Learning about the energy density of liquid and semi-solid foods

Background:People learn about a food's satiating capacity by exposure and consequently adjust their energy intake.Objective:To investigate the effect of energy density and texture on subsequent energy intake adjustments during repeated consumption.Design:In a randomized crossover design, participants (n=27, age: 21±2.4?years, body mass index: 22.2±1.6?kg?m(-2)) repeatedly consumed highly novel foods that were either low-energy-dense (LE: 30?kcal per 100?g) or high-energy-dense (HE: 130?kcal per 100?g), and either liquid or semi-solid, resulting in four product conditions. In each condition, a fixed portion of test food was consumed nine times as an obligatory part of breakfast, lunch and dinner on 3 consecutive days. All meals continued with an ad libitum buffet; food items for evening consumption were provided and the intake (kcal per day) was measured.Results:Buffet intake depended on energy density and day of consumption of the test foods (day*energy interaction: P=0.02); daily buffet intake increased from day 1 (1745±577?kcal) to day 3 (1979±567?kcal) in the LE conditions; intake did not change in the HE conditions (day 1: 1523±429?kcal, day 3: 1589±424?kcal). Food texture did not affect the intake (P=0.56).Conclusions:Intake did depend on energy density of the test foods; participants increased their buffet intake over days in response to learning about the satiating capacity of the LE foods, but did not change buffet intake over days when repeatedly consuming a HE food as part of their meal. The adjustments in intake were made irrespective of the food texture.     

Effects of test-meal palatability on compensatory eating following disguised fat and carbohydrate preloads

OBJECTIVE: To test whether the palatability of a test meal altered compensatory eating following disguised high-energy fat and carbohydrate preloads. DESIGN: Effects of preload energy (low, 265 kJ, or high, 1510 kJ) and test-meal palatability (bland or palatable) were contrasted within-subjects, with a between-subjects contrast of fat and carbohydrate preloads. SUBJECTS: Twenty-four healthy, normal men (age 23.6+/-1.0 y, (body mass index) BMI 21.3+/-0.5). MEASUREMENTS: Microstructural analysis of test meal intake and rated appetite in the four test conditions, plus diary-based weighed intake analysis of energy intake post-lunch. RESULTS: Subjects ate significantly less at lunch after disguised high-energy fat or carbohydrate preloads relative to the low-energy preload, and ate significantly more of the palatable than bland lunch in all conditions. The reduction in eating following the high-energy preload was significantly less in the palatable condition. Intake post-lunch did not differ between conditions, and overall subjects had higher daily energy intake on the days they consumed the high-energy preloads. Rated hunger was significantly less 30 min after the high- than low-energy preloads, but increased on tasting the palatable food in all conditions. The high-energy preloads suppressed appetite immediately post-lunch. No differences between fat and carbohydrate were found on any measure. CONCLUSIONS: Manipulation of the palatability of a test meal modified the ability to respond to disguised high-energy preloads, with over-consumption most evident when disguised high-energy preloads were followed by a palatable food. Subsequent voluntary intake compensated for over-consumption of the palatable lunch, but not the high-energy preload.     

Gastrointestinal adaptation to diets of differing fat composition in human volunteers.

The effect of a low fat diet (9 MJ) v a high fat diet (19.26 MJ), each consumed separately for four and 14 days, on gastric emptying and mouth to caecum transit time of a high fat test meal and body weight and satiety were examined in groups of 10 and six normal male volunteers. The half time for gastric emptying (t1/2) and the mouth to caecum transit time of a high fat test meal was significantly faster after the high fat diet than the low fat diet when consumed for 14 days (t1/2=98 (80-116) v 147 (88-206) minutes (median (range)), p less than 0.05; mouth to caecum transit time 240 (130-350) v 360 (200-520) minutes, p less than 0.05), but not when consumed for only four days. The mean (SEM) body weight of all subjects significantly increased during the 14 day high fat diet (74.7 (1.3) v 72.7 (1.6) kg, p less than 0.05) but was not influenced during the consumption of the low fat diet. When subjects were given an appetising meal to consume on the day that they had consumed the transit test meal, they ate similar amounts irrespective of their recent dietary history, though the eating rate was significantly slower after the high fat diet (mean (SEM)) 46.7 (1.9) v 71.3 (14.8)/min, p less than 0.05). Maintaining normal subjects on a high or low fat diet for two weeks resulted in a desensitisation or sensitisation respectively of the mechanisms by which nutrients regulate gastrointestinal transit. These findings emphasise the importance of the recent dietary history in the interpretation of gastric emptying and small bowel transit time data.     

Loss of meal-induced decrease in plasma ghrelin levels in patients with anorexia nervosa

Studies have shown that ghrelin plays a major role in energy homeostasis and modulation of feeding behavior. However, little is known about the influence of food consumption on plasma ghrelin levels in humans. Therefore, we investigated responses of plasma ghrelin to food intake, meal volume and meal nutritional value in healthy volunteers and women with anorexia nervosa (AN). After overnight fasting, all subjects received either a standardized breakfast or fiber. Plasma ghrelin levels were measured before and after the meal. Fasting plasma ghrelin was significantly higher in AN patients than in controls (1,800.6 +/- 47.0 vs. 795.9 +/- 24.3 pg/ml, P < 0.001) (606.8 +/- 15.8 vs. 268.2 +/- 8.2 pmol/l, P < 0.001), and correlated negatively with percentage of body fat in both groups. Ghrelin levels markedly fell after consumption of either a standardized meal or fiber in controls, but not in anorexic women. Thus, we concluded that the acute plasma ghrelin response to food intake, which in healthy individuals is independent of meal caloric value, is impaired in women with AN. This abnormality may be part of a chronic adaptation to prolonged food restriction, which attempts to restore a normal feeding conduct by maintaining the drive to eat.     

Effects of insulin-induced hypoglycaemia on energy intake and food choice at a subsequent test meal

BACKGROUND AND AIMS: Hypoglycaemia is assumed to increase food intake, but there is little data on the magnitude or qualitative nature of this effect. We have therefore investigated the effects of insulin-induced hypoglycaemia on food intake at a test meal. METHODS: Sixteen healthy men (age 29.8 +/- 11 years; mean +/- SD) were studied; either insulin (0.05 units/kg) or saline was given intravenously in a double-blind crossover design. Blood glucose was monitored at regular intervals. Participants were given an ad libitum breakfast 20 min after injections and food intake and appetite scores were recorded. RESULTS: Blood glucose was unchanged following saline (4.3 +/- 0.4 to 4.4 +/- 0.3 mmol/L). There was a transient decline in blood glucose after insulin with a nadir at 20 min (4.31 +/- 0.34 to 2.41 +/- 0.45 mmol/L, p < 0.0001), which returned to baseline at 40 min. Total energy intake was 17% higher (1701.1 +/- 895.3 kcal vs 1427.7 +/- 815 kcal, p = 0.026) following insulin administration compared to that following saline. Macronutrient analysis revealed a significant increase in high-fat foods (muffins) (69.2 +/- 54.1 vs 29 +/- 42.3 g, p = 0.009) after insulin. Appetite scores were similar after saline and insulin despite these changes in food intake. CONCLUSIONS: Transient insulin-induced hypoglycaemia increases energy intake. Participants consumed more fat after insulin compared to that after saline. High-fat foods can lead to passive overconsumption and have a low glycaemic index, which may prolong hypoglycaemia. Both factors could ultimately promote weight gain in individuals with recurrent hypoglycaemia.     

Thermic responses to vegetarian meals and yoga exercise.

The thermic effect (TEF) of vegetarian meals was measured for breakfast and lunch in 6 lean healthy men (18-25 years) during normal feeding (NF) and with 20% overfeeding (OF) on 28 successive days. The energy contents of breakfast were 223 +/- 10 and 330 +/- 48 kcal, and those of lunch were 1,033 +/- 220 and 1,247 +/- 222 kcal in NF and OF, respectively. In NF, the TEF per 180 min was 32.7 +/- 8.6 and 54.8 +/- 6.3 kcal for breakfast and lunch, respectively. In OF, the TEF was 38.3 +/- 8.3 kcal for breakfast and 57.2 +/- 5.4 kcal for lunch. The increase in total TEF due to OF was nonsignificant (p greater than 0.2). In response to 20% OF, adaptive thermogenesis was manifested mainly through an increase in the resting metabolic rate of 4.9% (p less than 0.001). In both feeding, regimes, the percent TEF was higher for breakfast than for lunch (p less than 0.05). Regression analysis of TEF versus calorie load indicated a stable component of 42 kcal with a 2% rate of increase. Yoga exercises were performed from 16.00 to 17.00 daily. The thermic effect of yoga exercises observed from 17.10 to 18.30 was 21 kcal and persisted beyond 90 min, indicating the role of yoga in energy metabolism.     

Circadian rhythm of energy intake and corpulence status in adults

The relationship between circadian distribution of energy intake and corpulence was studied in 1312 subjects seeking medical advice for their weight. The corpulence categories (non-obese, mildly obese and massively obese) were defined on the basis of NHANES II. Food consumption was assessed through the dietary history method. The 24 h energy intake increased with corpulence. The lunch represented higher (P less than 0.001) proportions of daily intake in mildly and in massively obese than in non-obese. The reverse occurred for the breakfast (P less than 0.001). The relationships of corpulence with breakfast and lunch persisted after adjustment for nutrient intake. No difference was found for dinner and extra-prandial food intake. Such data suggests several behavioural and/or metabolic hypothesis.     

Effects of a high-protein meal (meat) and a high-carbohydrate meal (vegetarian) on satiety measured by automated computerized monitoring of subsequent food intake, motivation to eat and food preferences

We have examined the effects on satiety of equicaloric meals with different protein and carbohydrate content. Twenty normal weight healthy women were served cooked lunch meals made of commonly used natural food items with either a high-protein (43 energy %) (a meat casserole) or a high-carbohydrate (69 energy %) (a vegetarian casserole) content in a counterbalanced repeated measures design. The subsequent ad libitum evening meal intake (4 h after lunch) was measured by a 'universal eating monitor' and subjective feelings of motivation to eat and food preferences were assessed repeatedly. At the subsequent evening meal subjects ate 12 per cent less (P less than 0.05) after the high-protein meal compared to the high-carbohydrate meal. There was no difference in motivation to eat between meals. This could partly be explained by a difference in palatability between the meals. The food-preference lists showed that before lunch there was relative preference for high-protein foods in favour of high-carbohydrate foods. After lunch either meal produced instead a relative 'aversion' for high-protein foods. This 'aversion' was greater after the high-protein lunch meal than after the high-carbohydrate lunch meal.     

The effect of meals at different mealtimes on blood pressure and symptoms in geriatric patients with postprandial hypotension

BACKGROUND: The variability of postprandial hypotension (PPH) during the day in elderly patients is unknown. We examined the effect of meals administered at different mealtimes on postprandial blood pressure (BP) responses in geriatric patients. METHODS: In 14 geriatric patients (6 men and 8 women, aged 66-97) previously diagnosed with PPH, standardized liquid test meals were given in random order at breakfast, lunchtime, or dinnertime on 3 separate days. Systolic BP (SBP), diastolic BP (DBP), and heart rate (HR) were measured with an ambulatory BP device every 10 minutes from 20 minutes before until 90 minutes after each meal. Postprandial symptoms were observed continuously. RESULTS: Significant decreases in SBP and DBP were present after each meal (p <.050). The maximum SBP decrease was significantly smaller at dinnertime (-18 +/- 3 mmHg) than at breakfast (-29 +/- 2 mmHg) or lunchtime (-34 +/- 4 mmHg) (p <.005 between groups). Eight patients showed no PPH in the evening, whereas all patients had PPH after breakfast and lunch. The duration of PPH was significantly shorter (p <.001), and postprandial symptoms were less frequent and less severe after dinner compared to breakfast and lunch. CONCLUSIONS: In geriatric patients, postprandial BP responses show a variation during the day, with significantly less PPH and fewer symptoms in the evening. Clinical implication is that, in the diagnostic process and management of PPH, the variation of the occurrence of PPH during the day should be taken into account. Through adjustment of BP decreasing activities to the time PPH is least prevalent, the risk of developing symptomatic PPH can be reduced.     

Energy adaptation to glucocorticoid-induced hyperleptinemia in human beings

Recombinant leptin therapy potently decreases food intake and body weight in aleptinemic individuals with leptin gene mutations. However, it is unknown whether manipulation of endogenous leptin secretion alters ingestive behavior in otherwise healthy subjects. We therefore assessed energy consumption during administration of hydrocortisone (HC), a known leptin secretagogue. Six healthy adults were admitted overnight on 2 occasions and given HC (12.5 mg/h IV) or saline infusion for 24 hours (8:00 am -8:00 am ) in a randomized crossover design. Total energy and macronutrient intake was calculated using a computerized nutrient analysis program. Blood sampling for measurement of leptin, cortisol, glucose, and insulin was performed at baseline and every 1 to 2 hours. A rise in plasma leptin level was noted after approximately 5 hours of HC infusion and was sustained throughout the study period. The total energy consumed was 3004 +/- 231 kcal for saline and 2486 +/- 214 kcal for HC ( P = .005); breakfast energy values on day 1 were similar but energy values consumed at lunch, dinner, and day 2 breakfast were all significantly lower during induced hyperleptinemia. Analysis of macronutrients indicated significant decreases in carbohydrate and fat intake during glucocorticoid-induced hyperleptinemia as compared with placebo. These results indicate that stimulation of native leptin secretion decreases energy consumption, similar to the effect observed with recombinant leptin therapy. To our knowledge, this is the first report documenting anti-ingestive responses to a leptin secretagogue. Because chronic glucocorticoid therapy is fraught with adverse effects, we suggest that nonsteroidal or steroidomimetic leptin secretagogues may be good candidates for anorectic and antiobesity drug development.     

Energy and protein consumption in patients with senile dementia

Demented elderly patients unable to eat independently and often refusing food are threatened by malnutrition. Therefore, we determined in 6 female patients aged 74-100 with senile dementia the average daily food consumption within a 3-week period by the exact weighing methods on six occasions. The average daily energy intake was 7,364 kJ (carbohydrates 3,300, fat 3,030, and protein 1,034 kJ). Acceptance of food was best at breakfast; during lunch and dinner all patients refused nutrients in two-thirds of the meals. During the observation period the subjects remained in a steady state (weight, serum albumin). It is concluded that spontaneous nutrient intake is sufficient in stable conditions. In times of increased energy needs the observed eating habits may lead to malnutrition.     

Effect of ileal and intravenous infusions of fat emulsions on feeding and satiety in human volunteers

The effect of ileal infusion of a lipid emulsion, containing 50% corn oil and 3% albumen, on food intake and satiety was measured in paired experiments carried out in 6 healthy volunteers. Subjects ate for shorter periods of time during ileal infusions of fat emulsion compared with control infusions of albumen and saline (25 +/- 1 vs. 32 +/- 3 min, mean +/- SEM) and consumed a smaller amount of food (670 +/- 23 g vs. 884 +/- 89 g) and energy (1016 +/- 79 kcal vs. 1591 +/- 228 kcal). The quantity of liquid drunk and the rates of eating and drinking were not significantly affected by the infusion of fat emulsion. In a further series of experiments carried out in 5 normal volunteers, ileal infusion of corn oil emulsions delayed gastric emptying compared with ileal infusion of albumen and saline (t1/2 = 203 +/- 48 vs. 68 +/- 12 min, p less than 0.02). The possibility that the observed reductions in food intake were related to the effect of absorbed fat was investigated in 6 healthy volunteers during intravenous infusion of either fat emulsion or isosmotic saline. Food intake was not affected by intravenous infusion of lipid. Our results suggest that lipid may interact with ileal receptors to induce early satiety and reduce the amount of food consumed. The earlier inhibition of food intake during lipid infusion is perhaps best explained by early gastric distention caused by delayed gastric emptying, though the data would not exclude the release of an ileal mechanism, which has a direct action on the satiety centers.     

Gastrin response to meals of different composition in normal subjects.

The serum gastrin responses and the integrated gastrin responses to eating three meals of very different composition were studied in the same normal subjects on different days. Two meals, a milk meal of 500 ml, and a breakfast of eggs, toast, butter, marmalade, fruit juice and coffee, were eaten at breakfast time. The serum gastrin responses to these meals were compared and contrasted with the concentrations observed when the subjects fasted over the same time of day. A steak meal was eaten at lunch time. There were no significant differences between the mean serum gastrin concentrations to the three meals but each meal produced a significant increase in serum gastrin above fasting levels. When the prefeeding gastrin concentration was subtracted from the gastrin responses then the integrated responses to the steak meal were greater than those to either of the breakfast meals. Considerable variability in response to any one meal was observed within the group of subjects, but those subjects who produced high serum gastrin concentrations to one meal did so to the others. Conversely, at low response to one meal was reflected in low responses to the other two meals. Fasting serum gastrin concentration was correlated with the age of the subject. Repeatability of the response to one meal was tested in two subjects who ate the same meal on four separate occasions showing their responses to be repeatable.     

The influence of the type of dietary fat on postprandial fat oxidation rates: monounsaturated (olive oil) vs saturated fat (cream)

OBJECTIVE: To compare postprandial whole-body fat oxidation rates in humans, following high-fat (43% of total energy) mixed breakfast meals, of fixed energy and macronutrient composition, rich in either monounsaturated fat (MUFA) from extra virgin olive oil or saturated fat (SFA) from cream. DESIGN: Paired comparison of resting metabolic rate (RMR), thermic effect of a meal and substrate oxidation rates following consumption of isocaloric breakfast meals, differing only in the type of fat, administered in random order 1-2 weeks apart. SUBJECTS: Fourteen male volunteers, body mass index (BMI) in the range 20-32 kg/m(2), aged 24-49 y and resident in Melbourne, Australia, were recruited by advertisement in the local media or by personal contact. MEASUREMENTS: Body size and composition was determined by anthropometry and dual energy X-ray absorptiometry (DEXA). Indirect calorimetry was used to measure RMR, thermic effect of a meal, post-meal total energy expenditure and substrate oxidation rate. Blood pressure and pulse rates were measured with an automated oscillometric system. Fasting and 2 h postprandial glucose and insulin concentrations and the fasting lipid profile were also determined. RESULTS: In the 5 h following the MUFA breakfast, there was a significantly greater postprandial fat oxidation rate (3.08+/-4.58 g/5 h, P=0.017), and lower postprandial carbohydrate oxidation rate (P=0.025), than after the SFA breakfast. Thermic effect of a meal was significantly higher (55 kJ/5 h, P=0.034) after the MUFA breakfast, in subjects with a high waist circumference (HWC > or = 99 cm) than those with a low waist circumference (LWC<99 cm). This difference was not detected following the SFA breakfast (P=0.910). CONCLUSION: If postprandial fat oxidation rates are higher after high MUFA, rather than SFA meals, then a simple change to the type of dietary fat consumed might have beneficial effects in curbing weight gain in men consuming a relatively high-fat diet. This may be particularly evident in men with a large waist circumference.     

Acute appetite reduction associated with an increased frequency of eating in obese males

OBJECTIVE: To investigate the effects of altered feeding frequencies on the relationship between perceived hunger and subsequent food intake and appetite control in obese men. DESIGN: Obese men reported in a fasted state in the morning to the laboratory where an isoenergetic pre-load (4100+/-234 kJ, which was 33% average daily energy requirement (ADER) of each subject) comprising 70% carbohydrate, 15% protein, and 15% fat was given. This was administered either as a SINGLE meal, or divided evenly over 5 meals given hourly as a MULTI feeding pattern. Five hours after the first pre-load, an ad libitum test meal was given to determine whether there was a difference in the amount of energy that was consumed between the two eating patterns. SUBJECTS: Seven non-diabetic, non-smoking, unrestrained obese men (age 37.4+/-18.5; BMI 40.02+/-10. 93 kg/m-2) were recruited for this study. Subjects were not told the precise reasons for this study but rather were informed that changes in blood glucose, insulin and free fatty acids with meal frequency were to be monitored. MEASUREMENTS: Blood glucose, serum insulin and free fatty acid (FFA) concentrations, and visual analogue scales (VAS) were measured prior to commencing the feeding regime and thereafter hourly for 5 h. Thereafter an ad libitum meal was given. The weight (and energy content) of the food consumed, and the time taken to eat lunch were recorded. Following this ad libitum lunch, the same variables were determined again (15, 45, and 75 min post-test meal). RESULTS: When given a SINGLE pre-load, 27% more (t=2.651; P<0.05) energy was consumed in the ad libitum test meal (5261+/-1289 kJ) compared to that eaten after the MULTI pre-load (3763+/-1986 kJ). This increase in food intake occurred despite no significant change in subjective hunger ratings. Over the 315 min pre-load period, peak insulin concentrations were significantly higher (F6,72=7.95, P<0.01) on the SINGLE treatment (171.2+/-129.8 microU ml-1) than on the MULTI treatment (133.7+/-70.2 microU ml-1). Serum insulin remained elevated for longer on the MULTI meal treatment, resulting in no difference in the area under the insulin curves between the two feeding treatments. There was a positive correlation (r=0.87) between the amount of energy consumed at lunch and insulin concentration before lunch in the SINGLE group. However, this relationship was not apparent when subjects were given the MULTI meal preload. CONCLUSION: Obese males fed an isoenergetic pre-load sub-divided into a multi-meal plan consumed 27% less at a subsequent ad libitum test meal than did the same men when given the pre-load as a single meal. Prolonged but attenuated increases in serum insulin concentration on the multi-meal programme may facilitate this acute reduction in appetite.     

Effect of glycemic index on whole-body substrate oxidation in obese women

BACKGROUND: Glycemic index is hypothesized to determine fuel partitioning through serum plasma insulin modifications induced by dietary carbohydrates, thereby modulating fat accretion or oxidation. OBJECTIVE: To assess the glycemic effects on postprandial fuel oxidation and blood response. DESIGN: In all, 12 obese women were fed on a randomized crossover design with two test meals (breakfast+lunch). High- or low-glycemic meals were provided on separate days. Energy intake on high-glycemic meal was 7758+/-148 kJ and for low-glycemic meal was 7806+/-179 kJ. Carbohydrates supplied were 273+/-5 and 275+/-6 g, respectively. Macronutrient distribution was 55% carbohydrates, 30% fat and 15% protein. Fuel oxidation was measured continuously in a respiratory chamber for 10 h. Serum glucose, free fatty acids (FFA), insulin and glucagon samples were taken for 5 h after breakfast. RESULTS: Glucose AUC changed significantly in response to different glycemic breakfast. Low- vs high-glycemic breakfast was 211+/-84 and 379+/-164 mmol/l (P<0.05). Similarly, insulin changed from 94+/-37 and 170+/-87 nmol/l (P<0.05), respectively. The rate of increment for serum glucose and insulin reached by the high- vs low-glycemic meal was 1.8 times more with the high-glycemic breakfast. Serum FFA were similarly suppressed by both meal types by 3 h after meal intake, but then raised significantly more with the low-glycemic meal by the fourth and fifth hour (P<0.05). Plasma glucagon did not show a significant variation with glycemic index. Carbohydrate and fat oxidation was not modified by glycemic meal characteristics, being virtually the same for low- vs high-glycemic comparisons in the 5 h following breakfast and lunch (P=NS). CONCLUSION: This study demonstrates that dietary glycemic characteristics were unable to modify fuel partitioning in sedentary obese women.     

No appetite efficacy of a commercial structured lipid emulsion in minimally processed drinks

Background/Objectives:Fabuless (Olibra) is a commercially structured lipid emulsion, claimed to be a food ingredient that is effective for food intake and appetite reduction. The present study assessed its efficacy in a yoghurt-based mini-drink undergoing low or minimal food manufacturing (thermal and shear) processes.Subjects/Methods:Study 1: Twenty-four healthy volunteers (16 female, 8 male; age: 18-47 years; body mass index (BMI): 17-28?kg?m(-2)) took part in a randomised, placebo-controlled, double-blind parallel crossover trial. Consumption of a minimally processed 'preload' mini-drink (containing two different doses of Fabuless or a control fat) at 2?h after breakfast was followed by appetite and mood ratings, and food intake measured in ad libitum meals at 3 and 7?h post consumption of the preload. Study 2: As Study 1 (16 female, 8 male; age: 20-54 years; BMI: 21-30?kg?m(-2)). A chilled, virtually unprocessed, preload breakfast mini-drink (containing minimally processed Fabuless or a control fat) was provided 5?min after a standardised breakfast, followed by appetite and mood ratings, and food intake measured in ad libitum meals at 4 and 8?h post consumption of the preload.Results:The structured lipid emulsion tested had no significant effect on the primary measures of food intake or appetite.Conclusions:Even when exposed to minimal food-manufacturing conditions, Fabuless showed no efficacy on measures of appetite and food intake.     

Thermogenesis in humans during overfeeding with medium-chain triglycerides

To test whether excess dietary energy as medium-chain triglycerides (MCT) affects thermogenesis differently from excess dietary energy as long chain triglycerides (LCT), ten male volunteers (ages 22 to 44) were overfed (150% of estimated energy requirement) liquid formula diets containing 40% of fat as either MCT or LCT. Each patient was studied for one week on each diet in a double-blind, crossover design. Resting metabolic rate (RMR) did not change during either week of overfeeding. The thermic response to food (TEF) was greater on day 1 following a meal (1,000 kcal) containing MCT than following an isocaloric meal containing LCT (8 +/- .8% v 5.8 +/- .8% of ingested energy; P less than .05). Moreover, the TEF observed after a 1,000 kcal meal containing MCT increased significantly to 12% (+/- 1.3%) overfeeding. The TEF of the 1,000 kcal meal containing LCT was unchanged by five days of LCT overfeeding (6.6 +/- 1.0% of ingested energy). Energy expenditure during a 20-hour continuous enteral infusion of the diet on day 7 was also significantly higher with the MCT diet than with the LCT diet (15.7 +/- 1.7% v 7.3 +/- .9% of ingested energy; P less than .05). Our results demonstrate that excess dietary energy as MCT stimulates thermogenesis to a greater degree than does excess energy as LCT. This increased energy expenditure, most likely due to lipogenesis in the liver, provides evidence that excess energy derived from MCT is stored with a lesser efficiency than is excess energy derived from dietary LCT.     

Is a low fat diet the optimal way to cut energy intake over the long-term in overweight people?

Successful weight loss depends on maintaining a sustained negative energy balance. This can be achieved on diets with a normal (40% energy) fat content as well as on low fat diets. Using a 'modified fat' (MF) diet enriched with monounsaturated fat (MUFA), body weight may be lost either by calorie counting, or by allowing ad libitum food intake with careful food selection. In the latter approach high energy, high MUFA foods (predominantly olive oil, but also may include nuts and avocado) should contribute no more than 20% total energy to the diet, and other foods should be selected to minimise meal energy density. This can be achieved simply by the consumption of a wide variety of vegetables and whole grain cereal foods. It is also important to restrict foods high in saturated fat and to encourage regular exercise. Such a 'modified fat' low energy diet designed for weight loss should also contribute numerous health benefits in relation to improved metabolic control in Type 2 diabetes and reduced cardiovascular disease risk (as the diet is not only rich in MUFA but also in a range of dietary antioxidants and other bio-active phytochemicals).     

Metabolic changes in ageing Drosophila melanogaster

As Drosophila melanogaster ages, the amount of food eaten per day increases. The amount of uric acid excreted falls, probably because there is a decline in the efficiency of synthesis. Reserves of body fat and glycogen also fall. These changes are found both for flies kept on a high fat/low carbohydrate diet and for those kept on a low fat/high carbohydrate diet. The rate of food intake is greater for old flies kept on the high fat diet. Flies transferred from this diet to the low fat diet reduce their food intake, while with the reverse transfer food intake is increased. These results suggest that old flies may have impaired energy metabolism, that they eat more to compensate for this, and that carbohydrate is a more effective energy source than fat. The shorter lifespan of flies kept on a high fat diet may be associated with an increased dependence on carbohydrate for energy metabolism.