Comparative Effects of Co-Ingesting Whey Protein and Glucose Alone and Combined on Blood Glucose, Plasma Insulin and Glucagon Concentrations in Younger and Older Men

Randomized, double-blind, crossover study in healthy men, with separate younger and older groups. Each active intervention arm included 10 younger men and 10 older men, with testing repeated on four occasions separated by about 7 to 10 days.

Participants received oral test drinks on four randomized crossover occasions: 30 g glucose monohydrate, 30 g whey protein, 30 g whey protein plus 30 g glucose, or flavored water as control. The glucose and whey protein drinks were each about 120 kcal, and the combined whey protein plus glucose drink was about 240 kcal; drinks were consumed within 2 minutes.

Co-ingesting whey protein with glucose substantially blunted postprandial glycemia in both younger and older men, and the glucose-lowering effect was preserved with aging. Compared with glucose alone, whey protein plus glucose reduced the postprandial blood glucose rise by 44 ± 38% over 3 h, with reductions of 50 ± 13% in the first hour and 66 ± 33% in the second hour, all significant. The combined drink also produced a more than additive insulin response, with Net iAUC 0-180 min of 28.3 ± 4.7 vs 21.3 ± 3.2 mU/L * min for whey protein plus glucose versus the sum of the individual drinks (p = 0.002). Whey protein markedly increased glucagon concentrations, and no adverse effects were reported. The authors concluded that whey protein may be useful for improving postprandial glucose control and potentially for diabetes prevention/management in older adults.

Small acute crossover study with only 20 healthy male participants, limiting precision and generalizability. Findings were based on short-term postprandial responses rather than clinical diabetes outcomes, and the population did not include women or people with diabetes. Some secondary outcomes, including gastric emptying and ad libitum energy intake, were assessed in limited analyses and were not definitive.