Caloric restriction for 24 hours increases mean night growth hormone

In obesity, serum growth hormone (GH) is usually low, confounding GH assessment of short obese children. We evaluated whether 24-h caloric restriction would permit better discrimination between normal GH secretion and GH deficiency (GHD) by elevating night GH levels.

Serum was obtained every 20 minutes 2000-0800 h before and 2200-0400 h after 24 hours of caloric restriction (8% of usual calories) in 24 normal height children [14 normal (weight for height 10-90th percentile); 10 obese (weight for height > 95th percentile)] and in 31 short children (height shorter than -2.0 SD below mean for age). All samples from both nights per child were assayed for GH simultaneously to eliminate interassay variability.

Mean GH increased significantly in all groups after caloric restriction (P < 0.01). Obese children had lower baseline mean GH and GH amplitude compared to normal (P < 0.01); GH increased into normal range after restriction. Basal GH studies in short children were not significantly below normal. Surprisingly, some with low stimulated GH increased their night GH into the normal range after caloric restriction.

Caloric restriction for 24 h enhances night GH similarly in short and in normal children, and thus does not increase the diagnostic utility of night GH studies in non-obese short children. Caloric restriction reverses suppressed GH secretory state of obese children, perhaps by decreasing diet-dependent somatostatin inhibition of GH secretion.