Effects of a supra-sustained gelatin-milk protein diet compared with (supra-)sustained milk protein diets on body-weight loss

Protein supplements after weight loss do not improve weight maintenance compared with recommended dietary protein intake despite beneficial effects on appetite sensation and energy expenditure: a randomized, controlled, double-blinded trial

Background: High-protein diets increase weight loss (WL) during energy restriction; therefore, it has been suggested that additional protein intake may improve weight maintenance (WM) after WL.Objective: We investigated the effect of protein supplements from either whey with or without calcium or soy on WM success after WL compared with that of a control.Design: In a randomized, controlled, double-blinded trial, 220 participants aged 18-60 y with body mass index (in kg/m²) from 27.6 to 40.4 were included. The study was initiated with an 8-wk WL period followed by a 24-wk WM period. During WM, participants consumed the following isocaloric supplements (45-48 g/d): whey and calcium (whey+), whey, soy, or maltodextrin (control). Data were collected at baseline, before WM, and after WM (weeks 0, 8, and 32, respectively) and included body composition, blood biochemistry, and blood pressure. Meal tests were performed to investigate diet-induced-thermogenesis (DIT) and appetite sensation. Compliance was tested by 24-h urinary nitrogen excretion.Results: A total of 151 participants completed the WM period. The control and 3 protein supplements did not result in different mean ± SD weight regains (whey+: 2.19 ± 4.6 kg; whey: 2.01 ± 4.6 kg; soy: 1.76 ± 4.7 kg; and control: 2.23 ± 3.8 kg; P = 0.96), fat mass regains (whey+: 0.46 ± 4.5 kg; whey: 0.11 ± 4.1 kg; soy: 0.15 ± 4.1 kg; and control: 0.54 ± 3.3 kg; P = 0.96), or improvements in lean body mass (whey+: 1.87 ± 1.7 kg; whey: 1.94 ± 1.3 kg; soy: 1.58 ± 1.4 kg; and control: 1.74 ± 1.4 kg; P = 0.50) during WM. Changes in blood pressure and blood biochemistry were not different between groups. Compared with the control, protein supplementation resulted in higher DIT (∼30 kJ/2.5 h) and resting energy expenditure (243 kJ/d) and an anorexigenic appetite-sensation profile.Conclusion: Protein supplementation does not result in improved WM success, or blood biochemistry after WL compared with the effects of normal dietary protein intake (0.8-1.0 g · kg^-1 · d^-1). This trial was registered at clinicaltrials.gov as NCT01561131.

Protein diets, body weight loss and weight maintenance

PURPOSE OF REVIEW

The review addresses briefly the relevance of protein diets for body weight loss and weight maintenance. The addition of recent findings on age-dependent protein requirements, specific effects of protein intake and protein source, the relevance of the other dietary macronutrients, especially of 'low-carb', 'protein leverage', the mechanisms of protein-induced satiety, and food-reward makes the review up-to-date.

RECENT FINDINGS

Different effects of protein diets in different age groups result from age-dependent protein requirements that are primarily related to effects on body composition. A protein intake of 0.8 g/kg/day is sufficient to sustain a negative energy balance in adults, irrespective of the protein source. 'Low-carb' diets trace back to the protein-induced effects. Evidence that protein intake drives energy intake as suggested by the 'Protein leverage hypothesis' is scarce and equivocal. Finally, limited protein-induced food reward may affect compliance to a protein diet.

SUMMARY

An implication of the findings for clinical practice is that a protein intake of 0.8-1.2 g/kg/day is sufficient to sustain satiety, energy expenditure, and fat-free mass, independent of a dietary 'low-carb' content. Limited protein-induced food reward may affect compliance to a protein diet.

Effect of dairy proteins on appetite, energy expenditure, body weight, and composition: a review of the evidence from controlled clinical trials

Evidence supports that a high proportion of calories from protein increases weight loss and prevents weight (re)gain. Proteins are known to induce satiety, increase secretion of gastrointestinal hormones, and increase diet-induced thermogenesis, but less is known about whether various types of proteins exert different metabolic effects. In the Western world, dairy protein, which consists of 80% casein and 20% whey, is a large contributor to our daily protein intake. Casein and whey differ in absorption and digestion rates, with casein being a "slow" protein and whey being a "fast" protein. In addition, they differ in amino acid composition. This review examines whether casein, whey, and other protein sources exert different metabolic effects and targets to clarify the underlying mechanisms. Data indicate that whey is more satiating in the short term, whereas casein is more satiating in the long term. In addition, some studies indicate that whey stimulates the secretion of the incretin hormones glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide more than other proteins. However, for the satiety (cholecystokinin and peptide YY) and hunger-stimulating (ghrelin) hormones, no clear evidence exists that 1 protein source has a greater stimulating effect compared with others. Likewise, no clear evidence exists that 1 protein source results in higher diet-induced thermogenesis and promotes more beneficial changes in body weight and composition compared with other protein sources. However, data indicate that amino acid composition, rate of absorption, and protein/food texture may be important factors for protein-stimulated metabolic effects.

Dietary protein - its role in satiety, energetics, weight loss and health

Obesity is a serious health problem because of its co-morbidities. The solution, implying weight loss and long-term weight maintenance, is conditional on: (i) sustained satiety despite negative energy balance, (ii) sustained basal energy expenditure despite BW loss due to (iii) a sparing of fat-free mass (FFM), being the main determinant of basal energy expenditure. Dietary protein has been shown to assist with meeting these conditions, since amino acids act on the relevant metabolic targets. This review deals with the effects of different protein diets during BW loss and BW maintenance thereafter. Potential risks of a high protein diet are dealt with. The required daily intake is 0·8-1·2 g/kg BW, implying sustaining the original absolute protein intake and carbohydrate and fat restriction during an energy-restricted diet. The intake of 1·2 g/kg BW is beneficial to body composition and improves blood pressure. A too low absolute protein content of the diet contributes to the risk of BW regain. The success of the so-called 'low carb' diet that is usually high in protein can be attributed to the relatively high-protein content per se and not to the relatively lower carbohydrate content. Metabolic syndrome parameters restore, mainly due to BW loss. With the indicated dosage, no kidney problems have been shown in healthy individuals. In conclusion, dietary protein contributes to the treatment of obesity and the metabolic syndrome, by acting on the relevant metabolic targets of satiety and energy expenditure in negative energy balance, thereby preventing a weight cycling effect.