Preferential reductions in intermuscular and visceral adipose tissue with exercise-induced weight loss compared with calorie restriction

Abstract

Intermuscular adipose tissue (IMAT) and visceral adipose tissue (VAT) are associated with insulin resistance. We sought to determine whether exercise-induced weight loss (EX) results in greater reductions in IMAT and VAT compared with similar weight loss induced by calorie restriction (CR) and whether these changes are associated with improvements in glucoregulation. Sedentary men and women (50-60 yr; body mass index of 23.5-29.9 kg/m(2)) were randomized to 1 yr of CR (n = 17), EX (n = 16), or a control group (CON; n = 6). Bilateral thigh IMAT and VAT volumes were quantified using multi-slice magnetic resonance imaging. Insulin sensitivity index (ISI) was determined from oral glucose tolerance test glucose and insulin levels. Weight loss was comparable (P = 0.25) in the CR (-10.8 ± 1.4%) and EX groups (-8.3 ± 1.5%) and greater than in the control group (-2.0 ± 2.4%; P < 0.05). IMAT and VAT reductions were larger in the CR and EX groups than in the CON group (P ≤ 0.05). After controlling for differences in total fat mass change between the CR and EX groups, IMAT and VAT reductions were nearly twofold greater (P ≤ 0.05) in the EX group than in the CR group (IMAT: -45 ±5 vs. -25 ± 5 ml; VAT: -490 ± 64 vs. -267 ± 61 ml). In the EX group, the reductions in IMAT were correlated with increases in ISI (r = -0.71; P = 0.003), whereas in the CR group, VAT reductions were correlated with increases in ISI (r = -0.64; P = 0.006). In conclusion, calorie restriction and exercise-induced weight loss both decrease IMAT and VAT volumes. However, exercise appears to result in preferential reductions in these fat depots.

Fig. 1.

Changes in body weight and composition in response to 12 mo of weight loss induced by calorie restriction or exercise and in the control group. Values are means ± SE and have been adjusted for baseline values. CR, calorie restriction group; EX, exercise-induced weight loss group; CON, control group; VAT, visceral adipose tissue volume; SAT, subcutaneous adipose tissue volume; IMAT, thigh intermuscular adipose tissue volume; SCAT, thigh subcutaneous adipose tissue volume.

Fig. 2.

Abdominal and thigh adipose tissue volumes in response to 12 mo of calorie restriction or exercise-induced weight loss. Values are means ± SE and have been adjusted for baseline values and for between-group differences in total fat mass reductions.

Fig. 3.

Changes in indexes of glucoregulatory function in response to calorie restriction and exercise-induced weight loss, and in the control group. Values are means ± SE and have been adjusted for baseline values. Insulin sensitivity index values were log transformed for statistical analysis; however, untransformed, baseline-adjusted means are presented for ease of interpretation. AUC, area under the curve during the 2-h oral glucose tolerance test.

Fig. 4.

Associations between changes in visceral or intermuscular adipose tissue volume and changes in insulin sensitivity index in the calorie restriction and exercise groups. Correlation coefficients are from Pearson correlations. Because of several outlier values, non-parametric Spearman rank correlation analyses were also performed. The marginally significant correlation between changes in VAT and improvements in ISI in the EX group (top right) became more clearly nonsignificant (P = 0.12). The significance/nonsignificance of all other correlations was not altered by performing non-parametric analyses.