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BACKGROUND: It has been suggested that hunger may be delayed and food intake reduced under metabolic conditions that spare carbohydrate oxidation. OBJECTIVE: Our objective was to examine the role of glucose metabolism in the control of food intake in men by using medium-chain triacylglycerols (MCTs) to spare carbohydrate oxidation. DESIGN: In 10 male volunteers, isolated and deprived of any time cues, we studied the effects of 4 lunches on hunger ratings, the duration of satiety, the amount of food ingested at dinner, energy expenditure, substrate oxidation, and plasma variables until the time of the dinner request. One lunch was a basic 2310-kJ meal containing 40 kJ fat substitute (Sub lunch). The 3 other lunches consisted of the same basic meal supplemented with either 1200 kJ long-chain triacylglycerols (LCT lunch), 1200 kJ MCTs (MCT lunch), or 900 kJ carbohydrate plus 300 kJ LCTs (Cho lunch). RESULTS: Energy expenditure was not significantly different after the different lunches, but carbohydrate oxidation was lower after the MCT and LCT lunches than after the Cho lunch. Fat oxidation was greater after the MCT and LCT lunches. The time of the dinner request was significantly delayed after the Cho lunch. Food intake at dinner was significantly lower after the MCT lunch than after the Sub and Cho lunches, but the dinner meal request was not delayed. CONCLUSION: Carbohydrate may have a greater role in the duration of satiety than does fat, but MCTs may play an active role in other aspects of the control of food intake, especially in satiation at the next meal.

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BACKGROUND: It has been proposed that leptin provides a hormonal link between adipose stores and food intake. OBJECTIVE: This study investigated the role of leptin in the prandial pattern. DESIGN: In experiment 1, a spontaneous prandial pattern was recreated in 6 young, normal-weight men who were deprived of time cues and had blood withdrawn continuously at a frequency of one tube every 5 min. Meals were consumed ad libitum and dinner was requested voluntarily. Data from a second experiment, conducted in 8 subjects, were used to confirm the changes in leptin during the intermeal interval (IMI). RESULTS: Plasma leptin gradually rose to a peak (62 +/- 18% of the lunch concentration) during the IMI and declined before the dinner request (-21 +/- 4% of the peak concentration). This preprandial decline was confirmed in experiment 2 (-15 +/- 9%). The leptin concentration at lunch and fat-free mass were the only significant predictors of the IMI (both: r(2) = 0.91, P = 0.03). With fat intake at lunch, the leptin concentration at lunch was a positive predictor of the area under the curve of plasma fatty acids during the IMI (r(2) = 0.95, P = 0.01). Moreover, the leptin concentration at lunch was negatively correlated with energy intake in the first course of this meal (r = -0.95, P < 0.005). A similar result was found at dinner (r = -0.85, P < 0.05). Last, the change in leptin was predicted accurately by changes in glucose, triacylglycerol, and fatty acids (r(2) = 0.87, P < 10(-5)). CONCLUSION: Plasma leptin concentrations increase during a spontaneous IMI and decline before the onset of a meal. The results argue for a role of leptin in the prandial pattern through fatty acid peripheral disposal.

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We examined the effects of nutrient composition of a 1 MJ afternoon snack, consumed in a satiety state, on the spontaneous onset of the next meal in 11 young male subjects deprived of any temporal cues. All subjects attended four experimental sessions scheduled 2 weeks apart. The first, baseline, session served to establish: (1) the subjects' ad libitum lunch intake, (2) the latency of the spontaneous request for dinner following lunch, (3) ad libitum food intake at dinner. Lunches provided during the next three sessions were based on baseline lunch intakes. During the following three sessions, conducted in counterbalanced order, subjects were given a high-fat (58% of energy from fat), a high-protein (77%) or a high-carbohydrate (84%) snack to be consumed 240 min after the beginning of lunch. Latency to dinner and the amount of energy consumed at dinner were two dependent variables. Consumption of a high-protein snack delayed the request for dinner by 60 min. In contrast, high-fat snack delayed dinner request by 25 min, whereas high-carbohydrate snack delayed dinner request by 34 min. Snack composition had no impact on energy or macronutrient intakes during dinner.

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BACKGROUND: In view of the influence of dietary habits on obesity, human eating patterns merit study. OBJECTIVE: We investigated the behavioral and biological consequences of consumption of a 1-MJ snack by subjects in a satiety state. DESIGN: Eleven lean young men were deprived of time cues and subjected to continuous blood withdrawal over each of 4 sessions scheduled 2 wk apart. The first session was a basal session designed to determine the following in each subject: 1) the amount eaten in an ad libitum lunch; 2) the temporal patterns of plasma concentrations of glucose, insulin, fatty acids, and triacylglycerols between lunch and the spontaneous dinner request; and 3) the latency of the dinner request. In the 3 other sessions, each subject ingested the same lunch as in the basal session and a nutritionally well-balanced snack either 5 min before his individual peak of hyperglycemia observed in the first session, 40 min after this peak, or 120 min before the time he had requested his dinner in the first session. RESULTS: There was no significant difference in latency of the dinner request or the energy intake at dinner between sessions. Insulin secretion increased but glucose profiles did not change significantly regardless of the time of snack intake. CONCLUSION: A snack consumed in a satiety state fails to prolong the intermeal interval and would thus tend to favor storage.

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Hunger may be delayed and food intake reduced under metabolic conditions that spare carbohydrate oxidation, especially during oxidation of medium-chain triacylglycerols (MCTs) or monounsaturated triacylglycerols. In 12 healthy, adult, male volunteers isolated and deprived of any time cues, we compared the effects of 4 high-carbohydrate breakfasts (1670 kJ) supplemented either with a fat substitute (Sub; 70 kJ) or with 1460 kJ fat as monounsaturated long-chain triacylglycerols (LCT-U), saturated long-chain triacylglycerols (LCT-S), or MCTs. In the first session we investigated the effects of these breakfasts on the following food intake variables: hunger ratings at repeated intervals, the time until the spontaneous request for the next 2 free-choice meals, and the amount of food consumed. In a second session with fixed lunches, we studied the effects of the same breakfasts on plasma glucose, insulin, triacylglycerol, fatty acid, and beta-hydroxybutyrate concentrations. The addition of any of the fats to the high-carbohydrate breakfasts did not alter hunger ratings, but significantly delayed the request for lunch compared with the low-fat breakfast. The free-choice lunch eaten after the MCT breakfast was also significantly smaller. Blood glucose and insulin concentrations were lower after the 3 fat breakfasts, followed by larger increases in glucose and enhanced insulin responses 30 min after the lunch. No differences were observed between the LCT-U and LCT-S conditions. We conclude that MCTs decreased food intake by a postabsorptive mechanism, although the exact effect of these lipids on carbohydrate oxidation will require further studies involving nutrient balance measurements.

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Perceptions of sugar, fat and moisture contents, as well as their influences on pleasantness were investigated in commercial foods. One-hundred-and-two-normal-weight men rated the "pleasantness", "flavour intensity", "moisture", "sweetness" and "fatness" of 39 different biscuits and cakes. Sugar content was accurately perceived up to a maximum content of about 33% weight/weight. The perception of fat content was less accurate and depended on both fat and sugar contents. High sugar contents seemed to decrease perception of fatness. Pleasantness was influenced mainly by sugar content and less by fat content. Pleasantness was better predicted by rated contents than by actual contents; it was even better predicted by the overall flavour intensity. Preferences for high fat stimuli did not appear to be based on conscious perception of their fat content. We conclude that the classical results obtained with simple experimental stimuli remain valid, as a first approximation, for commercial biscuits and cakes, despite their complex sensory characteristics.

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Detection threshold for the taste of PROP (6-n-propyl thiouracil) in aqueous solution was determined in 173 French Caucasian women deprived of retronasal olfaction by blowing an air stream into the nostrils. As expected, the detection thresholds were bimodally distributed, although as many as 73% of the subjects had thresholds above the antimode concentration and therefore qualified as non-tasters. Detection threshold, difference threshold, intensity perceptions and preference ratings were then determined for NaCl, sucrose, caffeine, Na saccharin and naringin in 20 tasters and 20 non-tasters. No differences were found between tasters and non-tasters for detection or difference thresholds of the various tastants. Intensity and preference ratings for solutions of NaCl, saccharin or caffeine were not influenced by taster status. Although ratings of sweetness intensity for sucrose solutions did not differ between tasters and non-tasters, concentrated sucrose solutions were more disliked by non-tasters than by tasters. Non-tasters rated naringin solutions as more bitter than tasters, but naringin preference ratings were independent of taster status. Some of these findings were unexpected and further studies are required to find out whether they stem from the odour-preventing procedure or are of biological or cultural origin.

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We compared the influence of three solid/liquid preloads to a no-preload condition given at lunchtime on hunger ratings and energy intake of the lunch and subsequent dinner in 12 lean and 10 overweight young men. The preloads (vegetables and water, strained vegetable soup, chunky soup) were of the same composition and volume but differed in distribution of nutrients between the liquid and the solid phases, and in the size of solid particles. Hunger ratings were reduced by the preloads; there was a significantly greater suppression of hunger after the chunky soup than after the vegetables and water. In both groups, the soups reduced energy intake at lunch, although the chunky soup had the most effect. In the overweight subjects, a reduced lunch intake was also followed by a reduced dinner intake. The benefit to weight control of large particles in soup should be evaluated.

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Accumulating evidence suggest that a good way to compare the satiety power of meals with different compositions or energy contents is to measure the onset latency of the next meal when freely requested by subjects deprived of any time cues. This study was performed in normal-weight young men (aged 19-24 y) isolated from time cues. At sessions 1 and 2, we studied the effects of two high-carbohydrate pasta lunchs with either 50 g low-energy butter substitute (lunch A) or 50 g butter (lunch B) on hunger ratings, on the latency of the dinner request, and on energy and nutrient intakes at the offered ad libitum dinner. Sessions 3 and 4 were designed to examine the effects of the two lunchs on the postlunch and predinner profiles of plasma glucose, insulin, glucagon, and lipids; consequences on the metabolic and hormonal responses to the fixed dinner offered on request also were tested. The addition of 1588 kJ butter to the pasta lunch compared with the addition of 67 kJ butter substitute had no effect on hunger ratings but significantly delayed the onset of dinner by approximately 38 min; however, neither energy intake nor nutrient intakes were different. The high-fat lunch led to a slightly different postlunch plasma glucose concentration profile but, as expected, to higher plasma triacylglycerol and fatty acid concentrations. The high-fat lunch also led to postdinner glucose intolerance with normal insulin and high fatty acid concentrations that may help explain the partial and delayed adjustment in energy intake after a high-fat meal as reported by some studies.

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The sweet taste of nonnutritive sweeteners has been reported to increase hunger and food intake through the mechanism of cephalic-phase insulin release (CPIR). We investigated the effect of oral sensation of sweetness on CPIR and other indexes associated with glucose metabolism using nutritive and nonnutritive sweetened tablets as stimuli. At lunchtime, 12 normal-weight men sucked for 5 min a sucrose, an aspartame-polydextrose, or an unsweetened polydextrose tablet (3 g) with no added flavor. The three stimuli were administered in a counterbalanced order, each on a separate day at 1-wk intervals. Blood was drawn continuously for 45 min before and 25 min after the beginning of sucking and samples were collected at 1-min intervals. Spontaneous oscillations in glucose, insulin, and glucagon concentrations were assessed as were increments (slopes) of fatty acid concentrations during the baseline period. The nature of the baseline (oscillations: glucose, insulin, and glucagon; and slopes: fatty acids) was taken into account in the analyses of postexposure events. No CPIR and no significant effect on plasma glucagon or fatty acid concentrations were observed after the three stimuli. However, there was a significant decrease in plasma glucose and insulin after all three stimuli. Only the consumption of the sucrose tablet was followed by a postabsorptive increase in plasma glucose and insulin concentrations starting 17 and 19 min, respectively, after the beginning of sucking. In conclusion, this study suggested that oral stimulation provided by sweet nonflavored tablets is not sufficient for inducing CPIR.

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In the energy balance equation, physical activity represents one component of energy expenditure. From various studies it appears that exercise-training does not affect clearly thermogenesis which depends on brown adipose tissue (BAT) activity. In the present work we examine how exercise-training can influence food intake and body weight regulation in relation to BAT thermogenesis. The proton conductance of the uncoupling protein of BAT was examined in male adult Wistar trained 2 h/day for 20 days and compared to that of sedentary (2 h of fasting instead of exercise) or control animals. All animals were provided with separate sources of the 3 macronutrients (protein, fat and carbohydrate) containing an identical percentage of vitamins, salt mixture and cellulose powder. At the end of training, rats were placed at 5 degrees C during 10 days, then during 4 days at 28 degrees C. This condition has been demonstrated to favour and amplify BAT responsiveness to moderate modifications of stimulation. The body weight of trained rats became significantly lower than that of the control and sedentary rats and this difference persisted all throughout the experiment. When placed at 5 degrees C, all rats increased their total ingestion: control rats enhanced fat intake, while sedentary and trained rats enhanced carbohydrate ingestion. When placed at 28 degrees C, all rats had identical total energy and that of the 3 items intakes. BAT proton conductance was about 40% lower in the trained compared with the sedentary plus the control rats. This indicated a lower BAT thermogenic activity in the trained animals. It could be concluded that exercise-training in rats induces negative energy balance; the reduced BAT activity could restrain weight loss and overeating.

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Few studies have examined the effects of exercise training on macronutrient self-selection in rats. It has been observed that trained rats decreased carbohydrate and increased fat and protein intakes. In the present experiment, total energy intake and macronutrient self-selection were examined in adult male rats placed on a self-selection regimen and submitted to 2 h of treadmill exercise daily for 20 days at the beginning of the nocturnal period. Two control groups of rats were examined during the same time: a sedentary group that was food and water deprived during the same 2 h while trained rats were exercising, and a control group that was examined only for body weight gain and 24-h food intake. Food intakes of sedentary and trained rats were continuously recorded. At the end of the experiment, body weight of trained rats was lower than that of sedentary and control rats. The 24-h cumulative intake of trained rats was significantly reduced; this reduction was due to a decrease in fat intake, whereas carbohydrate intake was increased. In sedentary rats, 24-h intake was not modified but fat intake was significantly increased from the beginning to the end of the experiment. During the first 6 h of the night, protein and fat intakes of trained rats were reduced, and carbohydrate ingestion remained the same. Daytime food intake represented only 8.7% of the 24-h intake. Exercise training significantly increased this intake. It is noteworthy that during the middle part of the day (3-9 h) trained rats significantly enhanced protein and carbohydrate ingestion.(ABSTRACT TRUNCATED AT 250 WORDS)

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This study examined the effects of four breakfast preloads of different sweetness and energy content on motivational ratings, taste preferences, and energy intakes of 12 obese and 12 lean women. The preloads consisted of creamy white cheese (fromage blanc) and were either plain, sweetened with sucrose or aspartame, or sweetened with aspartame and supplemented with maltodextrin. Their energy content was either 300 kcal (1,255 kJ) or 700 kcal (2,929 kJ). Motivational ratings of hunger and the desire to eat were obtained prior to and at 30 min intervals after breakfast. Taste preferences were measured prior to and 150 min after breakfast. The subjects ate buffet-style lunch, snack, and dinner meals in the laboratory. Obese women consumed significantly more energy at meals (2,596 kcal or 10,862 kJ) than did lean women (1,484 kcal or 6,209 kJ); derived a greater proportion of energy from fat (39.9% vs. 35.5%), and had lower dietary carbohydrate-to-fat ratios. Consumption of low-energy as opposed to high-energy breakfast preloads was associated with elevated motivational ratings by noon. However, energy intakes at lunch, snack, or dinner did not vary as a function of preload type, and no compensation was observed for the energy consumed at breakfast. Taste preferences were not affected by preload ingestion or by preload type. The study provided no evidence that aspartame promotes hunger or results in increased energy intakes in obese or in lean women.

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A buffet-type meal was presented to 28 young men after participation in various athletic activities and to 30 subjects kept inactive. At 30 min after 2h of exercise, total energy intake was about 25% greater than after the rest situation. The food choices after exercise yielded an energy intake from proteins that was significantly larger than after rest, but not of carbohydrate or fat.

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A covertly fat-reduced and low-calorie dish was provided at lunchtime once a week to normal-weight human subjects. A normal-calorie version of the dish was served for the first 3 weeks, the low-calorie version for the following 4 weeks and the normal-calorie version again for the last 3 weeks. Participants did not compensate for the 840-kJ (201 kcal) fat reduction of their main dish during the lunchtime meal. This lack of compensation persisted after four successive weekly presentations. When the normal-caloric version was offered again, energy intake at lunch immediately recovered. There was 80% adjustment in 24-h energy intake from the first to the last test day on the low-calorie dish, and a return to the baseline level when the normal energy content of the dish was restored. No compensation specific to fat occurred after the consumption of the low-fat dish and so the proportion of energy intake derived from fat decreased from 39.6% in the period on the normal-caloric dish to 36.1% in the 4 weeks on the low-calorie dish. Thus, fat-reduced dishes seem a good means to improve the composition of the diet.

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Food intake and body weight gain were examined in two groups of male rats (7 weeks): an inbred strain, Dark Agouti (DA, n = 12) and a noninbred strain, Wistar (n = 13). The animals were allowed to select their diet from separate sources of the three macronutrients protein, fat, and carbohydrate. After 10 days of adaptation to the diets, body weights and food intakes were measured for 3 weeks. During this period, meal patterns were recorded for at least 5 days in each rat. Then, rats were switched to a chow diet (UAR, A.O4) for 10 days. The total caloric intake of DA rats was 60% that of Wistar rats, while their body weight gain was 25% that of Wistar rats (1.3 g/day in DA vs. 5.3 g in Wistar). However, when energy intake was related to total body weight, there was no difference in energy ingestion. It was observed that DA rats ingested mainly proteins (45%) and fats (41%), while Wistar rats ingested an identical proportion of proteins and carbohydrates (40%). The percent of total white adipose tissue to total body weight was identical in both strains (6% on average). Brown adipose tissue thermogenic activity of DA rats was threefold higher than in Wistar rats. This could be one of the elements responsible for the lower body weight gain of this group of rats. Self-selected food intake of the inbred DA strain of rats, in contrast to what was expected, was greatly variable.

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