Effects of postprandial exercise timing on Irisin and metabolic responses in adults with prediabetes

Objective: To evaluate the effects of different postprandial exercise timings (30, 60, 90, and 120 minutes after meal intake) on serum irisin levels, lipid profile, anthropometric indices, and substrate metabolism in middle-aged adults with prediabetes. Methods: This controlled, repeated-measures experimental study was conducted on twenty-five sedentary adults aged 30–40 years with prediabetes at Khyber Medical University, Peshawar, Pakistan, from July 2022 to December 2023. Participants served as their own controls and completed four treadmill-walking sessions (40 minutes at 50% predicted maximum heart rate), performed one week apart at varying postprandial intervals. Venous blood samples were collected at fasting, pre-exercise, and 60-, 90-, and 120-minutes post-exercise across the study weeks to assess serum irisin and lipid profile. Substrate metabolism (VO₂, respiratory quotient), perceived exertion, and anthropometric measures were assessed at baseline and at the end of the study. Results: Exercise performed 30 minutes after meal produced maximum rise in serum irisin (Δ = +115 pg/mL, p <0.001), and significant reductions in total cholesterol, LDL-C, and triglycerides, with an increase in HDL-C (p <0.001). Fat oxidation peaked at the 30-minute exercise condition (p =0.015), whereas carbohydrate oxidation was highest when exercise was initiated 120 minutes post-meal (p = 0.026). Anthropometric indices (BMI, waist circumference, body fat %) showed significant improvement over the study duration. Perceived stress remained largely unchanged, although participants subjectively reported better mood and energy following exercise. Conclusion: Initiating postprandial exercise, particularly within 30–60 minutes after meals, optimally improves lipid metabolism, substrate utilization, and irisin response in prediabetes.