Dietary carbohydrate and metabolism of ingested protein.

Six normal people were fed a lean beef meal while on a normal diet and after seven days on a very low carbohydrate (greater than 25 g/day) 2000 kcal/day diet. After carbohydrate restriction, the protein-induced rise in branched chain aminoacids was 40-50% greater than the rise after the control diet. Intravenous leucine also produced a 40% greater rise in plasma-leucine after carbohydrate restriction. Three days of fasting exaggerated protein-induced increases in plasma branched-chain aminoacids by 55-77%. Hypocaloric, pure carbohydrate refeeding restored the branched-chain aminoacid responses to normal. Severe carbohydrate restriction thus leads to increased accumulation of plasma branched-chain aminoacids after protein feeding which is at least in part due to reduced utilisation of these aminoacids.