Journal Title (Medline/Pubmed accepted abbreviation): J Nutr
Page numbers: 1489-1494
Summary of background and research design:
Background: Dietary manipulation is one potential method to control hunger and energy intake. Short-term studies have suggested that dietary protein is more satiating than isoenergetic intake of fat or carbohydrate. Long-term studies of increased protein intake have yielded conflicting outcomes regarding body weight or composition, and protein sources may cause the differential effects observed.
Hypothesis:In overweight and obese adults, supplementation with whey protein (WP) would decrease body weight and fat compared with adults supplemented with isonitrogenous soy protein (SP) or isoenergetic carbohydrate (CHO).
Subjects: Ninety overweight or obese (body mass index [BMI] > 28 to < 38 kg/m2), but healthy, volunteers participated in this study; 73 completed the study. Mean age, height, weight, and BMI ranges for the 3 groups were 49 to 53 ± 9 years, 1.7 ± 0.1 m, 90.3 to 91.5 ± 10.4 to 13.7 kg, and 30.9 to 31.1 ± 2.2 to 2.5 kg/m2, respectively.
Experimental design: Randomized, double-blind
Treatments and protocol: Volunteers were randomized to 1 of 3 treatment groups for 23 weeks (stratified by sex, BMI , and age): WP (cheese derived), SP (isoflavone free), or isoenergetic CHO (maltodextrin) as a beverage twice daily (breakfast and dinner). Protein supplementation provided ~56 g/day of protein (1,670 kJ/day). No dietary advice was provided. All volunteers received a vitamin and mineral supplement. Dietary intake was assessed every 10 days. Satiety and hunger were assessed daily. Physical activity was assessed semi-monthly. Body weight and composition were measured monthly. Fasting plasma or serum insulin, glucose, total ghrelin, and insulin-like growth factor (and binding protein) were assessed at baseline and after Weeks 12, 16, 20, and 23.
Summary of research findings:
- Dietary intake was not different between the groups.
- Mean percentage of energy intake from protein was 14 for the CHO group and 24 for the WP and SP groups.
- Dietary treatments did not affect satiety, and there were no interactions with sex or time.
- Physical activity was not different between the groups.
- At 23 weeks, body weight in the WP groups was 1.8 kg (2%) lower compared with the CHO group (P < .006), and there was a significant interaction with time (but not sex).
- Body weight in the SP group was 0.9 kg lower compared with the CHO group and 0.9 kg higher compared with the WP group, but was not significantly different.
- Similar results were observed for body fat mass: 2.3-kg lower in the WP group compared with the CHO group (P < .005) and 1.2-kg lower in the SP group compared with the CHO group (P = not significant).
- Lean body mass was not different between groups.
- Among the biologic tests, only ghrelin was significantly different between groups (lower in the WP group compared with the SP [P = .04] and CHO groups [P = .007]).
Interpretation of findings/Key practice applications:
Weight gain should have exceeded 10 kg; however, energy compensation can and did occur in each group, especially the WP group. The study was sufficiently powered to detect small weight changes, although the dietary assessment was not sensitive enough to detect small energy changes. Additionally, timing of supplementation may make a difference (before, during, or after a meal), with preloading increasing the observed differences. There was also no placebo group as a standard. Nevertheless, protein supplementation, especially WP, may aid body weight maintenance without energy restrictions in overweight or obese individuals.