Effect of a carbohydrate-restricted, calorie-reduced diet on the growth of young rats and on serum growth hormone, somatomedins, total thyroxine and triiodothyronine, free T4 index, and total corticosterone.

We have studied the effect of a carbohydrate-restricted, calorie-reduced diet on the growth of young rats and on serum levels of GH, somatomedins [insulin-like growth factors (IGFs) I and II], total T4 and T3, free T4 index, and total corticosterone. Experimental animals consumed the same quantities of protein and fat as controls, but only 50.3% as much carbohydrate and 76% as many calories. While the experimental group grew at 69.4% of the control rate, their mean (+/- SEM) GH level (175.7 +/- 36.9 ng/mL) was not significantly different from that in the control group (180 +/- 30 ng/mL). In contrast, serum total IGF and IGF-I, while not correlated with serum GH levels, were significantly correlated in all animals with body weight (r = .87 and r = .82, respectively, P less than .01) and tail length (r = .61 and r = .62, respectively, P less than .01). The somatomedin levels of the carbohydrate-restricted rats were significantly lower than those of their age-matched, but not weight-matched, controls by the eighth day of study. Serum T4, T3, and free T4 index were not significantly different in these two groups, while total corticosterone in the experimental group (245 +/- 73 ng/mL) was slightly lower than in controls (292 +/- 80 ng/mL, P less than .05). These data indicate that by restricting carbohydrate intake we have compromised the anabolic use of dietary protein by growing rats, resulting in a retardation of growth and a reduction in serum total IGF and IGF-I levels.