Table of Contents
Journal of Amino Acids
Volume 2013 (2013), Article ID 964637, 6 pages
Clinical Study

Ingestion of Leucine + Phenylalanine with Glucose Produces an Additive Effect on Serum Insulin but Less than Additive Effect on Plasma Glucose

1Endocrinology, Metabolism, and Nutrition Section, Minneapolis VA Health Care System, One Veterans Drive, Minneapolis, MN 55417, USA
2Department of Medicine, University of Minnesota, Minneapolis, MN 55455, USA
3Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108, USA

Received 19 December 2012; Revised 26 March 2013; Accepted 10 April 2013

Academic Editor: Imre Sovago

Copyright © 2013 Jennifer F. Iverson et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Most individual amino acids stimulate insulin secretion and attenuate the plasma glucose response when ingested with glucose. We determined whether ingestion of two amino acids simultaneously with glucose would result in an additive effect on the glucose area response compared with ingestion of amino acids individually. Leucine and phenylalanine were chosen because they were two of the most potent glucose-lowering amino acids when given individually. Eight healthy subjects were studied on four separate days. Test meals were given at 0800. The first meal was a water control. Subjects then received 25 g glucose or leucine + phenylalanine (1 mmol/kg fat free body mass each) ±25 g glucose in random order. Glucose, insulin and glucagon were measured frequently for 2.5 hours thereafter. Net areas under the curves were calculated using the mean fasting value as baseline. The insulin response to leucine + phenylalanine was additive. In contrast, the decrease in glucose response to leucine + phenylalanine + glucose was less than additive compared to the individual amino acids ingested with glucose. Interestingly, the insulin response to the combination was largely due to the leucine component, whereas the glucose response was largely due to the phenylalanine component. Glucose was unchanged when leucine or phenylalanine, alone or in combination, was ingested without glucose. This trial is registered with NCT01471509.