1 Unité Mixte de recherche de Physiologie de la Nutrition et du comportement alimentaire, Institut National de la Recherche Agronomique, Institut National Agronomique Paris-Grignon, F75231 Paris; and 2 Recherche et Développement, Lactalis, 53089 Laval Cedex 9, France
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The composition of
the preexercise food intake is known to affect substrate utilization
during exercise and thus can affect long-term changes in body weight
and composition. These parameters were measured in male rats exercised
2 h daily over 5 wk, either in the fasting state or 1 h after
they ingested a meal enriched with glucose (Glc), whole milk
protein (WMP), or -lactalbumin-enriched whey protein (CP
L).
Compared with fasting, the Glc meal increased glucose oxidation and
decreased lipid oxidation during and after exercise. In contrast, the
WMP and CP
L meals preserved lipid oxidation and increased protein
oxidation, the CP
L meal increasing protein oxidation more than the
WMP meal. At the end of the study, body weight was larger in the WMP-,
Glc-, and CP
L-fed rats than in the fasted ones. This resulted from
an increased fat mass in the WMP and Glc rats and to an increased lean
body mass, particularly muscles, in the CP
L rats. We conclude that
the potential of the CP
L meal to preserve lipid oxidation and to
rapidly deliver amino acids for use during exercise improved the
efficiency of exercise training to decrease adiposity.
indirect calorimetry; glucose; lactate; glycerol; free fatty acids
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
THE CHALLENGE OF OVERWEIGHT people involved in a weight-reducing program, as well as of athletes that have to compete in weight categories, is to face up to the energetic demand of exercise training while promoting mobilization of fat and simultaneously maintaining lean body mass, specifically muscle mass (1, 14).
Lipid oxidation is most enhanced when exercise is performed in the postabsorptive state, i.e., when plasma insulin concentration and glycogen stores are low, but this may also promote the release of glucocorticoids to synthesize glucose from amino acids and thus induce muscle protein catabolism. A preexercise carbohydrate meal can be given before exercise to sustain a high workload of long duration, whereas during exercise, periodic intakes of glucose are able to delay fatigue, particularly nervous fatigue, by helping to maintain circulating blood glucose levels (19). When a carbohydrate meal is given before exercise, it can prevent protein catabolism, but a possible adverse effect is related to the glucose-induced stimulation of insulin secretion that may reduce both glycogen and lipid release and utilization as oxidative substrates (4, 6, 12, 15) and thus impair the capacity to perform the exercise as well as the capacity of exercise to reduce fat mass.
A means of preventing catabolism of endogenous protein during exercise while maintaining high endogenous utilization of lipid is to provide a dietary source of amino acids. This kind of meal has the advantage of producing little insulin and thus no impairment of fat mobilization, while having the potential to bring exogenous substrates to active muscles under the form of branched-chain amino acids and glucose produced through the gluconeogenic pathway (2, 5). The production of glucose from exogenous protein should have a sparing effect on endogenous protein catabolism observed in such situations when exercise is performed during an energy deficit (11, 13). In this case, the ability of the protein source to deliver amino acids rapidly into the blood may be critical to increase amino acid availability.
The aim of the present study was to examine whether a preexercice
protein-enriched meal would be able to maintain a high rate of lipid
oxidation during exercise while providing simultaneously an ergogenic
aid to exercise performance. For this purpose, rats were trained 5 days
per week for 5 wk. The exercises were performed in four different
situations: in the postabsorptive state (fasting) or 1 h after the
ingestion of a preload that was enriched with glucose (Glc), whole milk
proteins (WMP), or -lactalbumin (CP
L).
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Animals and diets.
All of the procedures used were in strict accordance with the French
guide for the care and use of laboratory animals. Twenty-four rats
(Harlan France) were housed in individual cages kept in a temperature-controlled room (24 ± 1°C) with an artificial
12:12-h light-dark cycle, lights on at 0600. The experimental diets
were prepared under strict laboratory conditions by the "Unité
de Preparation des Aliments Experimentaux" (Institut National de la
Recherche Agronomique-UPAE, Jouy-en-Josas, France). Whole milk protein
and -lactalbumin-enriched preparations were supplied by Lactalis
(Laval, France). To prevent spillage, the food was made semi-liquid by
dilution with water (1:1).
Experimental design. The following experiment, designed for a group of six rats, was repeated four times to get six rats in each group.
During the 1st wk, the six rats had free access to a semi-synthetic powdered food containing 14% of milk protein (P14-diet, Table 1). The average food intake of the first group of rats measured during this 1st wk was taken as the reference 100% ad libitum intake for all of the rats throughout the study.
|
Experimental procedure in the metabolic chamber and treadmill. The rats were housed in the metabolic chamber at 1700. A polyethylene tube supported by an articulated arm balanced with a counterweight was linked to the head piece of the implanted catheter, and an infusion of hypotonic saline (0.45%, 6 ml/h) was started immediately and continued throughout the study, including during the period of exercise, to induce a regular flow of urine. The urine was collected via a peristaltic pump from the V-shaped bottom of the metabolic cage and distributed in 10-ml tubes coated with 10 µl of an 18% HCl solution. A fraction collector was used to change the collecting tube every 30 min. The urine lost on the treadmill during exercise was collected at the end of the exercise by rinsing the treadmill belt and collecting the effluent in tissues that were subsequently rinsed on a water-driven vacuum pump. The rats were given their nighttime meal (65% of ad libitum food intake) immediately after being housed in the metabolic chamber. At 0900 the next day, i.e., 1 h before the onset of exercise, the preexercise meal was introduced in the food cup (using a syringe via a tube pushed through a hole in the chamber wall so that the measurement of the respiratory exchanges was not affected).
Blood sample procedures.
Twenty microliters of an antiprotease solution composed of EDTA and
aprotinin (Trasylol, 10,000 units; Bayer, Leverkusen, Germany) were
added to each 500-µl blood sample. The plasma was then separated by
centrifugation (15 min at 3,000 g), frozen, and stored at
80°C. After each blood sample, the catheter was washed with
citrated physiological serum [Citric Acid anhydrous + Citric Acid
Trisodium Salt Dihydrate Sigma Ultra (Sigma Diagnostics, St. Quentin
Fallavier, France) + NaCl (9.0 g/l solution; B. Braun Medical, Boulogne, France)].
Assays. Urea in urine and plasma was assayed with the Bun (Endpoint) Urea Nitrogen Kit from Sigma Diagnostics. Glucose and lactate were assayed with the Glucose RTU and Lactate PAP kits (bioMérieux, Lyon, France). Triacylglycerol and glycerol were assayed with the triglyceride (GPO-Trinder) kit from Sigma Diagnostics. Free fatty acids were assayed using the NEFA C kit from Wako (Wako Chemicals, Richmond, VA).
Tissue samples and glycogen dosage.
Rats were deeply anesthetized with an overdose of anesthetic
(pentobarbital sodium, 48 mg/kg) and exsanguinated by section of the
abdominal aorta and vena cava. Liver and hindlimb muscles were
immediately dissected out, frozen in liquid nitrogen, and stored at
80°C for further glycogen dosage by the method described by Lo et
al. (16). Then, the main organs and tissues were removed, blotted dry, and immediately weighed to the nearest 0.01 g. After completion of the dissection, the remainder of the body, i.e., muscle
mass plus skeleton (excluding tail and feet), was weighed and
classified as "carcass." Lean body mass (LBM) in this study was
taken as total body mass minus adipose tissues (10).
Substrate oxidation.
Protein oxidation (Pox) between 1700 and 0900 the next day was computed
from the amount of nitrogen released in urine urea. During the
periexercise period, i.e., 0900-1600, changes in Pox were computed
by using simultaneously urinary urea production and changes in plasma
urea concentrations. Changes in whole body urea were extrapolated from
changes in plasma urea with the assumptions that urea diffuses freely
in the body water compartment and that body water accounts for 66.8%
of body weight (18). Urea production was thus computed
according to the following formula
![]() |
Statistical analysis. All values are expressed as means ± SE. ANOVA and repeated-measures ANOVA were used to assess differences between groups and were completed by a post hoc Scheffé test when appropriate. A probability of P < 0.05 was chosen as the criterion for acceptance of a statistical significance. The statistical tests were performed with the SAS program (SAS Institute, Cary, NC).
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Body weight and body composition.
Body weight increased more in the CPL, WMP, and Glc groups
than in the fasted group (Fig.
1). Analysis of body composition showed
that LBM was significantly smaller in the fasted rats than in the three
other groups (Table 2). All of the rats
showed a reduced adiposity (5.7-7.8% FAT) compared with sedentary
ad libitum P14-fed Wistar rats of similar body weight, in which fat
usually amounts to 20% of TBW (10). This lower adiposity
was mainly the result of food restriction, because in a preliminary
study done on 24 rats put on the same dietary schedule but without
exercise, we observed that %FAT was reduced nearly as much as in the
present study and was similar between the groups (8.0 ± 0.7% for
fasted, 8.3 ± 1.1% for Glc, 9.2 ± 0.7% for WMP, and
8.7 ± 0.8% for CP
L rats). In contrast, in the rats of the
present study, fat mass adjusted for body weight (adiposity index,
%FAT) was smaller in the fasted and CP
L rats than in the WMP rats.
In the exercised rats, carcass weight adjusted for body weight (%CARC)
was larger in the fasted rats than in the WMP and Glc rats and larger
in the CP
L rats than in the WMP rats. The size of the vastus
lateralis (part of the quadriceps femoris), which works as an extensor
of the shank and was strongly requested during the run, was the largest in the CP
L rats (data not shown, P < 0.05). No
changes were observed on the other components of body weight.
|
|
Metabolic rate and respiratory quotient.
Resting metabolic rate (RMR) measured at 0800, i.e., 15 h after
the meal was given at 1700, has been taken as the basal metabolic rate
(BMR) of the rats. BMR was higher in the CPL group (2.44 ± 0.14 W) than in the other groups (1.82 ± 0.13 W for fasted, 1.95 ± 0.14 W for WMP, and 2.1 ± 0.09 W for Glc rats;
P < 0.05). Ingestion of the preexercise meals promoted
an increase in BMR during the hour preceding the exercise because of
the thermogenic effect of the meal (Fig.
2A). This increase was not
different among the three meals. On the other hand, glucose ingestion
promoted a marked increase in respiratory quotient (RQ) (Fig.
2B). After the exercise, all of the rats recovered rapidly
their preexercise BMR; i.e., no excess postexercise
QO2 was observed.
|
Rates of oxidation of protein, glucose, and lipid.
Before introduction of the preexercise meal, Pox, Gox, and Lox were low
and similar in the four groups (Fig. 3).
As illustrated by the RQ increase (Fig. 2B), the preexercise
glucose-enriched meal induced an increase in Gox, a decrease in Lox,
and a slight decrease in Pox. The WMP and CPL preexercise meal
increased Pox to ~0.35 W. During the exercise bout, Pox remained
elevated in the WMP group but did not increase further despite the
increased metabolic demand. In contrast, Pox continued to increase
during exercise in the CP
L group and reached 0.65 W at the end of
exercise, i.e., two times more than in the WMP group and four times
more than in the Glc and fasted groups. A protein-sparing effect was observed in the Glc group in which Pox was the lowest. The relative Pox
participation to energy expenditure during exercise was significantly higher in the CP
L group (8.7%) than in all of the other groups (P < 0.05), and higher in the WMP (6.4%) group than in the
fasted (3.6%) or glucose (2.0%)-fed groups (P < 0.05).
|
Plasma substrates.
Ingestion of the preexercise glucose-enriched meal promoted a rapid
increase in plasma glucose concentration that was apparent after 30 min
of exercise ([glucose] at t 90 min > [glucose] at t 50 min, P < 0.05) and remained above plasma glucose values observed in the fasted,
WMP, and CPL groups throughout the exercise period (Fig.
4). However, a rather large variability
in the individual responses prevented this difference from reaching
significance. In contrast, plasma glucose was the same in the fasted,
WMP, and CP
L groups throughout. In agreement with the changes
observed in plasma glucose, plasma lactate remained low in the fasted
WMP and CP
L groups and was increased in the Glc group.
|
|
Hepatic and hindlimb muscle glycogen content.
Before the exercise, glycogen content was higher in the liver of both
the fasted and Glc rats than in that of the WMP and CPL rats, and
higher in the red vastus lateralis of the glucose-fed than of the
fasted and CP
L-fed rats (Table 3).
Liver glycogen was more mobilized by exercise in the fasted and Glc
groups than in the WMP and CP
L groups. CP
L rats, in particular,
used very low amounts of liver glycogen: 7, 4.4, and 2.6 times less
than the fasted, Glc, and WMP rats, respectively. Fewer differences were observed according to the utilization of muscle glycogen; however,
overall, the WMP-fed rats used less muscle glycogen than the rats of
the other groups.
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In this study, we compared the effects of three different meals on
the rates of oxidation of glucose, lipid, and protein and on the
long-term consequences on body weight and body composition. The main
observations are that 1) the preexercise protein meals maintained a high rate of lipid oxidation during exercise equivalent to
fasted conditions; 2) the preexercise CPL meal appeared
more efficient to sustain LBM at the expense of fat mass.
Ingestion of the Glc meal 1 h before exercise increased Gox and decreased Pox and Lox. This phenomenon was induced by the fact that, immediately after the meal, lipolysis was reduced, leading to a rapid increase in the participation of Gox in basal metabolism and a subsequent decrease in fat oxidation (12). The influence of the preexercise rate of Gox on the subsequent rate of Gox during exercise has already been suggested (9) and is probably part of the mechanism that links the composition of the usual diet with the rate of substrate oxidation during exercise (19). Another potential mechanism for the enhanced Gox in the Glc-fed rats is the observation that, in these rats, liver as well as muscle glycogen was higher than in the other groups, a phenomenon that has also been shown to increase Gox during exercise (4, 15). These rats, in contrast to the fasted ones, which had some difficulties in completing the 2 h of exercise (this is also revealed in Fig. 2 by the fact that their metabolic rate tended to decrease before the end of the exercise), also completed their daily exercise program without revealing any sign of tiredness, showing that the Glc meal improved their endurance (6). The negative effect, however, was that part of the extra energy brought about by the Glc meal was not used but was stored in adipocytes. Therefore, when the main goal of exercise training is to reduce body adiposity, the ingestion of carbohydrates before exercise may be counterproductive.
In contrast to Glc, ingestion of the protein-rich meals before exercise
did not significantly affect Gox and Lox compared with the fasted
condition. In addition, Pox was increased and the reliance on
endogenous glycogen reserves reduced (20). Comparison of
the metabolic responses of the protein-fed and Glc-fed rats clearly
indicates that the primum movens of this difference was initiated
before the onset of exercise by the fact that neither of the protein
meals reduced preexercise lipid oxidation, and both increased amino
acid oxidation. Two observations suggest that Pox was stimulated
specifically by the amino acids brought by the meal: first, none of the
fasted and Glc-fed rats increased their rate of amino acid oxidation
during exercise; second, Pox was already increased in the CPL and
WMP rats before the onset of exercise. These rats also ran with more
ease than the fasted ones, and the CP
L-fed ones in particular
exhibited a certain will to run, as testified by their high and
sustained metabolic rates during the exercise. This last observation
argues in favor of the fact that both protein meals, but particularly
the CP
L meal, brought exogenous amino acids that could be used
during exercise to face the energy demand of the run.
Interestingly, CPL-fed rats gained more weight but fixed most of
this extra weight in their lean tissues, whereas Glc-fed and WMP-fed
rats gained mainly fat. This result suggests that increasing the rate
of lipid oxidation during and after exercise is not, per se, a
sufficient mechanism to favor the selective mobilization of adipose
reserves in the long term. Clearly, compensatory mechanisms must have
developed away from the exercise to induce tiny modifications in the
fate of the nutrients ingested with the night meal that allowed the
WMP-fed rats to recover during the night the excess lipids used during
exercise. The major difference in the metabolic response to CP
L and
WMP was the time course of utilization of the amino acids brought by
the meal. The higher solubility of the CP
L meal allowed Pox to
increase steadily during exercise, whereas Pox leveled in the WMP-fed
rats. This observation indicates that the delivery of amino acids by
the gut was less reduced in the CP
L-fed than in the WMP-fed rats. As
a result, the CP
L-fed rats ended the exercise with a rate of Pox
about two times higher than the rate in the WMP-fed ones. In addition, this high Pox rate continued after the completion of exercise, whereas
by only 2 h after the termination of exercise, Pox increased again
in the WMP-fed rats. All together, these data indicate that amino acid
availability was larger during and early after exercise in the
CP
L-fed rats. It is thus tempting to hypothesize that this kinetic
played in favor of a better fixation of the exogenous amino acids in
muscles and LBM in the CP
L-fed rats, in particular because more
amino acids were available immediately after exercise, i.e., at a
critical time to maximally enhance the processes of restoration of
proteins degraded during exercise (17, 21, 22).
In conclusion, this study revealed that ingestion of a protein meal
before exercise improved lipid oxidation but that this phenomenon was
not as sufficient to reduce adiposity in the long term as it was in the
CPL rats. Other mechanisms must thus be looked at to understand the
specific effect of the CP
L protein in this study. The data suggest
that the kinetic of delivery of dietary amino acids by the digestive
tract played a critical role, but the role played by the amino acid
composition of CP
L also deserves further investigation.
![]() |
ACKNOWLEDGEMENTS |
---|
This work was supported in part by a grant from the Ministère de la Recherche et de la Technologie (B01270).
![]() |
FOOTNOTES |
---|
Address for reprint requests and other correspondence: P. C. Even, UMR INRA/INA P-G, Physiologie de la Nutrition et du Comportement Alimentaire, Institut National de la Recherche Agronomique, 16 rue Claude Bernard, 75005 Paris, France (E-mail: even{at}inapg.inra.fr).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
May 15, 2002;10.1152/ajpendo.00132.2002
Received 25 March 2002; accepted in final form 30 April 2002.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Ballor, DL,
Katch VL,
Becque MD,
and
Marks CR.
Resistance weight training during caloric restriction enhances lean body weight maintenance.
Am J Clin Nutr
47:
19-25,
1988[Abstract].
2.
Bowtell, JL,
Leese GP,
Smith K,
Watt PW,
Nevill A,
Rooyackers O,
Wagenmakers AJ,
and
Rennie MJ.
Modulation of whole body protein metabolism, during and after exercise, by variation of dietary protein.
J Appl Physiol
85:
1744-1752,
1998
3.
Burvin, R,
Zloczower M,
and
Karniely E.
Double-vein jugular/inferior vena cava clamp technique for long term in vivo studies in rats.
Physiol Behav
63:
511-515,
1998[ISI][Medline].
4.
Costill, DL.
Carbohydrate nutrition before, during, and after exercise.
Fed Proc
44:
364-368,
1985[ISI][Medline].
5.
Dohm, GL,
Beeker RT,
Israel RG,
and
Tapscott EB.
Metabolic responses to exercise after fasting.
J Appl Physiol
61:
1363-1368,
1986
6.
El-Sayed, MS,
MacLaren D,
and
Rattu AJ.
Exogenous carbohydrate utilisation: effects on metabolism and exercise performance.
Comp Biochem Physiol
118:
789-803,
1997[ISI].
7.
Even, PC,
Perrier E,
Aucouturier JL,
and
Nicolaïdis S.
Utilisation of the method of Kalman filtering for performing the on-line computation of background metabolism in the free-moving, free-feeding rat.
Physiol Behav
49:
177-187,
1991[ISI][Medline].
8.
Even, PC,
Mokhtarian A,
and
Pelé A.
Practical aspects of indirect calorimetry in laboratory rats.
Neurosci Biobehav Rev
18:
435-447,
1994[ISI][Medline].
9.
Even, PC,
Rieth N,
Roseau S,
and
Larue Achagiotis C.
Substrate oxidation during exercise in the rat cannot fully account for training-induced changes in macronutrients selection.
Metabolism
47:
777-782,
1998[ISI][Medline].
10.
Even, PC,
Rolland V,
Roseau S,
Bouthegourd JC,
and
Tomé D.
Prediction of basal metabolism from organ size in the rat: relationship to strain, feeding, age, and obesity.
Am J Physiol Regul Integr Comp Physiol
280:
R1887-R1896,
2001
11.
Halseth, AE,
Flakoll PJ,
Reed EK,
Messina AB,
Krishna MG,
Lacy DB,
Williams PE,
and
Wasserman DH.
Effect of physical activity and fasting on gut and liver proteolysis in the dog.
Am J Physiol Endocrinol Metab
273:
E1073-E1082,
1997
12.
Horowitz, JF,
Mora-Rodriguez R,
Byerkey LO,
and
Coyle EF.
Lipolytic suppression following carbohydrate ingestion limits fat oxidation during exercise.
Am J Physiol Endocrinol Metab
273:
E768-E775,
1997
13.
Kasperek, GJ,
Conway GR,
Krayeski DS,
and
Lohne JJ.
A reexamination of the effect of exercise on rate of muscle protein degradation.
Am J Physiol Endocrinol Metab
263:
E1144-E1150,
1992.
14.
Katzeff, HL,
Ojamaa KM,
and
Klein I.
The effects of long-term aerobic exercise and energy restriction on protein synthesis.
Metabolism
44:
188-192,
1995[ISI][Medline].
15.
Levine, L,
Evans WJ,
Cadarette BS,
Fisher EC,
and
Bullen BA.
Fructose and glucose ingestion and muscle glycogen use during submaximal exercise.
J Appl Physiol
55:
1767-1771,
1983
16.
Lo, S,
Russell JC,
and
Taylor AW.
Determination of glycogen in small tissue samples.
J Appl Physiol
28:
234-236,
1970
17.
Rasmussen, BB,
Tipton KD,
Miller SL,
Wolf SE,
and
Wolfe RR.
An oral essential amino acid-carbohydrate supplement enhances muscle protein anabolism after resistance exercise.
J Appl Physiol
88:
386-392,
2000
18.
Sharp, PE,
and
La Regina MC.
The Laboratory RatA Volume in the Laboratory Animal Pocket Reference Series. Boca Raton, FL: CRC, 1998.
19.
Sherman, M.
Metabolism of sugars and physical performance.
Am J Clin Nutr
62, Suppl:
228S-241S,
1995[Abstract].
20.
Shimomura, Y,
Murakami T,
Nakai N,
Nagasaki M,
Obayashi M,
Li Z,
Xu M,
Sato Y,
Kato T,
Shimomura N,
Fujitsuka N,
Tanaka K,
and
Sato M.
Suppression of glycogen consumption during acute exercise by dietary branched-chain amino acids in rats.
J Nutr Sci Vitaminol
46:
71-77,
2000[ISI][Medline].
21.
Tipton, KD,
Ferrando AA,
Phillips DD,
Doyle D, JR,
and
Wolfe RR.
Postexercise net protein synthesis in human muscle from orally administered amino acids.
Am J Physiol Endocrinol Metab
276:
E628-E634,
1999
22.
Tipton, KD,
Rasmussen BB,
Miller SL,
Wolf SE,
Owens-Stovall SK,
Petrini BE,
and
Wolfe RR.
Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise.
Am J Physiol Endocrinol Metab
281:
E197-E206,
2001