Metabolic adaptation to protein restriction in insulin-dependent diabetes mellitus

Eight normal subjects, four subjects with intensively treated insulin-dependent diabetes mellitus (IDDM), and six subjects with conventionally treated IDDM consumed a test meal of 0.5 g protein and 10 kcal per kg body weight, first while adapted to a conventional diet high in protein, and then again after 5 days of dietary protein restriction. Metabolic N balance (N consumed minus urea production) and net protein utilization were measured over the 9 h after consumption of the test meal, as was recovery in urea of 15N from a tracer dose of [15N]alanine included in each test meal. After the first test meal, N balance and net protein utilization were similar and close to zero for all groups. After the second test meal, N balance and net protein utilization became positive for all groups (P < 0.05) but significantly less so (P < 0.05) for the conventionally treated than for the normal and intensively treated diabetic subjects. 15N recovery in urea was reduced for all groups after the second test meal (P < 0.05) but probably less effectively (P < 0.09) for the conventionally treated diabetic subjects. Metabolic adaptation to protein restriction may be less effective than normal in conventionally treated IDDM.