Meals with similar energy densities but rich in protein,fat, carbohydrate,or alcohol have different effects on energy expenditure and substrate metabolism but not on appetite and energy intake

BACKGROUND: It has been suggested that the satiating power of the 4 macronutrients follows the oxidation hierarchy: alcohol > protein > carbohydrate > fat. However, the experimental evidence for this is still scarce. OBJECTIVE: The goal was to investigate the effects on appetite, energy intake and expenditure, and substrate metabolism of meals rich in 1 of the 4 macronutrients. DESIGN: Subjective appetite sensations, ad libitum food intake, energy expenditure, substrate metabolism, and hormone concentrations were measured for 5 h after breakfast meals with similar energy density and fiber contents but rich in either protein (32% of energy), carbohydrate (65% of energy), fat (65% of energy), or alcohol (23% of energy). Subjects were normal-weight, healthy women (n = 9) and men (n = 10) studied in a crossover design. RESULTS: There were no significant differences in hunger or satiety sensations or in ad libitum energy intake after the 4 meals. Diet-induced thermogenesis was larger after the alcohol meal (by 27%; P < 0.01), whereas protein produced an intermediary response (17%; NS) compared with carbohydrate and fat (meal effect: P < 0.01). After the alcohol meal, fat oxidation and leptin concentrations were greatly suppressed (meal effects, P < 0.0001 and P < 0.05) and triacylglycerol concentrations were as high as after the fat meal. CONCLUSION: Intake of an alcohol-rich meal stimulates energy expenditure but suppresses fat oxidation and leptin more than do isoenergetically dense meals rich in protein, carbohydrate, or fat. Despite differences in substrate metabolism and hormone concentrations, satiety and ad libitum energy intake were not significantly different between meals. Our data, therefore, do not support the proposed relation between the macronutrient oxidation hierarchy and the satiety hierarchy.     

Ghrelin and glucagon-like peptide 1 concentrations, 24-h satiety, and energy and substrate metabolism during a high-protein diet and measured in a respiration chamber

BACKGROUND: The mechanism of protein-induced satiety remains unclear. OBJECTIVE: The objective was to investigate 24-h satiety and related hormones and energy and substrate metabolism during a high-protein (HP) diet in a respiration chamber. DESIGN: Twelve healthy women aged 18-40 y were fed in energy balance an adequate-protein (AP: 10%, 60%, and 30% of energy from protein, carbohydrate, and fat, respectively) or an HP (30%, 40%, and 30% of energy from protein, carbohydrate, and fat, respectively) diet in a randomized crossover design. Substrate oxidation, 24-h energy expenditure (EE), appetite profile, and ghrelin and glucagon-like peptide 1 (GLP-1) concentrations were measured. RESULTS: Sleeping metabolic rate (6.40 +/- 0.47 compared with 6.12 +/- 0.40 MJ/d; P < 0.05), diet-induced thermogenesis (0.91 +/- 0.25 compared with 0.69 +/- 0.24 MJ/d; P < 0.05), and satiety were significantly higher, and activity-induced EE (1.68 +/- 0.32 compared with 1.86 +/- 0.41; P < 0.05), respiratory quotient (0.84 +/- 0.02 compared with 0.88 +/- 0.03; P < 0.0005), and hunger were significantly lower during the HP diet. There was a tendency for a greater 24-h EE during the HP diet (P = 0.05). Although energy intake was not significantly different between the diet groups, the subjects were in energy balance during the HP diet and in positive energy balance during the AP diet. Satiety was related to 24-h protein intake (r2 = 0.49, P < 0.05) only during the HP diet. Ghrelin concentrations were not significantly different between diets. GLP-1 concentrations after dinner were higher during the HP than during the AP diet (P < 0.05). CONCLUSION: An HP diet, compared with an AP diet, fed at energy balance for 4 d increased 24-h satiety, thermogenesis, sleeping metabolic rate, protein balance, and fat oxidation. Satiety was related to protein intake, and incidentally to ghrelin and GLP-1 concentrations, only during the HP diet.     

Diet induced thermogenesis

OBJECTIVE: Daily energy expenditure consists of three components: basal metabolic rate, diet-induced thermogenesis and the energy cost of physical activity. Here, data on diet-induced thermogenesis are reviewed in relation to measuring conditions and characteristics of the diet. METHODS: Measuring conditions include nutritional status of the subject, physical activity and duration of the observation. Diet characteristics are energy content and macronutrient composition. RESULTS: Most studies measure diet-induced thermogenesis as the increase in energy expenditure above basal metabolic rate. Generally, the hierarchy in macronutrient oxidation in the postprandial state is reflected similarly in diet-induced thermogenesis, with the sequence alcohol, protein, carbohydrate, and fat. A mixed diet consumed at energy balance results in a diet induced energy expenditure of 5 to 15 % of daily energy expenditure. Values are higher at a relatively high protein and alcohol consumption and lower at a high fat consumption. Protein induced thermogenesis has an important effect on satiety.In conclusion, the main determinants of diet-induced thermogenesis are the energy content and the protein- and alcohol fraction of the diet. Protein plays a key role in body weight regulation through satiety related to diet-induced thermogenesis.     

Effect of meal frequency on the thermic effect of food in women

The effect of meal frequency on the thermic effect of food (TEF), also referred to as dietary induced thermogenesis (DIT), was investigated in eighteen non-obese female subjects. Their metabolic rate before and after consuming the test meal was measured by open circuit indirect calorimetry using the Douglas bag technique, while the subjects were in the resting state (lying down). Eight subjects consumed a high carbohydrate-low fat (HCLF) meal providing 70, 19 and 11 per cent of the energy content from carbohydrate, fat and protein, respectively, and ten other subjects consumed a low carbohydrate-high fat (LCHF) meal providing 24, 65 and 11 per cent of the energy from carbohydrate, fat and protein, respectively. On two separate occasions, each subject consumed the appropriate diet either as one large meal containing 5040 kJ (1200 kcal) or as two smaller meals each containing 2520 kJ (600 kcal). TEF values were calculated for 6 h after the test meal and the mean values after consuming the HCLF meal were 377.0 +/- 30.0 kJ (90 +/- 7.2 kcal) and 381.0 +/- 26.5 kJ (91.0 +/- 6.3 kcal) for the one meal and the two meals, respectively. The mean TEF values for the subjects who consumed the LCHF meal wre 356.0 +/- 23.0 kJ (85.0 +/- 5.5 kcal) and 340 +/- 15.9 kJ (81.0 +/- 3.8 kcal) for the one meal and the two meals, respectively. No significant differences were found between the two feeding regimens (HCLF, P = 0.94; LCHF, P = 0.64) as well as between the compositions (P = 0.57). Thus, meal frequency and meal composition did not seem to influence the TEF.     

High protein high fibre snack bars reduce food intake and improve short term glucose and insulin profiles compared with high fat snack bars

The replacement in the diet of refined carbohydrate and fat with fibre and protein has been shown to promote satiety and improve glucose and insulin profiles. It is less clear whether the macronutrient composition of individual foods such as snacks have any meaningful impact on metabolic parameters and satiety. We examined if the consumption of higher protein higher fibre snack bars would result in reducing outcome measures such as food intake and glucose and insulin patterns compared to a conventional isocaloric high fat high refined carbohydrate snack bar. Twenty three women were randomized in a single blind cross over study with 2 interventions, a high fat high sugar snack bar and a comparatively higher protein, higher fibre snack bar intervention. Snack bars were eaten at mid morning and mid afternoon, and a standard breakfast and ad libitum buffet lunch. The glucose and insulin responses over 9 hours were significantly lower (P = 0.014 and P = 0.012 respectively) during the high protein snack bar intervention. Peak glucose levels were also 16% lower after the morning HP bar (P <0.001). The morning high protein bar reduced the energy intake at the buffet lunch meal by 5% (4657 +/- 1025KJ vs 4901 +/- 1186KJ, P < 0.05). Altering the macronutrient composition of a snack bar can assist in reducing the energy intake at a subsequent meal and improve short term glucose and insulin profiles.     

Diet-induced thermogenesis: variations among three isocaloric meal-replacement shakes

OBJECTIVE: We determined whether significant differences exist in diet-induced thermogenesis among three low-calorie (1042 kJ, or 250 kcal), liquid meal-replacement shakes of different macronutrient compositions: 1) 100% protein; 2) 62% protein, 28% carbohydrate, and 10% fat (high protein/low carbohydrate); and 3) 17% protein, 75% carbohydrate, and 8% fat (low protein/high carbohydrate). METHODS: Eight subjects (three men and five women) completed a randomized, double-blind, crossover investigation involving three separate resting-and-reclining energy expenditure measurements taken before and after consumption of one of the shakes. Resting-and-reclining metabolic gas-exchange measurements were taken for 30 min; subjects then drank a 20-oz shake, after which 3 h of additional resting-and-reclining gas-exchange measurements were taken. RESULTS: A statistically significant difference in diet-induced thermogenesis (P<0.02) was found between the low protein/high carbohydrate shake (79+- 48 kJ) and the high protein/low carbohydrate shake (209+/-108 kJ). No significant differences in diet-induced thermogenesis were found in comparison with the 100% protein shake (136+/-81 kJ). No significant differences in the respiratory exchange ratio over 3 h (P=0.33) were found. CONCLUSIONS: Different types of low-calorie meal-replacement shakes do invoke significantly different thermogenic responses over a 3-h period. However, the 130-kJ (31-kcal) difference found in diet-induced thermogenesis represents only a small contribution to daily energy expenditure so that practical applications for weight-control management appear to be minimal.     

Energy expenditure, satiety, and plasma ghrelin, glucagon-like peptide 1, and peptide tyrosine-tyrosine concentrations following a single high-protein lunch

High-protein (HP) foods are more satiating and have a higher thermogenic effect than normal protein foods over the short-term as well as the long-term. We hypothesized that acute effects of higher protein intake on satiety may be related to acute metabolic and hormonal responses. The study was a single-blind, randomized, crossover design. Subjects underwent 2 indirect calorimetry tests for measurement of energy expenditure (EE) and substrate oxidation. After a standard subject-specific breakfast, subjects received 1 of 2 randomly assigned treatments: an appropriate protein (AP) lunch (10% energy (E) protein, 60%E carbohydrate, 30%E fat), or a HP lunch (25%E protein, 45%E carbohydrate, 30%E fat). The increase in postlunch EE tended to be greater after the HP lunch (0.85 +/- 0.32 kJ/min) than after the AP lunch (0.73 +/- 0.22 kJ/min) (P = 0.07). The respiratory quotient did not differ between the HP (0.84 +/- 0.04) and the AP (0.86 +/- 0.04) treatments. Satiety visual analogue scales (VAS) scores were significantly higher 30 and 120 min after the HP lunch than after the AP lunch. The area under the curve of the VAS score for satiety was higher after the HP lunch (263 +/- 61 mm/h) than after the AP lunch (AP 236 +/- 76 mm/h) (P < 0.02). Effects of the meals on satiety and diet-induced thermogenesis did not occur simultaneously with changes in plasma ghrelin, glucagon-like peptide 1, and peptide tyrosine-tyrosine concentrations. A single HP lunch, therefore, does not exert its acute effect on satiety through increased concentrations of satiety-related hormones. Other factors, which may explain the HP effect on satiety, may be metabolites or amino acids.     

The cafeteria diet--an inappropriate tool for studies of thermogenesis

Diet-induced thermogenesis (DIT) is defined as a regulatory, facultative component of energy expenditure, stimulated by overeating, which helps maintain energy balance. DIT may play a central role in the regulation of energy expenditure and in the etiology of certain types of obesity. Most experiments testing the existence or the mechanisms of DIT have used the cafeteria diet for the purposes of stimulating hyperphagia, a requisite for studies of DIT. Yet such a diet is inappropriate for studies of thermogenesis because its use prevents researchers from obtaining an experimental outcome that can be clearly interpreted. The primary limitation of the cafeteria diet is that its nutritional composition is uncontrolled. The diet is self-selected from a variety of supermarket foods that tend to be high in fat and/or carbohydrate and low in protein, vitamins and minerals. Hence, the diets consumed by the animals are likely to be deficient in protein, vitamins or minerals. There is evidence that dietary deficiency of protein, vitamins and minerals can increase thermogenesis and in protein-adequate diets, the balance of fat and carbohydrate in the diet can also influence thermogenesis with high carbohydrate diets increasing thermogenesis more than isoenergetic high fat diets. Hence, an observed increase in thermogenesis in cafeteria fed animals might be interpreted incorrectly to be the result of increased energy consumption when it is attributable to dietary imbalance or deficiency. Because the diet is self-selected, it is possible for each animal to choose a diet that varies in nutritional composition from that selected by every other animal, so control of dietary intake is compromised.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of dietary fatty acid composition on substrate utilization and body weight maintenance in humans

Background/purpose

Dietary fat content is a primary factor associated with the increase in global obesity rates. There is a delay in achieving fat balance following exposure to a high-fat (HF) diet (≥ 40 % of total energy from fat) and fat balance is closely linked to energy balance. Exercise has been shown to improve this rate of adaptation to a HF diet. Recently, however, the role of dietary fatty acid composition on energy and macronutrient balance has come into question.

Methods

We chose studies that compared monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), and saturated fatty acids (SFA). We have reviewed studies that measured diet-induced thermogenesis (DIT), energy expenditure (EE), or fat oxidation (FOx) in response to a HF meal challenge, or long-term dietary intervention comparing these fatty acids.

Results

While single-meal studies show that SFA induce lower DIT and FOx compared to unsaturated fats, the effect of the degree of unsaturation (MUFA vs. PUFA) appears to yet be determined. Long-term dietary interventions also support the notion that unsaturated fats induce greater EE, DIT, and/or FOx versus SFA and that a high MUFA diet induces more weight loss compared to a high SFA diet. Sex and BMI status also affect the metabolic responses to different fatty acids; however, more research in these areas is warranted.

Conclusion

SFA are likely more obesigenic than MUFA, and PUFA. The unsaturated fats appear to be more metabolically beneficial, specifically MUFA ≥ PUFA > SFA, as evidenced by the higher DIT and FOx following HF meals or diets.     

The acute effects of olive oil v. cream on postprandial thermogenesis and substrate oxidation in postmenopausal women

The influence of the source of dietary fat on postprandial thermogenesis and substrate oxidation rates, was examined in twelve postmenopausal women aged 57-73 years, with BMI 21.9-38.3 kg/m(2). A single blind, randomised, paired comparison of two high-fat, isoenergetic, mixed test meals was conducted. The major source of fat was either cream (CREAM) or extra virgin olive oil (EVOO). RMR, diet-induced thermogenesis (DIT) and substrate oxidation rates over 5 h were measured by indirect calorimetry. There were no differences in body weight, RMR, fasting carbohydrate or fat oxidation rates between the two occasions. DIT (EVOO 97 (SD 46) v. CREAM 76 (SD 69) kJ/5 h and EVOO 5.2 (SD 2.5) v. CREAM 4.1 (SD 3.7)% energy) did not differ between the two test meals. The postprandial increase in carbohydrate oxidation rates, relative to their respective fasting values (DeltaCOX), was significantly lower following the EVOO meal (EVOO 10.6 (SD 8.3) v. CREAM 17.5 (SD 10) g/5 h; paired t test, P=0.023), while postprandial fat oxidation rates (DeltaFOX) were significantly higher (EVOO 0.0 (SD 4.4) v. CREAM -3.6 (sd 4.0) g/5 h; P=0.028). In the eight obese subjects, however, DIT was significantly higher following the EVOO meal (EVOO 5.1 (SD 2.0) v. CREAM 2.5 (sd 2.9) %; P=0.01). This was accompanied by a significantly lower DeltaCOX (EVOO 10.9 (SD 9.9) v. CREAM 17.3 (SD 10.5) g/5 h; P=0.03) and significantly higher DeltaFOX (EVOO 0.11 (SD 4.4) v. CREAM -4.1 (SD 4.5) g/5 h, P=0.034). The present study showed that olive oil significantly promoted postprandial fat oxidation and stimulated DIT in abdominally obese postmenopausal women.     

Effect of liquid dietary supplements on energy intake in the elderly

BACKGROUND: Undernutrition is a risk factor for increased mortality in older adults. Therapeutic intervention includes the administration of liquid dietary supplements. OBJECTIVE: We investigated the effect of liquid dietary supplements on satiation, satiety, and energy intake in older adults. DESIGN: This study had 2 phases in a within-subject, repeated-measures design. The energy intake of 15 elderly (aged >70 y) and 15 younger (aged 20-40 y) healthy subjects was measured after 4 liquid preloads: water, high fat, high carbohydrate, and high protein. The preloads were administered within 5 min of a test meal in phase 1 and >or=60 min before the test meal in phase 2. Palatability, fullness, and hunger were assessed by using visual analogue scales. RESULTS: Mean energy consumption of the test meals was significantly lower in the older than in the younger subjects (P = 0.001), as was mean macronutrient consumption of fat and carbohydrate (P = 0.002 and 0.001, respectively). Mean energy intake and macronutrient consumption were higher in phase 2 than in phase 1 in both older and younger subjects (P < 0.05). Satiety lasted longer in older than in younger subjects after the high-protein and high-fat preloads (P = 0.001). CONCLUSION: In the elderly, administration of dietary supplements between meals instead of with meals may be more effective in increasing energy consumption.     

Carbohydrate-restricted diets high in either monounsaturated fat or protein are equally effective at promoting fat loss and improving blood lipids

BACKGROUND: When substituted for carbohydrate in an energy-reduced diet, dietary protein enhances fat loss in women. It is unknown whether the effect is due to increased protein or reduced carbohydrate. OBJECTIVE: We compared the effects of 2 isocaloric diets that differed in protein and fat content on weight loss, lipids, appetite regulation, and energy expenditure after test meals. DESIGN: This was a parallel, randomized study in which subjects received either a low-fat, high-protein (LF-HP) diet (29 +/- 1% fat, 34 +/- 0.8% protein) or a high-fat, standard-protein (HF-SP) diet (45 +/- 0.6% fat, 18 +/- 0.3% protein) during 12 wk of energy restriction (6 +/- 0.1 MJ/d) and 4 wk of energy balance (7.4 +/- 0.3 MJ/d). Fifty-seven overweight and obese [mean body mass index (in kg/m(2)): 33.8 +/- 0.9] volunteers with insulin concentrations >12 mU/L completed the study. RESULTS: Weight loss (LF-HP group, 9.7 +/- 1.1 kg; HF-SP group, 10.2 +/- 1.4 kg; P = 0.78) and fat loss were not significantly different between diet groups even though the subjects desired less to eat after the LF-HP meal (P = 0.02). The decrease in resting energy expenditure was not significantly different between diet groups (LF-HP, -342 +/- 185 kJ/d; HF-SP, -349 +/- 220 kJ/d). The decrease in the thermic effect of feeding with weight loss was smaller in the LF-HP group than in the HF-SP group (-0.3 +/- 1.0% compared with -3.6 +/- 0.7%; P = 0.014). Glucose and insulin responses to test meals improved after weight loss (P < 0.001) with no significant diet effect. Bone turnover, inflammation, and calcium excretion did not change significantly. CONCLUSION: The magnitude of weight loss and the improvements in insulin resistance and cardiovascular disease risk factors did not differ significantly between the 2 diets, and neither diet had any detrimental effects on bone turnover or renal function.     

The effect of etomoxir on 24-h substrate oxidation and satiety in humans

BACKGROUND: The carnitine O-palmitoyltransferase I (EC 2.3.1.21) inhibitor etomoxir inhibits fatty acid oxidation, and hepatic fatty acid oxidation has been suggested to be a metabolic satiety signal in subjects who consume high-fat diets. OBJECTIVE: We investigated substrate oxidation and satiety after repeated administrations of etomoxir or placebo in subjects who consumed a high-fat diet. DESIGN: In a randomized crossover design consisting of three 5-d treatments, we fed 10 healthy men [mean +/- SE age: 25.6 +/- 1.7 y; mean +/- SE body mass index (in kg/m(2)): 21.8 +/- 0.3] a high-fat diet twice and a low-fat diet once. The subjects consumed each diet at home for 3 consecutive days, after which they spent 36 h in energy balance in a respiration chamber. During the chamber stays with the high-fat treatments, etomoxir or placebo was administered in 5 doses (600 mg etomoxir in total). Blood samples were obtained on the mornings of days 4 and 5 of each treatment, and appetite profiles were assessed. RESULTS: Mean (+/-SE) 24-h respiratory quotients were significantly (P < 0.05) higher with repeated administrations of etomoxir (0.833 +/- 0.004) than with repeated administrations of placebo (0.814 +/- 0.006), and mean (+/-SE) 24-h whole-body fat oxidation tended to be less (13.7%, P = 0.06) with administration of etomoxir (136.0 +/- 5.2 g/d) than with administration of placebo (157.5 +/- 5.6 g/d). With the etomoxir treatment, fat balance was positive (P < 0.0001) and carbohydrate balance was negative (P < 0.001), whereas with the placebo treatment, neither of the balances was significantly different from zero. Hunger and satiety ratings were not affected under these conditions. CONCLUSIONS: Etomoxir decreased whole-body fat oxidation, as indicated by the respiratory quotients in the healthy subjects. With the current protocol, however, hunger and satiety ratings were not affected.     

The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review

For years, proponents of some fad diets have claimed that higher amounts of protein facilitate weight loss. Only in recent years have studies begun to examine the effects of high protein diets on energy expenditure, subsequent energy intake and weight loss as compared to lower protein diets. In this study, we conducted a systematic review of randomized investigations on the effects of high protein diets on dietary thermogenesis, satiety, body weight and fat loss. There is convincing evidence that a higher protein intake increases thermogenesis and satiety compared to diets of lower protein content. The weight of evidence also suggests that high protein meals lead to a reduced subsequent energy intake. Some evidence suggests that diets higher in protein result in an increased weight loss and fat loss as compared to diets lower in protein, but findings have not been consistent. In dietary practice, it may be beneficial to partially replace refined carbohydrate with protein sources that are low in saturated fat. Although recent evidence supports potential benefit, rigorous longer-term studies are needed to investigate the effects of high protein diets on weight loss and weight maintenance.     

Oral supplements differing in fat and carbohydrate content: effect on the appetite and food intake of undernourished elderly patients

BACKGROUND & AIMS: Since fat, relative to other macronutrients, has low satiety and high energy density, it may have therapeutic application for supplementing energy intake. This study compared the effect of isoenergetic (1050 kJ) high fat or high carbohydrate oral supplements, given at breakfast, on the short-term appetite and energy intake in undernourished elderly subjects. METHODS: Sixteen hospitalised, undernourished (body mass index: 20 +/- 3 kg/m2), elderly (77 +/- 8 yr) people were randomly allocated to a control or 1 of 2 supplement groups [fat: carbohydrate: protein (% energy) was 70:25:5 or 25:70:5]. In each group, energy intake (24-h food consumption) and appetite (visual analogue scales) were assessed over 3 consecutive days. RESULTS: Mean energy intake significantly (P = 0.0035) increased following supplementation: high fat 6973 kJ/d, high carbohydrate 6906 kJ/d vs. control 6079 kJ/d but mean voluntary 24-h energy intake remained unaffected. Compared to controls, supplemented subjects experienced reduced hunger (P = 0.07) between breakfast and lunch, but showed no difference over the whole day (P = 0.55). CONCLUSIONS: Under these study conditions a 1050 kJ oral supplement, irrespective of macronutrient composition, does not cause voluntary short-term energy intake compensation in undernourished elderly people.     

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.     

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.     

Basal and postprandial substrate oxidation rates in obese women receiving two test meals with different protein content

BACKGROUND & AIMS: Fuel utilisation and storage in lean and obese subjects seem to be differently affected by the macronutrient distribution intake. The aim of this intervention study was to explore the extent to which the fat mass status and the macronutrient composition of an acute dietary intake influence substrate oxidation rates. METHODS: Fuel utilisation in 26 women, 14 obese (BMI = 37.1 +/- 1.1 kg/m2) and 12 lean (BMI = 20.6 +/- 0.5 kg/m2) was measured over 6 h to compare the metabolic effect of a single balanced protein (HC) meal and a high protein (HP) single meal, which were designed to supply similar energy contents (1672 kJ). The macronutrient composition as a percentage of energy of the HC meal was 55% carbohydrate, 15% protein and 30% fat, while the HP meal contained 40% carbohydrate, 30% protein and 30% fat. Nutrient oxidation rates and energy expenditure were calculated by indirect calorimetry (hood system), whereas exogenous amino acid oxidation was estimated from the 13C isotopic enrichment of breath after oral administration of L[1-13C]leucine. RESULTS: Fasting lipid oxidation was higher in the obese than in the lean women (P < 0.05), and it was significantly correlated with body fatness (P < 0.01). A single HP meal consumption produced higher postprandial fat oxidation as compared with HC meal intake (P < 0.02), in both obese and lean subjects, with no apparent changes in glucose oxidation rates. Furthermore, postprandial fat utilisation after the test meal intake was higher in obese than in the lean women (P < 0.01). The time course of 13CO2 in breath followed a similar pattern in both dietary groups, although a non-statistically significant higher trend in protein and 13C-leucine oxidation was found in the HP group. CONCLUSIONS: Net lipid oxidation depends on both short-term dietary composition intake and fat body mass, being significantly higher after a relatively high protein meal as compared to a balanced diet intake and in obese women as compared to lean controls.     

Food and macronutrient intake of male adolescent Kalenjin runners in Kenya

A nutritional survey based on twelve adolescent male Kalenjin runners in Kenya during a 2-week field study was carried out in order to determine the composition of their diet and make a comparison with macronutrient recommendations for athletes. Food samples were collected for analysis of macronutrient distribution and energy content from main meals and the macronutrient distribution and energy content of additional food intake were based on the information of a 24 h recall interview and estimated from food tables. The diet of the Kalenjin runners was very high in carbohydrate (71 % 8.7 g/kg body weight per d) and very low in fat (15 %). Intake of total protein (13 %; 1.6 g/kg body weight per d) was above the daily intake recommended by the Food and Agriculture Organization/World Health Organization/United Nations University (FAO/WHO/UNU), while essential amino acid intake was estimated to be in the borderline-to-low range based on FAO/WHO/UNU recommendations for children <12 years and adults. The energy intake was mainly derived from vegetable sources (90 %) with maize and kidney beans as the staple food (81 %). The diet of the Kalenjin runners met recommendations for endurance athletes for total protein and most essential amino acid intake as well as carbohydrate intake even though it was based on a small range of food items.     

Oxidative and nonoxidative macronutrient disposal in lean and obese men after mixed meals.

Oxidative and nonoxidative macronutrient disposal rates were measured in lean and obese males randomly fed mixed meals containing 0, 33, 67, 100, and 134 kJ/kg fat-free mass (0, 8, 16, 24, and 32 kcal/kg). Body composition, preprandial and postprandial energy expenditure, and macronutrient concentrations in the extracellular space were measured. Relationships among carbohydrate, fat, and protein disposal rates; body weight; and body composition were examined. Oxidative and nonoxidative disposals of macronutrients were not different between the lean and obese groups. Glucose was preferentially oxidized and fat was preferentially stored after nutrient ingestion. Macronutrient storage increased linearly with caloric intake. Oxidative and nonoxidative macronutrient disposals were completed within 8 h after ingesting the meals. Serum insulin concentrations rose to 3000-6000 pmol/L in two obese men after their two largest meals. Eight hours after nutrient ingestion, concentrations of macronutrient substrates, metabolic products, and insulin were indistinguishable from preprandial values.