Abstract
Lack of insulin results in a catabolic state in subjects with insulin-dependent diabetes mellitus which is reversed by insulin treatment. Amino acid supply, especially branched chain amino acids such as leucine, enhances protein synthesis in both animal and human studies. This small study was undertaken to assess the acute effect of supplemental leucine on protein metabolism in adolescents with type 1 diabetes. L-[1-13C] Leucine was used to assess whole-body protein metabolism in six adolescent females (16–18 yrs) with type 1 diabetes during consumption of a basal diet (containing 58 μmoles leucine/kg/h) and the basal diet with supplemental leucine (232 μmoles leucine/kg/h). Net leucine balance was significantly higher with supplemental leucine (56.33 ± 12.13 μmoles leucine/kg body weight/hr) than with the basal diet (−11.7 ± −5.91, P < .001) due to reduced protein degradation (49.54 ± 18.80 μmoles leucine/kg body weight/hr) compared to the basal diet (109 ± 13.05, P < .001).
Highlights
Whole body protein catabolism results when the rate at which body protein is synthesized is less than the rate at which body protein is degraded
The amount of insulin required to maintain these levels of plasma glucose was significantly different on the two study days, with greater amounts of insulin required on the study day with supplemental leucine (36 ± 3 units) compared with the day when the basal diet was consumed (30 ± 3 units, P = .02) and higher levels of plasma insulin (Figure 2)
If an anabolic effect were observed, the study had the potential to provide information about the importance of insulin in mediating the effect of leucine in the human context, since these subjects were unable to increase circulating insulin concentrations in response to supplemental dietary leucine. This acute study, conducted over two study days of 6 hours each, suggests that supplemental dietary leucine equivalent to four times the leucine content of the basal diet may improve the net accumulation of whole-body protein through a decrease in the rate at which protein is degraded
Summary
Whole body protein catabolism results when the rate at which body protein is synthesized is less than the rate at which body protein is degraded. Insulin is among the many factors which regulate body protein metabolism. Studies of whole-body protein metabolism in adult humans with type 1 diabetes [8,9,10,11,12,13] and prepubertal children [14] have suggested that the primary effect of insulin is a reduction in the rate of protein degradation rather than a stimulation of the rate of protein synthesis. While provision of insulin to individuals with type 1 diabetes enhances the accretion of body protein mass, there are data from adults [15] and adolescents females [16] suggesting that long-term insulin therapy results in accumulation of body fat compared to nondiabetic individuals. The current study was undertaken to determine if the anabolic effect of insulin on protein metabolism could be enhanced by the concurrent provision of a diet enriched with the amino acid, leucine
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