Increased efficiency of weight gain and altered cellularity of brown adipose tissue in rats with impaired glucose tolerance during diet-induced overfeeding.

We examined the relationship among glucose tolerance, efficiency of weight gain, and cellularity of brown adipose tissue (BAT) in rats (initial weight: 362 +/- 1 g) made hyperphagic and obese by feeding on a highly palatable "cafeteria" (CAF) diet for 4-8 wk. As compared with chow-fed controls, CAF feeding resulted in a 45-60% increase in caloric intake (P less than 0.01), a 40-50% increase in weight gain (P less than 0.01), and hyperinsulinemia. Glucose disposal rate (K) on intravenous glucose tolerance test (IVGTT) was greater than or equal to 1.4% in all chow-fed rats, but fell to less than or equal to 1.3 in 10 of 23 CAF-fed rats. As compared with the chow-fed controls, rats with normal glucose tolerance demonstrated a 12% decline in efficiency of weight gain (g/100 kcal of food consumed) in response to CAF feeding (P less than 0.05). In marked contrast, in rats with impaired glucose tolerance, efficiency of weight gain failed to decline in response to overfeeding and was 18% higher than in the overfed group with normal glucose tolerance (P less than 0.01). Although CAF feeding increased the mass of interscapular BAT by 110-130% in rats with normal as well as impaired glucose tolerance, DNA content of BAT rose only in the normal-K CAF-fed rats (0.19 +/- 0.01 mg DNA/100 mg versus 0.12 +/- 0.02 in chow-fed controls and 0.12 +/- 0.01 in low-K rats).(ABSTRACT TRUNCATED AT 250 WORDS)