581
Gastric Emptying of Carbohydrate — Medium Chain Triglyceride Suspensions at Rest F. .1 Beckers, A. F. Jeukendrup, F Brouns, A. I M Wagenmakers, W H. M. Saris
E. I Beckers, A. E. Jeukendrup, F Brouns,
in lipoproteins. Fat entering the duodenum decreases phasic contractions (13) and inhibits gastric antral contractions (35), which reduces the GE rate of a meal. Both GE and absorption are potentially limiting steps in the oxidation of orally supplied
A. I M. Wagenmakers and W H. M. Saris, Gastric Emptying of Carbohydrate — Medium Chain Triglyceride Suspensions at Rest. mt j Sports Med, Vol 13, No 8, pp 58 1—584, 1992.
substrates such as carbohydrate. Any reduction, induced by oral fat, would therefore be of disadvantage to exercising athletes. However, medium chain triglycerides (MCT) (chain length of
Abstract
Accepted after revision: July 31, 1992
Nine male volunteers participated in 4 gastric emptying (GE) tests of liquid equicaloric mixtures of CHO (maltodextrins) and MCT of the following composition (% CHO — % MCT): Drink (Dr) 1: 70 %—30 %, Dr2: 80
%—20%, Dr3: 90%—10%, Dr4: 100%—0%. GE was measured at rest for 90 mm according to the modified double sampling technique. GE rate, expressed as t 1/2 (SEM), was
23(2.3), 24 (1.6), 27 (2.2) and 36 (2.9) mm, respectively, from drink 1 to drink 4. Statistical analysis showed that all MCT containing drinks emptied faster than the 100% CH0 drink. Two mechanisms may explain this observation: 1) the
CHO content and osmolality increases from Dr 1 to Dr 4 (both are regulators of GE); 2) MCT may not inhibit GE as common fat does, due to a better water solubility and absorption in the small intestine, resulting in a decreased duodenalgastric feedback.
such effects. MCT is broken down by lipase in the stomach and duodenum to glycerol and medium chain fatty acids (MCFA).
Because these MCFA are moderately polar they are water soluble and able to pass the unstirred water layer and cell membrane of the intestine rapidly, without going through the lymph system (2). If absorption of MCFA is rapid, feed back signals from the intestine to the stomach to inhibit GE should be minimal. Meanwhile few studies have been performed in
which oral MCT has been given prior to exercise. In these studies MCT has been observed to be readily oxidized during endurance exercise (9,25,27), however, with a high incidence of gastrointestinal distress.
The objective of the present study, therefore, was to determine whether oral MCT reduces the rate of gastric emptying.
Methods
Key words
Gastric emptying, exogenous substrates, MCT, free fatty acids, maltodextrins
Introduction
the esterified fatty acids are 6 to 12 C-atoms) may not cause
_________
______
In the last decade the use of carbohydrate (CHO) solutions during exercise has been described as a factor to delay fatigue in endurance performance (3,6,8,21). Therefore, it is general practice today, to ingest CH0 in a liquid form
during endurance competition events, such as triathlon and multi-day endurance events, e.g. "Tour de France". Fat has not been considered as a valuable alternative oral energy source during exercise in order to spare endogenous CHO. The absorption of fat in the intestine is relatively slow, involving bile salts, the lymph system and incorporation mt. J. Sports Mcd. 13(1992) 581—584 Georg Thieme Verlag Stuttgart . New York
Subjects Nine healthy male volunteers (age 24 3 years; body weight 73±5kg; height 183±6cm, mean±standard deviation (SD)) with no history of gastrointestinal disease and all familiar with gastric intubation and testing were asked to participate in 4 GE tests. All subjects received a complete written description of the experiment and signed an informed consent. The study was approved by the university ethical committee. Technique
GE was determined with the double sampling technique as described by George (19) and modified by Beckers (1) with phenoired as nonabsorbable indicator. Phenolred measurements and calculation of gastric contents and residual meal were performed according to Beckers (1). Gastric samples were
at 40000 g before analyzing for phenoired to overcome the problem of cloudiness in the centrifuged for 15 mm
samples due to the MCT.
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Dept. Human Biology, Nutrition Research Centre, Rijksuniversiteit, Limburg, P. 0. Box 616, 6200 MD, Maastricht, The Netherlands
582 mt. J. Sports Med. 13 (1992)
E. J Beckers, A. E. Jeukendrup, F Brouns, A. I. M. Wagenmakers, W H. M. Saris positioning of the tube (16,22). A bolus of 8 mi/kg body weight (average 585±42 ml) of one of the test meals, containing 15m1
Test meals
On every occasion subjects consumed a liquid isocaloric test meal consisting of CHO (maltodextrin DE 20, Ma1dex2O®, Amylum, Belgium) with different concentrations of MCT (Estasan® GT 8—60, fatty acid chain length: 3% C6, 50—65% C8 and 35—45% ClO) (Table 1). The test meal was prepared from a CHO-MCT powder (provided by Sandoz Nutrition Ltd, Bern, Switzerland) which after mixing in water gave a stable suspension. Meal temperature was kept constant at 20 'C. The order in which test meals were given was randomized and blind for the subjects.
/1 phenolred, was administered via the tube, mixed with whatever gastric contents, and an initial sample was taken in order to account for the gastric contents. Samples for the determination of GE were taken at 10mm intervals for 90mm according to George's double sampling technique (19). Successive tests were at least 48 hours apart.
Calculations and Statistics As a measure of GE rate half emptying time a simple exponential curve fit Computer Programs, P-series
(t 1/2) (11) was calculated from (f= / t 1/2)) using Biomedical
2t
Subjects arrived at the laboratory at 8 am. after
an overnight fast where a naso-gastric tube (Vygon silicone gastro-duodenal tube, Levin type, Charrier 14) was placed. The stomach was emptied and rinsed until no further residue was obtained and a recovery test was performed for control of the
(BMDPar) (12).
For comparison of results the non-parametric Friedman test in combination with the Fischer PLSD test was used. Results
Table 2 shows the volumetric data (mean±
Table 1 Composition of various test drinks.
MCT
gr/lOOmI Maldex 20 gr/lOOmI Fat
Drink 1
Drink 2
Drink 3
Drink 4
2.40
1.60 14.04 20 80
0.80 15.85 10 90
0.00 17.66
12.22
Energy % Energy % Energy %
30 70
0
0
0
0
mmol/I Osmolality mosm/kg
20 174
20 198
20 222
20 251
CHO Protein
NaCI
Table 2 Gastric volume (GV), rest volume (RV), and CHO: (ml), mean
0
100
SEM) for gastric content, rest volume and secretion volume, for all time points and all drinics. Table 3 represents the t 1/2 values for the individual subjects as well as the average and SD. Fig. 1 depicts the average GE curves as the percentage of the original bolus left in the stomach against time. Analysis of the data by
Friedman's non-parametric test showed a highly significant difference in emptying rate (p-value = 0.0056) of all MCT containing drinks, as compared to the pure CHO drink. Between the MCT containing drinks no significant difference could be observed.
and gastric secretion over time of 4 equicaloric drinks with different amounts of MCT
drink 1 MCT 30 %/CHO 70% time (mm)
0 10
20 30 40 50
60 70
80 90
time (mm)
0 10 20 30 40 50 60 70 80 90
GV
RV
643 (31) 488 (27) 416 (30) 382 (28) 293 (28) 249 (27) 184 (23) 159 (30) 78 (17) 66 (18)
585 (14) 397 (27) 310 (24) 264 (26) 190 (25) 146 (24) 95 (20)
71(20)
26 (8) 15 (6)
58(28)
0
92 (7) 105 (9)
10
89(14) 88(19)
20 30 40 50 60 70
52 (11)
80
51(14)
90
666 (17) 453 (29) 431 (19) 398 (32) 335 (43) 244 (19) 195 (18) 146 (23) 97 (19) 58 (14)
time (mm)
GV
0 10
445 (23)
20 30 40 50 60 70 80 90
427 (21) 412 (16) 381 (26) 315 (28) 269 (33) 227 (34) 193 (32) 124 (22)
119 (12)
102 (9) 103 (10)
drink 3 MCT 10 %/CHO 90% RV secretion
GV
650 (21) 464 (27) 454 (28) 388 (40) 338 (20) 293 (23) 231 (24) 174 (26) 129 (20)
585 (14) 395 (28) 365 (29) 292 (33) 236 (23) 190 (20) 140 (19) 95 (19) 60 (14)
69 (9)
21 (6)
drink 2 MCT 30 %/CHO 80% GV RV secretion
secretion
65 (10)
68 (6) 90(11) 96(14)
102 (9) 103 (12)
91(10) 80(10)
69 (8) 48 (5)
585 (14) 375 (29) 333 (21) 281 (22) 217 (27) 142 (12)
103 (9)
81
(8)
78 98 117(17) 118 102 93
64 (11)
35 (9) 14 (4)
62 (11) 43 (10)
drink 4 MCT 0 %/CHO 100% RV secretion
642 (18)
585 (14) 403 (17) 370 (16) 334 814) 334 (14) 231 (22) 191 (25) 153 (25)
57 42
121(25)
72 (8)
67 (16)
56 (8)
57 (8) 78 (6) 78
84 (9) 78(10) 74(11)
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Daily protocol
Table 3 Rate of gastric emptying of various test drinks expressed as tl/2 in minutes. tii2 (mm)
Subject
# 1
2 3 4 5 6 7 8 9 Average St. Dev. SEM
Drink 1
Drink 2
Drink 3
Drink 4
11.3 22.9 25.5 25.7 25.0 19.7 22.2 19.7 37.0
21.9 27.3 24.9
24.5
29.0 26.4 25.6 49.7 45.8 34.9
19.4 16.3
19.9 30.5
23.2 6.8 2.3
24.0 4.9 1.6
27.5 6.6
35.1
30.3 36.8 19.9 20.0
25.1
29.8 20.2 31.0
30.1 30.1
30.1
42.3 35.8 8.8 2.9
2.2
% —fl— drl (30 En% MCT) —.-— dr2 (20 Eri% MCT) —a--- dr3 (10 En% MCT) dr4 ( 0 En% MCT)
80
mt. .1 Sports Med. 13 (1992) 583
____________
Looking at these data, one might conclude that MCT fat has an accelerating effect on GE rate, a conclusion which is in contradiction with the general existing opinion on the effect of fat on GE rate. However, Hunt (24) examined the influence of fatty acids with chain lengths from C2 to C18 on the rate of GE. His conclusion was that fatty acids with a chain length of C 10 or less influenced GE only marginally, while chain lengths of C12 and higher have an inhibiting effect. The most effective inhibi-
tors were 14C fatty acids. Moberg (29) and Houghton (23) came basically to the same conclusion. They found that liquid meals containing fat (Moberg, Intralipid®, average chain length of carbonic group C18; Houghton, Sunflower margarine, 90%
chain length C18) emptied significantly slower from the stomach than those without fat. The major difference in these studies compared to ours is that in chain length of the esterified fatty acids. More than 90% of the fatty acids of the MCT used here have a chain length of C8 and ClO and exert almost no effect on GE (24). The reason for this is probably the different way in which the gut handles fatty acids with different chain length. C8 and ClO fatty acids are moderately polar and therefore water soluble, diffuse comparatively easy through the unstirred water layer and are mainly absorbed into the portal vein.
The longer chains are apolar and have to pass through the lymph system (2).
Figure 1 and Table 3 show that there is a tendency for a faster GE if the amount of MCT increases. The reason for this may be twofold. First, CHO concentrations above 8 % progressively slow GE (28, 32). Secondly, with increasing CHO concentration, also the osmolality of the drinks increases (Table 1). Both hypertonicity and carbohydrate den-
60
sity are known to reduce GE rate (24,29). The inclusion of
40
progressively increasing amounts of MCT in a CHO-MCT sus-
pension, while maintaining isocalority, decreases both CHO concentration and osmolality.
This study clearly shows that the GE rate of
60
80
time (mm) Fig. 1 Average gastric emptying curves presented as % of origv nal bolus left in the stomach.
Discussion
Gastric emptying (GE) is the first regulating step in the supply of exogenous substrates at rest and during exercise. In contrast to CHO, long chain triglycerides (LCT), which decrease GE rate and are known to be relatively slowly absorbed in the intestine, may not be an appropriate additional exogenous energy source. Since it is speculated that MCT does
not have the same inhibiting effects as LCT, the aim of this study was to investigate the effect of different amounts of medium chain triglycerides on the GE rate of MCT-CHO suspensions.
The results from the GE tests show that all drinks containing MCT (Dr 1, 2 and 3) empty from the stomach at a faster rate compared to an equicaloric CHO solution (Dr 4).
isocaloric CHO-MCT suspensions is faster than of CHO solution alone. Although all GE tests in this study were performed in resting subjects, the results may be extrapolated to exercise settings, since there is no difference in GE rate between rest and
exercise up to @70% TO2max (7,16,32).
This opens the possibility to combine MCT with CHO in a liquid form to provide additional energy rich substrates for exercising (ultra-) endurance athletes. This is of interest in the light of a number of observations: 1) even though considerable amounts of CHO can be ingested, not all of the exogenous CHO emptied from the stomach is oxidized during exercise (27,3 1). In Rehrer's experiment (31), a four-fold increase in the amount of CHO ingested led to a doubling of the amount which passed through the stomach, but did not increase the amount of exogenous CHO oxidized.
Thus, the maximal contribution of oral CHO to substrate utilization during exercise is limited. 2) Gastric emptying rate decreases with increasing CHO concentration and osmolality (7, 26,28,31). Consequently, highly concentrated CHO solutions have been observed to increase the frequency of gastrointestinal distress in endurance athletes (4,33).
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Gastric Emptying of Carbohydrate
584 mt. .1 Sports Med. 13 (1992)
E. i Beckers, A. E. Jeukendrup, F Brouns, A. J M. Wagenmakers, W H. M Saris
3) CHO supplementation counteracts the effect of exercise on lipolytic activity, thus suppresses blood free fatty acid concentration and utilization, which increases the use of CHO (5,10,14,18,30,34). When the CHO supply is relatively small in relation to total CHO utilization, this may lead to an increased rate of endogenous CHO depletion, which may reduce the time to fatigue (17,20, 30). Supplementation of a CHO-fat suspension may counteract the CHO induced depression of blood fatty acids, and could thus lead to optimal supply of exogenous substrates to the working muscle. Future testing of the metabolic effects of MCTCHO suspensions is needed to verify the true practical value.
gastric tube during gastric emptying secretory studies. Br Med J 4: 458—461, 1972.
16 Fordtran J. S., Saltin B.: Gastric emptying and intestinal absorption during prolonged severe exercise. JAppi Physiol 23 (3): 332—335, 1967.
17 Foster C., Costill D. L., Fink W. J.: Effects of pre-exercise feedings on endurance performance. Med Sci Sports II: 1—5, 1979. 18 Fritz I. B., Davis D. G., Holtrop R. H., Dunder H.: Fatty acid oxidation by skeletal muscle during rest and activity. Am J Physiol 194: 379—386, 1957. 19 George J. D.: New clinical method for measuring the rate of gastric emptying: the double sampling technique. Gut 9: 237—242, 1968. 20 Hargreaves M., Costill D. L., Coggan A.: Effect of carbohydrate feedings on muscle glycogen utilization and exercise performance. Med Sci Sports Exerc 16: 219—222, 1984. 21 Hargreaves M.: Carbohydrates and exercise. J Sport Sci 9 (Suppl):
_____________
This study was supported by an "Isostar Research
Grant" from Sandoz Nutrition, Bern, Switzerland.
References 1 Beckers E. J., Rehrer N. J., Brouns F., Ten Hoor F., Saris W H. M.: Determination of total gastric volume, gastric secretion and residual meal using the double sampling technique of George. Gut 29: 1725 —1729, 1988.
2 Bloom B., Chaikof I. L., Reinhardt W 0.: Intestinal lymph as pathway for transport of absorbed fatty acids of different chain length. AmJPhysiol 166: 451, 1951. Brouns F, Saris W. H. M., Beckers E.: Metabolic changes induced by sustained exhaustive cycling and diet manipulation. mt J Sports Med 10: S49—S62, 1989.
Brouns F: Etiology of gastrointestinal disturbances during endurance events. Scand J Med Sci Sports 1: 66—7 7, 1991. BOber V., Felber I. P, Vanotti A.: Glucose tolerance improvement
after acute medicamentous lowering of plasma free fatty acids. SchweizMedWochenschr99: 711, 1968. 6 Coggan A. R., Coyle E. F: Carbohydrate ingestion during prolonged exercise: effects on metabolism and performance. In: Holloszy, J. 0. (ed). Exercise and Sport Sciences Reviews, Vol 19, St. Louis, Williams & Wilkins, 1—40, 1991. Costill D. L.: Gastric Emptying of Fluids During Exercise. In: Gisolfi C. V., Lamb D. R. (eds): Perspectives in Exercise Science and Sports Medicine, Vol 3, Fluid Homeostasis During Exercise, Benchmark Press, Inc., Carniel, Indiana 1990, pp 97—127. 8 Coyle E. F.: Carbohydrate Feedings: Effects on Metabolism, Performance and Recovery. In: Brouns E, Saris W. H. M., Newsholme E. A. (eds): Advances in Nutrition and Top Sport, Med Sport Sci Karger, Basel 1991; 32: 1—14. Décombaz J., Arnaud M.-J., Milon H., Moesch H.: Energy metabolism of medium-chain triglycerides versus carbohydrates during exercise. EurJAppl Physiol 52: 9—14, 1983. lo Eaton P., Steinberg D.: Effects of medium fatty acid concentration, epinephrine and glucose on palmitate-1-C14 oxidation and incorporation into neutral lipids by skeletal muscle in vivo. JLipid Res 2: 376—382, 1961. Elashoff J. D., Reedy T. J., Meyer J. H.: Analysis of gastric emptying data. Gastroenterology 8: 1306—1312, 1982.
12 Engelman L., Frame J. W, Jemrich R. I.: Biomedical Computer Programs, P-series, Derivative-free nonlinear regression. In: BMDP Statistical Software, University of California Press Ltd, Berkeley, Los Angeles 1988, 305—314. Farrel J. L., Ivy A. C.: Studies on the motility of the transplanted gastric pouch. An7 JPhysiol 76: 227—288, 1926. 14 Felber J. P., Vanotti A.: Effect of fat infusion on glucose tolerance and insulin plasma levels. Med Exp (Basel) 10: 153—160, 1964. '5 Findlay J. M., Prescott R. J., Sircus W: Comparative evaluation of water recovery test and fluoroscopic screening in positioning a naso-
22 Hassan M. A., Hobsley M.: Positioning of subject and nasogastric tube during a gastric secretion study. Br Med J 1: 458—460, 1970. 23 Houghton L. A., Mangnall Y. F., Read N. W: Effect of incorporating fat into a liquid test meal on the relation between intragastric distribution and gastric emptying in human volunteers. Gut 31: 1226— 1229, 1990. 24 Hunt J. N., Knox M. T.: Regulation of gastric emptying. In: Handbook of Physiology, American Physiological Society, Volume 4: Alimentary Canal 1968; Chapt 94: 1917—1935. 25 Ivy J. L., Costill D. L., Fink W. J., Maglischo E.: Contribution of medium and long chain triglyceride intake to energy metabolism during prolonged exercise. IntJSports Med 1: 15—20, 1980. 26 Leiper J. B., Davidson J., Maughan R. J.: Gastric emptying of glucose solutions in man. JPhysiol 438: 352p, 1991. 27 Massicotte D., Péronnet F., Brisson G., Hillaire-Marcel C.: Exogenous 13C lipids and 13C glucose oxidized during prolonged exercise in man. Med Sd Sports Exerc 2: 52, abstr 310, 1990. 27 Mitchell J. B., Costill D. L., Houmard J. A., Fink W J., Robergs R. A., Davis J. A.: Gastric emptying: influence of prolonged exercise and carbohydrate concentration. Med Sci Sports Exerc 21: 269—274, 1989.
29 Moberg S., Carlberger G.: The effect on gastric emptying of test
meals with various fat and osmolar concentrations. Scand J Gastroenterol 9: 29—32, 1974. 30 Newsholme E. A., Leech A. R.: Integration of carbohydrate and lipid metabolism. In: Biochemistry for the Medical Sciences. Chichester, John Wiley and Sons, 1983, pp 336—356.
' Rehrer N. J., Wagenmakers A. J. M., Beckers E. J., Halliday D., Leiper J. B., Brouns F.: Gastric emptying, absorption and carbohydrate oxidation during prolonged exercise. JAppi Physiol 72: 468— 475, 1992. 32 Rehrer N. J., Beckers E. J., Brouns F, Ten Hoor F., Saris W H. M.: Exercise and training effects on gastric emptying of carbohydrate beverages. Med Sci Sports Exerc 21: 540—549, 1989. 33 Rehrer N. J., van Kemenade M. C., Meester T. A., Brouns F, Saris W H. M.: Gastrointestinal complaints in relation to dietary intakes in triathletes. lntJSportNutr 2: 48—59, 1992.
34 Rennie M. J., Winder W W, Holloszy J. 0.: A sparing effect of increased plasma fatty acids on muscle and liver glycogen content in the exercising rat. Biochem J 156: 647—655, 1976. 5 Thomas J. E.: Mechanics and regulation of gastric emptying. Physiol Rev 37: 453—474, 1957.
F. I Beckers Dept. Human Biology Nutrition Research Centre Rijksuniversiteit Limburg P.O. Box 616 6200 MD, Maastricht The Netherlands
Downloaded by: Georgetown University Medical Center. Copyrighted material.
18—28, 1991.
Acknowledgements
Gastric Emptying of Carbohydrate — Medium Chain Triglyceride Suspensions at Rest F. .1 Beckers, A. F. Jeukendrup, F Brouns, A. I M Wagenmakers, W H. M. Saris
E. I Beckers, A. E. Jeukendrup, F Brouns,
in lipoproteins. Fat entering the duodenum decreases phasic contractions (13) and inhibits gastric antral contractions (35), which reduces the GE rate of a meal. Both GE and absorption are potentially limiting steps in the oxidation of orally supplied
A. I M. Wagenmakers and W H. M. Saris, Gastric Emptying of Carbohydrate — Medium Chain Triglyceride Suspensions at Rest. mt j Sports Med, Vol 13, No 8, pp 58 1—584, 1992.
substrates such as carbohydrate. Any reduction, induced by oral fat, would therefore be of disadvantage to exercising athletes. However, medium chain triglycerides (MCT) (chain length of
Abstract
Accepted after revision: July 31, 1992
Nine male volunteers participated in 4 gastric emptying (GE) tests of liquid equicaloric mixtures of CHO (maltodextrins) and MCT of the following composition (% CHO — % MCT): Drink (Dr) 1: 70 %—30 %, Dr2: 80
%—20%, Dr3: 90%—10%, Dr4: 100%—0%. GE was measured at rest for 90 mm according to the modified double sampling technique. GE rate, expressed as t 1/2 (SEM), was
23(2.3), 24 (1.6), 27 (2.2) and 36 (2.9) mm, respectively, from drink 1 to drink 4. Statistical analysis showed that all MCT containing drinks emptied faster than the 100% CH0 drink. Two mechanisms may explain this observation: 1) the
CHO content and osmolality increases from Dr 1 to Dr 4 (both are regulators of GE); 2) MCT may not inhibit GE as common fat does, due to a better water solubility and absorption in the small intestine, resulting in a decreased duodenalgastric feedback.
such effects. MCT is broken down by lipase in the stomach and duodenum to glycerol and medium chain fatty acids (MCFA).
Because these MCFA are moderately polar they are water soluble and able to pass the unstirred water layer and cell membrane of the intestine rapidly, without going through the lymph system (2). If absorption of MCFA is rapid, feed back signals from the intestine to the stomach to inhibit GE should be minimal. Meanwhile few studies have been performed in
which oral MCT has been given prior to exercise. In these studies MCT has been observed to be readily oxidized during endurance exercise (9,25,27), however, with a high incidence of gastrointestinal distress.
The objective of the present study, therefore, was to determine whether oral MCT reduces the rate of gastric emptying.
Methods
Key words
Gastric emptying, exogenous substrates, MCT, free fatty acids, maltodextrins
Introduction
the esterified fatty acids are 6 to 12 C-atoms) may not cause
_________
______
In the last decade the use of carbohydrate (CHO) solutions during exercise has been described as a factor to delay fatigue in endurance performance (3,6,8,21). Therefore, it is general practice today, to ingest CH0 in a liquid form
during endurance competition events, such as triathlon and multi-day endurance events, e.g. "Tour de France". Fat has not been considered as a valuable alternative oral energy source during exercise in order to spare endogenous CHO. The absorption of fat in the intestine is relatively slow, involving bile salts, the lymph system and incorporation mt. J. Sports Mcd. 13(1992) 581—584 Georg Thieme Verlag Stuttgart . New York
Subjects Nine healthy male volunteers (age 24 3 years; body weight 73±5kg; height 183±6cm, mean±standard deviation (SD)) with no history of gastrointestinal disease and all familiar with gastric intubation and testing were asked to participate in 4 GE tests. All subjects received a complete written description of the experiment and signed an informed consent. The study was approved by the university ethical committee. Technique
GE was determined with the double sampling technique as described by George (19) and modified by Beckers (1) with phenoired as nonabsorbable indicator. Phenolred measurements and calculation of gastric contents and residual meal were performed according to Beckers (1). Gastric samples were
at 40000 g before analyzing for phenoired to overcome the problem of cloudiness in the centrifuged for 15 mm
samples due to the MCT.
Downloaded by: Georgetown University Medical Center. Copyrighted material.
Dept. Human Biology, Nutrition Research Centre, Rijksuniversiteit, Limburg, P. 0. Box 616, 6200 MD, Maastricht, The Netherlands
582 mt. J. Sports Med. 13 (1992)
E. J Beckers, A. E. Jeukendrup, F Brouns, A. I. M. Wagenmakers, W H. M. Saris positioning of the tube (16,22). A bolus of 8 mi/kg body weight (average 585±42 ml) of one of the test meals, containing 15m1
Test meals
On every occasion subjects consumed a liquid isocaloric test meal consisting of CHO (maltodextrin DE 20, Ma1dex2O®, Amylum, Belgium) with different concentrations of MCT (Estasan® GT 8—60, fatty acid chain length: 3% C6, 50—65% C8 and 35—45% ClO) (Table 1). The test meal was prepared from a CHO-MCT powder (provided by Sandoz Nutrition Ltd, Bern, Switzerland) which after mixing in water gave a stable suspension. Meal temperature was kept constant at 20 'C. The order in which test meals were given was randomized and blind for the subjects.
/1 phenolred, was administered via the tube, mixed with whatever gastric contents, and an initial sample was taken in order to account for the gastric contents. Samples for the determination of GE were taken at 10mm intervals for 90mm according to George's double sampling technique (19). Successive tests were at least 48 hours apart.
Calculations and Statistics As a measure of GE rate half emptying time a simple exponential curve fit Computer Programs, P-series
(t 1/2) (11) was calculated from (f= / t 1/2)) using Biomedical
2t
Subjects arrived at the laboratory at 8 am. after
an overnight fast where a naso-gastric tube (Vygon silicone gastro-duodenal tube, Levin type, Charrier 14) was placed. The stomach was emptied and rinsed until no further residue was obtained and a recovery test was performed for control of the
(BMDPar) (12).
For comparison of results the non-parametric Friedman test in combination with the Fischer PLSD test was used. Results
Table 2 shows the volumetric data (mean±
Table 1 Composition of various test drinks.
MCT
gr/lOOmI Maldex 20 gr/lOOmI Fat
Drink 1
Drink 2
Drink 3
Drink 4
2.40
1.60 14.04 20 80
0.80 15.85 10 90
0.00 17.66
12.22
Energy % Energy % Energy %
30 70
0
0
0
0
mmol/I Osmolality mosm/kg
20 174
20 198
20 222
20 251
CHO Protein
NaCI
Table 2 Gastric volume (GV), rest volume (RV), and CHO: (ml), mean
0
100
SEM) for gastric content, rest volume and secretion volume, for all time points and all drinics. Table 3 represents the t 1/2 values for the individual subjects as well as the average and SD. Fig. 1 depicts the average GE curves as the percentage of the original bolus left in the stomach against time. Analysis of the data by
Friedman's non-parametric test showed a highly significant difference in emptying rate (p-value = 0.0056) of all MCT containing drinks, as compared to the pure CHO drink. Between the MCT containing drinks no significant difference could be observed.
and gastric secretion over time of 4 equicaloric drinks with different amounts of MCT
drink 1 MCT 30 %/CHO 70% time (mm)
0 10
20 30 40 50
60 70
80 90
time (mm)
0 10 20 30 40 50 60 70 80 90
GV
RV
643 (31) 488 (27) 416 (30) 382 (28) 293 (28) 249 (27) 184 (23) 159 (30) 78 (17) 66 (18)
585 (14) 397 (27) 310 (24) 264 (26) 190 (25) 146 (24) 95 (20)
71(20)
26 (8) 15 (6)
58(28)
0
92 (7) 105 (9)
10
89(14) 88(19)
20 30 40 50 60 70
52 (11)
80
51(14)
90
666 (17) 453 (29) 431 (19) 398 (32) 335 (43) 244 (19) 195 (18) 146 (23) 97 (19) 58 (14)
time (mm)
GV
0 10
445 (23)
20 30 40 50 60 70 80 90
427 (21) 412 (16) 381 (26) 315 (28) 269 (33) 227 (34) 193 (32) 124 (22)
119 (12)
102 (9) 103 (10)
drink 3 MCT 10 %/CHO 90% RV secretion
GV
650 (21) 464 (27) 454 (28) 388 (40) 338 (20) 293 (23) 231 (24) 174 (26) 129 (20)
585 (14) 395 (28) 365 (29) 292 (33) 236 (23) 190 (20) 140 (19) 95 (19) 60 (14)
69 (9)
21 (6)
drink 2 MCT 30 %/CHO 80% GV RV secretion
secretion
65 (10)
68 (6) 90(11) 96(14)
102 (9) 103 (12)
91(10) 80(10)
69 (8) 48 (5)
585 (14) 375 (29) 333 (21) 281 (22) 217 (27) 142 (12)
103 (9)
81
(8)
78 98 117(17) 118 102 93
64 (11)
35 (9) 14 (4)
62 (11) 43 (10)
drink 4 MCT 0 %/CHO 100% RV secretion
642 (18)
585 (14) 403 (17) 370 (16) 334 814) 334 (14) 231 (22) 191 (25) 153 (25)
57 42
121(25)
72 (8)
67 (16)
56 (8)
57 (8) 78 (6) 78
84 (9) 78(10) 74(11)
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Daily protocol
Table 3 Rate of gastric emptying of various test drinks expressed as tl/2 in minutes. tii2 (mm)
Subject
# 1
2 3 4 5 6 7 8 9 Average St. Dev. SEM
Drink 1
Drink 2
Drink 3
Drink 4
11.3 22.9 25.5 25.7 25.0 19.7 22.2 19.7 37.0
21.9 27.3 24.9
24.5
29.0 26.4 25.6 49.7 45.8 34.9
19.4 16.3
19.9 30.5
23.2 6.8 2.3
24.0 4.9 1.6
27.5 6.6
35.1
30.3 36.8 19.9 20.0
25.1
29.8 20.2 31.0
30.1 30.1
30.1
42.3 35.8 8.8 2.9
2.2
% —fl— drl (30 En% MCT) —.-— dr2 (20 Eri% MCT) —a--- dr3 (10 En% MCT) dr4 ( 0 En% MCT)
80
mt. .1 Sports Med. 13 (1992) 583
____________
Looking at these data, one might conclude that MCT fat has an accelerating effect on GE rate, a conclusion which is in contradiction with the general existing opinion on the effect of fat on GE rate. However, Hunt (24) examined the influence of fatty acids with chain lengths from C2 to C18 on the rate of GE. His conclusion was that fatty acids with a chain length of C 10 or less influenced GE only marginally, while chain lengths of C12 and higher have an inhibiting effect. The most effective inhibi-
tors were 14C fatty acids. Moberg (29) and Houghton (23) came basically to the same conclusion. They found that liquid meals containing fat (Moberg, Intralipid®, average chain length of carbonic group C18; Houghton, Sunflower margarine, 90%
chain length C18) emptied significantly slower from the stomach than those without fat. The major difference in these studies compared to ours is that in chain length of the esterified fatty acids. More than 90% of the fatty acids of the MCT used here have a chain length of C8 and ClO and exert almost no effect on GE (24). The reason for this is probably the different way in which the gut handles fatty acids with different chain length. C8 and ClO fatty acids are moderately polar and therefore water soluble, diffuse comparatively easy through the unstirred water layer and are mainly absorbed into the portal vein.
The longer chains are apolar and have to pass through the lymph system (2).
Figure 1 and Table 3 show that there is a tendency for a faster GE if the amount of MCT increases. The reason for this may be twofold. First, CHO concentrations above 8 % progressively slow GE (28, 32). Secondly, with increasing CHO concentration, also the osmolality of the drinks increases (Table 1). Both hypertonicity and carbohydrate den-
60
sity are known to reduce GE rate (24,29). The inclusion of
40
progressively increasing amounts of MCT in a CHO-MCT sus-
pension, while maintaining isocalority, decreases both CHO concentration and osmolality.
This study clearly shows that the GE rate of
60
80
time (mm) Fig. 1 Average gastric emptying curves presented as % of origv nal bolus left in the stomach.
Discussion
Gastric emptying (GE) is the first regulating step in the supply of exogenous substrates at rest and during exercise. In contrast to CHO, long chain triglycerides (LCT), which decrease GE rate and are known to be relatively slowly absorbed in the intestine, may not be an appropriate additional exogenous energy source. Since it is speculated that MCT does
not have the same inhibiting effects as LCT, the aim of this study was to investigate the effect of different amounts of medium chain triglycerides on the GE rate of MCT-CHO suspensions.
The results from the GE tests show that all drinks containing MCT (Dr 1, 2 and 3) empty from the stomach at a faster rate compared to an equicaloric CHO solution (Dr 4).
isocaloric CHO-MCT suspensions is faster than of CHO solution alone. Although all GE tests in this study were performed in resting subjects, the results may be extrapolated to exercise settings, since there is no difference in GE rate between rest and
exercise up to @70% TO2max (7,16,32).
This opens the possibility to combine MCT with CHO in a liquid form to provide additional energy rich substrates for exercising (ultra-) endurance athletes. This is of interest in the light of a number of observations: 1) even though considerable amounts of CHO can be ingested, not all of the exogenous CHO emptied from the stomach is oxidized during exercise (27,3 1). In Rehrer's experiment (31), a four-fold increase in the amount of CHO ingested led to a doubling of the amount which passed through the stomach, but did not increase the amount of exogenous CHO oxidized.
Thus, the maximal contribution of oral CHO to substrate utilization during exercise is limited. 2) Gastric emptying rate decreases with increasing CHO concentration and osmolality (7, 26,28,31). Consequently, highly concentrated CHO solutions have been observed to increase the frequency of gastrointestinal distress in endurance athletes (4,33).
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Gastric Emptying of Carbohydrate
584 mt. .1 Sports Med. 13 (1992)
E. i Beckers, A. E. Jeukendrup, F Brouns, A. J M. Wagenmakers, W H. M Saris
3) CHO supplementation counteracts the effect of exercise on lipolytic activity, thus suppresses blood free fatty acid concentration and utilization, which increases the use of CHO (5,10,14,18,30,34). When the CHO supply is relatively small in relation to total CHO utilization, this may lead to an increased rate of endogenous CHO depletion, which may reduce the time to fatigue (17,20, 30). Supplementation of a CHO-fat suspension may counteract the CHO induced depression of blood fatty acids, and could thus lead to optimal supply of exogenous substrates to the working muscle. Future testing of the metabolic effects of MCTCHO suspensions is needed to verify the true practical value.
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_____________
This study was supported by an "Isostar Research
Grant" from Sandoz Nutrition, Bern, Switzerland.
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F. I Beckers Dept. Human Biology Nutrition Research Centre Rijksuniversiteit Limburg P.O. Box 616 6200 MD, Maastricht The Netherlands
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18—28, 1991.
Acknowledgements
