The physical state of a meal affects hormone release and postprandial thermogenesis

There is evidence that food consistency may influence postprandial physiological responses. Recently we found that homogenization of a vegetable-rich meal significantly delayed the gastric emptying rate and was more satiating than the same meal in solid-liquid form. In this present study we investigated whether homogenization also influences endocrine and metabolic responses to the meal. Eight healthy men, aged 21-28 (mean 24.5) years, were given the meal (cooked vegetables 250 g, cheese 35 g, croutons 50 g and olive oil 25 g, with water 300 ml; total energy 2.6 MJ) in both solid-liquid (SM) and homogenized (HM) form, in random order, at 1-week intervals. Variables assayed were plasma glucose, insulin and glucose-dependent insulinotropic peptide (GIP) levels for 2 h and diet-induced thermogenesis (DIT) for 5 h. Plasma glucose pattern was similar after both meals. However, HM induced significantly greater insulin, GIP and DIT responses than SM. Mean integrated areas under the curves (AUC) were 1.7 (SEM 0.38) v. 1.2 (SEM 0.33) U/l per 120 min (P = 0.005) for insulin, 19.9 (SEM 2.44) v. 16 (SEM 1.92) nmol/l per 120 min (P = 0.042) for GIP, and 237.7 (SEM 16.32) v. 126.4 (SEM 23.48) kJ/300 min (P = 0.0029) for DIT respectively. Differences between GIP-AUC after HM and SM correlated significantly with differences between insulin-AUC after HM and SM (r2 0.62, P = 0.021). These findings demonstrate that homogenization of a meal results in a coordinated series of changes of physiological gastroentero-pancreatic functions and confirm that the physical state of the meal plays an important role in modulating endocrine and metabolic responses to food.     

In vivo imaging of intragastric gelation and its effect on satiety in humans

Previous studies indicated that physical characteristics of food influence satiety, but the relative importance of the oral, gastric, and intestinal behaviors of the food is unclear. The aim of this study was to investigate the satiating effects of 2 types of alginates, which gel weakly or strongly on exposure to acid, compared with guar gum whose viscosity is unaffected by acid. Subjects (n = 12; 3 men, 9 women) ingested a 325-mL sweetened, milk-based meal replacer beverage on 4 separate occasions, either alone as a control or including 1% by weight alginate or guar gum. Intragastric gelling, gastric emptying, and meal dilution were assessed by serial MRI while satiety was recorded for 4 h. MR images showed that all of the meals became heterogeneous in the stomach except for guar, which remained homogeneous. The alginate meals formed lumps in the stomach, with the strong-gelling alginate producing the largest volume. Although gastric emptying was similar for all 4 meals, the sense of fullness at the same gastric volume was significantly greater for all 3 viscous meals than for the control. Compared with the control meal, the strong-gelling alginate (P = 0.031) and guar (P = 0.041) meals increased fullness at 115 min, and the strong-gelling alginate decreased hunger by the 115-min (P = 0.041) and 240-min (P = 0.041) time points. Agents that gel on contact with acid may be useful additions to weight-reducing diets. We hypothesize that this effect is due to distension in the gastric antrum and/or altered transport of nutrients to the small intestine in the lumps.     

Appetite sensations as a marker of overall intake

The aim of this study was to evaluate the clinical utility of appetite sensations to characterize individual overall energy intake. A group of men (n 28) and women (n 23) was recruited to record their 'desire to eat', 'hunger', 'fullness' and 'prospective food consumption' (PFC) on visual analogue scales before a standardized meal test, immediately after and every 10 min for a period of 1 h after the meal. The 1 h post-meal area under the curve (1 h AUC) and the satiety quotient (SQ) were calculated for all appetite sensations. In a second visit, all participants were invited to eat three meals in order to measure total energy intake (TEI) and food preferences. Metabolic rate (MR) was also assessed to derive daily relative energy intake (REI) by subtracting this variable from TEI (TEI-MR=REI). The Three-Factor Eating Questionnaire scores were also calculated for all participants. One h AUC for fullness was the appetite sensation most strongly associated with TEI and REI (r-0.42, P< or =0.003 and r-0.32, P< or =0.05, respectively). SQ for fullness was the only predictor of TEI and REI (r-0.42, P< or =0.0003 and r-0.30, P< or =0.05, respectively). Restraint, disinhibition and hunger scores were not associated with appetite sensation variables. These results suggest that the fullness dimension seems to be a useful appetite sensation to predict long-term TEI and REI. Thus, assessment of appetite sensation such as fullness in response to a fixed load may be useful to evaluate individual overall energy intake.     

A protein-rich beverage consumed as a breakfast meal leads to weaker appetitive and dietary responses v. a protein-rich solid breakfast meal in adolescents

The purpose of the present study was to determine whether a protein-rich beverage leads to a differential response in appetite, satiety and subsequent energy intake compared with an energy- and macronutrient-matched solid version in young people. A total of fifteen adolescents (eight girls and seven boys; age 14 (SEM 1) years, BMI percentile 79 (SEM 4) %) randomly completed two testing days that included protein-rich (PR) breakfast meals (38 % of energy as protein, 48 (SEM 2) g/meal) provided as a solid (S) or beverage (B). Breakfast was 24 % of estimated daily energy needs (2146 (SEM 96) kJ/meal). Perceived appetite and satiety responses were collected over 5 h followed by an ad libitum lunch buffet. The PR-S meal led to greater reductions in 4 h postprandial appetite (- 6221 (SEM 1171) mm × 240 min) v. the PR-B meal (- 3570 (SEM 957) mm × 240 min; P < 0·05). When examining the data according to hourly responses, the PR-S meal led to greater reductions in appetite during postprandial hours 2, 3 and 4 v. the PR-B meal (all comparisons, P < 0·05). No differences in postprandial hourly or total (4 h) fullness were observed following the PR-S v. PR-B meals. The PR-S meal led to approximately 480 kJ less energy consumed at the ad libitum lunch buffet (1418 (SEM 222) kJ) v. the PR-B meal (1900 (SEM 326) kJ; P < 0·05). These data indicate that, although the food form of the PR breakfast meals had little, if any, effect on satiety, the appetitive responses were diminished and the subsequent food intake was greater when protein was consumed as a beverage v. a solid meal.     

Interaction of fat availability and sex on postprandial satiety and cholecystokinin after mixed-food meals

BACKGROUND: Cholecystokinin (CCK) is associated with fat-induced satiety. OBJECTIVE: The primary objective of the present study was to determine, in an acute meal setting, whether the availability of dietary fat for alimentary processing, and hence the stimulation of CCK, affects the postmeal satiety response in men and women. DESIGN: In a within-subjects design, subjects (8 men, 7 women) consumed 1 of 3 isoenergetic mixed-food test meals 1 wk apart in random order. The test meals contained 30% of energy from fat, of which more than two-thirds was derived from whole almonds, almond oil, or a mix of safflower and corn oils. Visual analogue scales were used to assess indexes of satiety at defined time points up to 6 h after meal consumption. Blood was sampled at corresponding time points for measurement of CCK, glucose, insulin, and triacylglycerol. Subsequent food intake was also assessed. RESULTS: All meals suppressed hunger and induced a pattern of satiety that was sex-specific and corresponded with the CCK response. Women had higher plasma CCK concentrations and experienced greater satiety after the almond oil and control meals (fat as oil) than after the whole almond meal (fat in whole food structure). Men showed no differential response among meals for CCK and satiety. Plasma triacylglycerol differed by time among meals but not by sex, and no significant differences in glucose and insulin were found. CONCLUSIONS: The satiety response to dietary fat provided in oil or whole food form is influenced by sex and is dependent on the availability of fat to stimulate CCK release in women but not in men.     

Gastric response to increased meal viscosity assessed by echo-planar magnetic resonance imaging in humans

Normal meals are highly viscous, and viscosity is a key factor in influencing gastric emptying of food. However, the process of meal dilution and mixing is difficult to assess with the use of conventional methods. The aim of this study was to validate an in vivo, novel, noninvasive, echo-planar magnetic resonance imaging (EPI) technique, capable of monitoring the viscosity of a model meal, and to use this to investigate the effects of viscosity on gastric emptying, meal dilution and satiety. Healthy volunteers (n = 8) ingested 500 mL of locust bean gum (0.25, 0.5, 1.0 or 1.5 g/100 g), nonnutrient, liquid meals of varying viscosities, and labeled with a nonabsorbable marker, phenol red. Meal viscosity was calibrated against the water proton transverse relaxation rate (T(2)(-1)) in vitro before ingestion, thus viscosity was measured in vivo via EPI measurements of T(2)(-1). Viscosity and dilution were also measured directly using nasogastric aspirates. Gastric volumes as measured by EPI, fullness, appetite and hunger were also assessed serially. Before ingestion, the log of initial meal viscosity was linearly related to T(2)(-1) (n = 8, r(2) = 0.95). Similarly, T(2)(-1) measured in vivo was also linearly related to the viscosity of the aspirates (r(2) = 0.88). All meals underwent rapid dilution, leading to a reduction in viscosity, which was greatest for the most viscous meal (P < 0.01). Surprisingly, despite the fact that the initial meal viscosity varied 1000-fold, there was only a small delay in gastric emptying (P for trend < 0.05). The area under the curve for satiety increased with initial meal viscosity, whereas that for hunger decreased (P < 0.05). In conclusion, the viscosity of a meal in vivo can be measured noninvasively using EPI. The stomach responds to meal ingestion by rapid intragastric dilution, causing a reduction of meal viscosity, and gastric emptying is minimally delayed. However, increased viscosity is associated with more prolonged satiety.     

Preventing gastric sieving by blending a solid/water meal enhances satiation in healthy humans

Separation of solids and liquids within the stomach allows faster gastric emptying of liquids compared with solids, a phenomenon known as sieving. We tested the hypothesis that blending a solid and water meal would abolish sieving, preventing the early rapid decrease in gastric volume and thereby enhancing satiety. We carried out 2 separate studies. Study 1 was a 2-way, crossover, satiety study of 22 healthy volunteers who consumed roasted chicken and vegetables with a glass of water (1008 kJ) or the same blended to a soup. They completed satiety visual analogue scales at intervals for 3 h. Study 2 was a 2-way, crossover, mechanistic study of 18 volunteers who consumed the same meals and underwent an MRI to assess gastric emptying, gallbladder contraction, and small bowel water content (SBWC) at intervals for 3 h. In Study 1, the soup meal was associated with reduced hunger (P = 0.02). In Study 2, the volume of the gastric contents after the soup meal decreased more slowly than after the solid/liquid meal (P = 0.0003). The soup meal caused greater gallbladder contraction (P < 0.04). SBWC showed a biphasic response with an initial "gastric" phase during which SBWC was greater when the solid/liquid meal was consumed (P < 0.001) and a later "small bowel" phase when SBWC was greater when the soup meal was consumed (P < 0.01). Blending the solid/liquid meal to a soup delayed gastric emptying and increased the hormonal response to feeding, which may contribute to enhanced postprandial satiety.     

Energy intake and appetite are related to antral area in healthy young and older subjects

BACKGROUND: Gastric distension reduces food intake, and antral, rather than proximal, gastric distension may be the dominant mechanism in the induction of appetite-related sensations. Healthy aging is associated with reduced appetite. OBJECTIVE: We examined the effects of different energy preloads on appetite, plasma cholecystokinin, antral area, and subsequent energy intake in healthy older and young subjects. DESIGN: On 3 separate days, 12 young and 12 older subjects consumed 400 mL of a drink containing either 0 kcal (water), 250 kcal, or 750 kcal 70 min before a buffet-style meal. RESULTS: Hunger was less in the older than in the young subjects (P < 0.001). Both nutrient preloads reduced hunger and increased fullness more than did water (P < 0.02), and older subjects were more full than were the young (P < 0.05). Antral area was greater after the nutrient preloads than after water (P = 0.001) and greater in the older than in the young subjects (P = 0.005). In both groups, food intake was suppressed in an energy-dependent manner (P = 0.008). Plasma cholecystokinin was greater in the older than in the young subjects (P = 0.003). Immediately before the meal, hunger (r = -0.59) and energy intake (r = -0.90) were inversely related and fullness (r = 0.66) was directly related to antral area (all: P < 0.001). Antral area, but not plasma cholecystokinin, was a predictor of subsequent energy intake. CONCLUSION: In healthy young and older subjects, the suppression of subsequent energy intake by a liquid preload is nutrient dependent and comparable, and both satiation and satiety are related to antral area and (presumably) antral distension.     

Reproducibility of energy intake, gastric emptying, blood glucose, plasma insulin and cholecystokinin responses in healthy young males

Gastric emptying, as well as intragastric meal distribution, and gastrointestinal hormones, including cholecystokinin (CCK), play an important role in appetite regulation. The evaluation of gastrointestinal factors regulating food intake is commonly performed in healthy, lean, young male participants. It has, however, been suggested that there is a marked interindividual variability in the effects of nutrient 'preloads' on energy intake in this group. Whether there is significant intraindividual variation in acute energy intake after a nutrient preload, and, if so, how this relates to day-to-day differences in gastric emptying and gastrointestinal hormone release, is unclear. The purpose of the present paper is to evaluate the hypothesis that energy intake after a nutrient preload would be reproducible and associated with reproducible patterns of gastric emptying, intragastric distribution and gastrointestinal hormone release. Fifteen healthy men (age 25 (sem 5) years) consumed a glucose preload (50 g glucose in 300 ml water; 815 kJ) on three occasions. Gastric emptying and intragastric meal distribution (using three-dimensional ultrasound), blood glucose, plasma insulin and CCK concentrations and appetite perceptions were evaluated over 90 min, and energy intake from a cold buffet-style meal was then quantified. Energy intake was highly reproducible within individuals between visits (intraclass correlation coefficient, ri = 0.9). Gastric emptying, intragastric meal distribution, blood glucose, plasma insulin and CCK concentrations and appetite perceptions did not differ between visits (ri>0.7 for all). In healthy males, energy intake is highly reproducible, at least in the short term, and is associated with reproducible patterns of gastric emptying, glycaemia, insulinaemia and CCK release.     

Satiety and test meal intake among women with binge eating disorder

OBJECTIVE: The purpose of the study was to measure test meal consumption and the changes in hunger and fullness during a test meal in obese individuals with and without binge eating disorder (BED) and normal-weight controls. METHOD: Twelve women with BED, 12 obese control participants, and 12 normal-weight control participants participated in two single-item test meal sessions. In one session participants were instructed to "binge," and the other eat a normal meal. Participants made ratings of hunger and fullness on visual analog scales after every 75-g increment of food. RESULTS: In comparison to obese or normal-weight controls, patients with BED consumed significantly more food to reach a similar level of fullness or hunger. CONCLUSION: Individuals with BED consumed significantly more food and showed blunted changes in hunger and fullness during both the binge and nonbinge meals. These findings suggest that individuals with BED may have disturbances in satiety that in some ways resemble those described among individuals with bulimia nervosa.     

Effect of intragastric acid stability of fat emulsions on gastric emptying, plasma lipid profile and postprandial satiety

Fat is often included in common foods as an emulsion of dispersed oil droplets to enhance the organoleptic quality and stability. The intragastric acid stability of emulsified fat may impact on gastric emptying, satiety and plasma lipid absorption. The aim of the present study was to investigate whether, compared with an acid-unstable emulsion, an acid-stable fat emulsion would empty from the stomach more slowly, cause more rapid plasma lipid absorption and cause greater satiety. Eleven healthy male volunteers received on two separate occasions 500 ml of 15 % (w/w) [13C]palmitate-enriched olive oil-in-water emulsion meals which were either stable or unstable in the acid gastric environment. MRI was used to measure gastric emptying and the intragastric oil fraction of the meals. Blood sampling was used to measure plasma lipids and visual analogue scales were used to assess satiety. The acid-unstable fat emulsion broke and rapidly layered in the stomach. Gastric emptying of meal volume was slower for the acid-stable fat emulsion (P < 0.0001; two-way ANOVA). The rate of energy delivery of fat from the stomach to the duodenum was not different up to t = 110 min. The acid-stable emulsion induced increased fullness (P < 0.05), decreased hunger (P < 0.0002), decreased appetite (P < 0.0001) and increased the concentration of palmitic acid tracer in the chylomicron fraction (P < 0.04). This shows that it is possible to delay gastric emptying and increase satiety by stabilising the intragastric distribution of fat emulsions against the gastric acid environment. This could have implications for the design of novel foods.     

Effect of Muesli with 4 g Oat β-Glucan on Postprandial Blood Glucose,Gastric Emptying and Satiety in Healthy Subjects: A Randomized Crossover Trial

Objective: Products enriched with oat β-glucan have been shown to reduce postprandial glucose and insulinemic responses. The aim of this study was to evaluate the effect of an extruded muesli product based on oat β-glucan on the rate of gastric emptying, postprandial blood glucose and satiety in healthy subjects.

Methods: Gastric emptying rate (GER) was measured by standardized real-time ultrasonography. Twelve healthy subjects were assessed using a randomized crossover double blind trial. The meals were administered after 8 hours’ fasting after measuring the subject's normal fasting blood glucose level. Blood glucose measurements were made before, 30 and 60 min after the end of the meal. Satiety scores were estimated 15 and 90 min after the end of the meal. The GER was calculated as the percentage change in the antral cross-sectional area 15 and 90 minutes after ingestion of vanilla yoghurt with muesli containing 4 g oat β-glucan (GER1) or vanilla yoghurt with muesli containing cornflakes (GER2).

Results: The median values were 60% for GER1 and 44% for GER2. The effect of 4 g oat β-glucan on the rate of gastric emptying was not statistically significant compared with corn flakes. Muesli with 4 g oat β-glucan lowered the postprandial glucose response significantly compared to the cornflakes meal (p = 0.045). The effect of oat β-glucan on satiety was not statistically significantly.

Conclusions: The results of this study suggest that intake of muesli with 4 g oat β-glucan does not affect the gastric emptying rate or satiety but lowers the postprandial blood glucose response, indicating that the GER does not regulate the blood glucose level.     

Relationship of satiety to postprandial glycaemic, insulin and cholecystokinin responses.

The effect of plasma glucose on satiety and the capacity of carbohydrates to stimulate cholecystokinin (CCK) remain unclear. The aim of this study was to test the hypothesis that the magnitude of the postprandial plasma glucose and insulin response is inversely related to the CCK response and to subjective satiety. Seven healthy, male volunteers consumed equal carbohydrate portions (0.5 g/kg body weight) of six test meals (Rice Bubbles, Sustain, Vita-Brits, All-Bran, porridge and white bread) in random order after an overnight fast. An egg and bacon meal was consumed as a non-carbohydrate control providing 0.5 g protein/kg body weight. Serum CCK, plasma glucose and insulin and subjective satiety (measured by a rating scale) were assessed over 3 h and quantified using the glycaemic index (GI), insulin index (II), the peak satiety score and area under the incremental curve (AUC). The observed GIs (mean +/- SE) ranged from 42.5 +/- 2.6 for All-Bran to 116.2 +/- 11.4 for Rice Bubbles, using white bread as the reference food (GI = 100). Peak satiety scores varied eightfold from 0.21 +/- 0.4 for Sustain to 1.64 +/- 0.4 for All-Bran. Significant inverse relationships were observed between the peak satiety score and both the glycaemic and insulin index of the seven meals (r = -0.916, p less than 0.001 and r = -0.926, p less than 0.001). A direct relationship was observed between satiety (AUC) and the CCK response (AUC) (r = 0.73 p less than 0.01). The results suggest that glycaemic and insulin responses to carbohydrate foods are inversely proportional to the CCK response and satiety.     

Food intake and plasma ghrelin response during potato-, rice- and pasta-rich test meals

Objective Complex carbohydrates such as potato, rice and pasta are frequently consumed accompaniments of meat meals and have different effects on satiety, food intake, glucose, and insulin concentrations. The orexigenic gastric hormone ghrelin contributes to feeding regulation and as yet it is unknown whether there is any differential ghrelin response to these starchy food items corresponding to their effects on food intake. Methods In 11 subjects the effect of satiating amounts of potatoes, rice or pasta consumed together with 150g pork steak was examined on hunger/satiety ratings, food intake, plasma insulin, glucose and ghrelin concentrations. Results All meals led to comparable quantities of food intake while energy intake was significantly lower after potatoes. Satiety/hunger ratings were significantly different from basal for the entire 4 h period after rice and pasta meals, while they had returned to basal during the 4th hour after potatoes. After rice and pasta insulin rose significantly for 4 h. Ghrelin decreased during the 2nd and 3rd hour. In contrast potatoes stimulated insulin for the initial 2 h only while ghrelin rose significantly by 120 pg/ml over the 4 h period. A significant correlation was observed between ghrelin and hunger ratings while subsequent second meal food and energy intake did not differ irrespective of the preceding ghrelin concentration. Conclusion Compared to rice and pasta satiating amounts of potatoes coingested with meat result in lower energy intake and postprandial insulin concentrations, which is not counterbalanced during subsequent food intake despite higher ghrelin concentrations. The present data support the concept that ghrelin can affect hunger sensations but not necessarily food and energy intake.     

Pork, beef and chicken have similar effects on acute satiety and hormonal markers of appetite

The effects of three different meat-containing breakfast meals (pork, beef or chicken) on acute satiety and appetite regulatory hormones were compared using a within-subjects study design. Thirty fasting non-smoking pre-menopausal women attended a research centre on three test days to consume, a meat-containing meal matched in energy (kJ) and protein content, palatability, and appearance. No difference was found between meat groups for either energy intake or macronutrient profile of food consumed at a subsequent ad libitum buffet lunch, or over the rest of the day. Visual Analogue Scale (VAS) ratings for hunger and satiety over an 180 min period did not differ between test meals. After consumption of the test meals, a significant difference was found in PYY response between pork and chicken meals (P=0.027) but not for levels of CCK, ghrelin, insulin or glucose. This study positions pork, beef, and chicken as equal in their effect on satiety and release of appetite-related intestinal hormones and of insulin.     

Age-Related Variations of Appetite Sensations of Fullness and Satisfaction with Different Dietary Energy Densities in a Large,Free-Living Sample of Japanese Adults

BackgroundThe effective energy density (ED) diet model for customized meal plans has not been adequately explored, and the specific differences in appetite sensation among age groups remain unclear.DesignA randomized, crossover study was conducted in 2010 to examine the effects of lunches with different dietary EDs on sensory properties across age groups.Participants/settingIn this experiment, 276 healthy Japanese subjects aged 22 to 59 years consumed packed lunches over six sessions. Using the control meal (150 g cooked rice, sautéed beef menu containing 40 g raw beef, and 240 g vegetable) as a reference, a high-meat/low-rice meal, a low-vegetable meal, a medium-fat/low-vegetable meal, a high-fat meal, and a high-fat/low-vegetable meal were served as modified test meals with varying macronutrient distribution and ED.Main outcome measuresSubjective levels of fullness and satisfaction were assessed over time by visual analogue scale ratings.Statistical analyses performedData were analyzed using analysis of variance with body mass index as a covariate followed by Bonferroni post hoc tests.ResultsMeals with high vegetable content resulted in greater fullness and satisfaction than meals with low vegetable content, regardless of the diner’s age. Particularly among the 500-kcal low-ED meals, a high-meat meal resulted in greater fullness and satisfaction than a medium-fat/low-vegetable meal among participants aged 30 to 40 years. Postprandial fullness was significantly higher with control meal than with high-meat meal among participants aged 40 to 50 years.ConclusionsThis study indicated that high vegetable content in the low-ED diet model provided sufficient fullness and satisfaction despite the low energy content and increased rice content is more effective for satiety than increased meat content for Japanese adults aged around 40 years.     

Gastrointestinal Contributions to the Postprandial Experience

Food ingestion induces homeostatic sensations (satiety, fullness) with a hedonic dimension (satisfaction, changes in mood) that characterize the postprandial experience. Both types of sensation are secondary to intraluminal stimuli produced by the food itself, as well as to the activity of the digestive tract. Postprandial sensations also depend on the nutrient composition of the meal and on colonic fermentation of non-absorbed residues. Gastrointestinal function and the sensitivity of the digestive tract, i.e., perception of gut stimuli, are determined by inherent individual factors, e.g., sex, and can be modulated by different conditioning mechanisms. This narrative review examines the factors that determine perception of digestive stimuli and the postprandial experience.     

No effect of glucagon-like peptide-1 on short-term satiety and energy intake in man

Centrally administered glucagon-like peptide-1 (GLP-1) inhibits feeding in fasted rats, but its role in human satiety has been largely unexplored. The present study investigated the effect of peripheral GLP-1 infusion on gastric emptying and satiety in man. Ten non-obese male subjects were infused in a randomized single-blind within-subject crossover study using saline infusion as control. They received either a GLP-1 infusion (1.2 pmol/kg per min) or a saline infusion for 1 h, at 18.00 hours. At 20 min after starting the infusion the gastric emptying of a 400 ml water load was measured. Subjects completed behavioural self-rating scales to assess hunger and satiety. After 40 min subjects were given a buffet meal ad libitum and their food intake was recorded. GLP-1 infusion raised circulating GLP-1 concentrations to approximately twice those seen following a meal. It did not affect circulating insulin levels but caused a small fall in glucose levels. Gastric emptying of the water load was significantly delayed by the GLP-1 infusion. Energy intake from the buffet was unaffected by GLP-1 infusion. Self-assessment of hunger and satiety was similarly unaffected by the infusion before the buffet meal, although subjects tended to be less hungry after the buffet meal following GLP-1 infusion (P < 0.09). GLP-1 infusion delayed gastric emptying but had a minimal effect on food intake and satiety. This study casts doubts on whether GLP-1 is a major satiety factor in man, although a raised circulating plasma glucose level, as would normally occur postprandially, might be necessary for GLP-1 to increase satiety.     

The effects of fiber enrichment of pasta and fat content on gastric emptying,GLP-1, glucose,and insulin responses to a meal

OBJECTIVE: To assess whether the addition of viscous fiber at an amount recommended by the US FDA to allow a 'low saturated fat, cholesterol, soluble fiber and coronary heart disease', health claim label on a food package (1.7 g psyllium) and/or fat (30 g sunflower oil and 3 g sodium propionate) to a pasta meal would affect gastric emptying, postprandial glucose, insulin and GLP-1 concentrations. DESIGN: Ten subjects participated in a two-by-two single blind randomized crossover study. Four meals containing 50 g of available carbohydrate were consumed: pasta with or without psyllium enrichment served with a tomato sauce with (520 kcal per meal) and without (240 kcal per meal) fat. Blood samples were taken for 240 min following the meal and all subjects consumed a buffet meal at the end of the study. Gastric emptying was measured using the paracetamol absorption test. Blood was analysed for glucose, insulin, GLP-1. Visual analog scales were used to record feelings of hunger, pleasantness and nausea. RESULTS: The psyllium-enriched pasta had no significant effect on gastric emptying or the incremental area under the curve (IAUC) for GLP-1, insulin or glucose compared with the control pasta. The addition of polyunsaturated fat and sodium propionate significantly increased the IAUC for GLP-1 (P<0.001), delaying gastric emptying (P<0.002), and decreasing glucose (P<0.002). CONCLUSIONS: A dose of 1.7 g psyllium did not evoke measurable effects on gastric emptying, postprandial GLP-1, insulin or glucose metabolism. However the addition of 30 g of oil and 3 g of sodium propionate to the pasta did reduce gastric emptying, increase GLP-1 and reduce glucose and insulin concentrations. While this short-term study may have implications in terms of reducing the risk of diabetes and improving coronary risk factor profiles the long term effects of these nutrients need to be studied.     

High-calorie fibre-rich breakfast: its effect on satiety

This study was designed to test whether a substantial fibre-rich breakfast could influence satiety sensations and daily energy. In non-consecutive weeks 24 volunteers were given two high-fibre cereals (Kellogg's ‘Bran Flakes’ and Kellogg's ‘All Bran’) in a breakfast meal that accounted for about 20% of the total daily energy intake. During the trial a questionnaire for hunger and satiety sensations was filled out just before, immediately after and 1, 2, 3 and 4 h after breakfast. The more reliable questions in evaluating sensations correlated to hunger and satiety were: ‘How satiated do you feel?’ and ‘How full do you feel?’. Significant differences in the satiety sensations were found for the experimental breakfasts compared to the usual one. There was no statistical differences between the two cereal breakfast meals, however, the highest scores of fullness and satiety always corresponded to the highest fibre content. Furthermore, after the two experimental breakfasts the calorie intake at lunch was lower than after the habitual one. Regression analysis showed a positive linear correlation between the scores corresponding to satiety sensations and the fibre and energy intakes. The findings indicate that a substantial breakfast rich in fibre has a positive impact on subsequent food intake and the sensations associated with satiety.