Meiji-backed trial: L-phenylalanine supplementation aids fat breakdown during exercise

Previous studies had noted that pre-ingestion of a mixture of specific amino acids accelerated fat mobilisation.

However, the effects of single AAs combined with exercise on fat oxidation were unclear.

“We hypothesised that consumption of a specific amino acid, L-phenylalanine, may result in the secretion of glucagon, and when combined with exercise, may promote fat oxidation,”​ wrote researchers led by scientists from Meiji.

Six healthy, active male volunteers were randomised in a crossover study to ingest either L-phenylalanine supplied by Kyowa Hakko Bio (3g/dose) or a placebo.

Thirty minutes after ingestion, each subject performed workload trials on a cycle ergometer for one hour at 50% of maximal oxygen consumption.

“​​Oral intake of phenylalanine caused a significant increase in the concentrations of plasma glycerol and glucagon during exercise. The respiratory exchange ratio was also decreased significantly, following ingestion of phenylalanine,”​ wrote the researchers.

The main mechanism for the stimulation of fat oxidation following supplementation may be via glucagon secretion.

Glucagon is a key hormone involved in fat catabolism during exercise.

Functional effects

“To the author’s knowledge, this is the first study to examine the effects of Phe on human fat oxidation combined with exercise,”​ added the researchers in the Journal of the International Society of Sports Nutrition​​

“Although considerable evidence exists on the safety of (amino acid) consumption in humans, there is no evidence on the functional effects related to fat oxidation combined with exercise.​

“The data presented in this study lay the groundwork for further investigations on L-phenylalanine supplementation in sport.”​

The paper noted that the number of participants was small and that the researchers did not measure blood insulin levels.

“Insulin signalling is a key factor for glucagon secretion, so further studies are needed to demonstrate the effect of Phe combined with exercise for insulin secretion,”​ they added.

Nevertheless, they concluded: “These results suggested that pre-exercise supplementation of phenylalanine may stimulate whole body fat oxidation. No serious or study-related adverse events were observed.”​

The study was supported by a grant from Meiji Co. The researchers K Ueda, C Sanbongi, M Yamaguchi, and S Ikegami are employees of Meiji Co.

Source: Journal of the International Society of Sports Nutrition​​

https://doi.org/10.1186/s12970-017-0191-x​

“The effects of phenylalanine on exercise-induced fat oxidation: a preliminary, double-blind, placebo-controlled, crossover trial”

Authors: Keisuke Ueda, et al.​