Clinical Science (1992) 83, 483-487 (Printed in Great Britain)
483
Relative effects of fat-, Carbohydrate- and proteiwcontaining liquid diets on cardiac output in healthy adult subjects Susan K. HAWLEY and Kevin S. CHANNER Department of Cardiology, Royal Hallamshire Hospital, Shefield, U.K. (Received 8 May 1992; accepted 9 June 1992)
1. Nine healthy adult subjects consumed four types of proprietary liquid diet of similar volume and calorific value but of different nutritional composition. The effects on resting cardiac output, mean blood pressure and pulse rate were measured. 2. A significant rise in cardiac output occurred with the balanced, protein and carbohydrate diets but not with the fat diet. The greatest rise was seen with the balanced diet. Water alone had no effect on cardiac output. 3. The average time taken to reach peak cardiac output was shortest with the carbohydrate diet and longest with the fat diet. 4. The increases in cardiac output resulted from a rise in both pulse rate and stroke volume. The carbohydrate diet produced the most sustained rise in pulse rate but the least sustained elevation in stroke volume. 5. No significant changes were seen in mean blood pressure when each liquid meal was compared with water. 6. Our data show that the increase in cardiac output with liquid ingestion is related to the dietary components. These effects are additive. INTRODUCTION
Over the last 50 years, many experiments have been performed to investigate the effects of food on cardiac output in humans. Recently, there has been a revival of interest in these postprandial changes, as they are relevant to sports medicine and to dietary advice in the elderly and patients with cardiac disease, particularly those with postprandial angina. In general, most investigators have demonstrated a postprandial rise in cardiac output of up to 62% of resting values, this rise comprising an increase in both heart rate of about 17% and stroke volume of 41% in healthy subjects [l]. Since blood pressure does not change in normal subjects, this suggests a reduction in peripheral resistance. Researchers have compared the haemodynamic effects of the volume
of liquids [a], different sizes of meals [S] and different meal constituents [4, 51 and have shown that meal size and energy content correlate with the size and duration of the changes in heart rate, cardiac output and stroke volume [3]. None has comprehensively investigated the cardiovascular effects of dietary constituents in liquid form in healthy adults. The liquid diets used in this study were all readily available standard manufactured brands. Their use is widespread as oral supplements in sick patients who have specific nutritional requirements, yet little is known of their possible effects on the cardiovascular system. The purpose of this study was to investigate whether changing the constituents of a liquid diet would have an effect on cardiac output and other haemodynamic variables in fit young adult subjects. METHODS Subjects
Nine adults (four males, five females) of mean age 24 years (21-33 years) and mean weight 66 kg (5482 kg) were enrolled into the study. All were drawn from the hospital staff, were physically fit with no history of cardiac disease or hypertension and were not taking any medication. Approval was obtained from the local Ethics Committee and all the subjects gave their informed consent. Protocol
The subjects were fasted for at least 5 h before the beginning of the study. No caffeine, alcohol or cigarettes had been consumed for the preceding 9 h. The experiments were performed in a warm, quiet room with subdued lighting and the subjects remained on a bed in a supine or semi-recumbent position, being allowed to read or sleep as preferred. After a period of 15min in the supine position, basal measurements of cardiac output, pulse rate and blood pressure were made.
Key words: carbohydrate, cardiac output, fat, liquid diet, protein.
Abbreviation: AUC, area under the cardiac output-time curve. Correspondence: Dr
K. S.
Channer, Department of Cardiology, Royal Hallamshire Hospital, Glorsop Road, Sheffield SIO ZJF, U.K.
S. K. Hawley and K. S. Channer
484
Table I.Composition of liquid test diets (600ml volume)
Name Amount (ml) Added water (ml) Total volume(m1) Added K + (mmol) Added Na’ (mmol) Total energy(kJ) Carbohydrate (9) Fat (g) Protein (9) Total K + (mmol) Total Na’ (mmol)
Fat diet
Carbchydrate diet
Protein diet
Balanced diet
Calogen
Fortical
Maxipro
220 380
400
600
600 24
loo* 600 600
Fortisip Energy Plus 600 600 Nil Nil
24 10
200
4142
10 41 I7
Nil I10 Nil 26 I2
Nil Nil 24 12
146
Nil Nil 3209 10 13 I60 24 II
Water
6 0 0 6 0 0 Nil Nil 3766 I08
40 30 24 20
24 10 Nil Nil Nil Nil 24 10
*Value in g.
Each subject consumed four different liquid diets and an equal volume of water as control in random order with at least 48h between study days. The diets were ingested at room temperature, over a 10min period. Liquid diets of protein, fat and carbohydrate and the balanced diet were chosen from commercially available sources used as food supplements in the hospital. Each diet was of equal volume and approximately equal calorific value. The protein diet had the lowest calorific value, as it proved impossible to dissolve more than 200g in 600ml of water. Small amounts of low-calorie orange flavouring (‘Robinsons Special R ) were used, if required, and water was added to bring the total volume to 600ml. An equal volume of water alone acted as a control; two subjects additionally underwent a sham test with no fluid ingestion at all. As the protein and balanced diets contained sodium and potassium, soluble supplements of these were added to the others to balance the electrolyte content (‘Sparklets’, British Oxygen Company; 5 mmol of effervescent sodium bicarbonate/tablet, and ‘Sando K’, Sandoz Pharmaceuticals, 12 mmol of effervescent potassium chloride/tablet). The overall composition of the diets is shown in Table 1. Detailed dietary constituents are described below. Protein. This was provided as soluble milk whey protein (Maxipro; Scientific Hospital Supplies, Liverpool, U.K.) with the following amino acid composition per 100 g: L-alanine, 3.8 g; L-arginine, 1.7g; L-aspartic acid, 8.7 g; L-cystine, 2.1 g; L-glutamic acid, 14.6g; L-glycine, 1.5g; L-histidine, 1.5g; L-isoleucine, 5.7 g; L-leucine, 7.8 g; L-lysine, 6.9 g; L-methionine 1.9 g; L-proline, 5.9 g; L-phenylalanine, 3.9 g; L-serine, 4.3 g; L-threonine, 7.0 g; Ltryptophan, 1.7 g; L-tyrosine 3.7 g; L-valine 5.5 g. Carbohydrate. This was provided as glucose polymer maltodextrin (Fortical; Cow and Gate, Trowbridge, Wilts., U.K.) with the following average analysis per 100ml: carbohydrate, 62 g; glucose, 2 g;
maltose, 7.7 g; polysaccharides, 51.8 g; citric acid, 0.5 g. Fat. This was provided as emulsified peanut oil (Calogen, Scientific Hospital Supplies U.K.) with the following fatty acid profile per lOOg of fatty acids: lauric acid, 0.1 g; myristic acid 0.5 g; palmitic acid 8.3 g; stearic acid, 4.1 g; arachidic acid, 2.5 g; lignoceric acid, 2.1 g; oleic acid, 57.0g; eicosenoic acid, 1.0g; linoleic acid, 22.6 g; linolenic acid, 0.8 g. Balanced diet. This was provided as Fortisip Energy Plus (Cow and Gate) containing per 100ml 5 g of protein, 6.5 g of fat and 17.9 g of carbohydrate (as 14.3 g of maltodextrin, 3.2 g of sucrose and 0.4g of other carbohydrates). The amino acid composition per lOOg of protein was: L-isoleucine, 5.7 g; L-leucine, 10.5 g; L-lysine, 10.2 g; L-methionine, 3.3 g; L-cystine, 0.3 g; L-phenylalanine, 5.6 g; L-tyrosine, 6.1 g; L-threonine, 4.9 g; L-tryptophan, 1.4 g; L-valine, 7.2 g; L-arginine, 4.0 g; L-histidine, 3.2 g; L-alanine, 3.4 g; L-aspartic acid, 7.8 g; L-glutamic acid, 25.0 g; glycine, 2.0 g; L-proline, 10.0 g; L-serine, 6.6 g. Haemodynamic measurements
Measurements of cardiac output, mean blood pressure and pulse rate were recorded at intervals of 15min for the first hour from the end of ingestion and then half-hourly for the next 3h. Cardiac output was measured using non-invasive transcutaneous Doppler aortovelography (‘Sci-Med PC Dop 842’, Bristol, U.K.). This technique produces reproducible results, having a coefficient of variation for repeated measurements on the same subject of less than 5% when used by the same experienced observer in our hands. The aortic flow velocity was estimated according to the formula: V = A f x ~ /f2x cos 8
where V=magnitude of blood velocity, A f =measured change in sound frequency, c=velocity of sound in tissue, f =frequency of emitted Doppler signal and 8=angle between the direction of blood flow and the Doppler signal. The value of 8 is zero because the direction of the Doppler beam is directed along the ascending aorta. This is facilitated by the use of the specifically angled 2MHz pulsed Doppler probe which produces a wide beam. The mean Doppler shift frequency is extracted from the Doppler spectrum which is displayed in real time. Mean velocity is obtained from the first moment of the Doppler power spectrum which is computed automatically. Cardiac output is then obtained from the product of the time-averaged mean velocity and cross-sectional area of the aorta. Standard aortic root diameters of 30mm for males and 28mm for females and an angle of insonation of 0 degrees were assumed throughout. Subjects were screened beforehand to ensure that they had suitable Doppler signals and all measurements were performed by the
Pcstprandial cardiac output and liquid diets
485
Table 2. Mean AUC values for changes in cardiac output with time after ingestion of four different liquid diets, with water as a control
1345. I 1456.1 1553.5 1580.1 1658.4
Water Fat diet Carbohydrate diet Protein diet Balanced diet
0
I
2
4
3
Time (h)
v,
P
m).
same person (S.K.H.). Six to ten cardiac output recordings were taken over 3-5min and the average value was calculated. Mean blood pressure was measured automatically in one arm (‘Dinamap 845’, Critikon, Tampa, FL, U.S.A.). Statistical analysis
The haemodynamic changes were plotted against time for each subject and for each of the liquid diets. The overall change in the cardiac output over the 4 h study period was assessed using the area under the cardiac output-time curve (AUC) as described by Matthews et al. [6]. The AUC was calculated using the trapezoidal rule. The differences between the different diets were assessed using oneway analysis of variance with P
483
Relative effects of fat-, Carbohydrate- and proteiwcontaining liquid diets on cardiac output in healthy adult subjects Susan K. HAWLEY and Kevin S. CHANNER Department of Cardiology, Royal Hallamshire Hospital, Shefield, U.K. (Received 8 May 1992; accepted 9 June 1992)
1. Nine healthy adult subjects consumed four types of proprietary liquid diet of similar volume and calorific value but of different nutritional composition. The effects on resting cardiac output, mean blood pressure and pulse rate were measured. 2. A significant rise in cardiac output occurred with the balanced, protein and carbohydrate diets but not with the fat diet. The greatest rise was seen with the balanced diet. Water alone had no effect on cardiac output. 3. The average time taken to reach peak cardiac output was shortest with the carbohydrate diet and longest with the fat diet. 4. The increases in cardiac output resulted from a rise in both pulse rate and stroke volume. The carbohydrate diet produced the most sustained rise in pulse rate but the least sustained elevation in stroke volume. 5. No significant changes were seen in mean blood pressure when each liquid meal was compared with water. 6. Our data show that the increase in cardiac output with liquid ingestion is related to the dietary components. These effects are additive. INTRODUCTION
Over the last 50 years, many experiments have been performed to investigate the effects of food on cardiac output in humans. Recently, there has been a revival of interest in these postprandial changes, as they are relevant to sports medicine and to dietary advice in the elderly and patients with cardiac disease, particularly those with postprandial angina. In general, most investigators have demonstrated a postprandial rise in cardiac output of up to 62% of resting values, this rise comprising an increase in both heart rate of about 17% and stroke volume of 41% in healthy subjects [l]. Since blood pressure does not change in normal subjects, this suggests a reduction in peripheral resistance. Researchers have compared the haemodynamic effects of the volume
of liquids [a], different sizes of meals [S] and different meal constituents [4, 51 and have shown that meal size and energy content correlate with the size and duration of the changes in heart rate, cardiac output and stroke volume [3]. None has comprehensively investigated the cardiovascular effects of dietary constituents in liquid form in healthy adults. The liquid diets used in this study were all readily available standard manufactured brands. Their use is widespread as oral supplements in sick patients who have specific nutritional requirements, yet little is known of their possible effects on the cardiovascular system. The purpose of this study was to investigate whether changing the constituents of a liquid diet would have an effect on cardiac output and other haemodynamic variables in fit young adult subjects. METHODS Subjects
Nine adults (four males, five females) of mean age 24 years (21-33 years) and mean weight 66 kg (5482 kg) were enrolled into the study. All were drawn from the hospital staff, were physically fit with no history of cardiac disease or hypertension and were not taking any medication. Approval was obtained from the local Ethics Committee and all the subjects gave their informed consent. Protocol
The subjects were fasted for at least 5 h before the beginning of the study. No caffeine, alcohol or cigarettes had been consumed for the preceding 9 h. The experiments were performed in a warm, quiet room with subdued lighting and the subjects remained on a bed in a supine or semi-recumbent position, being allowed to read or sleep as preferred. After a period of 15min in the supine position, basal measurements of cardiac output, pulse rate and blood pressure were made.
Key words: carbohydrate, cardiac output, fat, liquid diet, protein.
Abbreviation: AUC, area under the cardiac output-time curve. Correspondence: Dr
K. S.
Channer, Department of Cardiology, Royal Hallamshire Hospital, Glorsop Road, Sheffield SIO ZJF, U.K.
S. K. Hawley and K. S. Channer
484
Table I.Composition of liquid test diets (600ml volume)
Name Amount (ml) Added water (ml) Total volume(m1) Added K + (mmol) Added Na’ (mmol) Total energy(kJ) Carbohydrate (9) Fat (g) Protein (9) Total K + (mmol) Total Na’ (mmol)
Fat diet
Carbchydrate diet
Protein diet
Balanced diet
Calogen
Fortical
Maxipro
220 380
400
600
600 24
loo* 600 600
Fortisip Energy Plus 600 600 Nil Nil
24 10
200
4142
10 41 I7
Nil I10 Nil 26 I2
Nil Nil 24 12
146
Nil Nil 3209 10 13 I60 24 II
Water
6 0 0 6 0 0 Nil Nil 3766 I08
40 30 24 20
24 10 Nil Nil Nil Nil 24 10
*Value in g.
Each subject consumed four different liquid diets and an equal volume of water as control in random order with at least 48h between study days. The diets were ingested at room temperature, over a 10min period. Liquid diets of protein, fat and carbohydrate and the balanced diet were chosen from commercially available sources used as food supplements in the hospital. Each diet was of equal volume and approximately equal calorific value. The protein diet had the lowest calorific value, as it proved impossible to dissolve more than 200g in 600ml of water. Small amounts of low-calorie orange flavouring (‘Robinsons Special R ) were used, if required, and water was added to bring the total volume to 600ml. An equal volume of water alone acted as a control; two subjects additionally underwent a sham test with no fluid ingestion at all. As the protein and balanced diets contained sodium and potassium, soluble supplements of these were added to the others to balance the electrolyte content (‘Sparklets’, British Oxygen Company; 5 mmol of effervescent sodium bicarbonate/tablet, and ‘Sando K’, Sandoz Pharmaceuticals, 12 mmol of effervescent potassium chloride/tablet). The overall composition of the diets is shown in Table 1. Detailed dietary constituents are described below. Protein. This was provided as soluble milk whey protein (Maxipro; Scientific Hospital Supplies, Liverpool, U.K.) with the following amino acid composition per 100 g: L-alanine, 3.8 g; L-arginine, 1.7g; L-aspartic acid, 8.7 g; L-cystine, 2.1 g; L-glutamic acid, 14.6g; L-glycine, 1.5g; L-histidine, 1.5g; L-isoleucine, 5.7 g; L-leucine, 7.8 g; L-lysine, 6.9 g; L-methionine 1.9 g; L-proline, 5.9 g; L-phenylalanine, 3.9 g; L-serine, 4.3 g; L-threonine, 7.0 g; Ltryptophan, 1.7 g; L-tyrosine 3.7 g; L-valine 5.5 g. Carbohydrate. This was provided as glucose polymer maltodextrin (Fortical; Cow and Gate, Trowbridge, Wilts., U.K.) with the following average analysis per 100ml: carbohydrate, 62 g; glucose, 2 g;
maltose, 7.7 g; polysaccharides, 51.8 g; citric acid, 0.5 g. Fat. This was provided as emulsified peanut oil (Calogen, Scientific Hospital Supplies U.K.) with the following fatty acid profile per lOOg of fatty acids: lauric acid, 0.1 g; myristic acid 0.5 g; palmitic acid 8.3 g; stearic acid, 4.1 g; arachidic acid, 2.5 g; lignoceric acid, 2.1 g; oleic acid, 57.0g; eicosenoic acid, 1.0g; linoleic acid, 22.6 g; linolenic acid, 0.8 g. Balanced diet. This was provided as Fortisip Energy Plus (Cow and Gate) containing per 100ml 5 g of protein, 6.5 g of fat and 17.9 g of carbohydrate (as 14.3 g of maltodextrin, 3.2 g of sucrose and 0.4g of other carbohydrates). The amino acid composition per lOOg of protein was: L-isoleucine, 5.7 g; L-leucine, 10.5 g; L-lysine, 10.2 g; L-methionine, 3.3 g; L-cystine, 0.3 g; L-phenylalanine, 5.6 g; L-tyrosine, 6.1 g; L-threonine, 4.9 g; L-tryptophan, 1.4 g; L-valine, 7.2 g; L-arginine, 4.0 g; L-histidine, 3.2 g; L-alanine, 3.4 g; L-aspartic acid, 7.8 g; L-glutamic acid, 25.0 g; glycine, 2.0 g; L-proline, 10.0 g; L-serine, 6.6 g. Haemodynamic measurements
Measurements of cardiac output, mean blood pressure and pulse rate were recorded at intervals of 15min for the first hour from the end of ingestion and then half-hourly for the next 3h. Cardiac output was measured using non-invasive transcutaneous Doppler aortovelography (‘Sci-Med PC Dop 842’, Bristol, U.K.). This technique produces reproducible results, having a coefficient of variation for repeated measurements on the same subject of less than 5% when used by the same experienced observer in our hands. The aortic flow velocity was estimated according to the formula: V = A f x ~ /f2x cos 8
where V=magnitude of blood velocity, A f =measured change in sound frequency, c=velocity of sound in tissue, f =frequency of emitted Doppler signal and 8=angle between the direction of blood flow and the Doppler signal. The value of 8 is zero because the direction of the Doppler beam is directed along the ascending aorta. This is facilitated by the use of the specifically angled 2MHz pulsed Doppler probe which produces a wide beam. The mean Doppler shift frequency is extracted from the Doppler spectrum which is displayed in real time. Mean velocity is obtained from the first moment of the Doppler power spectrum which is computed automatically. Cardiac output is then obtained from the product of the time-averaged mean velocity and cross-sectional area of the aorta. Standard aortic root diameters of 30mm for males and 28mm for females and an angle of insonation of 0 degrees were assumed throughout. Subjects were screened beforehand to ensure that they had suitable Doppler signals and all measurements were performed by the
Pcstprandial cardiac output and liquid diets
485
Table 2. Mean AUC values for changes in cardiac output with time after ingestion of four different liquid diets, with water as a control
1345. I 1456.1 1553.5 1580.1 1658.4
Water Fat diet Carbohydrate diet Protein diet Balanced diet
0
I
2
4
3
Time (h)
v,
P
m).
same person (S.K.H.). Six to ten cardiac output recordings were taken over 3-5min and the average value was calculated. Mean blood pressure was measured automatically in one arm (‘Dinamap 845’, Critikon, Tampa, FL, U.S.A.). Statistical analysis
The haemodynamic changes were plotted against time for each subject and for each of the liquid diets. The overall change in the cardiac output over the 4 h study period was assessed using the area under the cardiac output-time curve (AUC) as described by Matthews et al. [6]. The AUC was calculated using the trapezoidal rule. The differences between the different diets were assessed using oneway analysis of variance with P
