Leucine + phenylalanine modify the glucose and insulin response to glucose

Abstract

We have shown that phenylalanine (Phe) or leucine (Leu), when ingested with glucose, reduced the glucose response. Leu increased, whereas Phe had little effect on the insulin response. We then were interested in whether the effects would be additive if Phe and Leu were ingested together with glucose. On 4 separate days, 8 healthy subjects were studied. Test meals were given at 0800. Subjects received water, or 25 g glucose, or Leu+Phe (1 mmol/kg fat free body mass each) ± 25 g glucose. Blood glucose, insulin and glucagon were measured frequently thereafter for 2.5 hrs. Net areas under the curve were calculated. The insulin area response increased by 77% (p<0.05) and the glucose area response decreased by 66% (p<0.05) after ingestion of glucose+Leu+Phe compared to ingestion of glucose alone. The insulin response to Leu+Phe was additive compared to previous results obtained when the individual amino acids (AA) were ingested with glucose. In contrast, the decrease in glucose response to Leu+Phe+glucose was less than additive compared to the individual AA ingested with glucose. Blood glucose was unchanged when Leu or Phe, alone or in combination, were ingested without glucose. Thus, ingestion of Leu+Phe with glucose produced an additive increase in insulin area response but a less than additive reduction in glucose area response in healthy subjects.