Predictors of the acute postprandial response to breaking up prolonged sitting

Purpose: To identify predictors of favourable changes to postprandial insulin and glucose levels in response to interrupting prolonged sitting time with standing or light intensity physical activity. Methods: Data were combined from four similarly designed randomised acute cross-over trials (n=129; BMI range 19.6 to 44.6kg/m2; South Asian=31.0%; dysglycaemia=27.1%). Treatments included: prolonged sitting (6.5hours) or prolonged sitting broken-up with either standing or light-intensity physical activity (5 minutes every 30 minutes). Time-averaged postprandial responses for insulin and glucose were calculated for each treatment (mean±95% CI). Mutually adjusted interaction terms were used to examine whether anthropometric (BMI), demographic (age, sex, ethnicity (white European vs. South Asian)) and a cardiometabolic variable (HOMA-IR) modified responses. Results: Postprandial insulin and glucose were reduced when individuals interrupted prolonged sitting with bouts of light physical activity, but not with standing. Reductions in time-averaged postprandial insulin were more pronounced if individuals were South Asian compared with white European (-18.9mU/L (-23.5%) vs. -8.2mU/L (-9.3%)), female compared to male (-15.0mU/L (-21.2%) vs. -12.1mU/L (-17.6%)) or had a BMI ≥27.2kg/m2 (-20.9mU/L (-22.9%) vs. -8.7mU/L (-18.2%)). Similarly, being female (-0.4mmol/L (-0.6mmol/L, -0.2mmol/L) (-6.8%) vs. –0.1mmol/L (-0.3mmol/L, 1mmol/L) (-1.7%)) or having a BMI ≥27.2kg/m2 (-0.4mmol/L (-0.6mmol/L, -0.2mmol/L) (-6.7%) vs. –0.2mmol/L (-0.4mmol/L, 0.0mmol/L) (-3.4%)) modified the postprandial glucose response. No significant interactions were found for HOMA-IR or age. Conclusion: Being female, South Asian or having a higher BMI, all predicted greater reductions in postprandial insulin, while being female and having a higher BMI predicted greater reductions in postprandial glucose when sitting was interrupted with light physical activity. These results could help to guide personalised interventions in high-risk participants for whom breaking prolonged sitting time with light activity may yield the greatest therapeutic potential