High rates of exogenous carbohydrate oxidation from a mixture of glucose and fructose ingested during prolonged cycling exercise

A recent study from our laboratory has shown that a mixture of glucose and fructose ingested at a rate of 1.8 g/min leads to peak oxidation rates of approximately 1.3 g/min and results in approximately 55% higher exogenous carbohydrate (CHO) oxidation rates compared with the ingestion of an isocaloric amount of glucose. The aim of the present study was to investigate whether a mixture of glucose and fructose when ingested at a high rate (2.4 g/min) would lead to even higher exogenous CHO oxidation rates (>1.3 g/min). Eight trained male cyclists (VO2max: 68+/-1 ml/kg per min) cycled on three different occasions for 150 min at 50% of maximal power output (60+/-1% VO2max) and consumed either water (WAT) or a CHO solution providing 1.2 g/min glucose (GLU) or 1.2 g/min glucose+1.2 g/min fructose (GLU+FRUC). Peak exogenous CHO oxidation rates were higher (P<0.01) in the GLU+FRUC trial compared with the GLU trial (1.75 (SE 0.11) and 1.06 (SE 0.05) g/min, respectively). Furthermore, exogenous CHO oxidation rates during the last 90 min of exercise were approximately 50% higher (P<0.05) in GLU+FRUC compared with GLU (1.49 (SE 0.08) and 0.99 (SE 0.06) g/min, respectively). The results demonstrate that when a mixture of glucose and fructose is ingested at high rates (2.4 g/min) during 150 min of cycling exercise, exogenous CHO oxidation rates reach peak values of approximately 1.75 g/min.     

Effect of glycemic index and fructose content in lunch on substrate utilization during subsequent brisk walking

The purpose of the present study was to investigate the effect of glycemic index (GI) and fructose content in lunch on substrate utilization during subsequent brisk walking. Ten healthy young males completed 3 main trials in a counterbalanced crossover design. They completed 60 min of brisk walking at approximately 50% maximal oxygen consumption after consuming a standard breakfast and 1 of 3 lunch meals, i.e., a low GI meal without fructose (LGI), a low GI meal that included fructose beverage (LGIF), or a high GI meal (HGI). The 3 lunch meals were isocaloric and provided 1.0 g·kg?1 carbohydrate. Substrate utilization was measured using indirect respiratory calorimetry method. Blood samples were collected at certain time points. During the 2-h postprandial period after lunch, the incremental area under the blood response curve values of glucose and insulin were higher (p < 0.05) in the HGI trial than those in the LGI and LGIF trials (HGI vs. LGI and LGIF: glucose, 223.5 ± 24.4 vs. 92.5 ± 10.4 and 128.0 ± 17.7 mmol·min·L?1; insulin, 3603 ± 593 vs. 1425 ± 289 and 1888 ± 114 mU·min·L?1). During brisk walking, decreased carbohydrate oxidation was observed (p < 0.05) in the LGI trial than in the LGIF and HGI trials (LGI vs. LGIF and HGI: 60.8 ± 4.0 vs. 68.1 ± 6.0 and 74.4 ± 4.7 g). No difference was found in fat oxidation among the 3 trials (LGI vs. LGIF vs. HGI: 21.6 ± 2.3 vs. 19.2 ± 2.3 vs. 16.4 ± 2.2 g). It appeared that fructose content was an important influencing factor when considering the effect of different GI lunch meals on substrate utilization during subsequent moderate intensity exercise.     

Partial Substitution of Glucose with Xylitol Suppressed the Glycolysis and Selectively Inhibited the Proliferation of Oral Cancer Cells

Suitable diet for cancer survivors remains an unresolved challenge. Increased glucose utilization is a hallmark of various cancers. Therefore, alternative carbohydrate supplying normal tissue but retarding cancer growth is needed. This study investigated the effect of sugar alcohols on the proliferation of oral cancer cells compared to nontransformed cells and explored the mechanism. Six oral squamous cell carcinoma (CAL-27, FaDu, SCC4, SCC9, SCC15, and SCC25) and one nontransformed oral keratinocyte (OKF6/TERT2) lines were cultured in media containing 1 mg/ml glucose and 5.8 mg/ml xylitol or sorbitol, yielding equal energy input to control group (4.5 mg/ml glucose). Partial substitution of glucose with sugar alcohols especially xylitol significantly suppressed proliferation of oral cancer but not nontransformed cells. Despite the addition of isocaloric quantities of the sugars, cancer cells exposed to low glucose plus xylitol had retarded ATP generation and decreased activity of phosphofructokinase (PFK), the rate-limiting enzyme in glycolysis. Furthermore, D-xylulose, its key metabolic intermediate, enhanced the anticancer effect of xylitol. These findings suggested a selective anticancer activity of xylitol and the potential mechanism involving inhibition of glucose utilization. Partial substitution of glucose with xylitol may be a proper nutrient for oral cancer survivors, deserving further investigation in animal and clinical settings.     

Carbohydrate supplementation of horses during endurance exercise: comparison of fructose and glucose

To delay the onset of fatigue, endurance horses are often fed at rest stops during races. The resulting increase in blood insulin may adversely inhibit lipolysis. In humans, ingestion of fructose produces a smaller insulin rise than glucose. This study compared glucose and fructose as carbohydrate supplements for endurance horses. Three Arabian geldings were given 300 g of fructose (F), glucose (G) or 50% glucose: 50% fructose (GF), in 1.5 L water, by stomach tube. In the Resting Test, carbohydrate was administered at rest. Following treatment, blood samples were taken every 30 min for 8 h, and feces were collected for 24 h. Treatment did not affect fecal weight or water content. Plasma glucose and insulin responses did not differ among treatments. Post-treatment (60 min), plasma L-lactate tended to be higher (P = 0.06) after the F and GF treatments than after the G treatment. In the Exercise Test, two treadmill exercise bouts at 0 degrees incline (Bout 1: 90 min; Bout 2: 120 min) were separated by a 1-h rest period. A total distance of 36.84 km was covered at a mean speed of 2.9 m/s. Carbohydrate was administered 45 min before Bout 2. Plasma glucose and insulin at the start of Bout 2 were higher (P = 0.02 and 0.03, respectively) with the GF treatment than with the F treatment. However, during exercise, plasma glucose concentrations did not differ among treatments. We conclude that fructose is well-absorbed by horses and rapidly converted to glucose.     

Thermogenesis in men and women induced by fructose vs glucose added to a meal

Energy expenditure (EE) was measured by indirect calorimetry in 20 subjects (10 men and 10 women) for 30 min before and 6 h after the ingestion of a mixed meal containing 20% protein, 33% fat, and either 75 g glucose or 75 g fructose as carbohydrate source (47%). Diet-induced thermogenesis (DIT) and the rate of carbohydrate oxidation were significantly greater with fructose (12.4 +/- 0.6% and 54.8 +/- 2.1 g/6 h, respectively) than with glucose (10.7 +/- 0.7%, p less than 0.01, and 48.3 +/- 2.4 g/6 h, p less than 0.01, respectively). The DIT of male (12.1 +/- 1% and 13.9 +/- 0.8% with glucose and fructose, respectively) was greater than that of female subjects (9.2 +/- 0.7%, p less than 0.05, and 11.0 +/- 0.7%, p less than 0.05, respectively). In contrast to the glucose meal, negligible changes in plasma levels of glucose and insulin were observed with the fructose meal but plasma levels of lactate increased more with fructose than with glucose (peak values: 3.3 +/- 0.6 vs 1.5 +/- 0.1 mmol/L, respectively). When fructose provides the only carbohydrate source of a mixed meal, it induces a larger increase in carbohydrate oxidation and thermogenesis than when glucose is the carbohydrate source.     

Comparison of exogenous glucose, fructose and galactose oxidation during exercise using 13C-labelling

Six subjects exercised for 120 min on a cycle ergometer (65 (se 3) % VO2max) when ingesting a placebo or glucose, fructose or galactose (100 g in 1000 ml water) labelled with 13C. The oxidation of energy substrates including exogenous hexoses was compared using indirect respiratory calorimetry and 13CO2 production at the mouth. Total carbohydrate progressively decreased and total fat oxidation increased over the 120 min exercise period in the four experimental situations. During the 120 min of exercise, the amount of fructose oxidized (38.8 (se 2.6) g; 9.0 (se 0.6) % energy yield) was not significantly (approximately 4 %) lower than that of exogenous glucose (40.5 (se 3.4) g; 9.2 (se 0.8) % energy yield), while that of galactose (23.7 (se 3.5) g; 5.5 (se 0.9) % energy yield) was only 59 % and 61 % that of glucose and fructose, respectively. When compared with the placebo, the ingestion and oxidation of the three hexoses did not significantly modify fat oxidation or total carbohydrate oxidation, but it significantly reduced (9-13 %) endogenous carbohydrate oxidation. The present data indicate that fructose and exogenous glucose ingested during exercise could be oxidized at a similar rate, but that the oxidation rate of galactose was only approximately 60 % that of the exogenous glucose and fructose, presumably because of a preferential incorporation of galactose into liver glycogen (Leloir pathway). The reduction in endogenous carbohydrate oxidation was, however, similar with the three hexoses.     

Metabolic effects of glucose compared with invertose and a mixture of fructose, glucose and xylitol before and after moderate surgical trauma

The metabolic and clinical effects of different isocaloric carbohydrate infusions were studied perioperatively in 54 female patients undergoing cholecystectomy. The patients were randomized to six treatment groups, who received infusions only postoperatively (group 1, 2 and 3) or pre- as well as postoperatively (group 4, 5 and 6). One litre was given during 8 h as a 12% infusion solution. Glucose (group 1 and 4) was compared to invertose (group 2 and 5) and to a mixture of fructose, glucose and xylitol 2:1:1 i.e. Triofusin (group 3 and 6). The glycogen content in liver biopsies, taken peroperatively, was significantly higher when infusions were given preoperatively. No significant differences were found between groups, when comparing the different carbohydrate infusions. A minor glucose intolerance was noticed postoperatively, especially in group 4, whereas no fructose or xylitol intolerance was seen. Lactataemia was insignificant and acid-base balance normal in all groups. Serum urea concentrations were lower when preoperative infusions were given but without differences between groups 4, 5 and 6. Electrolytes, creatinine, hemoglobin, hematocrite and liver function tests were unaltered and the clinical course was uncomplicated in all cases. No side effects were observed. It is concluded that the infusion of one litre 12% Triofusin can be used as effectively and safely as 12% glucose and invertose before and after moderate surgical trauma. But no obvious advantage with Triofusin was revealed.     

Post-exercise substrate utilization after a high glucose vs. high fructose meal during negative energy balance in the obese

OBJECTIVE: To assess the effects of negative energy balance on the metabolic response of a meal containing either glucose or fructose as the primary source of carbohydrate after exercise in obese individuals in energy balance, or negative energy balance. RESEARCH METHODS AND PROCEDURES: Fourteen adults with mean body mass index (BMI) 30.3 +/- 1 kg/m2, age 26 +/- 2 years, and weight 93.5 +/- 5.4 kg, adhered to an energy-balanced (EB) or a negative energy-balanced (NEB) diet for 6 days. On Day 7, subjects exercised at 70% VO2peak for 40 minutes then consumed either high glucose (50 g of glucose, HG) or high fructose (50 g of fructose, HF) liquid meal. Substrate utilization was measured by indirect calorimetry for 3 hours. Blood samples were collected before exercise and 0, 30, 60, 120, and 180 minutes after consuming the meal. RESULTS: The HG produced 15.9% greater glycemic (p < 0.05) and 30.9% larger insulinemic (p < 0.05) responses than the HF under both EB and NEB conditions. After the NEB diet, carbohydrate and fat oxidation did not differ for HG and HF. In contrast, carbohydrate oxidation increased 31%, and fat oxidation decreased 39% with HF compared with HG after the EB diet. Thus, HF and HG consumed after exercise produced marked differences in macronutrient oxidation when obese subjects followed an EB diet, but no difference when adhering to a NEB diet. DISCUSSION: The data suggest that the use of fructose in supplements/meals may provide no additional benefit in terms of substrate utilization during a weight loss program involving diet and exercise.     

Carbohydrate feedings 1 h before exercise improves cycling performance

The effects of consuming two different amounts of liquid carbohydrate 1 h before exercise on the metabolic responses during exercise and on exercise performance were determined. Subjects consumed either 1.1 g (LC) or 2.2 g (HC) carbohydrate/kg body mass or a placebo (P). Subjects cycled at 70% of maximal oxygen consumption (VO2max) for 90 min and then underwent a performance trial. Blood glucose and insulin responses during exercise were different among the three trials. Total carbohydrate oxidation was greater for the carbohydrate trials compared with P. Time-trial performance was significantly improved by LC and HC. Despite elevated insulin concentrations at the start of and during exercise, and despite an initial drop in blood glucose, consumption of between 1.1 and 2.2 g liquid carbohydrate/kg body mass 60 min before moderately intense prolonged exercise can improve performance, presumably via enhanced carbohydrate oxidation.     

Comparative continuous-indirect-calorimetry study of two carbohydrates with different glycemic indices

Six healthy young men were studied by indirect calorimetry for 6 h after eating a meal composed of glucose or manioc starch (equivalent to 50 g dextrose). Blood was drawn every 30 min for 6 h to measure plasma glucose, free fatty acid (FFA), and insulin concentrations. The glycemic index of the starch was 57%. Plasma insulin and glucose concentrations were significantly higher from 150 to 210 min and FFA concentrations remained significantly lower from 210 to 360 min after starch than after glucose. Carbohydrate oxidation rose from a similar initial concentration for glucose and starch, to a constant concentration until 200 min before becoming significantly higher for the starch load until the end of the test. Total glucose oxidation was significantly higher with starch. Total fat oxidation did not differ after the two loads. A negative correlation was found between glucose oxidation and plasma FFA concentrations. Use of low-glycemic-index carbohydrates increases carbohydrate oxidation because of lower plasma FFA concentrations and fat oxidation.     

Effect of total parenteral nutrition with xylitol on protein and energy metabolism in thermally injured rats

The use of xylitol as an alternative carbohydrate calorie source in total parenteral nutrition may offer unique pharmacologic and nutritional properties in the therapy of the thermally injured. Male Sprague-Dawley rats (250 g) received a 15-second dorsal scald injury (25-30% BSA) and were parenterally fed isovolemic diets (60 ml/day) that provided 200 kcal/kg/d, 9.68 g of amino acids/kg/d, and 23.5% nonprotein calories (NPC) as fat for 3 days. The balance of NPC were provided as dextrose (Dex) or 50% xylitol:50% dextrose (Xyl/Dex). Rectus muscle and liver fractional protein synthetic rates (FSR, %/day), whole body leucine appearance (Flux), oxidation (OX), protein breakdown (PB), and synthesis (PS) were estimated using a 4-hour iv infusion of [1-14C]leucine on day 3. Mean values (+/- SE) for leucine kinetics (mumol leucine/hr/100 g), cumulative nitrogen balance (mg N) and plasma insulin concentration (Table I). (microU/mL). The partial replacement of dextrose calories with xylitol did not significantly alter whole body and tissue leucine kinetics, daily and cumulative nitrogen balance, insulin concentration, and energy expenditure (indirect calorimetry). These data indicate that xylitol may be useful as an alternative carbohydrate calorie source in parenteral nutrition to avoid possible deleterious side effects of glucose overfeeding in the critically ill but did not improve protein metabolism under the conditions of this study.     

Effects of glucocorticoids on hepatic sensitivity to insulin and glucagon in man

AIMS: This study was undertaken to determine the effects of a short-term dexamethasone treatment on hepatic sensitivities to insulin and glucagon. METHODS: Eleven healthy subjects were studied during one or several of four protocols. In all protocols, somatostatin was infused continuously to inhibit pancreatic hormone secretion. In protocol 1, basal insulin was infused over 300 min while glucagon was infused at a rate of 0.5 mg/kg(-1)/min(-1)during 180 min, then at a rate of 1.5 ng/kg(-1)/min(-1)during 150 min. In protocol 2, the same experiment was performed after a 2 day treatment with 8 mg/day dexamethasone. In protocol 3, the two-step glucagon infusion was performed during insulin infusion at a rate aimed to reproduce the hyperinsulinemia observed during protocol 2. In protocol 4, continuous basal insulin and low glucagon (0.5 mg/kg(-1)/min(-1)) were infused over 330 min. RESULTS: In protocol 1, plasma glucose rose transiently by 2.0 +/- 0.3 mmol/l when the glucagon rate was increased and glucose production increased by 1.4 +/- 0.5 micromol/kg(-1)/min(-1). In protocol 2, the insulin infusion rate (1.85 +/- 0.36 nmol/kg(-1)/min(-1)) required to maintain glycemia was 3.3-fold higher than during protocol 1. Glucagon-induced stimulation of glycemia (by 1.47 +/- 0.5 mmol/l) and endogenous glucose production (by 0.8 +/- 0.3 micromol/kg(-1)/min(-1)) were blunted, but not abolished. In protocol 3, endogenous glucose production was suppressed by 75% by hyperinsulinemia and was not stimulated when the glucagon infusion rate was increased. In protocol 4, endogenous glucose production did not change significantly with time. CONCLUSION: These results indicate that high dose glucocorticoids induce a marked hepatic insulin resistance. Stimulation of glucose production by hyperglucagonemia was maintained in spite of hyperinsulinemia which can be attributed to either hepatic insulin resistance and/or increased hepatic glucagon sensitivity.     

Effects of pure sugar vs. mixed starch fructose loads on food intake

Using a within-subject design, we gave subjects three different 520-530 kcal preloads in the form of puddings in a randomized fashion at weekly intervals. The puddings contained either 50 g of fructose or glucose as the sole carbohydrate source in a protein and fat mixture, or 50 g fructose plus 15 g of starch. Food intake was assessed 2.25 h after the preload was completed. Blood was drawn throughout and assayed for concentrations of glucose and insulin. When the preload contained fructose alone as the sole source of carbohydrate, subjects ate significantly fewer calories and less fat than when the preload contained glucose alone. When starch was added to the fructose preload, there was no significant reduction in calorie and fat intake. Effects on food intake paralleled the rise in plasma insulin levels produced by the different preloads. Implications for use of fructose as an adjunct to weight control efforts are discussed.     

Nutritional knowledge, attitudes, and dietary practices of the elderly

Non-nutritive sweeteners have been utilized in the diet of diabetic patients as agents to replace glucose and sucrose. Since saccharin might be removed from the market place, the nutritive sweeteners, fructose, xylitol, and sorbitol, are being considered as possible atlernatives. This review considers the effects of these nutritive sweeteners on the main dietary concerns in the diabetic diet, i.e., control of blood glucose levels, obesity, and hyperlipidemia. The potential side effects of these agents are also reviewed.     

Macronutrient disposal during controlled overfeeding with glucose, fructose, sucrose, or fat in lean and obese women

BACKGROUND: Previous short-term studies (< or =6 h) showed differences in energy expenditure (EE) and macronutrient oxidation in response to overfeeding with different types of dietary carbohydrate. This finding could have implications for obesity. OBJECTIVE: We used 96-h continuous whole-body calorimetry in 8 lean and 5 obese women to assess metabolic disposal (energy dissipation and glycogen or fat storage) of a controlled excess of dietary energy supplied as different carbohydrate sources or as fat. DESIGN: Five dietary treatments were applied in random order: energy balance (control) and overfeeding by 50% of energy requirements with fat (O(fat)) or predominantly with glucose, fructose, or sucrose (O(cho)). Macronutrient oxidation rates were assessed from nonprotein gaseous exchanges. Net macronutrient balances were calculated as cumulative differences between intake and oxidation. RESULTS: Increased EE in response to overfeeding dissipated 7.9% of the energy excess with a variation in EE of <1.7% across overfeeding treatments (NS). EE during the O(fat) treatment significantly exceeded that during the control treatment in the lean but not in the obese women. There were no significant differences between lean and obese women in macronutrient oxidation or balances, so data were pooled. O(cho) induced glycogen storage on day 1 ( approximately 100 g) but thereafter progressively stimulated carbohydrate oxidation so that balance was reached on days 3 and 4. Fat oxidation was proportionately suppressed. Of the excess carbohydrate, 74% was oxidized; there were no significant differences between the various O(cho) treatments. O(fat) stimulated fat oxidation by 18% and suppressed carbohydrate oxidation. On average, 12% of the excess energy was stored as glycogen and 88% as fat; there was no significant difference between overfeeding treatments. CONCLUSION: There was no significant difference in fat balance during controlled overfeeding with fat, fructose, glucose, or sucrose.     

Preventive action of food seasoning spices mixture on fructose-induced lipid abnormalities

High fructose feeding in rats induces insulin resistance, hyperinsulinemia, hyperglycemia and dyslipidemia. The present study was undertaken to determine the hypolipidemic effect of food seasoning spices mixture on fructose-fed insulin resistant rats. Male Wistar rats received a daily diet containing either 60% fructose or 60% starch. They were administered with the spices mixture at three different doses (10 mg, 30 mg or 50 mg/day/rat) orally 15 days later. At the end of 45 days of the experimental period fructose-fed rats displayed elevated plasma glucose and insulin levels and dyslipidemia which included elevated levels of cholesterol, triglycerides, free fatty acids, reduced high density lipoprotein cholesterol and increased very low density lipoprotein cholesterol. Alterations in tissue lipid levels were also observed. Simultaneous treatment with spices mixture along with fructose diet resulted in the normalization of plasma glucose and insulin levels and restoration of lipid levels in plasma and tissues. The insulin potentiating action of the active principles in these spices may contribute to the hypolipidemic effect of spices mixture in high fructose-fed rats.     

Effect of preexercise ingestion of modified cornstarch on substrate oxidation during endurance exercise

The purpose of this study was to investigate differences in substrate oxidation between dextrose (DEX) and unmodified (UAMS) and acid/alcohol-modified (MAMS) cornstarches. Seven endurance-trained men (VO2peak = 59.1 +/- 5.4 mL.kg-1.min-1) participated in 2 h of exercise (66.4% +/- 3.3% VO2peak) 30 min after ingesting 1 g/kg body weight of the experimental carbohydrate or placebo (PLA). Plasma glucose and insulin were elevated after DEX (P < 0.05) compared with UAMS, MAMS, and PLA. Although MAMS and DEX raised carbohydrate oxidation rate through 90 min of exercise, only MAMS persisted throughout 120 min (P < 0.05 compared with all trials). Exogenous-carbohydrate oxidation rate was higher in DEX than in MAMS and UAMS until 90 min of exercise. Acid/alcohol modification resulted in augmented carbohydrate oxidation with a small, sustained increase in exogenous-carbohydrate oxidation rate. MAMS appears to be metabolizable and available for oxidation during exercise.     

Metabolic effects of fructose and glucose: implications for food intake

Differential effects of fructose and glucose preloads on carbohydrate metabolism and later food intake were examined in both lean and obese subjects. In study 1, a preload of either 50 g of fructose or glucose was administered in solution, and food intake at a buffet lunch presented 2.25 h after preload was assessed. Significant differences in caloric intake were observed between load conditions with the fructose group consuming fewer calories than the glucose group. Obese subjects demonstrated significantly greater insulin responses to the preload compared with lean subjects, and insulin levels of obese subjects at 15, 30, and 45 min after preload were found to correlate significantly with amount consumed. Incorporation of fructose or glucose into a mixed meal format in study 2 revealed no differences in subsequent caloric intake as a function of either type of preload or percent overweight. Differing insulin levels are discussed as a possible mechanism for differential food intake.     

Comparison between a glucose-fructose-xylitol solution and a sole glucose solution for surgical patients with glucose tolerance impairment

The metabolic response to the postoperative delivery of a sole glucose solution or a glucose-fructose-xylitol solution, and their effects upon carbohydrate metabolism, in patients with glucose tolerance impairment, were evaluated. Twenty four patients who showed an abnormal 75g-OGTT or were noninsulin-dependent diabetics were divided in two groups. The GFX-B group (n = 11) received a 10.5% solution, containing glucose, fructose and xylitol at 4:2:1 ratio, and the PHY-3 group (n = 13) received a 10% glucose solution, both, continuously infused for 3 days postoperatively. The infusion of PHY-3 tended to produce a higher increase in blood glucose than the infusion of GFX-B, that was significantly different on the 3POD (P less than 0.05). The increase in IRI and CPR was also significantly greater in PHY-3 group than in GFX-B group on the 3POD (P less than 0.05). We concluded that it was not only the slight lower glucose load of the GFX-B solution, but also, the different infused carbohydrate substrate which had influenced the magnitude of insulin secretion and the blood glucose level. Then, its use in glucose intolerant patients may be of some benefit to partially minimize the postoperative hyperglycemic response.     

Glutamine supplementation increases postprandial energy expenditure and fat oxidation in humans

BACKGROUND: Glutamine interacts with insulin-mediated glucose disposal, which is a component of the increase in energy expenditure (EE) after a meal. The study aim was to examine if glutamine supplementation alters postmeal nutrient oxidation. METHODS: Ten healthy young adults consumed a mixed meal (6.5 kcal/kg, 14%:22%:64% = protein:fat:carbohydrate) containing either glutamine (GLN:1.05 kcal/kg) or an isocaloric amino acid mixture (alanine: glycine:serine = 2:1:0.5; CON). GLN and CON treatments were administered on separate days in random order for each subject. EE, nonprotein respiratory quotient (RQ), and fat and carbohydrate oxidation rates were assessed using indirect calorimetry for 30 minutes before and for 360 minutes after meal ingestion. RESULTS: Premeal EE and RQ were similar between treatments. The increase in EE above basal during both early (0-180 minutes) and late (180-360 minutes) postmeal phases was greater in GLN than in CON (p < .05), resulting in postmeal EE being 49% greater during the total postmeal phase (p < .05). Net change of carbohydrate oxidation was 38% higher during the early phase with GLN (p < .05), whereas it was 71% lower during the later phase (p < .05). GLN enhanced fat oxidation by approximately 42 kcal compared with CON during the late phase (p < .05). CONCLUSIONS: Glutamine supplementation with a mixed meal alters nutrient metabolism to increase postmeal EE by increasing carbohydrate oxidation during the early postmeal phase and fat oxidation during the late postmeal phase. Consideration must be given to the potential that these postprandial changes in EE are related to glutamine-mediated changes in insulin action and consequently glucose disposal.