Fasting hyperglycaemia blunts the reversal of impaired glucose tolerance after exercise training in obese older adults

Abstract

Aim: Lifestyle modification, consisting of exercise and weight loss, delays the progression from prediabetes to type 2 diabetes (T2D). However, no study has determined the efficacy of exercise training on glucose metabolism in the different prediabetes subtypes. Methods: Seventy‐six older (65.1 ± 0.6 years) obese adults with impaired fasting glucose (IFG; n = 12), impaired glucose tolerance (IGT; n = 9) and combined glucose intolerance (IFG + IGT = CGI; n = 22) were compared with normal glucose tolerant (NGT; n = 15) and T2D (n = 18) groups after 12 weeks of exercise training (60 min/day for 5 days/week at ∼85% HR_max). An oral glucose tolerance test was used to assess glucose levels. Insulin sensitivity (IS; euglycaemic hyperinsulinaemic clamp at 40 mU/m²/min), β‐cell function (glucose‐stimulated insulin secretion corrected for IS), body composition (hydrostatic weighing/computed tomography scan) and cardiovascular fitness (treadmill VO₂max) were also assessed. Results: Exercise training reduced weight and increased cardiovascular fitness (p < 0.05). Exercise training lowered fasting glucose levels in IFG, CGI and T2D (p < 0.05) and 2‐h glucose levels in IGT, CGI and T2D (p < 0.05). However, 2‐h glucose levels were not normalized in adults with CGI compared with IGT (p < 0.05). β‐Cell function improved similarly across groups (p < 0.05). Although not statistically significant, IS increased approximately 40% in IFG and IGT, but only 17% in CGI. Conclusion: The magnitude of improvement in glucose metabolism after 12 weeks of exercise training is not uniform across the prediabetes subtypes. Given the high risk of progressing to T2D, adults with CGI may require more aggressive therapies to prevent diabetes.