Exercise, abdominal obesity, skeletal muscle, and metabolic risk: evidence for a dose response

Abstract

The obese are at increased risk for cardiovascular disease and type 2 diabetes. However, some who are obese have no metabolic abnormalities. So, it is not adipose tissue per se, but perhaps where it is located that is important for determining metabolic consequences. Regular exercise is known to reduce risk for metabolic disease through numerous mechanisms. The purpose of this report is to highlight some of the efficacy-based data on the effects of exercise (and also a sedentary lifestyle) on abdominal obesity, visceral fat, and metabolic risk. We also discuss how impaired fatty acid oxidation (FAO) in skeletal muscle may be related to both insulin resistance and a contributor to weight gain. In summary, it is evident that exercise in sufficient amounts can lead to substantial decreases in body weight, total body fat, and visceral fat. Additionally, evidence now supports the conclusion that there is a dose-response relationship between exercise amount and these changes, i.e., more exercise leads to additional benefits. Additionally, there are a number of important cardiometabolic risk factors that were most favorably effected by moderate-intensity compared to vigorous-intensity exercise. Unfortunately, it is also apparent that in sedentary middle-aged men and women, short periods of physical inactivity lead to significant weight gain, substantial increases in visceral fat, and further metabolic deterioration. Finally, favorable modulation of mitochondrial oxidative capacity in skeletal muscle by exercise training may reduce a block for complete oxidation of fatty acids in muscle and thereby relieve a block to effective insulin signaling.

Figure 1

Relationship between amount of exercise per week and (a) body weight change, (b) fat mass change, and (c) visceral fat change. Figure adapted from data from Slentz et al. (37).

Figure 2

Relationship between amount of exercise per week and (a) low-density lipoprotein (LDL) particle number change, (b) LDL size change, and (c) high-density lipoprotein (HDL) size change. Data from Kraus et al. (11). Figure reprinted with permission from Slentz et al. (60).

Figure 3

Effect of exercise amount and intensity on metabolic syndrome score. Figure reprinted from Johnson et al. (12) with permission from Elsevier. NSD, no significant difference.