The effect of supplemental whey protein timing on postprandial glycaemia in centrally obese males

Consuming whey protein prior to a meal may reduce postprandial glucose excursions, however optimising timing of supplementation is important to improve its clinical utility. Thirteen centrally obese, insulin resistant males (waist circumference: 121 (SEM 3) cm; HOMA-IR: 6.4 (SEM 1.2)) completed four experimental conditions in a single-blind, crossover design. Participants consumed mixed-macronutrient breakfast and lunch meals on all occasions, with 20 g whey protein consumed 15 min prior to (PRE), alongside (DUR) or 15 min post-breakfast (POST), or omitted (CON). Capillary glucose and plasma concentrations of insulin, triglycerides and NEFA, in addition to subjective appetite ratings, were collected for 180 min after each meal. PRE and DUR reduced post breakfast glucose peak by 17.0 (SEM 1.9)% (P < 0.001) and 9.2 (SEM 2.9)% (P = 0.046) respectively, compared with CON. Post-breakfast glucose AUC was lower following PRE compared with POST and CON (PRE: 982 (SEM 30) vs POST: 1031 (SEM 36) and CON: 1065 (SEM 37) mmol/l x 180 min; P ≤ 0.042), but similar to DUR (1013 (SEM 32) mmol/l x 180 min; P = 0.77). Insulin was lower during PRE, when compared with POST and DUR (both P ≤ 0.042), but similar to CON. There were no between-condition differences in measures of postprandial lipaemia or appetite, and no effect of condition post-lunch. Consumption of whey protein as a preload or alongside a mixed macronutrient breakfast reduces postprandial glucose excursions in centrally-obese, insulin resistant males. Whey consumed as a preload has superior glycaemic lowering effects. Supplementation at breakfast does not alter glycaemic responses to subsequent meals.