Effects of Whey Protein Supplementation on Body Composition, Muscular Strength, and Cardiometabolic Health in Older...

Background/Objectives: Whey protein (WP) can play a role in improving muscle mass and function. However, the effects of WP supplementation on cardiometabolic health parameters such as fasting blood glucose, insulin, and homeostatic model assessment of insulin resistance (HOMA-IR), fasting triglyceride, total cholesterol, low-density lipo-protein cholesterol, and high-density lipoprotein cholesterol have not been fully elucidated in older adults and are therefore the aim of the present systematic review and pairwise meta-analysis. Methods: A comprehensive search of major databases (PubMed, Web of Science, and Scopus) was conducted up to January 2025 for English-language randomized controlled trials examining WP supplementation, either alone or in combination with resistance training in older adults. Eligible studies reported at least one of the following outcomes: body fat mass, body fat percentage, lean body mass, waist circumference, waist-to-hip ratio, muscular strength, glycemic parameters, and lipid profiles. Results: A total of 25 studies involving 1454 participants with mean ages ranging from 64 to 84 years, with body mass indexes ranging from 21 to 31 kg·m² were included, from an initial 868 records identified through database searches. Overall, compared with controls, WP supplementation increased lower-body muscular strength [SMD: 0.16 (95% CI: 0.04 to 0.28), p = 0.007; 19 trials], but without significantly changing upper-body muscular strength, body composition, or other cardiometabolic health markers. However, WP supplementation increased fasting insulin and homeostatic model assessment of insulin resistance. Subgroup analyses showed that whey protein plus resistance training increased lean body mass, while WP alone improved lower-body strength, with no other significant effects observed. Conclusions: WP supplementation moderately increases lower-body muscle strength in older adults. However, it does not show any significant benefits for body composition or cardiometabolic health markers. Conversely, increased fasting insulin and HOMA-IR were documented. These findings emphasize the need for careful examination of the metabolic effects of WP supplementation in future longer-term trials.