Acute effects of "exercise snacks" on postprandial glucose and insulin responses in populations at metabolic risk: a meta-analysis with exploratory meta-regression and vascular outcomes.

BACKGROUND: Exercise snacks-short, frequent bouts of physical activity that interrupt prolonged sitting-improve postprandial glucose metabolism, yet the moderating role of baseline metabolic status remains unquantified. METHODS: Six databases were searched for acute randomized crossover trials comparing exercise snacks with uninterrupted sitting in sedentary adults with metabolic risk. To preserve physiological purity, insulin data were isolated from C-peptide. Standard errors were hierarchically back-calculated from paired test statistics to avoid external assumptions. Standard random-effects models and exploratory meta-regression were applied. The risk of bias was assessed with the Cochrane RoB 2 tool for crossover trials. RESULTS: Eight trials (159 participants) were included. In the primary analysis limited to studies reporting postprandial glucose incremental area under the curve (iAUC; k = 5), exercise snacks significantly reduced glucose iAUC (MD = -5.69 mmol·h/L, 95% CI -9.38 to -2.00, P = 0.003). Substantial heterogeneity was present (I² = 85%), and the 95% prediction interval ranged from -13.53 to 2.15 mmol·h/L, crossing the null. Postprandial insulin iAUC showed a numerical reduction that did not reach statistical significance (MD = -902.64 pmol·h/L, 95% CI -1889.11 to 83.82, P = 0.073, k = 4) and displayed high heterogeneity (I² = 98%). Exploratory meta-regression did not confirm a significant moderating role of baseline metabolic status (P = 0.176) or exercise intensity (P = 0.057). Vascular outcomes were limited to two flow-mediated dilation studies and one endothelin-1 study, and were therefore treated as exploratory. CONCLUSIONS: Exercise snacks acutely reduce postprandial glucose under controlled laboratory conditions, but the evidence base is characterized by high heterogeneity, imprecise prediction intervals, and limited statistical power. The currently available data neither confirm a moderating role of baseline metabolic status nor support firm conclusions for insulin or vascular outcomes. Exercise snacks represent a promising adjunctive strategy for improving short-term postprandial glycemia, but cannot yet be recommended as a specific, evidence-based clinical prescription.