Exercise targeted on maximal lipid oxidation has long-term weight-reducing effects but improves insulin secretion and lipid oxidation before reducing fat mass

Introduction and purpose. - Exercise training at low intensity in the zone where lipid oxidation reaches a maximum (LIPOXmax training) has a slight but prolonged weight-lowering effect and improves both carbohydrate and lipid metabolism. We investigated in patients followed for long term LIPOXmax training which were the effect on body weight after 4 years and which were the early effects of 10 weeks of training on lipid oxidation during exercise and on insulin secretion and glucose disposal parameters measured with a standard meal. Methods. - We thus present here the extension over 4 years of a preceding series of 28 obese subjects followed for 3 years to assess long-term weight-lowering effects of LIPOXmax training. In a subgroup of 14 patients undertaking such a training protocol, a breakfast test with minimal model analysis of insulin secretion and insulin sensitivity and an exercise calorimetry were performed before and after 10 weeks of targeted training. Results. - Over 48 months patients had lost on the average -8.37 +/- 1.74 kg, i.e. -9.42 +/- 1.93% of the initial weight (P < 0.001). Between 36 and 48 months weight loss was still in progress (on the average -0.2 kg/month). The subgroup of 14 patients undertaking LIPOXmax training showed after the initial period of 10 weeks the expected modifications of body composition in only half of the subjects, while exercise calorimetry showed an improvement of the ability to oxidize lipids during exercise (P = 0.011) and an increase in first phase insulin secretion (P = 0.003). The expected increase in insulin sensitivity was found only in 4 subjects and changes in insulin sensitivity were negatively correlated to changes in fat mass (r = -0.608, P = 0.047) and also negatively correlated to changes in beta-cell sensitivity (a measurement of second phase insulin release) (r = -0.710, P = 0.032). There was also a correlation between changes in waist circumference and total prehepatic insulin release (r = -0.763, P = 0.046). Conclusion. - Exercise training performed in the zone of maximal lipid oxidation has a sustained weigh-reducing effect that persists more than 4 years. This study demonstrates also for the first time that there are early effects on metabolism that become significant even before any obvious change in body composition. Insulin sensitivity improves when fat mass decreases and is in turn correlated with a decrease in second phase insulin secretion. By contrast the ability to oxidize lipids during exercise improves earlier, as well as phase 1 insulin secretion. Therefore, LIPOXmax training rapidly improves lipid oxidation and first phase insulin secretion, and has long lasting weight-lowering effects that further improves insulin sensitivity and reverses the insulin resistance-related excess in insulin secretion. The latter effects are not fully obtained after 11 weeks. (C) 2021 Elsevier Masson SAS. All rights reserved.