The affinity of milk fat globule membrane fragments and buttermilk proteins to hydroxyapatite.

Buttermilk differs from skim milk by the presence of milk fat globule membrane (MFGM) fragments that are released during cream churning. Milk fat globule membrane is rich in health-promoting components, such as phospholipids and membrane proteins, but these compounds have a negative impact on buttermilk techno-functional properties in dairy applications. The isolation of MFGM from buttermilk improved its functionality while also recovering the MFGM bioactive components. Hydroxyapatite (HA) can be used to extract MFGM by adsorption via charged site interactions. However, the affinity of HA to MFGM or the main buttermilk proteins (casein micelles [CM], ß-LG, and α-LA) is not known. The influence of important physicochemical parameters such as pH and temperature on these interactions is also unclear. For each buttermilk component, a quartz crystal microbalance diffusion analysis was performed to determine the maximum adsorption time and the attached mass density on HA-coated gold sensors. The influence of pH, ionic strength (IS), and temperature (T) on the affinity of each buttermilk component for HA particles was assessed using a 3-levels and 3-factors Box-Behnken design. The absorption rate was highest for the CM, followed by ß-LG and α-LA, and then by the MFGM. Nevertheless, the final maximal attached mass densities to the HA were similar for the MFGM and CM, and 2.5 times higher than for ß-LG and α-LA. This difference can be explained by the higher number of binding sites found in CM and their heavier mass. The model obtained by the Box-Behnken design plan showed that the adsorption of the CM changed with T, pH, and IS. These results suggest that the techno-functional properties of buttermilk may be restored by specifically extracting MFGM with HA. Experiments are ongoing to determine conditions for fractionating MFGM directly from buttermilk.

Effect of reverse osmosis and ultra-high-pressure homogenization on the composition and microstructure of sweet buttermilk.

Buttermilk (BM), the by-product of butter making, is similar to skim milk (SM) composition. However, it is currently undervalued in dairy processing because it is responsible for texture defects (e.g., crumbliness, decreased firmness) in cheese and yogurt. One possible way of improving the incorporation of BM into dairy products is by the use of technological pretreatments such as membrane filtration and homogenization. The study aimed at characterizing the effect of preconcentration by reverse osmosis (RO) and single-pass ultra-high-pressure homogenization (UHPH) on the composition and microstructure of sweet BM to modify its techno-functional properties (e.g., protein gel formation, syneresis, firmness). The BM and RO BM were treated at 0, 15, 150, and 300 MPa. Pressure-treated and control BM and RO BM were ultracentrifuged to fractionate them into the following 3 fractions: a supernatant soluble fraction (top layer), a colloidal fraction consisting of a cloudy layer (middle layer), and a high-density pellet (bottom layer). Compositional changes in the soluble fraction [lipid, phospholipid (PL), protein, and salt], as well as its protein profile by PAGE analysis, were determined. Modifications in particle size distribution upon UHPH were monitored by laser diffraction in the presence and absence of sodium citrate to dissociate the casein (CN) micelles. Microstructural changes in pressure-treated and non-pressure-treated BM and RO BM particles were monitored by confocal laser scanning microscopy. Particle size analysis showed that UHPH treatment significantly decreased the size of the milk fat globule membrane fragments in BM and RO BM. Also, pressure treatment at 300 MPa led to a significant increase in the recovery of total lipids, CN, calcium, and phosphate in the BM soluble fraction (top layer) following ultracentrifugation. However, PL were primarily concentrated in the pellet cloud (middle layer), located above the pellet in BM concentrated by RO. In contrast, PL were evenly distributed between soluble and colloidal phases of BM. This study provides insight into the modifications of sweet BM constituents induced by RO and UHPH from a compositional and structural perspective.

Effect of alkalinization and ultra-high-pressure homogenization on casein micelles in raw and pasteurized skim milk.

Mechanical and physicochemical treatments of milk induce structural modifications of the casein (CN) micelles, affecting their techno-functional properties in dairy processing. Here, we studied the effect of alkalinization and ultra-high-pressure homogenization (UHPH) on CN micelles in raw skim milk (rSM) and pasteurized skim milk (pSM). The pH of both skim milks (approximately 6.7) was adjusted to 8.5 and 10.5 before UHPH at 100, 200, and 300 MPa. The structural changes of the CN micelles during the treatments were assessed using laser diffraction, transmission electron microscopy, and turbidity measurements. Finally, ultracentrifugation (70,000 × g for 1 h at 20°C) was carried out to evaluate the protein's distribution between the supernatant (serum phase) and the pellet (colloidal phase) by gel electrophoresis and protein concentration measurement. Alkalinization of both skim milks induced a significant reduction in turbidity, whereas an increase of the average particle size was observed, the effect being more severe in pSM than rSM. At alkaline pH, more proteins were recovered in the serum phase, which suggested that the CN underwent major rearrangements into nonsedimentable CN forms of various sizes, as confirmed by transmission electron microscopy. The amount of CN found in the serum phase at pH 8.5 also increased with the UHPH pressure. Although UHPH did not influence the average CN micelle size at pH 6.7 and 8.5, a pressure-dependent decrease was observed at pH 10.5 for both skim milks. The structural changes of the CN micelles observed in this study throughout the combination of alkalinization and UHPH could be of interest for developing new dairy ingredients with improved functionality.

On the use on hydroxyapatite suspensions for the separation of milk fat globule membrane components from buttermilk.

The milk fat globule membrane (MFGM), which surrounds and stabilizes the fat globules, is released in buttermilk during cream churning. MFGM has many health benefits due to its composition rich in phospholipids and membrane proteins. Many techniques have been tried to separate the MFGM from the remaining milk solids non-fat, but they are challenging to carry out at an industrial scale. This research proposes a new approach to separating MFGM from buttermilk. This paper assessed the efficacy of hydroxyapatite (HA) cristal in interacting with MFGM isolates obtained from either raw or pasteurized cream. Different HA to MFGM ratios were used (10:1 and 20:1) to determine the impact of HA concentration on the adsorption. The results showed a very high affinity of the MFGM for HA and suggested the potential for its separation from buttermilk to improve its valorization.

Use of X-ray micro tomography to study the microstructure of loose-packed and compacted milk powders.

The use of X-rays to evaluate food microstructure has developed considerably in recent years. In this work we used X-ray micro tomography (XMT) to visualize the microstructure of loose-packed and compacted samples of spray-dried skim milk powder (SMP) and whole milk powder (WMP) and to quantify the proportion of both interstitial and occluded air voids in each sample. Visual scrutiny of the acquired XMT images showed details of the microstructure of the milk powders such as the spherical morphology of the particles, the size of the particles and internal air voids of various sizes. Within loose-packed powders, the proportion of air voids was higher (13% average) in WMP than in SMP. This was reversed in the compacted powders, in which the proportion of air voids was higher in SMP. The disparity in the proportion of air voids in both loose-packed and compacted samples of SMP and WMP was attributed to the size, shape and surface properties of the particles.

The stimulus-secretion coupling of glucose-induced insulin release. VII. A proposed site of action for adenosine-3',5'-cyclic monophosphate.

Glucose-induced insulin release is thought to result from the following sequence of events in the beta cell: glucose metabolism leading to the production of a metabolic signal, net calcium uptake by the beta cell in response to the signal, and interaction between calcium and a microtubular-microfilamentous system, leading to emiocytosis of the secretory granules. Dibutyryl-cyclic AMP (db-cAMP) and theophylline are known to potentiate glucose-induced insulin release, their insulinotropic action being most marked at high glucose concentrations. Based on the above mentioned concepts, it was considered in the present experiments that the primary site of action of cAMP in the beta cell could correspond to either a facilitation of glucose metabolism, a modification of calcium distribution, or an interaction with the microtubular-microfilamentous system. The first of these hypotheses appeared unlikely because db-cAMP and theophylline, in sharp contrast with other agents known to affect glucose metabolism in the beta cell, did not modify glucose-induced calcium uptake by isolated islets incubated at high glucose concentrations. The last hypothesis also appeared unlikely since theophylline did not interfere with the deleterious effect of colchicine on the microtubular system, and since vincristine or colchicine did not differentially affect the respective insulinotropic action of glucose and theophylline. An effect of cAMP upon calcium distribution in the beta cell was suggested by the following findings. Whereas glucose and leucine were unable to promote insulin release in the absence of extracellular calcium, the addition of db-cAMP or theophylline to the calcium-depleted media partially restored theinsulinotropic action of glucose and leucine. Moreover, theophylline caused a dramatic increase in (45)Ca efflux from perifused islets, even in the absence of glucose. It is concluded that the insulinotropic action of cAMP could be due to a glucose-independent translocation of calcium within the beta cell, from an organelle-bound pool to a cytoplasmic pool of ionized calcium readily available for transport across the cell membrane.

Effect of iron saturation on the recovery of lactoferrin in rennet whey coming from heat-treated skim milk.

This study aimed to determine the effect of thermal treatments on the recovery of lactoferrin in whey coming from rennet-coagulated skim milk. The impact of lactoferrin iron saturation was also assessed using skim milk spiked with different lactoferrin iron forms. The recovery of lactoferrin in the rennet whey fraction was determined by reverse-phase HPLC. One- and 2-dimensional sodium dodecyl sulfate PAGE analyses were performed on rennet curds to characterize the protein interactions involving lactoferrin in heated milk. The extent of lactoferrin recovered in the whey fraction was found to reduce as the heating temperature increased. The binding of iron by lactoferrin improved its thermal stability and its recovery in the whey fraction. Poly-acrylamide gel electrophoresis results showed that the association of lactoferrin in the unheated milk rennet curd involved noncovalent interactions, whereas upon heating, lactoferrin also interacted via an intermolecular disulfide link. Depending on the severity of the heat treatment, lactoferrin aggregates with Cys-containing proteins (beta-lactoglobulin, alpha-lactalbumin, alpha(s2)-casein, and kappa-casein) occurred by intermolecular thiol/disulfide exchange reactions. These noncovalent and covalent interactions explained the lower recovery of lactoferrin in heated milk.

Total parenteral nutrition in the newborn: impact of the quality of infused energy on nitrogen metabolism.

To separate the respective influence of the level and source of infused energy on nitrogen metabolism, 32 studies were performed in 16 appropriate-for-gestational-age newborn infants (birth weight 2150 +/- 115 g, means +/- SEM). In a cross-over design, each patient received two 6-d periods of isocaloric and isonitrogenous (450 mg.kg-1.d-1) infusions, differing only by the source of calories (high or low fat intakes). Half of the patients were studied at 60 kcal.kg-1.d-1, the other half at 80 kcal.kg-1.d-1. Nitrogen balance, urinary 3-methylhistidine excretion, glycemia, and insulin were compared. The results suggest that for an intravenous energy intake ranging from 60 to 80 kcal.kg-1.d-1, glucose and fat provide an equivalent nitrogen sparing effect in the newborn infant. At an energy level covering maintenance requirements, it is the infant's clinical condition rather than the source of energy which affects most the magnitude of amino acids participation in energy metabolism.

Influence of a transscrotal testosterone propionate administration on the serum level of selected hormones of the hypophyso-gonadal axis.

This study was designed to examine the effect of a percutaneous scrotal administration of testosterone propionate (TP) on selected blood variables, in order to identify a reliable anti-doping probe liable to disclose the illicit use of testosterone. Twelve healthy adult males gave their informed consent for the study. Each morning (8:30) and for 10 consecutive days (D), a placebo (D:1,2,3,...8,9,10) or a testosterone propionate (200mg TP on D:... 4,5,6,7...) scrotal patch was installed. On D2 or D3 (placebo-treated) or D7 (TP-treated), venous blood samples were collected at 5 min intervals from 9:00 until 13:00. Serum LH, FSH, 17alpha-hydroxyprogesterone (17HP), testosterone (T), estradiol (E2) and SHBG contents were analysed by immunoassays. The high sampling frequency revealed that TP was associated with the complete abolition of serum LH pulses. Although statistically significant, TP treatment was not related to explicit changes in serum FSH, E2, T/E2 and T/SHBG. TP-induced effects were most significant on serum LH, T and 17HP and were most clearly illustrated by a bi-dimensional distribution plot of serum values of the latter variables. The expression of a combination of the latter parameters could eventually serve to detect testosterone misusers.

Metabolic availability of oral glucose during exercise: a reassessment.

The purpose of this study was to reassess the metabolic availability of oral glucose during prolonged exercise in man, using 13C-labeling and a computation procedure (J Appl Physiol 69:1047-1052, 1990) that correctly takes into account changes in isotopic composition of CO2 arising from oxidation of endogenous substrates (Rendo). These changes are due to glucose ingestion associated with exercise. Each of the seven subjects completed three 2-hour periods of exercise at 67% maximum oxygen consumption (VO2max) on an ergocycle, with ingestion of water (1,000 mL) or 60 g (in 1,000 mL water) of 13C-labeled glucose at two levels of enrichment (13C/12C = 1.11482% and 1.13303%). As expected, Rendo significantly increased from rest to exercise with water ingestion (1.09888% +/- .00196% to 1.09970% +/- .00175%) and with glucose ingestion (1.10002% +/- .00159%) due to changes in the respective contributions of endogenous carbohydrates and fat to energy requirements as assessed by the respiratory exchange ratio (RER). When changes in Rendo were taken into account, the estimated amount of exogenous glucose oxidized was 38.8 +/- 10.3 g. Much higher values were found when Rendo at rest or during exercise with water ingestion were used in the computation (42.3 +/- 10.3 to 65.1 +/- 20.5 g) according to the commonly used method. Examination of data in the literature indicates that the reported oxidation rate of exogenous glucose (g/min) is significantly related to oxygen consumption (VO2) (L/min; r = .592) and that exogenous glucose contributes approximately 14% to 17% to the energy requirement.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma atrial natriuretic peptide during brief upright and supine exercise in humans.

The factors associated with the exercise-induced increase in plasma atrial natriuretic peptide (ANP) have not been clearly established. Thus the purpose of the study was to further document the stimulus for the exercise-induced release of ANP and to examine the role of ANP in the control of hydromineral balance during exercise. Eight healthy male volunteers (25.1 +/- 4.5 yr) were submitted to a graded cycling exercise in both the upright and supine positions. Venous blood was sampled at rest and at the end of each 5-min work load at 40, 60, and 80% maximal oxygen uptake (Vo2max), at maximal exercise, and during recovery through an indwelling catheter for the determination of plasma vasopressin, aldosterone, catecholamines, plasma renin activity, and ANP concentrations. Results indicate a significant increase in ANP (pg/ml) from rest to maximal exercise in the upright position [rest, 21.9 +/- 10.2; 40%, 24.7 +/- 12.6; 60%, 32.4 +/- 17*; 80%, 47.8 +/- 27.7*; 100% Vo2max, 65.9 +/- 34.5* (*P less than or equal to 0.05)]. Supine concentrations were significantly higher than upright at 40 (37.9 +/- 15.2), 60 (54.0 +/- 18.8), and 80% Vo2max (68.9 +/- 16.6). Plasma ANP during maximal exercise was similar in both positions. Plasma vasopressin, aldosterone, renin activity, and catecholamines increased with increasing exercise intensity in both positions, although lower values were systematically observed in the supine position. The association of higher plasma ANP and blunted plasma vasopressin, plasma renin activity, and norepinephrine concentrations during supine exercise suggests that ANP may exert modulatory effects on the control of the hydromineral hormonal system during exercise.

Plasma atriopeptin response to prolonged cycling in humans.

The exercise-induced increase in plasma atriopeptin (ANP) has been related to exercise intensity. The independent effect of duration on the ANP response to dynamic exercise remains incompletely documented. The purpose of this study was to describe the time course of plasma ANP concentration during a 90-min cycling exercise protocol and to examine this in light of concurrent variations in plasma arginine vasopressin (AVP), aldosterone (ALD), and catecholamine (norepinephrine and epinephrine) concentrations as well as plasma renin activity (PRA). Seven male and four female healthy college students (23 +/- 2 yr) completed a prolonged exercise protocol on a cycle ergometer at an intensity of 67% of maximal O2 uptake. Venous blood was sampled through an indwelling catheter at rest, after 15, 30, 45, 60, and 90 min of exercise, and after 30 min of passive upright recovery. Results (means +/- SE) indicate an increase in ANP from rest (22 +/- 2.6 pg/ml) at 15 min of exercise (45.3 +/- 7.4 pg/ml) with a further increase at 30 min (59.4 +/- 9.8 pg/ml) and a leveling-off thereafter until completion of the exercise protocol (51.7 +/- 10.7 pg/ml). In plasma ALD and PRA, a significant increase was found from rest (ALD, 21.4 +/- 6.4 ng/dl), PRA, 2.5 +/- 0.5 ng.ml-1.h-1 after 30 min of cycling, which continued to increase until completion of the exercise (ALD 46.6 +/- 8.7 ng/dl, PRA 9.5 +/- 0.9 ng.ml-1.h-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Menstrual cycle phase dissociation of blood glucose homeostasis during exercise.

The purpose of this investigation was to evaluate the effects of 24-h carbohydrate-poor diet on metabolic and hormonal responses induced by prolonged exercise in both follicular (FP) and luteal (LP) phases of the menstrual cycle. At mid-FP and at mid-LP, seven eumenorrheic young women [means +/- SE; chronological age, 21.1 +/- 0.6 yr; O2 uptake (VO2) peak, 43.7 +/- 2.0 ml X kg-1 X min-1; body fat, 19.2 +/- 2.0%] were subjected to a 90-min bicycle exercise period at an intensity representing 63% of their measured VO2 peak. Venous blood samples obtained before and during exercise were analyzed for levels of substrates (glucose, lactate, free fatty acids, glycerol) and hormones (luteinizing hormone, progesterone, estradiol, insulin, glucagon, cortisol, catecholamines). Contrary to FP, a significant (P less than 0.01) decrease in blood glucose concentration was observed after 70 and 90 min of exercise during LP. Significant phase differences were also observed for blood lactate (highest in FP), cortisol (highest in LP), and progesterone (highest in LP). Although not significantly different, tendencies for menstrual phase dissociations were noticed for some of the other measured variables. Hence, a menstrual phase dissociation in circulating glucose level, unmasked by a prolonged exercise performed after a 24-h carbohydrate-poor diet, suggests to the authors a specific metabolic involvement for gonadotrophic and/or gonadal hormones.

Oxidation of exogenous medium-chain free fatty acids during prolonged exercise: comparison with glucose.

The purpose of this study was to compare the oxidation rate of exogenous 13C-labeled medium-chain triacylglycerols (MCT) with that of an isocaloric amount of exogenous [13C]glucose and to evaluate their respective effects on endocrine and metabolic responses to moderate prolonged exercise. To take into account changes in isotopic composition of 13CO2 arising from oxidation of endogenous substrates because of exercise and/or substrate ingestion that overestimates the oxidation rate of exogenous substrates, two levels of 13C enrichment were used for each substrate. Six young healthy males (20-26 yr of age) completed five 2-h periods of exercise at 65 +/- 3% maximal O2 uptake (VO2max) on a cycle ergometer at 7-day intervals: one control exercise with water ingestion, two trials with ingestion of 25 g of [13C]MCT (trioctanoate) 1 h before exercise, and two trials with 57 g of [13C]glucose (dissolved in 1,000 ml of water) ingested during exercise. Exogenous MCT and glucose began to be oxidized within the first 30 min of exercise, and the oxidation rate increased progressively until the end of exercise for both substrates. Over the 2-h period of exercise, 13.6 +/- 3.5 g of ingested MCT and 36.4 +/- 8.2 g of exogenous glucose were oxidized, which represent 54 and 64%, respectively, of the total amount ingested. The contribution of MCT (119 +/- 31 kcal) and glucose (140 +/- 36 kcal) was not significantly different and represented 7 and 8.5%, respectively, of the total energy expenditure.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of selective hepatic vagotomy on running endurance in rats.

The liver, through the afferent ways of the vagus hepatic nerve, may influence metabolic adaptations during exercise. This study assesses the functional significance of this hepatic innervation by determining the effect of a selective hepatic vagotomy (HV) on running endurance time during submaximal activity in rats subjected to an overnight 50% food restriction. The time to exhaustion was similar for the groups of HV and sham-operated (SHM) rats [66 +/- 15 vs. 64 +/- 21 (SD) min]. The HV group was associated with higher resting levels (P less than 0.05) of hepatic glycogen and plasma glucose. No significant differences were observed between HV and SHM rats at rest and after exercise for muscle glycogen, free fatty acids, insulin, glucagon, and lactate concentrations. These data indicate that if hepatic glucoreceptors do exist and contribute to the metabolic regulation of exercise, their functional significance is secondary to more important regulatory mechanisms.

Use of 13C substrates for metabolic studies in exercise: methodological considerations.

The purpose of this study is to outline a common mistake made when the rate of oxidation of exogenous substrates during prolonged exercise is computed using 13C naturally labeled substrates. The equation proposed and commonly used in the computation does not take into account that exercise and/or exogenous substrate ingestion modifies the composition of the mixture of endogenous substrates oxidized and, consequently, the isotopic composition of CO2 arising from oxidation of endogenous substrates. The recovery of 13C and the amount of exogenous substrate oxidized are thus overestimated. An adequate procedure for the computation of exogenous substrate oxidation taking into account changes in isotopic composition of CO2 arising from oxidation of endogenous substrates is suggested. Results from a pilot experiment (4 subjects) using this procedure indicate that over 2 h of exercise (66% of maximal O2 uptake), with ingestion of 60 g of glucose, 39 +/- 4 g of glucose were oxidized. Estimates made without taking into account changes in isotopic composition of CO2 arising from oxidation of endogenous substrates range between 70 +/- 8 and 44 +/- 3 g depending on 1) the isotopic composition of exogenous glucose and 2) the isotopic composition of expired CO2 taken as reference (rest or exercise without glucose ingestion). These observations suggest that results from previous studies of exogenous substrate oxidation during exercise using 13C labeling should be used with caution.

Oxidation of a glucose polymer during exercise: comparison with glucose and fructose.

The purpose of this study was to compare the oxidation of 13C-labeled glucose, fructose, and glucose polymer ingested (1.33 g.kg-1 in 19 ml.kg-1 water) during cycle exercise (120 min, 53 +/- 2% maximal O2 uptake) in six healthy male subjects. Oxidation of exogenous glucose and glucose polymer (72 +/- 15 and 65 +/- 18%, respectively, of the 98.9 +/- 4.7 g ingested) was similar and significantly greater than exogenous fructose oxidation (54 +/- 13%). A transient rise in plasma glucose concentration was observed with glucose ingestion only. However, plasma insulin levels were similar with glucose and glucose polymer ingestions and significantly higher than with water or fructose ingestion. Plasma free fatty acid and glycerol responses to exercise were blunted with carbohydrate ingestion. However, fat utilization was not significantly different with water (82 +/- 14 g), glucose (60 +/- 3 g), fructose (59 +/- 11 g), or glucose polymer ingestion (60 +/- 8 g). Endogenous carbohydrate utilization was significantly lower with glucose (184 +/- 22 g), glucose polymer (187 +/- 31 g), and fructose (211 +/- 18 g) than with water (239 +/- 30 g) ingestion. Plasma volume slightly increased with water ingestion (7.4 +/- 4.5%), but the decrease was similar with glucose (-7.6 +/- 5.1%) and glucose polymer (-8.2 +/- 4.6%), suggesting that the rate of water delivery to plasma was similar with the two carbohydrates.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma catecholamines in the aorta and the phrenicoabdominal vein in exercising dogs.

Plasma epinephrine and norepinephrine concentrations were measured in the aorta and phrenicoabdominal vein in five dogs at rest and during short-duration mild- and moderate-intensity exercise and during prolonged mild-intensity exercise. Plasma epinephrine and norepinephrine concentrations increased with exercise in both the aorta and the phrenicoabdominal vein. Plasma epinephrine concentration was much higher in the phrenicoabdominal vein than in the aorta (24-43 times). Plasma epinephrine concentrations in the aorta and phrenicoabdominal vein were significantly correlated (r = 0.88). This confirms that peripheral epinephrine concentration is a reliable index of the activity of the adrenal medulla during exercise. The epinephrine-to-norepinephrine ratio in the phrenicoabdominal vein was stable (4:1) throughout the experimental protocol, suggesting that the proportion of the two amines released by the adrenal medulla did not vary through this range of adrenal activity in dogs.

Respective oxidation of exogenous glucose and fructose given in the same drink during exercise.

We computed the respective amounts of exogenous glucose (G) and fructose (F), which are oxidized during exercise when ingested simultaneously, with the use of 13C labeling. Six subjects exercised for 2 h at 60.7 +/- 2.9% of maximal O2 uptake on a cycle ergometer while ingesting 50 or 100 g of G or F or a mixture of 50 g each of G and F in 500 ml of water. The amount of exogenous G oxidized increased from 37.8 +/- 2.2 to 58.3 +/- 8.1 g when the total amount ingested increased from 50 to 100 g. The amount of F oxidized was significantly lower (32.2 +/- 1.2 and 45.8 +/- 2.6 g for the 50 and 100 g ingested, respectively). When 50 g each of G and F were simultaneously ingested in the same drink, the amounts oxidized (39.5 +/- 4.8 and 34.1 +/- 1.5 g, respectively) were similar to those observed when 50 g of G or F were ingested separately. The cumulative amount of exogenous hexoses oxidized (73.6 +/- 6.6 g) was 21% larger than when 100 g of G were ingested. This finding could be due to the fact that the routes for absorption and metabolism of exogenous G and F are at least partly different, resulting in less competition for oxidation when a mixture of these two hexoses is ingested than when an isocaloric amount of G is ingested. From a practical point of view, these data may provide experimental support for using mixtures of carbohydrates in the energy supplements for endurance athletes.