Tina Akhavan

Whey Proteins in the Regulation of Food Intake and Satiety

Whey protein has potential as a functional food component to contribute to the regulation of body weight by providing satiety signals that affect both short-term and long-term food intake regulation. Because whey is an inexpensive source of high nutritional quality protein, the utilization of whey as a physiologically functional food ingredient for weight management is of current interest. At present, the role of individual whey proteins and peptides in contributing to food intake regulation has not been fully defined. However, Whey protein reduces short-term food intake relative to placebo, carbohydrate and other proteins. Whey protein affects satiation and satiety by the actions of: (1) whey protein fractions per se; (2) bioactive peptides; (3) amino-acids released after digestion; (4) combined action of whey protein and/or peptides and/or amino acids with other milk constituents. Whey ingestion activates many components of the food intake regulatory system. Whey protein is insulinotropic, and whey-born peptides affect the renin-angiotensin system. Therefore whey protein has potential as physiologically functional food component for persons with obesity and its co-morbidities (hypertension, type II diabetes, hyper- and dislipidemia). It remains unclear, however, if the favourable effects of whey on food intake, subjective satiety and intake regulatory mechanisms in humans are obtained from usual serving sizes of dairy products. The effects described have been observed in short-term experiments and when whey is consumed in much higher amounts.

Effect of premeal consumption of whey protein and its hydrolysate on food intake and postmeal glycemia and insulin responses in young adults.

BACKGROUND Dairy protein ingestion before a meal reduces food intake and, when consumed with carbohydrate, reduces blood glucose. OBJECTIVE The objective was to describe the effect of whey protein (WP) or its hydrolysate (WPH) when consumed before a meal on food intake, pre- and postmeal satiety, and concentrations of blood glucose and insulin in healthy young adults. DESIGN Two randomized crossover studies were conducted. WP (10-40 g) in 300 mL water was provided in experiment 1, and WP (5-40 g) and WPH (10 g) in 300 mL water were provided in experiment 2. At 30 min after consumption, the subjects were fed an ad libitum pizza meal (experiment 1) or a preset pizza meal (12 kcal/kg, experiment 2). Satiety, blood glucose, and insulin were measured at baseline and at intervals both before and after the meals. RESULTS In experiment 1, 20-40 g WP suppressed food intake (P < 0.0001) and 10-40 g WP reduced postmeal blood glucose concentrations and the area under the curve (AUC) (P < 0.05). In experiment 2, 10-40 g WP, but not WPH, reduced postmeal blood glucose AUC and insulin AUC in a dose-dependent manner (P < 0.05). The ratio of cumulative blood glucose to insulin AUCs (0-170 min) was reduced by > or =10 g WP but not by 10 g WPH. CONCLUSIONS WP consumed before a meal reduces food intake, postmeal blood glucose and insulin, and the ratio of cumulative blood glucose to insulin AUCs in a dose-dependent manner. Intact WP, but not WPH, contributes to blood glucose control by both insulin-dependent and insulin-independent mechanisms. This trial was registered at clinicaltrials.gov as NCT00988377 and NCT00988182.

Relation between estimates of cornstarch digestibility by the Englyst in vitro method and glycemic response, subjective appetite, and short-term food intake in young men

BACKGROUND Starch composition and rate of digestion are determinants of blood glucose concentrations and food intake (FI). OBJECTIVE Our objective was to describe relations between estimates of digestibility of starches by the in vitro Englyst method and their effect on blood glucose concentrations, subjective appetite, and FI in young men. DESIGN Subjects consumed 5 soups containing 50 g maltodextrin, whole-grain, high-amylose, regular cornstarch, or no added starch at 1-wk intervals. Ad libitum FI was measured at 30 min (experiment 1) or 120 min (experiment 2) later, which were the estimated times of digestion of a rapidly digestible starch (RDS) and slowly digestible starch, respectively. Blood glucose concentrations and appetite were measured pre- and postmeal. RESULTS At 30 min, FI was reduced by maltodextrin only [86% RDS, 12% resistant starch (RS); P < 0.05], but at 120 min FI was reduced by whole-grain (24% RDS, 66% RS), high-amylose corn (40% RDS, 48% RS), and regular corn (27% RDS, 39% RS) (P < 0.0001). The premeal blood glucose concentration at 30 and 120 min was highest and lowest after maltodextrin treatment, respectively (P < 0.0001). After the meal, the blood glucose area under the curve at 30 min was lower after all starch treatments (P < 0.05), but at 120 min the blood glucose area under the curve was lower only after the regular cornstarch treatment (P < 0.05). Premeal appetite decreased by all treatments (P < 0.05). CONCLUSION The in vitro estimates of starch digestibility by the Englyst method predicted the effects of starch composition on blood glucose concentrations and FI in young men 30 and 120 min after consumption. This trial was registered at clinicaltrials.gov as NCT00980941 for experiment 1 and NCT00988689 for experiment 2.

Reduced energy intake at breakfast is not compensated for at lunch if a high-insoluble-fiber cereal replaces a low-fiber cereal.

BACKGROUND In cohort studies, insoluble fiber has been associated with a reduced risk of obesity and diabetes; however, compared with soluble fiber, its role in the regulation of short-term food intake (FI) and satiety has received little attention. OBJECTIVE Our aim was to compare the effects of a high-insoluble-fiber (HF) cereal with a low-fiber (LF) cereal on FI, subjective appetite (SA), and plasma glucose (PG) in healthy individuals. DESIGN Males and females (n = 32) were randomly assigned to consume 60 g of either HF (26 g insoluble fiber, 120 kcal) or LF (1 g fiber, 217 kcal) breakfast cereal. Pre- and postlunch SA and PG were measured regularly for 4 h, and ad libitum FI was measured at 3 h. RESULTS The prelunch SA area under the curve did not differ between the 2 cereals, but when expressed as change in appetite per kilocalorie of cereal, HF suppressed SA more than did LF (-17.6 +/- 1.8 compared with -10.0 +/- 1.1 mm . min . kcal(-)(1), respectively; P < 0.01). Lunchtime FI did not differ between cereals, but cumulative energy intake (cereal + lunch) was lower after the HF than after the LF cereal (1330 +/- 57 compared with 1422 +/- 66 kcal, respectively; P = 0.01). The prelunch PG area under the curve (P < 0.0001) and the immediate postlunch PG (P = 0.01) were lower after HF cereal consumption. CONCLUSIONS An HF breakfast cereal contributes to a cumulative reduction in breakfast and lunch energy intake, possibly due to its high satiety value per kilocalorie. A short-term benefit of the HF cereal, compared with LF cereal, was lower PG concentration before and immediately after lunch.

Mechanism of action of pre-meal consumption of whey protein on glycemic control in young adults

Whey protein (WP), when consumed in small amounts prior to a meal, improves post-meal glycemic control more than can be explained by insulin-dependent mechanisms alone. The objective of the study was to identify the mechanism of action of WP beyond insulin on the reduction of post-meal glycemia. In a randomized crossover study, healthy young men received preloads (300 ml) of WP (10 and 20 g), glucose (10 and 20 g) or water (control). Paracetamol (1.5 g) was added to the preloads to measure gastric emptying. Plasma concentrations of paracetamol, glucose, and β-cell and gastrointestinal hormones were measured before preloads (baseline) and at intervals before (0-30 min) and after (50-230 min) a preset pizza meal (12 kcal/kg). Whey protein slowed pre-meal gastric emptying rate compared to the control and 10 g glucose (P<.0001), and induced lower pre-meal insulin and C-peptide than the glucose preloads (P<.0001). Glucose, but not WP, increased pre-meal plasma glucose concentrations (P<.0001). Both WP and glucose reduced post-meal glycemia (P=.0006) and resulted in similar CCK, amylin, ghrelin and GIP responses (P<.05). However, compared with glucose, WP resulted in higher post-meal GLP-1 and peptide tyrosine-tyrosine (PYY) and lower insulin concentrations, without altering insulin secretion and extraction rates. For the total duration of this study (0-230 min), WP resulted in lower mean plasma glucose, insulin and C-peptide, but higher GLP-1 and PYY concentrations than the glucose preloads. In conclusion, pre-meal consumption of WP lowers post-meal glycemia by both insulin-dependent and insulin-independent mechanisms.

Energy and macronutrient content of familiar beverages interact with pre-meal intervals to determine later food intake, appetite and glycemic response in young adults

The objective was to compare the effects of pre-meal consumption of familiar beverages on appetite, food intake, and glycemic response in healthy young adults. Two short-term experiments compared the effect of consumption at 30 (experiment 1) or 120 min (experiment 2) before a pizza meal of isovolumetric amounts (500 mL) of water (0 kcal), soy beverage (200 kcal), 2% milk (260 kcal), 1% chocolate milk (340 kcal), orange juice (229 kcal) and cows milk-based infant formula (368 kcal) on food intake and subjective appetite and blood glucose before and after a meal. Pre-meal ingestion of chocolate milk and infant formula reduced food intake compared to water at 30 min, however, beverage type did not affect food intake at 2h. Pre-meal blood glucose was higher after chocolate milk than other caloric beverages from 0 to 30 min (experiment 1), and after chocolate milk and orange juice from 0 to 120 min (experiment 2). Only milk reduced post-meal blood glucose in both experiments, suggesting that its effects were independent of meal-time energy intake. Combined pre- and post-meal blood glucose was lower after milk compared to chocolate milk and orange juice, but did not differ from other beverages. Thus, beverage calorie content and inter-meal intervals are primary determinants of food intake in the short-term, but macronutrient composition, especially protein content and composition, may play the greater role in glycemic control.

Milk proteins in the regulation of body weight, satiety, food intake and glycemia.

Consumption of dairy products and their milk proteins increase satiety and reduce food intake and blood glucose response when consumed alone or with carbohydrate. Dairy proteins are of interest because proteins are more satiating than either carbohydrate or fat, and they regulate food intake and metabolic functions by the combined actions of the intact protein, encrypted peptides and amino acids on gastrointestinal and central pathways. As shown in this review, milk proteins have physiologic functions that contribute to the maintenance of a healthy body weight and control of factors associated with the metabolic syndrome through their effects on mechanisms regulating food intake and blood glucose. More recent reports show that these benefits can be achieved within the range of usual consumption of dairy. In addition, recent research points to an intrinsic value of small amounts of milk protein or dairy consumed shortly before a meal to reduce the glycemic response to carbohydrate and that this is not at the cost of increased demand for insulin.

Mechanism of action of whole milk and its components on glycemic control in healthy young men.

Milk reduces post-meal glycemia when consumed either before or within an ad libitum meal. The objective of this study was to compare the effect of each of the macronutrient components and their combination with whole milk on postprandial glycemia, glucoregulatory and gastrointestinal hormones and gastric emptying in healthy young men. In a randomized, crossover study, 12 males consumed beverages (500 ml) of whole milk (3.25% M.F.) (control), a simulated milk beverage based on milk macronutrients, complete milk protein (16 g), lactose (24 g) or milk fat (16 g). Whole and simulated milk was similar in lowering postprandial glycemia and slowing gastric emptying while increasing insulin, C-peptide, peptide tyrosine tyrosine (PYY) and cholecystokinin (CCK), but simulated milk resulted in higher (41%) glucagon-like peptide-1 (GLP-1) and lower (43%) ghrelin areas under the curve (AUC) than whole milk (P=.01 and P=.04, respectively). Whole and simulated milk lowered glucose (P=.0005) more than predicted by the sum of AUCs for their components. Adjusted for energy content, milks produced lower glucose and hormone responses than predicted from the sum of their components. The effect of protein/kcal on the AUCs was higher than fat/kcal for insulin, C-peptide, insulin secretion rate, GLP-1, CCK and paracetamol (P<.0001), but similar to lactose except for CCK and paracetamol, which were lower. The response in PYY and ghrelin was similar per unit of energy for each macronutrient. In conclusion, milk lowers postprandial glycemia by both insulin and insulin-independent mechanisms arising from interactions among its macronutrient components and energy content.

Application of dairy-derived ingredients in food intake and metabolic regulation

This chapter discusses the role of milk and dairy products, and their ingredients in obesity and the regulation of food intake and components of metabolic syndrome. In addition to protein (whey and casein), fat (saturated, mono- and poly-unsaturated fatty acids) and carbohydrate (lactose), milk contains biologically active substances such as immunoglobulins, enzymes, antimicrobial peptides, oligosaccharides, hormones, cytokines and growth factors. Each of these may affect food intake and metabolic regulation through a large number of physiologic mechanisms. Thus, their actions may explain the positive health associations between more frequent dairy consumption, a healthier body weight, and decreased risk of developing the metabolic syndrome.