International Journal of Sport Nutrition and Exercise Metabolism, 2015, 25, 471  -479 http://dx.doi.org/10.1123/ijsnem.2014-0231 © 2015 Human Kinetics, Inc.

ORIGINAL RESEARCH

Hydration Status and Sodium Balance of Endurance Runners Consuming Postexercise Supplements of Varying Nutrient Content J. Luke Pryor, Evan C. Johnson, Jeffery Del Favero, Andrew Monteleone, Lawrence E. Armstrong, and Nancy R. Rodriguez Postexercise protein and sodium supplementation may aid recovery and rehydration. Preserved beef provides protein and contains high quantities of sodium that may alter performance related variables in runners. The purpose of this study was to determine the effects of consuming a commercial beef product postexercise on sodium and water balance. A secondary objective was to characterize effects of the supplementation protocols . on hydration, blood pressure, body mass, and running economy. Eight trained males (age = 22 ± 3 y, VO2max = 66.4 ± 4.2 ml·kg-1·min-1) completed three identical weeks of run training (6 run·wk-1, 45 ± 6 min·run-1, 74 ± 5% HRR). After exercise, subjects consumed either, a beef nutritional supplement (beef jerky; [B]), a standard recovery drink (SRD), or SRD+B in a randomized counterbalanced design. Hydration status was assessed via urinary biomarkers and body mass. No main effects of treatment were observed for 24 hr urine volume (SRD, 1.7 ± 0.5; B, 1.8 ± 0.6; SRD+B, 1.4 ± 0.4 L·d-1), urine specific gravity (1.016 ± 0.005, 1.018 ± 0.006, 1.017 ± 0.006) or body mass (68.4 ± 8.2, 68.3 ± 7.7, 68.2 ± 8.1 kg). No main effect of treatment existed for sodium intake—loss (-713 ± 1486; -973 ± 1123; -980 ± 1220 mg·d-1). . Mean arterial pressure (81.0 ± 4.6, 81.1 ± 7.3, 83.8 ± 5.4 mm Hg) and average exercise running economy (VO2: SRD, 47.9 ± 3.2; B, 47.2 ± 2.6; SRD+B, 46.2 ± 3.4 ml·kg-1·min-1) was not affected. Urinary sodium excretion accounted for the daily sodium intake due to the beef nutritional supplement. Findings suggest the commercial beef snack is a viable recovery supplement following endurance exercise without concern for hydration status, performance decrements, or cardiovascular consequences. Keywords: beef jerky, protein, sodium, rehydration, running economy Recovery nutrition for endurance athletes is becoming more comprehensive, expanding beyond fluid, electrolytes, and carbohydrate, with a focus on protein (Breen et al., 2011; Hansen et al., 2014; Lunn et al., 2012). Studies have targeted proteins of high biological value. Of particular interest is the essential branched chain amino acid leucine, which is a known nutrient signal for stimulating protein synthesis (Gran & Cameron-Smith, 2011; Pasiakos et al., 2011). The potential for beef jerky (B) to fit this criterion for a post endurance exercise supplement is founded on its high leucine content. However, B is a commercial product that contains relatively high amounts of sodium in the context of the recommended dietary reference intake (DRI) for sodium (49% of DRI) (Institute of Medicine Food and Nutrition Pryor, Johnson, Del Favero, Monteleone, and Armstrong are with the Human Performance Laboratory, Dept. of Kinesiology, and Rodriguez the Dept. of Nutritional Sciences, University of Connecticut, Storrs, CT. Address author correspondence to J. Luke Pryor at [email protected].

Board, 2005). Therefore, if athletes were to habitually consume B following an endurance exercise bout, total body sodium and/or water balance could be affected due to the influence of sodium on fluid retention (Heer et al., 2000; Heer et al., 2009; Kojima et al., 1987; Sagnella et al., 1989; Singer et al., 1994). Alterations in sodium and water balance may impact markers of hydration status, running economy, and blood pressure which affect running performance in endurance athletes. First, increases in dietary protein (Martin et al., 2006) and sodium (Maughan & Leiper, 1995) have been shown to increase urine specific gravity, a marker of hydration status (Voinescu et al., 2002). Second, some (Heer et al., 2009; Kojima et al., 1987; Sagnella et al., 1989; Singer et al., 1994) but not all studies (Drummer et al., 2000; Heer et al., 2000; Heer et al., 2009) have shown that fluid retention due to increased sodium ingestion may increase body mass, a common measure to determine euhydration and acute dehydration (Cheuvront et al., 2004; Cheuvront et al., 2010). Third, the metabolic cost (Kcal·min-1) or running economy is linearly proportional to body mass (Mahadeva et al., 1953) and is vital for

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Subjects

optimal performance in runners. Increasing body mass by only 1 kg, possible with fluid retention resulting from B ingestion, could increase aerobic demand 1–14%, decreasing performance (Saunders et al., 2004). Finally, although controversial, reviews of well controlled clinical trials documented a causal association between chronically elevated sodium intake levels and high blood pressure (Mohan & Campbell, 2009; Dietary Guidelines Advisory Committee, 2010). In contrast, others suggest acute sodium ingestion is safe, except in salt-sensitive individuals (Komaroff, 2012; Stachenfled, 2008). Although there may be potential detrimental effects of elevated sodium intake, endurance athletes who typically lose > 2% of body mass during exercise should supplement with electrolytes in fluids to replace sweat losses (Shirreffs, 2001). Sodium loss rates of ~3 g·h-1 have been documented during outdoor exercise bouts (Bergeron, 2003) therefore sodium intake above the recommended DRI of 1.5 g·d-1 may be considered safe and necessary (Komaroff, 2012). Therefore, the purpose of this study was to determine the effects of daily postexercise consumption of B on markers of hydration, running economy, and blood pressure in trained male runners. We hypothesized that daily postexercise consumption of a beef-based nutritional supplement would not influence these variables compared with a standard recovery drink.

Eight trained, male runners volunteered to participated in this study (mean± SD; . age = 22 ± 3 years, maximal oxygen consumption ( VO2max) = 66.4 ± 4.2 ml·kg-1·min-1, estimated body fat = 7.4 ± 2.5%, height = 177 ± 6 cm, weight = 68.2 ± 7.9 kg, body mass .index = 22.9 ± 3.5 kg·m-2). Inclusionary criteria were:  VO2max > 50 ml·kg1·min-1, training 4–7 days·week-1 totaling ≥ 30 miles·wk-1, a history of running > 2 years, body mass index between 18–27 kg·m–2, and not following either a high protein (i.e., Atkins) or vegetarian diet. Subjects reported no current musculoskeletal injury, use of nutritional supplements or medications that could impact fluid-electrolyte balance, gastrointestinal disorders affecting absorption of nutrients, or kidney or metabolic disease at the time of testing. All risks and benefits were explained to the participants before the investigation. Each subject signed an informed consent document that was approved by the University’s institutional review board.

Procedures Before the first training cycle, .baseline measures of anthropometry, a dietary log,  VO . 2max, and treadmill running speed that elicited 70%  VO2max were recorded. . Individual values for VO2max and the running speed at . 70%  VO2max dictated the laboratory training during the first supplementation and training week. Subsequently, weeks two and three mirrored the training intensity and duration of week one to best replicate the physiological stress between iterations. For each supplementation and training week, the subject ran on five consecutive days consuming the specified recovery snack immediately after each workout ( .10) and average exercise intensity measured by percent heart rate reserve (B = 74.7 ± 0.1; SRD = 72.7 ± 0.1; SRD+B = 74.2 ± 0.1%, p > .15) were similar between supplement cycles. Water and sodium balance were similar between all supplement cycles (Figures 2 and 3). Water balance was not different from zero for all trials (p ≥ .11) while sodium balance was negative during the SRD+B trial (p = .044); however, no differences were observed when values were corrected for α of 0.017. Biomarkers of hydration status were similar between trials for 24 hr urine volume, Usg (Figure 4), and BM (Figure 5). All subjects were hydrated (Usg < 1.025) before laboratory training sessions. Significant associations were found between net urinary sodium loss and dietary sodium intake (r = .46; p = .03), urinary sodium concentration (r = .62; p < .01), and total body sodium balance (r = −.77, p < .01). Total fluid intake was significantly correlated with sweat rate (r = .70, p < .01) while fluid intake during laboratory exercise sessions was associated with sweat (r = −.85, p < .01) and urinary (r = .59, p < .01) sodium concentration and 24-hr urine volume (r = −.41, p = .047). No differences were observed between trials for systolic blood pressure (SRD = 113 ± 7; B = 112 ± 9; SRD+B = 115 ± 6 mm Hg; p = .78), diastolic blood pressure (SRD = 65 ± 5; B = 64 ± 7; SRD+B = 68 ± 7 mm Hg; p = .38) or MAP (SRD = 81.0 ± 4.6; B = 81.1 ± 7.3; SRD+B = 83.8 ± 5.4; p = .55). Resting HR was similar during all training cycles (SRD = 57 ± 7; B = 59 ± 5; SRD+B= 64 ± 6 bpm;

Table 2  Daily Dietary Intake for All Supplement Experiments SRD

Calories

Carbohydrate (g)

Protein (g)

Fat (g)

Sodium (mg)

Water (ml)

2552 ± 392

345 ± 73

102 ± 9

93 ± 22

4043 ± 772

2916 ± 694

B

2425 ± 338

313 ± 60

110 ±12

88 ± 23

4434 ± 1197

2945 ± 718

SRD+B

2476 ± 361

333 ± 58

108 ± 9

86 ± 23

4555 ± 498

2734 ± 532

Note. SRD = standard recovery drink, B = beef jerky. No change in nutrient intake between cycles was observed (p > .05).

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Beef Jerky and Water and Sodium Balance  475

Figure 2 — Water balance. Water balance = total fluid intake—average sweat loss—24 hr urine volume. SRD = standard recovery drink, B = beef nutritional supplement.

Figure 3 — Sodium balance. Sodium balance = dietary sodium intake—sweat sodium—24 hr urine sodium. SRD = standard recovery drink, B = beef nutritional supplement.

p = .15) despite additional sodium consumption with the beef nutritional supplement. Neither running economy nor metabolic cost changed between training cycles (p > .28) . as subjects matched oxygen consumption to 70%  VO2max during all laboratory workouts (p = .67) (Table 3).

Discussion We observed that sodium and water balance were not affected by daily postexercise consumption of B alone or in combination with the SRD. The degree of increase and the habitual level of sodium intake influenced the physiological regulation of sodium balance and water balance (Heer et al., 2009). Data from several studies have shown increasing chronic (5–10 d) daily salt intake from low (e.g., 16–2920.0 mg·d-1 [10–50 mEq·d-1] to high (>8046.5 mg·d-1 [567.1 mEq·d-1]) (Heer et al., 2009; Sagnella et al., 1989; Singer et al., 1994) or using a large dosage

(220 mEq·d-1 [5060 mg·d-1], equivalent to 100% of daily sodium intake) (Heer et al., 2000) results in sodium and water retention. In the current study, increasing sodium intake by 990 mg·d-1 or 43 mEq·d-1 through the addition of B + SRD, from a baseline sodium intake of 4043 ± 772 mg·d-1 or 175.8 ± 33.6 mEq·d-1 was not a sufficient osmotic stimulus to alter sodium or water balance. Participants baseline habitual sodium intake was high in the context of DRI (1.5 g·d-1) (Institute of Medicine, 2005) but consistent with the United States national average of 4.0 g·d-1 (Cogswell et al., 2012). The additional sodium consumed with the supplementation protocols did not change overall daily sodium intake. While this may be due to the large intra- and intersubject variation in habitual sodium intake, correlational analyses determined that net urinary sodium loss and osmolality were associated with dietary sodium intake. This suggests that the sodium in B was effectively managed through normal renal function via changes in tubular sodium reabsorption. This finding

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68.3 ±7.7

68.2 ± 8.1

B

SRD+B

620 ± 69

628 ± 36

659 ± 44 45.0 ± 5.0

46.5 ± 2.6

47.7 ± 3.2 71.8 ± 1.9

72.6 ± 1.8

71.9 ± 3.3

. % VO2max

647 ± 32

659 ± 45

667 ± 48 47.0 ± 2.3

47.8 ± 3.3

48.3 ± 3.5

2nd 40-min run . Kcal VO2

71.3 ± 25

72.0 ± 1.9

70.2 ± 3.5

. % VO2max

. Note. SRD = standard recovery drink, B = beef jerky, Kcal = kilocalories. VO2 (ml·kg-1·min-1) and speed (km·h-1) averaged over each training run.

68.4 ± 8.2

SRD

Weight (kg)

1st 40-min run . Kcal VO2

Table 3  Running Economy Measured During Laboratory Workouts Within Each Treatment

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644 ± 40

652 ± 28

659 ± 43

Kcal

60-min run

46.8 ± 2.9

47.3 ± 2.0

47.7 ± 3.1

. VO2

70.5 ± 3.7

70.9 ± 2.6

67.8 ± 6.7

. % VO2max

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Beef Jerky and Water and Sodium Balance  477

Figure 4 — Urinary markers of hydration. p > .05 between trials. SRD = standard recovery drink, B = beef nutritional supplement.

Figure 5 — Body mass. Black outlined bars represent means and individual subjects are represented by lines. p > .05 between trials. SRD = standard recovery drink, B = beef nutritional supplement.

is supported by previous work (Armstrong et al., 1993; Heer et al., 2000; Heer et al., 2009; Sagnella et al., 1989; Singer et al., 1994). No differences were observed in preexercise measures of BM or Usg despite the varying sodium and protein content and high exercise sweat volume and sodium loss. These findings suggest that participants rehydrated ade-

quately between workouts which may be a consequence of our study design and instructions to subjects. The added sodium from SRD and/or B ingestion following all workouts (with ad libitum fluid ingestion) possibly stimulated thirst and contributed to a more complete restoration of body fluids and euhydration (Baker et al., 2005; Nose et al., 1988). Similarly, it could be that the high baseline sodium ingestion was adequate to allow for sufficient rehydration between exercise bouts. Since the supplemental sodium did not increase daily sodium intake or perturb hydration markers, B can be considered neutral with specific regard for postexercise rehydration practices. The Dietary Guidelines Advisory Committee (2010) concluded that a strong body of evidence documented a dose-response relationship between elevated sodium ingestion and blood pressure in adults. Daily sodium ingestion up to 990 mg did not differentially affect cardiovascular measures between trials, suggesting daily postexercise intake of B is safe in healthy trained male runners. Others support our finding that acute sodium intake in endurance trained males is safe, except in salt-sensitive individuals (Komaroff, 2012; Stachenfeld, 2008) due, in part, to the high sweat sodium losses during prolonged workouts common to most endurance runners. Several studies show BM increases up to 1.6 kg (Heer et al., 2000; Heer et al., 2009; Sagnella et al., 1989; Singer et al., 1994) with increased sodium consumption, which could affect running economy 1–14% (Saunders et al., 2004). The additional sodium from consuming B (from 4043 ± 772 mg·d-1 to 4555 ± 498 mg·d-1) did not affect BM, and thus metabolic cost and running economy during treadmill workouts were unchanged. In this context, B, a quality protein source, provides a viable postexercise recovery snack without concern for BM or performance consequences. The lack of differences between supplement cycles despite moderate increases in sodium ingestion may reflect methodological limitations. A single sweat sodium sample was used to calculate sodium balance across all supplement cycles so potential changes between cycles could not be determined. Previous research demonstrated similar sweat sodium concentrations between low and moderate dietary sodium intakes (Armstrong et al., 1993), suggesting minimal impact upon our results. Standardized meals were not provided to participants, thus variations in macronutrient and sodium intake between trials were evident. Yet, studying free living runners whose diets reflected habitual food intake and therefore sodium consumption, further strengthens the observation that what might be considered a sodium heavy recovery protocol (sports drink and beef nutritional supplement) does not carry any substantial concern for hydration indices or performance. In conclusion, postexercise supplementation with B did not impact the average intake of any dietary nutrient within this sample population. No detrimental physiological effects on sodium or water balance, body mass, running economy, or any cardiovascular measure were

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noted when trained runners consumed the B alone or in combination with SRD postexercise for one week. These findings indicate that moderate increases in daily sodium intake due to B even in conjunction with a typical postexercise sports drink can be managed through normal renal regulation of urinary sodium excretion and sweat sodium losses. Thus, B should be considered a viable source of protein and amino acids following endurance exercise without concern for deleterious alterations in hydration biomarkers, performance or cardiovascular function.

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Acknowledgments The authors are grateful to Brandon Yates, Megan Colletto, Alexavier Estrada, Alex Papanastassiou, Anna Roto, Corey Dwyer, Dylan Rausch, Joseph Koudelka, Matthew Burns, Michael Jeanfavre, Nicolas Aguila, and Tim Isselee for their data collection. The study was designed by ECJ, LEA, and NRR; data were collected and analyzed by JLP, ECJ, JDF, and AM; data interpretation and manuscript preparation were undertaken by JLP, ECJ, LEA, and NRR. All authors approved the final version. Funding was provided through the Beef Checkoff. The authors declare no conflicts of interest.

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Hydration Status and Sodium Balance of Endurance Runners Consuming Postexercise Supplements of Varying Nutrient Content.

Postexercise protein and sodium supplementation may aid recovery and rehydration. Preserved beef provides protein and contains high quantities of sodi...
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