Comparative effects of whey and casein proteins on satiety in overweight and obese individuals: a randomized controlled trial

Effects of supplementation with milk protein on glycemic parameters: a GRADE-assessed systematic review and dose-response meta-analysis

BACKGROUND

It is suggested that supplementation with milk protein (MP) has the potential to ameliorate the glycemic profile; however, the exact impact and certainty of the findings have yet to be evaluated. This systematic review and dose-response meta-analysis of randomized controlled trials (RCTs) assessed the impact of MP supplementation on the glycemic parameters in adults.

METHODS

A systematic search was carried out among online databases to determine eligible RCTs published up to November 2022. A random-effects model was performed for the meta-analysis.

RESULTS

A total of 36 RCTs with 1851 participants were included in the pooled analysis. It was displayed that supplementation with MP effectively reduced levels of fasting blood glucose (FBG) (weighted mean difference (WMD): -1.83 mg/dL, 95% CI: -3.28, -0.38; P = 0.013), fasting insulin (WMD: -1.06 uU/mL, 95% CI: -1.76, -0.36; P = 0.003), and homeostasis model assessment of insulin resistance (HOMA-IR) (WMD: -0.27, 95% CI: -0.40, -0.14; P < 0.001) while making no remarkable changes in serum hemoglobin A1c (HbA1c) values (WMD: 0.01%, 95% CI: -0.14, 0.16; P = 0.891). However, there was a significant decline in serum levels of HbA1c among participants with normal baseline body mass index (BMI) based on sub-group analyses. In addition, HOMA-IR values were significantly lower in the MP supplement-treated group than their untreated counterparts in short- and long-term supplementation (≤ 8 and > 8 weeks) with high or moderate doses (≥ 60 or 30-60 g/d) of MP or whey protein (WP). Serum FBG levels were considerably reduced upon short-term administration of a low daily dose of WP (< 30 g). Furthermore, the levels of serum fasting insulin were remarkably decreased during long-term supplementation with high or moderate daily doses of WP.

CONCLUSION

The findings of this study suggest that supplementation with MP may improve glycemic control in adults by reducing the values of fasting insulin, FBG, and HOMA-IR. Additional trials with longer durations are required to confirm these findings.

Macronutrients effects on satiety and food intake in older and younger adults: A randomised controlled trial

Older adults are advised to increase their protein intake to maintain their muscle mass. However, protein is considered the most satiating macronutrient and this recommendation may cause a decrease in total energy intake. To date, satiety studies comparing all three macronutrients have been undertaken in young adults, and it is unclear if the same response is seen in older adults. The objective of this study was to compare the effect of preloads high in protein, fat, and carbohydrate but equal in energy (∼300 kcal) and volume (250 ml) on energy intake, perceived appetite, and gastric emptying in younger and older adults. Twenty older and 20 younger adults completed a single-blinded randomised crossover trial involving three study visits. Participants consumed a standard breakfast, followed by a preload milkshake high in either carbohydrate, fat, or protein. Three hours after the preload, participants were offered an ad libitum meal to assess food intake. Visual analogue scales were used to measure perceived appetite and gastric emptying was measured via the 13C-octanoic acid breath test. There was no significant effect of preload type or age on energy intake either at the ad libitum meal, self-recorded food intake for the rest of the test day or subjective appetite ratings. There was a significant effect of preload type on gastric emptying latency phase and ascension time, and an effect of age on gastric emptying latency and lag phase such that older adults had faster emptying. In conclusion, energy intake, and perceived appetite were not affected by macronutrient content of the preloads in both younger and older adults, but gastric emptying times differed.

Effects of Poria cocos extract and protein powder mixture on glucolipid metabolism and rhythm changes in obese mice

Herein, we explored the effects of Poria cocos extract, protein powder mixture, and their combined intervention on weight loss in high-fat diet (HFD)-induced obese mice. Male C57BL/6J mice were selected and fed a HFD for 8 weeks; obese mice that were successfully modeled were divided into modeling and five intervention groups, and given the corresponding treatment for 10 weeks. Body weight, fat, and muscle tissue, blood glucose, lipids, inflammatory factors, and other glucose and lipid metabolism-related indicators were measured to evaluate the effect of P. cocos and protein powder intervention on weight loss in obese mice. The body weight of the intervention group was reduced compared with the HFD group. Fat content of mice in F3PM group decreased significantly (p < .05). Levels of blood glucose, lipids, adiponectin, leptin, and inflammatory factors, including interleukin-1 β and tumor necrosis factor- α showed improvement. Lipoprotein lipase (lower about 2.97 pg/ml, vs. HFD mice 10.65 mmoL/ml) and sterol regulatory element-binding transcription factor (lower about 1413.63 pg/ml, vs. HFD mice 3915.33 pg/ml) levels in liver tissue were decreased. The respiratory exchange rate (RER) of mice in the HFD and subject intervention groups had no circadian rhythm and was maintained at approximately 0.80. The protein powder mixture (PM) group had the lowest RER (p < .05), the P. cocos extract (FL) and F1PM groups had similar RER to the HFD group (p < .05), and the F2PM group had a higher RER than the HFD group (p < .05). And food intake and energy metabolism returned to circadian rhythm, with an increase in the dose of P. cocos extract, the feeding rhythms of F1PM, F2PM, and F3PM were closer to that of the normal diet (ND) group. Feeding intervention with P. cocos and protein powder improved fat distribution, glucolipid metabolism, and energy metabolism, with the combination of F3PM showing more diverse benefits.

Protein Source Influences Acute Appetite and Satiety but not Subsequent Food Intake in Healthy Adults

BACKGROUND

Although current recommendations encourage plant-based dietary patterns, data is limited as to whether the equivalent substitution of animal-based protein-rich foods with plant-based versions impacts ingestive behavior.

OBJECTIVE

To compare higher-protein preloads, varying in protein source, on appetite, satiety, and subsequent energy intake.

METHODS

Thirty-two adults (Age: 25±1y; Body Mass Index (BMI): 24.2±0.5kg/m) randomly consumed 250kcal, protein-preload beverages (24g protein), varying in protein source (whey, soy, pea protein isolates (WHEY, SOY, PEA) or micellar casein (CAS)) each morning for 3 acclimation days/preload. On day 4, participants completed a 4-h clinical testing day in which the respective preload was consumed followed by blood sampling and questionnaires every 30min for appetite and satiety. An ad libitum lunch was provided 4-h post-preload. On day 5, participants consumed the respective preload at home followed by an ad libitum breakfast 30min afterwards. For normally-distributed data, repeated-measures analysis of variance (ANOVA) or Friedman non-parametric test were utilized to compare main effects of protein source on study outcomes. Post-hoc pairwise comparisons using least significant differences (LSD) were then performed.

RESULTS

CAS (-3330±690mm*240min) and PEA (-2840±930mm*240min) reduced 4-h appetite vs. SOY (-1440±936mm*240min; both, P<0.05). WHEY was not different (-2290±930mm*240min). CAS (3520±84pg/ml*240min) and PEA (3860±864pg/ml*240min) increased 4-h PYY concentrations vs. SOY (2200±869pg/ml*240min; both, P<0.05). WHEY was not different (3870±932pg/ml*240 min). No differences in ad libitum energy intake were observed.

CONCLUSIONS

CAS and PEA, but not WHEY, elicited greater acute changes in appetite and satiety vs. SOY in healthy adults, supporting that not all protein sources are equivalent. This trial is registered at clinicaltrials.gov (NCT03154606).

Effects of whey protein supplementation on adiposity, body weight, and glycemic parameters: A synthesis of evidence

AIMS

The aim of this review was to analyze the evidence of whey protein supplementation on body weight, fat mass, lean mass and glycemic parameters in subjects with overweight or type 2 diabetes mellitus (T2DM) undergoing calorie restriction or with ad libitum intake.

DATA SYNTHESIS

Overweight and obesity are considered risk factors for the development of chronic noncommunicable diseases such as T2DM. Calorie restriction is a dietary therapy that reduces weight and fat mass, promotes the improvement of glycemic parameters, and decreases muscle mass. The maintenance of muscle mass during weight loss is necessary in view of its implication in preventing chronic diseases and improving functional capacity and quality of life. The effects of increased protein consumption on attenuating muscle loss and reducing body fat during calorie restriction or ad libitum intake in overweight individuals are discussed. Some studies have demonstrated the positive effects of whey protein supplementation on improving satiety and postprandial glycemic control in short term; however, it remains unclear whether long-term whey protein supplementation can positively affect glycemic parameters.

CONCLUSIONS

Although whey protein is considered to have a high nutritional quality, its effects in the treatment of overweight, obese individuals and those with T2DM undergoing calorie restriction or ad libitum intake are still inconclusive.

How dietary amino acids and high protein diets influence insulin secretion

Glucose homeostasis is the maintenance and regulation of blood glucose concentration within a tight physiological range, essential for the functioning of most tissues and organs. This is primarily achieved by pancreatic secretion of insulin and glucagon. Deficient pancreatic endocrine function, coupled with or without peripheral insulin resistance leads to prolonged hyperglycemia with chronic impairment of glucose homeostasis, most commonly seen in diabetes mellitus. High protein diets (HPDs) are thought to modulate glucose homeostasis through various metabolic pathways. Insulin secretion can be directly modulated by the amino acid products of protein digestion, which activate nutrient receptors and nutrient transporters expressed by the endocrine pancreas. Insulin secretion can also be modulated indirectly, through incretin release from enteroendocrine cells, and via vagal neuronal pathways. Additionally, glucose homeostasis can be promoted by the satiating effects of anorectic hormones released following HPD consumption. This review summarizes the insulinotropic mechanisms by which amino acids and HPDs may influence glucose homeostasis, with a particular focus on their applicability in the management of Type 2 diabetes mellitus.

Effects of the maize-derived protein zein, and the milk proteins casein, whey, and α-lactalbumin, on subjective measures of satiety and food intake in normal-weight young men

Protein is considered to be the most satiating food macronutrient and the satiating effect may be dependent on the source of the protein. The maize-derived protein zein and milk protein casein have been shown previously to lower stomach emptying rate more than dairy whey protein, but the effect of zein on satiety has not been evaluated. The objective was to compare the satiating effects of zein and casein, with whey protein and its protein component α-lactalbumin. The study was a randomised crossover design with thirteen normal-weight men (mean age 27.8 years and mean BMI 24.4 kg/m2) consuming isoenergetic (∼4000 kJ, ∼990 kcal) preload mixed meals enriched with Zein, Casein, whey protein isolate (Whey), α-lactalbumin (ALac), or maltodextrin carbohydrate (Carb). Consumption of an ad libitum standardised test meal of chicken fried rice and water provided 360 min following ingestion of the preload meal was measured, and subjective feelings of appetite (hunger, fullness, desire to eat, and prospective food consumption) were assessed using 100-mm visual analogue scales (VAS). There were no differences among the five preload mixed meals in the amount of chicken fried rice consumed at the ad libitum test meal (mean ± sem: 531.6 ± 35.0 g, p = 0.47) or total (preload + test meal) energy intakes (mean ± sem: 5780.5 ± 146.0 kJ, p = 0.29). The subjective VAS appetite ratings and total area under the curve responses for hunger, fullness, desire to eat, and prospective food consumption, were not different following consumption of all five preload mixed meals (p > 0.05). The findings indicate that the effects of zein and casein on satiety were not different from the satiating effects of whey protein and α-lactalbumin.

Whey-Adapted versus Natural Cow's Milk Formulation: Distinctive Feeding Responses and Post-Ingestive c-Fos Expression in Laboratory Mice

The natural 20:80 whey:casein ratio in cow’s milk (CM) for adults and infants is adjusted to reflect the 60:40 ratio of human milk, but the feeding and metabolic consequences of this adjustment have been understudied. In adult human subjects, the 60:40 CM differently affects glucose metabolism and hormone release than the 20:80 CM. In laboratory animals, whey-adapted goat’s milk is consumed in larger quantities. It is unknown whether whey enhancement of CM would have similar consequences on appetite and whether it would affect feeding-relevant brain regulatory mechanisms. In this set of studies utilizing laboratory mice, we found that the 60:40 CM was consumed more avidly than the 20:80 control formulation by animals motivated to eat by energy deprivation and by palatability (in the absence of hunger) and that this hyperphagia stemmed from prolongation of the meal. Furthermore, in two-bottle choice paradigms, whey-adapted CM was preferred against the natural 20:80 milk. The intake of the whey-adapted CM induced neuronal activation (assessed through analysis of c-Fos expression in neurons) in brain sites promoting satiation, but importantly, this activation was less pronounced than after ingestion of the natural 20:80 whey:casein CM. Activation of hypothalamic neurons synthesizing anorexigenic neuropeptide oxytocin (OT) was also less robust after the 60:40 CM intake than after the 20:80 CM. Pharmacological blockade of the OT receptor in mice led to an increase in the consumption only of the 20:80 CM, thus, of the milk that induced greater activation of OT neurons. We conclude that the whey-adapted CM is overconsumed compared to the natural 20:80 CM and that this overconsumption is associated with weakened responsiveness of central networks involved in satiety signalling, including OT.

Effects of a Low Carb Diet and Whey Proteins on Anthropometric, Hematochemical, and Cardiovascular Parameters in Subjects with Obesity

BACKGROUND

The best way to lose body weight, without using drugs and/or suffering hunger and stress, has not yet been defined. The present study tested a low carbohydrate diet, enriched with proteins, in subjects with overweight and obesity.

METHODS

The study enrolled 22 uncomplicated overweight and obese subjects. Several parameters were examined before and after 6 weeks of a low-carbohydrate diet, enriched with 18 g of whey proteins. Anthropometric (body mass index, waist circumference) variables, fasting hormones (insulin, TSH, FT3, FT4), and metabolic (glucose, prealbumin, and lipid levels) parameters were measured. 25- OH-vitamin D (25 (OH) D), parathyroid hormone (PTH) and osteocalcin, were also quantified. Body composition parameters (fat mass, fat-free mass, body cell mass, total body water) were measured by electrical bioimpedance analysis. As cardiovascular parameters, blood pressure, endothelium flowmediated dilation (FMD), and common carotid artery intima-media thickness were also measured.

RESULTS

The low-carbohydrate diet integrated with proteins induced a significant decrease in body weight (P < 0.001), waist circumference (P < 0.001), fat mass (P < 0.001), diastolic blood pressure (P < 0.01), triglycerides (P < 0.001), total cholesterol (P < 0.001), pre-albumin (P < 0.001), insulin (P < 0.001), HOMAIR (P < 0.001), FT3 (P < 0.05), and c-IMT (P < 0.001), and a significant increase in FMD (P < 0.001) and 25 (OH) D (P < 0.001) was also observed.

CONCLUSION

All these results suggest that a short-term non-prescriptive low carbohydrate diet, enriched with whey proteins, may be a good way to start losing fat mass and increase health.

Efficacy of Dietary and Supplementation Interventions for Individuals with Type 2 Diabetes

The prevalence of Type 2 diabetes (T2D) is increasing, which creates a large economic burden. Diet is a critical factor in the treatment and management of T2D; however, there are a large number of dietary approaches and a general lack of consensus regarding the efficacy of each. Therefore, the purpose of this narrative review is twofold: (1) to critically evaluate the effects of various dietary strategies on diabetes management and treatment, such as Mediterranean diet, plant-based diet, low-calorie and very low-calorie diets, intermittent fasting, low-carbohydrate and very low-carbohydrate diets, and low glycemic diets and (2) to examine several purported supplements, such as protein, branched-chain amino acids, creatine, and vitamin D to improve glucose control and body composition. This review can serve as a resource for those wanting to evaluate the evidence supporting the various dietary strategies and supplements that may help manage T2D.

Comparative Assessment of the Acute Effects of Whey, Rice and Potato Protein Isolate Intake on Markers of Glycaemic Regulation and Appetite in Healthy Males Using a Randomised Study Design

Global protein consumption has been increasing for decades due to changes in demographics and consumer shifts towards higher protein intake to gain health benefits in performance nutrition and appetite regulation. Plant-derived proteins may provide a more environmentally sustainable alternative to animal-derived proteins. This study, therefore, aimed to investigate, for the first time, the acute effects on glycaemic indices, gut hormones, and subjective appetite ratings of two high-quality, plant-derived protein isolates (potato and rice), in comparison to a whey protein isolate in a single-blind, triple-crossover design study with nine male participants (30.8 ± 9.3 yrs). Following a 12 h overnight fast, participants consumed an equal volume of the three isocaloric protein shakes on different days, with at least a one-week washout period. Glycaemic indices and gut hormones were measured at baseline, then at 30, 60, 120, 180 min at each visit. Subjective palatability and appetite ratings were measured using visual analogue scales (VAS) over the 3 h, at each visit. This data showed significant differences in insulin secretion with an increase in whey (+141.8 ± 35.1 pmol/L; p = 0.011) and rice (−64.4 ± 20.9 pmol/L; p = 0.046) at 30 min compared to potato protein. A significantly larger total incremental area under the curve (iAUC) was observed with whey versus potato and rice with p < 0.001 and p = 0.010, respectively. There was no significant difference observed in average appetite perception between the different proteins. In conclusion, this study suggests that both plant-derived proteins had a lower insulinaemic response and improved glucose maintenance compared to whey protein.

Consumption of High-Leucine-Containing Protein Bar Following Breakfast Impacts Aminoacidemia and Subjective Appetite in Older Persons

BACKGROUND

Limited data are available examining dietary interventions for optimizing protein and leucine intake to stimulate muscle protein synthesis (MPS) in older humans.

OBJECTIVES

We aimed to investigate the aminoacidemia and appetite responses of older adults after consuming breakfast, a meal frequently consumed with high-carbohydrate and below-par amounts of protein and leucine for stimulating MPS.

METHODS

Five men and 3 women (means ± SD; age: 74 ± 7 y, BMI: 25.7 ± 4.9 kg/m2, fat- and bone-free mass: 63 ± 7 kg) took part in this experiment in which they consumed breakfasts with low-protein (LP = 13 ± 2 g), high-protein (HP = 32 ± 5 g), and LP followed by a protein- and leucine-enriched bar formulation 2 h later (LP + Bar = 29 ± 2 g). The LP, HP, and LP + Bar breakfast conditions contained 519 ± 86 kcal, 535 ± 83 kcal, and 739 ± 86 kcal, respectively. Blood samples were drawn for 6 h and analyzed for amino acid, insulin, and glucose concentrations. Visual analog scales were assessed for hunger, fullness, and desire to eat.

RESULTS

The net AUC for essential amino acid (EAA) exposure was similar between the LP + Bar and HP conditions but greater in the HP condition compared with the LP condition. Peak leucinemia was higher in the LP + Bar condition compared with the HP, and both were greater than the LP condition. Net leucine exposure was similar between HP and LP + Bar, and both were greater than LP. Hunger was similarly reduced in LP + Bar and HP, and LP + Bar resulted in a greater hunger reduction than LP. Both LP + Bar and HP resulted in greater net fullness scores than LP.

CONCLUSIONS

Consuming our bar formulation increased blood leucine availability and net exposure to EAAs to a similar degree as consuming a high-protein meal. High-protein at breakfast results in a greater net exposure to EAAs and leucine, which could support MPS in older persons. This study was registered at clinicaltrials.gov as NCT03712761.

Whey peptides exacerbate body weight gain and perturb systemic glucose and tissue lipid metabolism in male high-fat fed mice

Consumption of milk-derived whey proteins has been demonstrated to have insulin-sensitizing effects in mice and humans, in part through the generation of bioactive whey peptides. While whey peptides can prevent insulin resistance in vitro, it is unclear whether consumption of whey peptides can prevent obesity-induced metabolic dysfunction in vivo. We sought to determine whether whey peptides consumption can protect from high fat (HF) diet-induced obesity and dysregulation of glucose homeostasis. Male C57BL/6J mice were fed either a low or HF diet for 13 weeks. HF diet fed mice were provided drinking water with no addition (control), undigested whey protein isolate (WPI, 1 mg ml^-1) or whey protein hydrolysate (WPH, 1 mg ml^-1) throughout the diet regimen. Mice consuming WPH gained more body weight and were more glucose intolerant compared to those consuming WPI or water only. Despite increased body weight gain, perigonadal adipose tissue weight and lipid accumulation were unchanged. However, excess lipids accumulated ectopically in the liver and skeletal muscle in mice consuming WPH, which was associated with elevated inflammatory markers systemically and in adipose tissue, liver, and skeletal muscle. In skeletal muscle, mitochondrial fat oxidation and electron transport chain proteins were decreased with WPH consumption, indicative of mitochondrial dysfunction. Taken together, our results demonstrate that WPH, but not WPI, exacerbates HF-induced body weight gain and impairs glucose homeostasis, which is accompanied by increased inflammation, ectopic fat accumulation and mitochondrial dysfunction. Thus, our results argue against the use of dietary whey peptide supplementation as a preventative option against HF diet-induced metabolic dysfunction.

Adjustment of Whey:Casein Ratio from 20:80 to 60:40 in Milk Formulation Affects Food Intake and Brainstem and Hypothalamic Neuronal Activation and Gene Expression in Laboratory Mice

Adjustment of protein content in milk formulations modifies protein and energy levels, ensures amino acid intake and affects satiety. The shift from the natural whey:casein ratio of ~20:80 in animal milk is oftentimes done to reflect the 60:40 ratio of human milk. Studies show that 20:80 versus 60:40 whey:casein milks differently affect glucose metabolism and hormone release; these data parallel animal model findings. It is unknown whether the adjustment from the 20:80 to 60:40 ratio affects appetite and brain processes related to food intake. In this set of studies, we focused on the impact of the 20:80 vs. 60:40 whey:casein content in milk on food intake and feeding-related brain processes in the adult organism. By utilising laboratory mice, we found that the 20:80 whey:casein milk formulation was consumed less avidly and was less preferred than the 60:40 formulation in short-term choice and no-choice feeding paradigms. The relative PCR analyses in the hypothalamus and brain stem revealed that the 20:80 whey:casein milk intake upregulated genes involved in early termination of feeding and in an interplay between reward and satiety, such as melanocortin 3 receptor (MC3R), oxytocin (OXT), proopiomelanocortin (POMC) and glucagon-like peptide-1 receptor (GLP1R). The 20:80 versus 60:40 whey:casein formulation intake differently affected brain neuronal activation (assessed through c-Fos, an immediate-early gene product) in the nucleus of the solitary tract, area postrema, ventromedial hypothalamic nucleus and supraoptic nucleus. We conclude that the shift from the 20:80 to 60:40 whey:casein ratio in milk affects short-term feeding and relevant brain processes.

Gastrointestinal In Vitro Digests of Infant Biscuits Formulated with Bovine Milk Proteins Positively Affect In Vitro Differentiation of Human Osteoblast-Like Cells

Infant biscuits (IBs) are part of complementary feeding from weaning up to the age of five years. They normally contain bovine milk proteins, which can influence bone development. This potential effect was investigated using experimental baked IBs, which were prepared from doughs containing different type of dairy proteins: milk protein concentrate (IB1), whey protein isolate (IB2), and skimmed milk powder (IB3). Dairy protein-free (IB0) and gluten-free (IB4) biscuits were also formulated. The in vitro gastrointestinal digests of IBs (IBDs) were tested on a co-culture of Caco-2/HT-29 70/30 cells as an in vitro model of human small intestine. None of the IBDs influenced cell viability and monolayer integrity, while IBD0 and IBD4 increased Peptide-YY production. The basolateral contents of Transwell plates seeded with Caco-2/HT-29 70/30 co-culture, mimicking metabolized IBDs (MIBDs), were tested on Saos-2 cells, an in vitro model of human osteoblast-like cells. After incubation, MIBD0, lacking dairy proteins, decreased the cell viability, while MIBD2, containing whey protein isolate, increased both the viability and the number of cells. MIBD2 and MIBD4, the latter containing both casein and whey proteins, increased alkaline phosphatase activity, a bone differentiation marker. These results highlight that IBs containing dairy proteins positively affect bone development.

Effects of whey protein and dietary fiber intake on insulin sensitivity, body composition, energy expenditure, blood pressure, and appetite in subjects with abdominal obesity

BACKGROUND

Recently, we demonstrated that whey protein (WP) combined with low dietary fiber improved lipemia, a risk factor for cardiovascular disease in subjects with abdominal obesity. In the present study, we investigated the effects of intake of WP and dietary fiber from enzyme-treated wheat bran on other metabolic parameters of the metabolic syndrome.

METHODS

The study was a 12-week, double-blind, randomized, controlled, parallel intervention study. We randomized 73 subjects with abdominal obesity to 1 of 4 iso-energetic dietary interventions: 60 g per day of either WP hydrolysate or maltodextrin (MD) combined with high-fiber (HiFi; 30 g dietary fiber/day) or low-fiber (LoFi; 10 g dietary fiber/day) cereal products. We assessed changes in insulin sensitivity, gut hormones (GLP-1, GLP-2, GIP, and peptide YY), body composition, 24-h BP, resting energy expenditure and respiratory exchange ratio (RER), and appetite.

RESULTS

Sixty-five subjects completed the trial. Subjective hunger ratings were lower after 12 weeks of WP compared with MD, independent of fiber content (P = 0.02). We found no effects on ratings of satiety, fullness or prospective food consumption for either of the interventions. Intake of WP combined with LoFi increased the postprandial peptide YY response. There were no effects of WP or fiber on insulin sensitivity, body composition, energy expenditure, incretins, or 24-h BP.

CONCLUSIONS

WP consumption for 12 weeks reduced subjective ratings of hunger in subjects with abdominal obesity. Neither WP nor dietary fiber from wheat bran affected insulin sensitivity, 24-h BP, gut hormone responses, body composition, or energy expenditure compared with MD and low dietary fiber.

Protein, amino acids and obesity treatment

Dietary proteins have been used for years to treat obesity. Body weight loss is beneficial when it concerns fat mass, but loss of fat free mass - especially muscle might be detrimental. This occurs because protein breakdown predominates over synthesis, thus administering anabolic dietary compounds like proteins might counter fat free mass loss while allowing for fat mass loss.Indeed, varying the quantity of proteins will decrease muscle anabolic response and increase hyperphagia in rodents fed a low protein diet; but it will favor lean mass maintenance and promote satiety, in certain age groups of humans fed a high protein diet. Beyond protein quantity, protein source is an important metabolic regulator: whey protein and plant based diets exercize favorable effects on the risk of developing obesity, body composition, metabolic parameters or fat free mass preservation of obese patients. Specific amino-acids like branched chain amino acids (BCAA), methionine, tryptophan and its metabolites, and glutamate can also positively influence parameters and complications of obesity especially in rodent models, with less studies translating this in humans.Tuning the quality and quantity of proteins or even specific amino-acids can thus be seen as a potential therapeutic intervention on the body composition, metabolic syndrome parameters and appetite regulation of obese patients. Since these effects vary across age groups and much of the data comes from murine models, long-term prospective studies modulating proteins and amino acids in the human diet are needed.

Effect of short- and long-term protein consumption on appetite and appetite-regulating gastrointestinal hormones, a systematic review and meta-analysis of randomized controlled trials

AIM

High-protein diets are considered as useful diets for weight loss programs. We collected randomized controlled trials that evaluated the effect of protein on appetite and gastrointestinal hormones involved in appetite regulation.

METHODS

Trials were included if participants were healthy adults and isocaloric treatments were used in control and treatment arms. Random-effects model was used to calculate mean difference and 95% confidence intervals.

RESULTS

In total, 49 publications for acute and 19 articles for long-term effect of protein were included. In acute interventions, protein decreased hunger (-7 mm visual analogue scale (VAS), P<0.001), desire to eat (-5 mm, P = 0.045), and prospective food consumption (-5 mm, P = 0.001) and increased fullness (10 mm, P<0.001) and satiety (4 mm, P<0.001). There was also a decrease in ghrelin (-20 pg/ml, P<0.001) and increase in cholecystokinin (30 pg/ml, P<0.001) and glucagon-like peptide-1 (GLP-1) (21 ng/ml, P<0.001), but no change in gastric inhibitory polypeptide and peptide YY was observed. Appetite markers were affected by protein doses < 35 g but ghrelin, cholecystokinin, and GLP-1 changed significantly after doses ≥ 35 g. Long-term ingestion of protein did not affect these outcomes, except for GLP-1 which showed a significant decrease.

CONCLUSION

Results of this meta-analysis showed that acute ingestion of protein suppresses appetite, decreases ghrelin, and augments cholecystokinin and GLP-1. Results of long-term trials are inconclusive and further trials are required before a clear and sound conclusion on these trials could be made.

Age- and duration-dependent effects of whey protein on high-fat diet-induced changes in body weight, lipid metabolism, and gut microbiota in mice

Bovine whey protein has been demonstrated to exert a positive effect on energy balance, lipid metabolism, and nutrient absorption. Additionally, it affects gut microbiota configuration. Thus, whey protein is considered as good dietary candidate to prevent or ameliorate metabolic diseases, such as obesity. However, the relationship that links energy balance, metabolism, and intestinal microbial population mediated by whey protein intake remains poorly understood. In this study, we investigated the beneficial effects attributed to whey protein in the context of high-fat diet (HFD) in mice at two different ages, with short or longer durations of whey protein supplementation. Here, a 5-week dietary intervention with HFD in combination with either whey protein isolate (WPI) or the control nonwhey milk protein casein (CAS) was performed using 5-week or 10-week-old C57BL/6J mice. Notably, the younger mice had no prior history of ingestion of WPI, while older mice did. 5-week-old HFD-WPI-fed mice showed a decrease in weight gain and changes in the expression of genes within the epidydimal white adipose tissue including those encoding leptin, inflammatory marker CD68, fasting-induced adipose factor FIAF and enzymes involved in fatty acids catabolism, relative to HFD-CAS-fed mice. Differences in β-diversity and higher proportions of Lactobacillus murinus, and related functions, were evident within the gut microbiota of HFD-WPI mice. However, none of these changes were observed in mice that started the HFD dietary intervention at 10-weeks-old, with an extended period of WPI supplementation. These results suggest that the effect of whey protein on mouse body weight, adipose tissue, and intestinal parameters depends on diet duration and stage of life during which the diet is provided. In some instances, WPI influences gut microbiota composition and functional potential, which might orchestrate observed metabolic and physiological modifications.

Whey protein consumption following fasted exercise reduces early postprandial glycaemia in centrally obese males: a randomised controlled trial

Purpose

Acute submaximal exercise and whey protein supplementation have been reported to improve postprandial metabolic and appetite responses to a subsequent meal independently. We aimed to examine the combination of these strategies on postprandial responses to a carbohydrate-rich breakfast.

Methods

Twelve centrally obese males (age 41 ± 3 years, waist circumference 123.4 ± 2.9 cm), completed three trials in a single-blind, crossover design. Participants rested for 30 min (CON) or completed 30 min low–moderate-intensity treadmill walking (51 ± 1% \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}O}}_{\text{2peak}}$$\end{document}V˙O2peak) followed immediately by ingestion of 20 g whey protein (EX + PRO) or placebo (EX). After 15 min, a standardised breakfast was consumed and blood, expired gas and subjective appetite were sampled postprandially. After 240 min, an ad libitum lunch meal was provided to assess energy intake.

Results

During EX + PRO, post-breakfast peak blood glucose was reduced when compared with EX and CON (EX + PRO: 7.6 ± 0.4 vs EX: 8.4 ± 0.3; CON: 8.3 ± 0.3 mmol l⁻¹, p ≤ 0.04). Early postprandial glucose AUC_0–60 min was significantly lower under EX + PRO than EX (p = 0.011), but not CON (p = 0.12). Over the full postprandial period, AUC_0–240 min during EX + PRO did not differ from other trials (p > 0.05). Peak plasma insulin concentrations and AUC_0–240 min were higher during EX + PRO than CON, but similar to EX. Plasma triglyceride concentrations, substrate oxidation and subjective appetite responses were similar across trials and ad libitum energy intake was not influenced by prior fasted exercise, nor its combination with whey protein supplementation (p > 0.05).

Conclusion

Following fasted low–moderate-intensity exercise, consuming whey protein before breakfast may improve postprandial glucose excursions, without influencing appetite or subsequent energy intake, in centrally obese males.

Trial registration number

NCT02714309.

Obesity and adiposity: the culprit of dietary protein efficacy

Obesity and increased body adiposity have been alarmingly increasing over the past decades and have been linked to a rise in food intake. Many dietary restrictive approaches aiming at reducing weight have resulted in contradictory results. Additionally, some policies to reduce sugar or fat intake were not able to decrease the surge of obesity. This suggests that food intake is controlled by a physiological mechanism and that any behavioural change only leads to a short-term success. Several hypotheses have been postulated, and many of them have been rejected due to some limitations and exceptions. The present review aims at presenting a new theory behind the regulation of energy intake, therefore providing an eye-opening field for energy balance and a potential strategy for obesity management.

Wheat gluten hydrolysate potently stimulates peptide-YY secretion and suppresses food intake in rats

The study was aimed to compare the satiating effect of various protein hydrolysates in rats and examine the underlying mechanism associated with the satiety hormones. Food intake and portal satiety hormone levels were measured in rats. Enteroendocrine cell-lines were employed to study the direct effect of protein hydrolysates on gut hormone secretions. The results showed that oral preload of wheat gluten hydrolysate (WGH) suppressed food intake greater and longer than other hydrolysates. The portal peptide-YY levels in WGH-treated rats at 2 h and 3 h were higher than those in control- and lactalbumin hydrolysate (LAH)-treated rats. In a distal enteroendocrine cell model, WGH more potently stimulated glucagon-like peptide-1 secretion than LAH, and the effect was largely enhanced by pepsin/pancreatin digestion of WGH. These results suggest WGH is potent in activating enteroendocrine cells to release satiety hormones leading to the prolonged suppression of food intake.

Satiety and gastrointestinal hormones during a Mixed Meal Tolerance Test after gastric bypass surgery: association with plasma amino acid concentrations

BACKGROUND

Circulating amino acids have been associated with both appetite and the secretion of anorexigenic hormones in healthy and obese populations. This effect has not been investigated in subjects having undergone Roux-en-Y gastric bypass surgery (RYGB).

OBJECTIVE

To investigate the association between postprandial plasma concentrations of amino acids and the anorexigenic hormones glucagon-like peptide-1 (GLP-1) and peptide tyrosine tyrosine (PYY), the orexigenic hormone ghrelin, and satiety and hunger in post-RYGB subjects.

SETTING

A Dutch surgical department.

METHODS

Participants after primary RYGB were studied during a Mixed Meal Tolerance Test (MMTT). Satiety and hunger were assessed every 30 minutes on visual analogue scales. Blood samples were collected at baseline, every 10 minutes during the first half hour and every 30 minutes until 210 minutes after the start. The samples were assessed for 24 amino acids and 3 gastrointestinal hormones. Incremental areas under the curve (iAUCs) were calculated. Exploratory analyses were performed in which subjects were divided into high and low responders depending on the median iAUC.

RESULTS

42 subjects, aged 48 ± 11 (mean ± SD) years, 31 to 76 months post-RYGB and with total weight loss of 30 ± 9% completed the MMTT. Subjects with high satiety scores had more than a 25% higher net iAUC of PYY and GLP-1 and at least a 10% higher net iAUC of 10 amino acids compared to subjects with low scores (P < 0.05). The net iAUC of five of these amino acids (i.e. arginine, asparagine, histidine, serine and threonine) was more than 10% higher in subjects with high responses on GLP-1 and/or PYY (P < 0.05).

CONCLUSIONS

Certain postprandial amino acids were associated with satiety and anorexigenic hormones and could therefore play a role in appetite regulation after RYGB; either by a direct effect on satiety, indirectly through gastrointestinal hormones, or both.

Consuming Lower-Protein Nutrition Bars with Added Leucine Elicits Postprandial Changes in Appetite Sensations in Healthy Women

BACKGROUND

Higher-protein meals (>25 g protein/meal) have been associated with enhanced satiety but the role of amino acids is unclear. Leucine has been proposed to stimulate satiety in rodents but has not been assessed in humans.

OBJECTIVE

We assessed the acute effects of lower-protein nutrition bars, enhanced with a leucine peptide (LP), on postprandial appetite sensations in combination with plasma leucine and peptide YY (PYY) in healthy women.

METHODS

Utilizing a double-blind randomized crossover design, 40 healthy women [28 ± 7.5 y; body mass index (BMI, in kg/m2): 23.5 ± 2.4] consumed the following isocaloric (180 kcal) pre-loads on 3 separate visits: control bar [9 g protein with 0 g added LP (0-g LP)] or treatment bars [11 g protein with 2 g added LP (2-g LP) or 13 g protein with 3 g added LP (3-g LP)]. Pre- and postprandial hunger, desire to eat, prospective food consumption (PFC), fullness, and plasma leucine were assessed every 30 min for 240 min. Plasma PYY was assessed hourly for 240 min (n = 24).

RESULTS

Main effects of time (P < 0.0001) and treatment (P < 0.03) were detected for postprandial hunger, desire to eat, PFC, and fullness. Post hoc analyses revealed that the 2-g and 3-g LP bars elicited greater increases in fullness and greater decreases in PFC compared with 0-g LP (all, P < 0.05) with no differences between the 2-g and 3-g LP bars. The 2-g bar elicited greater decreases in hunger and desire to eat compared with the 0-g LP bar (both, P ≤ 0.01), whereas 3-g LP did not. Appetite incremental areas under the curves (iAUCs) and PYY outcomes were not different between bars. A treatment × time interaction was detected for plasma leucine with increases occurring in a leucine-dose-dependent manner (P < 0.0001).

CONCLUSION

Despite the dose-dependent increases in plasma leucine following the consumption of lower-protein bars enhanced with LP, only the 2-g LP bar elicited consistent postprandial changes in select appetite sensations compared with the 0-g LP bar. This study was registered on clinicaltrials.gov as NCT02091570.

Comparable effects of breakfast meals varying in protein source on appetite and subsequent energy intake in healthy males

PURPOSE

The satiating effect of animal vs plant proteins remains unknown. The present study examined the effects of breakfasts containing animal proteins [milk (AP)], a blend of plant proteins [oat, pea and potato (VP)] or 50:50 mixture of the two (MP) compared with a carbohydrate-rich meal (CHO) on appetite, energy intake (EI) and metabolic measures.

METHODS

A total of 28 males [mean age 27.4 (±SD 4.2) years, BMI 23.4 (±2.1) kg/m2] consumed three isoenergetic (1674 kJ) rice puddings matched for energy density and macronutrient content as breakfast (25% E from protein) in a single-blind, randomised, cross over design. Appetite ratings and blood samples were collected and assessed at baseline and every 30 and 60 min, respectively, until an ad libitum test meal was served 3.5 h later. Free-living appetite was recorded hourly and EI in weighed food records for the remainder of the day.

RESULTS

No differences in subjective appetite ratings were observed after consumption of the AP, VP and MP. Furthermore, there were no differences between the AP, VP, MP and CHO breakfasts in ad libitum EI and self-reported EI during the remainder of the day. Although insulin metabolism was not affected, CHO induced a higher glucose response (P = 0.001) and total amino acids concentration was in the order of AP = MP > VP > CHO breakfast (P = 0.001).

CONCLUSION

Manipulating the protein source of foods consumed as breakfast, elicited comparable effects on appetite and EI at both laboratory and free-living environment in healthy men.

Peptide YY mediates the satiety effects of diets enriched with whey protein fractions in male rats

Dairy proteins-whey protein, in particular-are satiating and often recommended for weight control; however, little is known about the mechanisms by which whey protein and its components promote satiety and weight loss. We used diet-induced obese rats to determine whether the hypophagic effects of diets that are enriched with whey and its fractions, lactalbumin and lactoferrin, are mediated by the gut hormone, peptide YY (PYY). We demonstrate that high protein diets that contain whey, lactalbumin, and lactoferrin decreased food intake and body weight with a concurrent increase in PYY mRNA abundance in the colon and/or plasma PYY concentrations. Of importance, blockade of PYY neuropeptide Y receptor subtype 2 (Y2) receptors with a peripherally restricted antagonist attenuated the hypophagic effects of diets that are enriched with whey protein fractions. Diets that are enriched with whey fractions were less preferred; however, in a modified conditioned taste preference test, PYY Y2 receptor blockade induced hyperphagia of a lactoferrin diet, but caused a reduction in preference for Y2 antagonist-paired flavor, which suggested that PYY signaling is important for lactoferrin-induced satiety, but not essential for preference for lactoferrin-enriched diets. Taken together, these data provide evidence that the satiety of diets that are enriched with whey protein components is mediated, in part, via enhanced PYY secretion and action in obese male rats.-Zapata, R. C., Singh, A., Chelikani, P. K. Peptide YY mediates the satiety effects of diets enriched with whey protein fractions in male rats.

Dietary Protein and Energy Balance in Relation to Obesity and Co-morbidities

Dietary protein is effective for body-weight management, in that it promotes satiety, energy expenditure, and changes body-composition in favor of fat-free body mass. With respect to body-weight management, the effects of diets varying in protein differ according to energy balance. During energy restriction, sustaining protein intake at the level of requirement appears to be sufficient to aid body weight loss and fat loss. An additional increase of protein intake does not induce a larger loss of body weight, but can be effective to maintain a larger amount of fat-free mass. Protein induced satiety is likely a combined expression with direct and indirect effects of elevated plasma amino acid and anorexigenic hormone concentrations, increased diet-induced thermogenesis, and ketogenic state, all feed-back on the central nervous system. The decline in energy expenditure and sleeping metabolic rate as a result of body weight loss is less on a high-protein than on a medium-protein diet. In addition, higher rates of energy expenditure have been observed as acute responses to energy-balanced high-protein diets. In energy balance, high protein diets may be beneficial to prevent the development of a positive energy balance, whereas low-protein diets may facilitate this. High protein-low carbohydrate diets may be favorable for the control of intrahepatic triglyceride IHTG in healthy humans, likely as a result of combined effects involving changes in protein and carbohydrate intake. Body weight loss and subsequent weight maintenance usually shows favorable effects in relation to insulin sensitivity, although some risks may be present. Promotion of insulin sensitivity beyond its effect on body-weight loss and subsequent body-weight maintenance seems unlikely. In conclusion, higher-protein diets may reduce overweight and obesity, yet whether high-protein diets, beyond their effect on body-weight management, contribute to prevention of increases in non-alcoholic fatty liver disease NAFLD, type 2 diabetes and cardiovascular diseases is inconclusive.

The role of whey protein in postprandial glycaemic control

Epidemiological studies demonstrate that poor glycaemic control is an independent risk factor for CVD. Postprandial glycaemia has been demonstrated as a better predictor of glycated Hb, the gold standard of glycaemic control, when compared with fasting blood glucose. There is a need for more refined strategies to tightly control postprandial glycaemia, particularly in those with type 2 diabetes, and nutritional strategies around meal consumption may be effective in enhancing subsequent glycaemic control. Whey protein administration around meal times has been demonstrated to reduce postprandial glycaemia, mediated through various mechanisms including an enhancement of insulin secretion. Whey protein ingestion has also been shown to elicit an incretin effect, enhancing the secretion of glucose-dependent insulinotropic peptide and glucagon-like peptide-1, which may also influence appetite regulation. Acute intervention studies have shown some promising results however many have used large dosages (50-55 g) of whey protein alongside high-glycaemic index test meals, such as instant powdered potato mixed with glucose, which does not reflect realistic dietary strategies. Long-term intervention studies using realistic strategies around timing, format and amount of whey protein in relevant population groups are required.

Comparison of the Effects of Goat Dairy and Cow Dairy Based Breakfasts on Satiety, Appetite Hormones, and Metabolic Profile

The satiating effects of cow dairy have been thoroughly investigated; however, the effects of goat dairy on appetite have not been reported so far. Our study investigates the satiating effect of two breakfasts based on goat or cow dairy and their association with appetite related hormones and metabolic profile. Healthy adults consumed two breakfasts based on goat (G-Breakfast) or cow (C-Breakfast) dairy products. Blood samples were taken and VAS tests were performed at different time points. Blood metabolites were measured and Combined Satiety Index (CSI) and areas under the curves (AUC) were calculated. Desire to eat rating was significantly lower (breakfast &amp; time interaction p < 0.01) and hunger rating tended to be lower (breakfast &amp; time interaction p = 0.06) after the G-breakfast. None of the blood parameters studied were different between breakfasts; however, AUC_GLP-1 was inversely associated with the AUC_hunger and AUC_{desire-to-eat} after the G-Breakfast, whereas triglyceride levels were directly associated with AUC_CSI after the C-Breakfast. Our results suggest a slightly higher satiating effect of goat dairy when compared to cow dairy products, and pointed to a potential association of GLP-1 and triglyceride levels with the mechanisms by which dairy products might affect satiety after the G-Breakfast and C-Breakfast, respectively.

Effects of whey protein and its two major protein components on satiety and food intake in normal-weight women

Protein is the most satiating macronutrient and is source dependent, with whey protein thought to be particularly satiating. The purported satiating effect of whey protein may be due to the unique mixture of proteins in whey or to the major constituent individual proteins (β-lactoglobulin and α-lactalbumin). The objective of the study was to compare the effects of isoenergetic (~2100kJ, ~500kcal) preload meals enriched (~50g protein) with either whey protein isolate (WP), β-lactoglobulin (BL) isolate or α-lactalbumin (AL) isolate, on food intake at an ad libitum test meal 120min later and subjective ratings of appetite (hunger, desire to eat, prospective food consumption and fullness) using visual analogue scales (VAS). Twenty adult normal-weight women (mean age 24.2±0.8years; mean BMI 22.7±0.4kg/m²) participated in the study which used a single-blind completely randomised block design, where each subject consumed each of the three preload meals. Energy intake at the ad libitum test meal and total energy intakes (preload+test meal) did not differ between the three preload meals (p>0.05). There were no significant differences observed for the VAS scores and net incremental area under the curve (net iAUC) during the 120min following consumption of the three preload meals for subjective ratings of appetite (p>0.05). The findings show that the satiating effect of whey protein was similar to that of BL or AL individually and suggest that the major whey protein components BL and AL do not mediate the satiating effect of whey protein. The present human trial was registered with the Australian New Zealand Clinical Trials Registry (www.anzctr.org.au) as ACTRN12615000344594.

Bioactivity of food peptides: biological response of rats to bovine milk whey peptides following acute exercise

Background: Several physiologically beneficial effects of consuming a whey protein hydrolysate (WPH) have been attributed to the greater availability of bioactive peptides.

Aims: The aim was to investigate the effect of four branched-chain amino acid- (BCAA-)containing dipeptides, present in WPH, on immune modulation, stimulation of HSP expression, muscle protein synthesis, glycogen content, satiety signals and the impact of these peptides on the plasma free amino acid profiles.

Methods: The animals were divided in groups: control (rest, without gavage), vehicle (water), L-isoleucyl-L-leucine (lle-Leu), L-leucyl-L-isoleucine (Leu-lle), L-valyl-Lleucine (Val-Leu), L-leucyl-L-valine (Leu-Val) and WPH. All animals were submitted to acute exercise, except for control.

Results: lle-Leu stimulated immune response, hepatic and muscle glycogen and HSP60 expression, whereas Leu-Val enhanced HSP90 expression. All dipeptides reduced glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide, no changes were observed on leptin. All peptides inhibited NF-kB expression. The plasma amino acid time-course showed peptide-specific and isomer-specific metabolic features, including increases of the BCAAs.

Conclusion: The data indicate that lle-Leu was effective to attenuate immune-suppression exercise-induced, promoted glycogen content and stimulated anti-stress effect (HSP). Furthermore, Leu-Val increased HSP90, p-4EBP1, p-mTOR and p-AMPK expression. The data suggest the involvement of these peptides in various beneficial functions of WPH consumption.

Influence of dietary protein and its amino acid composition on postoperative outcomes after gastric bypass surgery: a systematic review

CONTEXT

Bariatric surgery is an effective method to reduce morbid obesity. Nutritional counseling is essential to achieve maximal treatment success and to avoid long-term complications. Increased dietary protein intake may improve various postoperative results.

OBJECTIVE

The aim of this systematic review is to examine the relationship between intake of dietary protein or supplementation with amino acids and postoperative outcomes after gastric bypass surgery.

DATA SOURCES

A systematic literature search was conducted in 4 electronic databases: Cochrane, Embase, PubMed, and Scopus.

STUDY SELECTION

The initial search retrieved 7333 hits, which included 2390 duplicates.

DATA EXTRACTION

Tweny-three studies with varying study designs, interventions, and outcomes were included.

RESULTS

Studies did not provide convincing evidence of a beneficial effect on any postoperative outcome.

CONCLUSIONS

The study of the influence of protein and its amino acid composition represents an important developing domain of knowledge and warrants further attention considering the popularity of bariatric surgery. Future studies should include a clear description of the quantity and composition of proteins and amino acids in the diet or supplement.

Effect of whey protein and a free amino acid mixture simulating whey protein on measures of satiety in normal-weight women

Dietary protein is considered more satiating than carbohydrate, and whey protein is more satiating than other protein sources. The purported satiating effect of whey protein may be due to direct effects of the unique mixture of proteins in whey, due to the effects of peptides released upon digestion and/or its amino acid composition. The objective of the present study was to compare the satiating effects of intact whey protein isolate (WPI) or a free amino acid mixture (AAM) simulating the amino acid composition of the WPI. A single-blind completely randomised block design included twenty, healthy, adult women (age 24·2 (sem 0·8) years) of normal weight (BMI 22·7 (sem 0·4) kg/m2). Following consumption of isoenergetic (approximately 1800 kJ) preload meals enriched (52 g amino acid equivalent) with WPI or AAM, consumption of an ad libitum test meal 120 min later and subjective feelings of appetite using visual analogue scales (VAS) were determined. There were no significant differences (P=0·24) in the ad libitum test meal intakes between the WPI (268·5 (sem 27·3) g) and the AAM (238·4 (sem 22·7) g) preload meals. Subjective VAS ratings of appetite did not differ significantly between the WPI and the AAM preload meals (P>0·05). Intact whey protein and a free AAM simulating the whey protein showed similar effects on satiety. This suggests that the satiating effect of whey protein may be related to its specific amino acid composition.

The impact of protein quality on the promotion of resistance exercise-induced changes in muscle mass

Protein supplementation during resistance exercise training augments hypertrophic gains. Protein ingestion and the resultant hyperaminoacidemia provides the building blocks (indispensable amino acids - IAA) for, and also triggers an increase in, muscle protein synthesis (MPS), suppression of muscle protein breakdown (MPB), and net positive protein balance (i.e., MPS > MPB). The key amino acid triggering the rise in MPS is leucine, which stimulates the mechanistic target of rapamycin complex-1, a key signalling protein, and triggers a rise in MPS. As such, ingested proteins with a high leucine content would be advantageous in triggering a rise in MPS. Thus, protein quality (reflected in IAA content and protein digestibility) has an impact on changes in MPS and could ultimately affect skeletal muscle mass. Protein quality has been measured by the protein digestibility-corrected amino acid score (PDCAAS); however, the digestible indispensable amino acid score (DIAAS) has been recommended as a better method for protein quality scoring. Under DIAAS there is the recognition that amino acids are individual nutrients and that protein quality is contingent on IAA content and ileal (as opposed to fecal) digestibility. Differences in protein quality may have important ramifications for exercise-induced changes in muscle mass gains made with resistance exercise as well as muscle remodelling. Thus, the purpose of this review is a critical appraisal of studies examining the effects of protein quality in supplementation on changes in muscle mass and strength as well as body composition during resistance training.

The Macronutrients, Appetite, and Energy Intake

Each of the macronutrients-carbohydrate, protein, and fat-has a unique set of properties that influences health, but all are a source of energy. The optimal balance of their contribution to the diet has been a long-standing matter of debate. Over the past half century, thinking has progressed regarding the mechanisms by which each macronutrient may contribute to energy balance. At the beginning of this period, metabolic signals that initiated eating events (i.e., determined eating frequency) were emphasized. This was followed by an orientation to gut endocrine signals that purportedly modulate the size of eating events (i.e., determined portion size). Most recently, research attention has been directed to the brain, where the reward signals elicited by the macronutrients are viewed as potentially problematic (e.g., contribute to disordered eating). At this point, the predictive power of the macronutrients for energy intake remains limited.

Protein-Pacing from Food or Supplementation Improves Physical Performance in Overweight Men and Women: The PRISE 2 Study

We recently reported that protein-pacing (P; six meals/day @ 1.4 g/kg body weight (BW), three of which included whey protein (WP) supplementation) combined with a multi-mode fitness program consisting of resistance, interval sprint, stretching, and endurance exercise training (RISE) improves body composition in overweight individuals. The purpose of this study was to extend these findings and determine whether protein-pacing with only food protein (FP) is comparable to WP supplementation during RISE training on physical performance outcomes in overweight/obese individuals. Thirty weight-matched volunteers were prescribed RISE training and a P diet derived from either whey protein supplementation (WP, n = 15) or food protein sources (FP, n = 15) for 16 weeks. Twenty-one participants completed the intervention (WP, n = 9; FP, n = 12). Measures of body composition and physical performance were significantly improved in both groups (p < 0.05), with no effect of protein source. Likewise, markers of cardiometabolic disease risk (e.g., LDL (low-density lipoprotein) cholesterol, glucose, insulin, adiponectin, systolic blood pressure) were significantly improved (p < 0.05) to a similar extent in both groups. These results demonstrate that both whey protein and food protein sources combined with multimodal RISE training are equally effective at improving physical performance and cardiometabolic health in obese individuals.

Co-Ingestion of Whey Protein with a Carbohydrate-Rich Breakfast Does Not Affect Glycemia, Insulinemia or Subjective Appetite Following a Subsequent Meal in Healthy Males

We aimed to assess postprandial metabolic and appetite responses to a mixed-macronutrient lunch following prior addition of whey protein to a carbohydrate-rich breakfast. Ten healthy males (age: 24 ± 1 years; body mass index (BMI): 24.5 ± 0.7 kg/m²) completed three trials in a non-isocaloric, crossover design. A carbohydrate-rich breakfast (93 g carbohydrate; 1799 kJ) was consumed with (CHO + WP) or without (CHO) 20 g whey protein isolate (373 kJ), or breakfast was omitted (NB). At 180 min, participants consumed a mixed-macronutrient lunch meal. Venous blood was sampled at 15 min intervals following each meal and every 30 min thereafter, while subjective appetite sensations were collected every 30 min throughout. Post-breakfast insulinemia was greater after CHO + WP (time-averaged area under the curve (AUC_{0–180 min}): 193.1 ± 26.3 pmol/L), compared to CHO (154.7 ± 18.5 pmol/L) and NB (46.1 ± 8.0 pmol/L; p < 0.05), with no difference in post-breakfast (0–180 min) glycemia (CHO + WP, 3.8 ± 0.2 mmol/L; CHO, 4.2 ± 0.2 mmol/L; NB, 4.2 ± 0.1 mmol/L; p = 0.247). There were no post-lunch (0–180 min) effects of condition on glycemia (p = 0.492), insulinemia (p = 0.338) or subjective appetite (p > 0.05). Adding whey protein to a carbohydrate-rich breakfast enhanced the acute postprandial insulin response, without influencing metabolic or appetite responses following a subsequent mixed-macronutrient meal.

Metabolic advantages of higher protein diets and benefits of dairy foods on weight management, glycemic regulation, and bone

The Inst. of Medicine and World Health Organization have determined that 0.8 to 0.83 g protein·kg(-1) ·d(-1) is the quantity of protein required to establish nitrogen balance in nearly all healthy individuals. However, consuming higher protein diets may be metabolically advantageous, particularly for overweight and obese adults attempting weight loss, and for physically active individuals such as athletes and military personnel. Studies have demonstrated that higher protein diets may spare lean body mass during weight loss, promote weight management, enhance glycemic regulation, and increase intestinal calcium absorption, which may result in long-term improvements in bone health. The extent to which higher protein diets are beneficial is largely attributed to the digestive and absorptive properties, and also to the essential amino acid (EAA) content of the protein. Proteins that are rapidly digested and absorbed likely contribute to the metabolic advantages conferred by consuming higher protein diets. The EAA profiles, as well as the digestive and absorptive properties of dairy proteins, such as whey protein and casein, are particularly advantageous because they facilitate a rapid, robust, and sustained delivery of EAAs to the periphery. This article reviews the scientific literature assessing metabolic advantages associated with higher protein diets on weight management, glycemic regulation, and bone, with emphasis given to studies evaluating the potential benefits associated with dairy.