (sic) and tense, and it writhes its body as if in the utmost agony. It sometimes becomes suddenly relieved, by eructating a considerable quantity of wind; or it passes downwards, carrying with it a very small portion of faeces. A Treatise of the Physical and Medical Treatment of Children, p. 292
Portrait of William Dewees (1768–1841), by John Neagle (courtesy Wikimedia Commons) —Contributed by Angel R. Colo´n, MD
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AND
NUTRITION
Effect of Fat- and Carbohydrate-Rich Diets on Metabolism and Running Performance in Trained Adolescent Boys
Patricia Guimaraes Couto, yHessel Marani Lima, zRuda Pinheiro Soares, Romulo Bertuzzi, z Fernando Roberto De-Oliveira, and yAdriano Eduardo Lima-Silva
ABSTRACT Objectives: A randomized crossover trial was designed to analyze the impact of a short-term, isoenergetic fat-rich or carbohydrate (CHO)-rich diet on substrate oxidation rates during submaximal exercise and on performance in a 10,000-m running time trial in trained, mid- to late-pubertal boys. Methods: An incremental test was performed to determine the peak oxygen uptake (VO2peak). After 2 days on a fat-rich (24.2% 0.8% CHO, 60.4% 0.3% fat, and 15.5% 1.0% protein), CHO-rich (69.3% 1.2% CHO, 15.9% 2.1% fat, and 15.1% 1.1% protein), or habitual (56.1% 7.0% CHO, 27.5% 4.9% fat, and 16.5% 4.0% protein) diet, 19 trained adolescent boys (15.2 1.5 years) performed a 10-minute constant run at 65% VO2peak to determine the respiratory exchange ratio (RER) during exercise and 10,000-m running on an outdoor track. Results: During the constant run, the RER and CHO contribution to energy expenditure were lower, and fat contribution higher, in the fat-rich diet than in the CHO-rich diet (P < 0.05), but the results were not different from those of the habitual diet. Performance in the 10,000-m run after consuming CHO- and fat-rich diets was similar to performance after a habitual diet (50.0 7.0, 51.9 8.3, and 50.9 7.4 minutes, respectively), but consuming a CHO-rich diet enhanced performance compared with that after a fat-rich diet (P ¼ 0.03). Conclusions: These findings indicate that a CHO-rich diet provides additional benefits to 10,000-m running performance in trained adolescent boys compared with a fat-rich diet. Key Words: aerobic exercise, children, dietary manipulation, running, substrate oxidation
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I
t has been widely reported that young boys have a larger oxidative capacity and oxidize greater amounts of fat throughout a wide range of exercise intensities when compared with adults (1,2). Oxidative capacity and fat oxidation amount are inversely Received January 10, 2014; accepted April 30, 2014. From the Endurance Performance Research Group, School of Physical Education and Sport, University of Sa˜o Paulo, Sa˜o Paulo, the ySport Science Research Group, Department of Physical Education and Sports Science (CAV), Federal University of Pernambuco and Federal University of Alagoas, Alagoas, and the zHuman Movement Studies Group, Physical Education Department, Federal University of Lavras, Lavras, Brazil. Address correspondence and reprint requests to Patricia Guimaraes Couto, Endurance Performance Research Group, School of Physical Education and Sport, University of Sa˜o Paulo, Prof Mello de Morais Ave, 65, Sa˜o Paulo 05508-030, Brazil (e-mail: [email protected]). The authors report no conflicts of interest. Copyright # 2014 by European Society for Pediatric Gastroenterology, Hepatology, and Nutrition and North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition DOI: 10.1097/MPG.0000000000000427
related to maturation and reduce progressively with the growth (1–4). When exogenous (orally ingested) carbohydrate (CHO) is consumed either before or during exercise, children and adolescent boys (ages 9–17 years) have considerably higher oxidation rates of exogenous CHO when compared with adult men, which lead to a greater contribution to the total energy expended from this source (4–6). Therefore, young boys have a well-developed capacity to oxidize both fat and CHO during exercise, but CHO is preferably selected when exogenous CHO is provided at a sufficient rate. Although it has been demonstrated that exogenous CHO ingestion increases CHO oxidation in young boys, previous studies investigating the effects of exogenous CHO on performance have produced conflicting results. For example, Hendelman et al (7) have found that preexercise CHO snacks (fig or candy bar) had no effect on respiratory gases, heart rate, blood glucose, and lactate concentrations measured during 75 minutes of cycling at 60% VO2max or on performance during high-intensity exercise (2500-m cycling time trial) in 14- to 16-year-old adolescent boys. In contrast, Riddell et al (8) showed a delayed time to exhaustion at 90% of maximal power output after young boys (age ranging from 10 to 14 years and Tanner stage from 2 to 4) had ingested glucose plus fructose solution or only glucose at 15-minute intervals during a previous 90-minute exercise at 55% VO2max compared with placebo ingestion. It is difficult to compare these results because they included different timing of feedings and forms of CHO. It should also be noted that these studies used a high (>90% VO2max) exercise intensity, whereas CHO ingestion may be more closely associated with performance when the exercise duration is 45 minutes or longer (9,10). Although it has been shown that short-term diet manipulation (from 1 to 3 days) increases CHO oxidation and benefits performance in adults (10,11), its effects on both substrate oxidation and performance in young boys remain unknown. In adults, it has been largely demonstrated that a short-term CHO-rich diet (70%–80% of CHO) elevates preexercise liver and muscle glycogen contents and increases muscle glycogen utilization during exercise, resulting in improved endurance performance (10,11). In contrast, a short-term fat-rich diet (60%–70% of fat) markedly increases fat oxidation and reduces CHO utilization during exercise (12). It also appears that a short-term fat-rich diet impairs performance in adults (13). Nevertheless, although largely investigated in adults, the effect of shortterm diet manipulation on exercise performance in young boys has not been investigated. Instead, studies in the present literature using young people (9–17 years) have examined the effect of acute preexercise CHO ingestion (4–8), which could provoke different metabolic and physiological alterations than short-term diet manipulation. Thus, it is unclear whether dietary intervention would be beneficial or harmful to performance in young boys. Therefore, the purpose of the present study was to investigate the influence of short-term CHO- and fat-rich diets on substrate oxidation during submaximal exercise and on running performance
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in a prolonged, high-intensity exercise in trained, mid- to latepubertal boys. Based on results from studies investigating the effects of CHO- and fat-rich diets in adults (10,11,13), we hypothesized that a short-term CHO-rich diet would increase CHO oxidation and performance and that a short-term fat-rich diet would have the opposite effect.
METHODS Participants A total of 20 adolescent boys (15.2 1.5 years) volunteered to participate in the present study. All of the participants were physically active, had been engaged in daily athletic training program for 2.5 years (general athletic training program), and were familiar with running on an athletics track. Their characteristics are summarized in Table 1. The present study was conducted according to the guidelines in the Declaration of Helsinki, and all procedures involving participants were approved by the ethics committee of the Federal University of Alagoas. Written informed consent was obtained from all of their guardians. Because of a muscle injury, the data from 1 participant were excluded from the statistical analysis. Thus, the statistical analysis was performed for the remaining 19 boys who completed all trials.
Design Each participant visited the laboratory to be measured for height, body mass, body fat, and pubertal stages. Body fat was estimated from triceps and subscapular skinfold thickness (14). The pubertal status of the boys was self-assessed and based on pubic hair development according to Tanner (15), a method that has proven valid and reproducible among boys (16). Based on this information, the participants were set as prepubertal if the pubic hair was classified as 1, early pubertal if it was 2, and mid- to late pubertal if the pubic hair ranged from 3 to 5 (6). All 20 adolescent boys enrolled in the present study were classified as mid- to late pubertal (Table 1). Thereafter, each subject participated in 3 experimental trials performed 7 to 14 days apart, in a randomized and repeatedmeasures crossover design. The experimental trials were identical, except for meal composition 48 hours before each trial (habitual, CHO-, or fat-rich diet).
Initial Testing To become familiar with the testing procedures, each participant performed a familiarization run on a treadmill (Explorer
ProAction, BH Fitness, Vitoria-Gasteiz, Spain). This allowed them to experience different exercise stages, increasing speed and breathing into the metabolic mouthpiece. A total of 48 hours after the familiarization session, peak oxygen uptake (VO2peak) was determined during a progressive exercise test until exhaustion. The test began at 8 km/h for 4 minutes, and the speed was increased by 1 km/h every 1 minute. The incline was set at 3% during the entire test. Measurements of the oxygen uptake (VO2), carbon dioxide output (VCO2), respiratory exchange ratio (RER), and pulmonary ventilation (VE) were made continuously every 10 seconds using open-circuit spirometry (PowerLab 4/30, ADInstruments, Bella Vista, Australia). The participants received verbal encouragement throughout the test. VO2peak was calculated from the average of the values in the last 30 seconds of the incremental test. The highest speed achieved during the test was recorded as Speedmax. When participants were not able to complete the last stage, the Speedmax was calculated using the following equation (17): TLIS Speedmax ¼ LCS þ 60 where LCS is the speed in the last complete stage, TLIS is the time in seconds sustained on the last incomplete stage, and 60 is the length of each stage in seconds.
Assessment and Dietary Manipulation Participants registered all of the foods consumed for 4 days (type, amount, and hour) using a food diary. After determining the subjects’ daily energy consumption from their food diaries, the individual isoenergetic CHO- and fat-rich diets were prepared and monitored by a dietitian from our laboratory. Participants followed a standardized fat-rich diet (25% CHO, 60% lipids, and 15% protein), CHO-rich diet (70% CHO, 15% lipids, and 15% protein), or replication of their habitual diet for 48 hours before the experimental trials. All foods were prepackaged before being offered to the participants. The diets were isoenergetic in accordance with the reported habitual diet of each participant. Training schedule was recuperative during the 48 hours of diet manipulation (low intensity, without running bouts or lower limb training). The training schedule was recorded and then replicated in the 48 hours before each subsequent experimental test session. During all of the experimental periods, participants trained and ate all of their meals at the university center under the supervision of a researcher from our laboratory who was not directly involved in the present study.
Experimental Trials TABLE 1. Participants’ characteristics
Age, y Height, m Body mass, kg Body fat, % Pubertal status Speedmax, km/h VO2peak, L/min VO2peak, mL kg1 min1 HRmax, bpm
Mean
SEM
15.2 1.71 59.9 14.0 4 16.6 3.6 61.8 208
0.3 0.02 3.5 0.8 3–5 0.3 0.2 2.7 2
HRmax ¼ maximal heart rate reached during the incremental test; SEM ¼ standard error of the mean; Speedmax ¼ maximal speed reached during the incremental test; VO2peak ¼ peak oxygen uptake. Pubertal status is reported as the median and range.
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After each diet period, the participants performed an experimental trial. All of the tests were performed at the same time of day, in the afternoon. Participants remained lying for 5 minutes and then performed a constant steady-state run for 10 minutes at a speed requiring 65% of their predicted VO2peak to estimate substrate utilization (18). Gas exchange measurements were obtained at 10second intervals throughout the test using standard open-circuit spirometry techniques (PowerLab 4/30), and a metabolic software program calculated the averages of VO2, VCO2, RER, and VE (LabChart 7 Pro, ADInstruments). The average of the last 2 minutes of rest and exercise data was used for further analysis. The CHO and fat oxidation rates were calculated using nonprotein stoichiometric equations (19) and expressed relative to total energy expenditure. Protein energy contribution was assumed to be negligible (20). Each subject then individually completed a 10,000-m running performance test on an outdoor 400-m track. They were instructed to
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finish the race as quickly as possible and encouraged during the entire event by a laboratory staff member who was unaware of the objectives of the study. No feedback about time was provided to participants until the end of the study.
Statistical Analysis The data are presented as mean standard error of the mean, unless otherwise noted. The Shapiro-Wilk test was used to check normality. Diet nutrient composition data were non-normally distributed, and the Friedman test was used. Pairwise comparisons were made with a Wilcoxon matched-pairs test with a Bonferroni adjustment. The effects of maturation and age on dependent variables were analyzed using analysis of covariance, but no such effects were detected. The time and mean speed during the 10,000-m running race and VO2, VCO2, RER, VE, and fat and CHO oxidation at 65% VO2peak were then compared across the experimental categories using 1-way repeated-measures analyses of variance (21). The Mauchly test was used to determine sphericity. If any violation of the assumptions of sphericity was found, the degrees of freedom were corrected using Greenhouse-Geisser or Huynh-Feldt epsilon correction factors where appropriate. The Tukey honest significant difference post hoc test was used to identify significant differences when analysis of variance yielded a significant F-ratio. Polynomial contrasts were also used to test any trend in the treatment means. For all statistical comparisons, the significance level was set at P < 0.05 (2-sided). Analyses were performed using Statistical Package for the Social Sciences software version 13.0 (SPSS, Chicago, IL).
RESULTS Diet The performed diet in the 3 experimental conditions is displayed in Table 2. The percentage of CHO intake during the 2-day dietary intervention was significantly lower in the fat-rich diet (24.2% 0.8%) than in the CHO-rich diet (69.3% 1.2%) and the habitual diet (56.1% 7.0%). The habitual diet also provided a lower percentage of CHO than the CHO-rich diet (P ¼ 0.0001). In contrast, the percentage of dietary fat intake was significantly
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higher in the fat-rich diet (60.4% 0.3%) than either the CHOrich diet (15.9% 2.1%) or the habitual diet (27.5% 4.9%). The habitual diet also provided a higher percentage of fat intake than the CHO-rich diet (P ¼ 0.0001). Similar results were found when expressed in absolute values (kilojoules). The protein intake across the diets was similar in both absolute and relative terms. No differences were found in total energy intake among the diets (P ¼ 0.14).
Ventilatory and Metabolic Responses During Submaximal Exercise No differences in VO2, VCO2, VE, and total energy expenditure were found among the diets during rest or during submaximal exercise (Table 3). The RER values in rest and exercise were lower in the fat-rich diet than in the CHO-rich diet (P ¼ 0.01 and 0.02, respectively); RER in neither the fat-rich nor the CHO-rich diets differed from the habitual diet (Table 3). Similarly, the CHO contribution during exercise was significantly lower after consuming the fat-rich diet when compared with the CHO-rich diet (P ¼ 0.01). On the contrary, fat contribution was significantly higher after consuming the fat-rich diet when compared with the CHO-rich diet (P ¼ 0.01). Total energy contributions from CHO and fat were similar when both CHO- and fat-rich diets were compared with the habitual diet (Table 3).
10,000-m Running Performance The 10,000-m running times after the fat-rich, habitual, and CHO-rich diets averaged 51.9 8.3, 50.9 7.4, and 50.0 7.0 minutes, respectively. The 10,000-m run times were significantly faster under the CHO-rich diet condition than under the fat-rich diet condition (P ¼ 0.03). No significant differences were found between the fat-rich and habitual diets (P ¼ 0.35) or between the CHO-rich and habitual diets (P ¼ 0.46) (Fig. 1). A linear trend toward the times was observed in the 10-km run; times were 1.9% longer after the fat-rich diet and 1.7% shorter after the CHO-rich diet, when compared with those after the habitual diet (P ¼ 0.03). Similar results were found for the average speeds.
TABLE 2. Nutrient composition of the study diets Diet condition Fat rich
Energy intake, kJ/day CHO, kJ Fat, kJ Protein, kJ CHO, % Fat, % Protein, % CHO, kJ kg1 day1 Fat, kJ kg1 day1 Protein, kJ kg1 day1
Habitual
CHO rich
Mean
SEM
Mean
SEM
Mean
SEM
9851 2410 ,y 5944 ,y 1502 24.2 ,y 60.7 ,y 15.5 41.9 ,y 103.6 ,y 26.3
732 199 441 92 0.9 0.3 1.0 3.8 8.7 2.0
9537 5244y,z 2758y,z 1526 56.0y,z 27.5y,z 16.5 91.6y,z 47.7y,z 26.6
776 454 227 125 7.2 5.0 4.1 8.9 4.9 2.5
9924 6839 ,z 1607 ,z 1476 69.3 ,z 16.1 ,z 15.1 119.3 ,z 28.3 ,z 25.8
725 512 130 94 1.2 2.2 1.1 10.1 2.8 2.0
CHO ¼ carbohydrate. Significantly different from the habitual diet. y Significantly different from the CHO-rich diet. z Significantly different from the fat-rich diet.
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TABLE 3. Rest and exercise cardiorespiratory and metabolic variables under the experimental conditions Fat-rich diet Rest
VO2, L/min VCO2, L/min RER, units VE, L/min Total energy expenditure, kJ Fat, % energy expenditure CHO, % energy expenditure
Habitual diet
Exercise
Rest
CHO-rich diet
Exercise
Rest
Exercise
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
0.42 0.31 0.75 10.9 8.3 66.5 33.5
0.06 0.04 0.02 1.4 1.2 7.7 7.7
2.43 1.85 0.76 55.5 437.7 77.5 22.5
0.15 0.12 0.01 3.3 29.1 2.2 2.2
0.45 0.36 0.78 12.5 9.0 44.3 55.7
0.06 0.05 0.03 1.4 1.1 9.9 9.9
2.55 1.97 0.77 58.2 436.9 74.0 26.0
0.16 0.10 0.01 3.4 26.1 2.4 2.4
0.42 0.35 0.83 11.5 7.8 50.7 49.3
0.05 0.04 0.01 1.1 1.1 6.6 6.6
2.61 2.07 0.79y 60.1 448.6 66.1y 33.9y
0.15 0.13 0.01 2.6 21.3 2.5 2.5
CHO ¼ carbohydrate; RER ¼ respiratory exchange ratio; SEM ¼ standard error of the mean; VE ¼ pulmonary ventilation; VCO2 ¼ carbon dioxide output; VO2 ¼ oxygen uptake. Significantly different from the fat-rich diet at rest. y Significantly different from the fat-rich diet during exercise.
DISCUSSION The main purpose of the present study was to investigate the influence of short-term CHO- and fat-rich diets on substrate oxidation and running performance during a 10,000-m running trial in trained, mid- to late-pubertal boys. To analyze the effect of altering the dietary CHO and fat intake on the CHO and fat contributions to the energy expenditure during a submaximal exercise and on running performance during a 10,000-m running race, 2 extreme profiles of diet composition (CHO- and fat-rich) were analyzed in the present study. We found that the CHO-rich diet increased CHO energy contribution compared with the fat-rich diet during submaximal exercise, whereas the fat-rich diet increased fat energy contribution compared with the CHO-rich diet. In addition, although performance in a 10,000-m running trial was unchanged when compared with the habitual diet, the CHO-rich diet resulted in an improved performance when compared with the fat-rich diet. In the present study, the CHO-rich diet provided a significantly higher CHO content than the fat-rich and habitual diets. On the contrary, the fat-rich diet had a higher fat content than either the CHOrich or habitual diet. Nonetheless, we successfully produced 3 representative diet conditions on an ‘‘increasing continuum’’ for the CHO content in each diet (24%, 56%, and 69% of CHO for the fatrich, habitual, and CHO-rich diets, respectively), with a corresponding ‘‘decreasing continuum’’ of the fat contents (60.7%, 27.5%, and 16.1%, respectively). In addition, the diets were isoenergetic (habitual 9537 776 kJ/day, CHO-rich diet 9924 725 kJ/day, and 54.0
Time (min)
53.0
*
52.0 51.0 50.0 49.0 48.0 Fat rich
Habitual
CHO rich
FIGURE 1. Running times for the 10,000-m running performance after the fat-rich, habitual, and CHO-rich diets. () CHO-rich diet is significantly lower than the fat-rich diet.
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fat-rich diet 9851 732 kJ/day; P ¼ 0.14). Therefore, manipulation of the diet enabled us to successfully verify the effect of different CHO and fat contents in the diet on both substrate contributions to the energy expenditure and exercise performance in adolescent boys. During constant running at moderate intensity (65% VO2peak), we found that the percentage of fat contribution to total energy expenditure was significantly higher after the fat-rich diet compared with that after the CHO-rich diet, but both were not different from that after the habitual diet. Previous studies showed that prepubertal and early pubertal boys are able to maintain high rates of fat oxidation during submaximal exercise (3,6), and that this higher relative contribution from fat persisted even when exogenous CHO was consumed during the exercise (4). This higher relative contribution from fat reduces progressively as maturation (1–4). In the present study, we have evaluated mid- to late-pubertal adolescent boys who must have had a reduced influence of the maturation on substrate oxidation. Despite the fact that advanced pubertal development is associated with a decrease in fat oxidation rate during exercise (2,3,6), it is noteworthy that our participants were trained and engaged in a regular training program, showing an elevated VO2peak (62 mL kg1 min1), which is higher than that predicted for a normal population of boys of the same age. It has been demonstrated that trained boys demonstrated an enhanced fat oxidation rate during submaximal exercise when compared with untrained boys (22). Therefore, the engagement in a training program seems to preserve the elevated fat oxidation rate during submaximal exercise observed in prepubertal and early pubertal boys, taking into account that our adolescent boys were able to maintain an elevated fat oxidation rate, mainly when they consumed a diet rich in fat. The mechanism controlling a higher fat oxidation with a high-fat diet in adolescent boys is unclear, but it may be attributed to the decreased release of liver-derived glucose into the circulation, a greater provision of nonesterified fatty acids, a larger reliance on intramyocellular lipids for oxidation, and extended fatty acid transport into mitochondria (23,24). CHO energy contribution was similar after short-term CHOrich and habitual diets. When compared with the fat-rich diet, increased CHO contribution to energy expenditure was observed after the CHO-rich diet. In addition, CHO contribution increased proportional to the CHO content in the diet. Our findings are partially consistent with the results from previous studies in adults, in which elevated CHO availability resulted in a greater CHO contribution (9–11) and also consistent with findings in boys ages 9 to 17 years, in which CHO ingestion increased CHO oxidation and led to a greater contribution to the total energy expended (4,6,8). It
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Guimaraes Couto et al has also been suggested that additional dietary CHO intakes may compensate for naturally lower CHO reserve in young boys (24). Results of the present study suggest that a 2-day, CHO-rich diet is sufficient to increase CHO contribution during exercise compared with an isoenergetic fat-rich diet. Hence, it seems that CHO and fat contributions seem to alter according to the main substrate provided by diet in trained, mid- to late-pubertal boys. It is noteworthy that CHO oxidation rates during neither the CHO-rich diet nor the fat-rich diet were different from those during the habitual diet. This suggests that an alteration in CHO oxidation rate is observed only when the extremes in a continuous of CHO diet content are compared. Although neither the CHO-rich nor the fat-rich diet affected the performance times in 10,000-m running trial compared with the habitual diet, the participants’ performance did improve after consuming a CHO-rich diet compared with performance after a fat-rich diet. It is worth noting that there was a linear trend showing that faster times were a function of an increase in the amount of dietary CHO consumed (1 minute faster in a CHO-rich diet and 1 minute slower in a fat-rich diet, both compared with a habitual diet). To the best of our knowledge, the present study is the first one showing that performance after a short-term CHO-rich diet is improved in trained, mid- to late-pubertal boys when compared with a fat-rich diet (1.9 minutes faster). In the same direction, although using younger boys than in the present study, Riddell et al (8) found that acute CHO ingestion (glucose or glucose plus fructose) during a previous exercise (90 minutes at 55% VO2max) increased exercise capacity during a subsequent cycling bout at 90% of maximal power output in 10- to 14-year-old boys, when compared with placebo. Although CHO ingestion has beneficial effects on performance, the mechanisms for this improvement are not fully understood (25). It should also be noted that although running times were 1.7% shorter after the CHO-rich diet compared those after the habitual diet, this was not statistically significant, so the performance benefits of this diet are only present when compared with a fat-rich diet. The fact that we also found similar performance among subjects consuming the fat-rich and habitual diets was somewhat surprising. In adults, a short-term high-fat diet actually impairs performance as a result of the inability for fat oxidation replenishment at the same rate as the energy requirement from high-intensity exercise (7). This conflicting result may have been because of greater fat contribution in youths compared with that in adults (1–4). Some studies have suggested that young boys have reduced muscle glycogen content and reduced release of hepatic-derived glucose than do adults (2,24,26). Youth seem to counterbalance the negative effects of reduced CHO availability by their increased transport of and higher oxidation rate for free fatty acids (14,23). It seems to be supported by the elevated fat contribution during the submaximal exercise in trained adolescent boys found in the present study (Table 3), when compared with data reported in the literature for adults (3). Because our participants were trained, mid- to latepubertal boys, it could be argued that performance may not have been affected after a short fat-rich diet period when compared with the habitual diet because participants in the present study already have a well-developed capacity to oxidize fat during exercise because of their conditioning level, which may sufficiently replenish the energy they require. When compared with a CHO-rich diet, performance was significantly diminished in subjects consuming a fat-rich diet, suggesting that increasing additional exogenous CHO may play a larger role in performance improvement than fat intake does. On the contrary, the potential harmfulness of the fat-rich diet is not clear when compared with a habitual diet, so its negative biological effect on performance is only apparent when compared with a CHO-rich diet.
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The present study has some limitations. It should be mentioned that participants of the present study were adolescent boys in mid- to late-puberty stages. Several studies showed a greater fat oxidation in prepubertal boys than in postpuberty stages (2). Therefore, differences in the performance between the diets may have been larger if prepubertal boys had been recruited. Furthermore, we assessed CHO and fat contributions in single-exercise intensity. Considering that many factors could influence fat and CHO oxidation rate such as intensity, duration, and mode of exercise, and habitual physical activity and aerobic capacity, it would have been difficult to cover all of these factors in a single study. In conclusion, the results of the present investigation demonstrated that a CHO-rich diet increases the CHO contribution to energy expenditure during a submaximal exercise, whereas a fat-rich diet increases fat contribution in trained, mid- to late-pubertal boys. Although neither the fat-rich nor the CHO-rich diet affected the 10,000-m running performance when compared with the habitual diet, increasing CHO intake with a short-term CHO-rich diet results in increased performance when compared with a fat-rich diet. Acknowledgments: The authors thank the participants for their enthusiastic participation throughout the study. The authors also thank Carla C. de Souza and Pedro Bigardi for technical assistance. P.G.C. is grateful to Coordination for the Improvement of Higher Education Personnel, Ministry of Education, Brazil, for the scholarship.
REFERENCES 1. Tonson A, Ratel S, Le Fur Y, et al. Muscle energetics changes throughout maturation: a quantitative 31P-MRS analysis. J Appl Physiol 2010; 109:1769–78. 2. Riddell MC, Jamnik VK, Iscoe KE, et al. Fat oxidation rate and the exercise intensity that elicits maximal fat oxidation decreases with pubertal status in young male subjects. J Appl Physiol 2008;105:742–8. 3. Stephens BR, Cole AS, Mahon AD. The influence of biological maturation on fat and carbohydrate metabolism during exercise in males. Int J Sport Nutr Exerc Metab 2006;16:166–79. 4. Timmons BW, Bar-Or O, Riddell MC. Oxidation rate of exogenous carbohydrate during exercise is higher in boys than in men. J Appl Physiol 2003;94:278–84. 5. Riddell MC, Bar-Or O, Schwarcz HP, et al. Substrate utilization in boys during exercise with (13C)-glucose ingestion. Eur J Appl Physiol 2000;83:441–8. 6. Timmons BW, Bar-Or O, Riddell MC. Influence of age and pubertal status on substrate utilization during exercise with and without carbohydrate intake in healthy boys. Appl Physiol Nutr Metab 2007;32:416– 25. 7. Hendelman DL, Ornstein K, Debold EP, et al. Preexercise feeding in untrained adolescent boys does not affect responses to endurance exercise or performance. Int J Sport Nutr 1997;7:207–18. 8. Riddell MC, Bar-Or O, Wilk B, et al. Substrate utilization during exercise with glucose and glucose plus fructose ingestion in boys ages 10–14 yr. J Appl Physiol 2001;90:903–11. 9. Jeukendrup A, Brouns F, Wagenmakers AJM, et al. Carbohydrateelectrolyte feedings improve 1 h time trial cycling performance. Int J Sports Med 1997;18:125–9. 10. Jeukendrup AE, Jentjens R. Oxidation of carbohydrate feedings during prolonged exercise: current thoughts, guidelines and directions for future research. Sports Med 2000;29:407–24. 11. Bergstrom J, Hermansen L, Hultman E, et al. Diet, muscle glycogen and physical performance. Acta Paediatr Scand 1967;71:140–50. 12. Phinney SD, Bistrianb BR, Evansc WJ, et al. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism 1983;32:769–76. 13. Burke LM, Hawley JA. Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. Med Sci Sports Exerc 2002;34:1492–8.
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Effect of Fat-/Carbohydrate-Rich Diets in Trained Adolescent Boys
14. Slaughter MH, Lohman TG, Boileau RA, et al. Skinfold equations for estimation of body fatness in children and youth. Hum Biol 1988; 60:709–23. 15. Tanner JM. Growth at Adolescence. Oxford, UK: Blackwell Scientific; 1962. 16. Matsudo SM, Matsudo VK. Self-assessment and physician assessment of sexual maturation in Brazilian boys and girls: concordance and reproducibility. Am J Hum Biol 1994;6:451–5. 17. Kuipers H, Verstappen FTJ, Keizer HA, et al. Variability of aerobic performance in the laboratory and its physiological correlates. Int J Sports Med 1985;6:197–201. 18. Boisseau N, Delamarche P. Metabolic and hormonal responses to exercise in children and adolescents. Sports Med 2000;30:405–22. 19. Pe´ronnet F, Massicotte D. Table of nonprotein respiratory quotient: an update. Can J Sport Sci 1991;16:23–9.
20. Jeukendrup AE, Saris WHM, Wagenmakers AJM. Fat metabolism during exercise: a review—part I: fatty acid mobilization and muscle metabolism. Int J Sports Med 1998;19:231–44. 21. Field A. Discovering Statistics With SPSS. 2nd ed. London: Sage Publications; 2005. 22. Duncan GE, Howley ET. Metabolic and perceptual responses to shortterm cycle training in children. Pediatr Exerc Sci 1998;10:110–22. 23. Aucouturier J, Baker JS, Duche´ P. Fat and carbohydrate metabolism during submaximal exercise in children. Sports Med 2008;38:213–38. 24. Riddell MC. The endocrine response and substrate utilization during exercise in children and adolescents. J Appl Physiol 2008;105:725–33. 25. Karelis AD, Smith JW, Passe DH, et al. Carbohydrate administration and exercise performance. What are the potential mechanisms involved? Sports Med 2010;40:747–63. 26. Eriksson B, Saltin B. Muscle metabolism during exercise in boys aged 11 to 16 years compared to adults. Acta Paediatr Belg 1974;28:257–65.
Dewees on Colic William Dewees (1768–1841) wrote the first truly comprehensive and authoritative American pediatric work in 1826, A Treatise of the Physical and Medical Treatment of Children. There were 8 editions of this popular, straightforward, and practical guide to child care. Of colic he wrote: Owing to improper feeding, or the peculiar quality of the mother’s milk, or perhaps in some instances to the particular constitution of the child, it becomes liable to severe attacks of pain in the bowels, which continue for several hours, with great suffering to the poor infant. . .the child may be seized at any time of the day . . .perhaps diarrhea, with green stools, is produced, or it may not have too many evacuations, but they are evidently the remains of ill-digested food. . . its little abdomen becomes swoln (sic) and tense, and it writhes its body as if in the utmost agony. It sometimes becomes suddenly relieved, by eructating a considerable quantity of wind; or it passes downwards, carrying with it a very small portion of faeces. A Treatise of the Physical and Medical Treatment of Children, p. 292
Portrait of William Dewees (1768–1841), by John Neagle (courtesy Wikimedia Commons) —Contributed by Angel R. Colo´n, MD
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