The Synergistic Effects of Whey Protein Supplementation and Physical Exercise on Glycemic Control and Metabolic Parameters in Type 2 Diabetes Mellitus: A Systematic Review

Purpose of Review Combining whey protein supplementation with exercise is biologically plausible because exercise enhances glucose transport, muscle oxidative capacity, and skeletal muscle remodeling, whereas whey protein provides essential amino acids that support muscle protein synthesis and may acutely stimulate insulin and incretin responses. Despite this potential complementarity, the added clinical value of whey protein in adults with type 2 diabetes mellitus (T2DM) remains uncertain. This review evaluated whether whey protein supplementation combined with structured exercise provides additional benefits for glycemic control, insulin-related outcomes, body composition, functional performance, and cardiovascular markers beyond those achieved with exercise alone. Recent Findings Four randomized trials involving 197 participants met the eligibility criteria. The included studies compared whey protein supplementation, generally administered around exercise sessions or incorporated into broader lifestyle interventions, with placebo or carbohydrate control in adults with T2DM. Across the available evidence, whey protein did not demonstrate a consistent additional benefit over exercise-based control conditions for blood glucose, HbA1c, insulin-related outcomes, or body composition. Substantial clinical and methodological heterogeneity was observed across studies, particularly regarding participant characteristics, exercise protocols, whey protein formulations, supplementation strategies, and outcome assessments. These differences precluded meaningful quantitative pooling, and the findings were therefore synthesized narratively. Individual trials showed that exercise or lifestyle interventions improved several outcomes over time in both groups, whereas the incremental contribution of whey protein remained inconsistent. Summary Although the combination of whey protein and exercise has a plausible anabolic and metabolic rationale, current evidence does not demonstrate a consistent additional benefit of whey protein supplementation beyond structured exercise in adults with T2DM. The certainty of evidence was very low because of small sample sizes, short intervention durations, methodological limitations, clinical heterogeneity, variation in exercise protocols, and differences in whey protein formulations. Whey protein may still be appropriate for selected individuals with inadequate protein intake, sarcopenia risk, or nutritional vulnerability, but the available evidence does not support its routine use as an adjunct to exercise for all adults with T2DM. Larger, longer-term randomized trials using more standardized exercise and supplementation protocols are needed to identify whether specific patient subgroups may benefit.