Abstract
<jats:p>Introduction. Insulin resistance is an early and clinically significant component of metabolic dysregulation. In physically active adults, metabolic biomarkers may remain within reference ranges, whereas body composition changes and abdominal adiposity can already indicate elevated cardiometabolic risk. Protein supplementation is widely used as a nutritional strategy during physical training; however, comparative evidence regarding the effects of animal- and plant-derived protein sources on insulin resistance markers in physically active individuals remains limited. Objective. To evaluate within-group and between-group changes in anthropometric parameters and insulin resistance–related biomarkers in physically active adults consuming whey protein, pea protein, or placebo under a stable training regimen. Participants and Methods. Fifty physically active adults were assigned to whey protein (n=20), pea protein (n=20), or placebo (n=10) groups. Male and female participants were analyzed as a pooled cohort. Body weight, body mass index (BMI), waist circumference, fasting glucose, fasting insulin, glycated hemoglobin (HbA1c), leptin, and HOMA-IR were assessed at baseline and after 5 weeks. Owing to non-normal data distribution, results were expressed as median and interquartile range (Me [Q1;Q3]). Within-group differences were analyzed using the Wilcoxon signed-rank test, whereas between-group comparisons of Δ values (post–pre) were performed using the Kruskal–Wallis test followed by pairwise Mann–Whitney tests with Bonferroni correction. Results. Baseline characteristics did not differ significantly between groups (p>0.05). Both protein supplementation groups demonstrated consistent improvements in anthropometric and metabolic parameters. Median body weight reduction was −4.50 kg [−5.90; −3.42] in the whey protein group and −3.50 kg [−4.48; −2.50] in the pea protein group (both p<0.0001), whereas the placebo group showed only a minor decrease (−0.60 kg [−0.97; −0.20], p=0.037). Compared with placebo, both protein interventions produced significantly greater reductions in body weight, BMI, waist circumference, fasting glucose, HbA1c, leptin, and HOMA-IR (adjusted p values predominantly <0.05). No statistically robust differences between whey and pea protein were observed for most Δ outcomes after correction for multiple comparisons. Conclusions. In physically active adults, protein shake supplementation in combination with a stable training regimen is associated with greater improvements in anthropometric measures and key insulin resistance–related biomarkers compared with placebo. Whey and pea protein demonstrated broadly comparable metabolic effects over the 5-week intervention period, although substantial interindividual variability persisted and appeared closely related to changes in adiposity.</jats:p>