Improvement in insulin sensitivity following a 1-year lifestyle intervention program in viscerally obese men: contribution of abdominal adiposity

Abstract

The objectives of the study were to quantify the effect of a 1-year healthy eating–physical activity/exercise lifestyle modification program on insulin sensitivity in viscerally obese men classified according to their glucose tolerance status and to evaluate the respective contributions of changes in body fat distribution vs changes in cardiorespiratory fitness (CRF) to the improvements in indices of plasma glucose/insulin homeostasis. Abdominally obese, dyslipidemic men (waist circumference ≥90 cm, triglycerides ≥1.69 mmol/L, and/or high-density lipoprotein cholesterol <1.03 mmol/L) were recruited. The 1-year intervention/evaluation was completed by 104 men. Body weight, composition, and fat distribution were assessed by dual-energy x-ray absorptiometry/computed tomography. Cardiorespiratory fitness and cardiometabolic risk profile were measured. After 1 year, insulin sensitivity improved in association with decreases in both visceral (VAT) and subcutaneous adiposity (SAT) as well as with the improvement in CRF, regardless of baseline glucose tolerance. Further analyses were performed according to changes in glucose tolerance status: improvement (group I, n = 39), no change (group N, n = 50), or worsening (group W, n = 15) after 1 year. Groups I and N improved their insulin sensitivity and their CRF, whereas group W did not, while losing less VAT than groups I and N. Multiple regressions showed that reduction in VAT was associated with an improvement in homeostasis model assessment of insulin resistance, whereas reduction in SAT was rather associated with improvement of the insulin sensitivity index of Matsuda. Changes in CRF were not independently associated with changes in indices of plasma glucose/insulin homeostasis. A 1-year lifestyle intervention improved plasma glucose/insulin homeostasis in viscerally obese men, including those with normal glucose tolerance status at baseline. Changes in SAT and VAT but not in CRF appeared to mediate these improvements.

Introduction

Abdominal obesity, characterized by excess visceral adipose tissue (VAT) and ectopic fat deposition, has been associated with a cluster of atherogenic and diabetogenic abnormalities [1]. However, pharmacological approaches to target VAT accumulation are virtually nonexistent since the withdrawal of some of the few available antiobesity drugs [2], [3]. Several lifestyle intervention studies using exercise as the treatment modality have shown its ability to mobilize VAT and improve the cardiometabolic risk (CMR) profile, even in the absence of weight loss [4], [5]. In the well-known Diabetes Prevention Study (DPS) [6] and Diabetes Prevention Program (DPP) [7], a 58% reduction in the incidence of type 2 diabetes mellitus (T2D) was reported in patients with glucose intolerance following a lifestyle modification program focusing on healthy eating and increased physical activity. However, only few studies have addressed the question of whether it has beneficial effects on indices of plasma glucose/insulin homeostasis specifically among men selected on the basis of their excess visceral adiposity who were further classified on the basis of their glucose tolerance [7], [8], [9]. For instance, a recent study has shown that the reduction in T2D's incidence related to physical activity was heterogeneous depending upon the glucose tolerance status of participants assessed at baseline [9].

The present study was designed as a body composition/adipose tissue distribution lifestyle intervention to examine how a healthy eating, physical activity/exercise program could improve the CMR profile of a group of viscerally obese men with the atherogenic dyslipidemia of insulin resistance. Participants did not have T2D; and the study included subjects with both normal and impaired glucose tolerance, aiming at specifically targeting excess visceral adiposity rather than metabolic disturbances. Key inclusion criteria were the presence of abdominal obesity and the high triglyceride/low high-density lipoprotein (HDL) cholesterol atherogenic dyslipidemia that is a lipid phenotype associated with excess VAT [10]. The primary end point of the intervention was visceral adiposity measured by computed tomography. We put forward the hypothesis that a 1-year lifestyle modification program integrating healthy eating habits combined with an increase in physical activity and endurance exercise could lead to improvements in insulin sensitivity, irrespective of patients' glucose tolerance status. We also examined whether changes in body fat distribution vs changes in cardiorespiratory fitness (CRF) would contribute to the improvements in indices of plasma glucose/insulin homeostasis.