Effect of calorie restriction with or without exercise on insulin sensitivity, beta-cell function, fat cell size, and ectopic lipid in overweight subjects

Abstract

Objective: The purpose of this article was to determine the relationships among total body fat, visceral adipose tissue (VAT), fat cell size (FCS), ectopic fat deposition in liver (intrahepatic lipid [IHL]) and muscle (intramyocellular lipid [IMCL]), and insulin sensitivity index (S(i)) in healthy overweight, glucose-tolerant subjects and the effects of calorie restriction by diet alone or in conjunction with exercise on these variables.

Research design and methods: Forty-eight overweight volunteers were randomly assigned to four groups: control (100% of energy requirements), 25% calorie restriction (CR), 12.5% calorie restriction +12.5% energy expenditure through structured exercise (CREX), or 15% weight loss by a low-calorie diet followed by weight maintenance for 6 months (LCD). Weight, percent body fat, VAT, IMCL, IHL, FCS, and S(i) were assessed at baseline and month 6.

Results: At baseline, FCS was related to VAT and IHL (P < 0.05) but not to IMCL. FCS was also the strongest determinant of S(i) (P < 0.01). Weight loss at month 6 was 1 +/- 1% (control, mean +/- SE), 10 +/- 1% (CR), 10 +/- 1% (CREX), and 14 +/- 1% (LCD). VAT, FCS, percent body fat, and IHL were reduced in the three intervention groups (P < 0.01), but IMCL was unchanged. S(i) was increased at month 6 (P = 0.05) in the CREX (37 +/- 18%) and LCD (70 +/- 34%) groups (P < 0.05) and tended to increase in the CR group (40 +/- 20%, P = 0.08). Together the improvements in S(i) were related to loss in weight, fat mass, and VAT, but not IHL, IMCL, or FCS.

Conclusions: Large adipocytes lead to lipid deposition in visceral and hepatic tissues, promoting insulin resistance. Calorie restriction by diet alone or with exercise reverses this trend.

Figure 1

In healthy overweight men and women at baseline, there was a strong positive correlation between abdominal subcutaneous FCS and VAT (A) and abdominal subcutaneous FCS and IHL (B). Groups were pooled for analysis. ●, CR; ○, CREX; △, LCD; ▼, control.

Figure 2

The improvement in insulin sensitivity with 6 months of calorie restriction was significantly associated with the loss of fat mass (A) and abdominal VAT depots (B) but not to the change in subcutaneous abdominal FCS (C) and IHL (D). ●, CR; ○, CREX; △, LCD; ▼, control. Analyses are reported with and without the control group included.