Can whey protein or its hydrolysate attenuate muscle loss while dieting? Original paper

Although weight loss can improve health markers among individuals with obesity, energy-restricted diets (ERDs) can exacerbate sarcopenia among older individuals. Whey protein (WP) is a popular supplement due to its high digestibility and essential amino acid content. Whey protein hydrolysate (WPH) is pretreated (with enzymes and acids) to reduce its particle size and increase the rate of amino acid absorption. Can supplementation with WP or WPH favorably affect body composition among older adults following an ERD?

In this 8-week randomized controlled trial, 60 women in China (ages 50–80; BMI of 24–35) were prescribed an ERD by a dietitian. The diet was designed to induce a 500 kcal per day energy deficit, with approximately 55%, 25%, and 20% of calories coming from carbohydrates, fat, and protein, respectively. The participants were randomized to supplement with 20 grams of WP per day (10 grams at breakfast and 10 grams at dinner), 20 grams of WPH, or nothing (control).

Before and after the study, the authors assessed weight, body composition (via bioelectrical impedance), glycemic markers, blood lipids, uric acid, inflammatory markers, free fatty acids, plasma metabolomics, and gut microbiome composition.

Overall, 48 of 60 participants completed the study. All three groups lost weight and body fat compared to baseline, with no changes in fat-free mass from baseline in any group.

Compared to the control group, the WPH group lost more weight (−2.34 vs. −1.11 kg) and body fat (−2.45 vs. −0.7 kg), whereas the WP group did not differ from the control group or WPH group in these outcomes. Paradoxically, compared to baseline, the WP group experienced an increase in fasting blood glucose, fasting insulin, and measures of insulin resistance.

Changes in four serum metabolites differed between groups. Mevalonic acid increased in the WP group compared to the control group. Citric acid, pyruvic acid, and glyceric acid increased in the WPH group compared to the control group. Citric acid increased in the WPH compared to the whey protein group, and pyruvic acid decreased in the control group compared to the WP group.

There were no significant changes in gut microbiota composition between the groups.

The authors stated that the participants were blinded to their intervention group. However, because the control group did not receive a placebo, the control group was not blinded to the intervention.