Pre-workout supplementation of phenylalanine may aid fat oxidation in men

By Adi Menayang contact

- Last updated on GMT

Photo: Katarzyna Bialasiewicz/iStock
Photo: Katarzyna Bialasiewicz/iStock

Related tags: Carbon dioxide, Metabolism

Taking the amino acid phenylalanine as a pre-workout supplement may stimulate whole body fat oxidation, known colloquially as ‘burning fat,’ according to a new study.

Researchers found that participants who consumed 3g of phenylalanine in a capsule thirty minutes before exercising exhibited increased concentrations of plasma glycerol and the hormone glucagon—both relevant in the process of converting fat into usable energy.

“The data presented in this study lay the groundwork for further investigations on phenylalanine supplementation in sport,”​ the researchers wrote in their report, published​ in the Journal of the International Society of Sports Nutrition.

The study was funded by Japanese confectionery giant Meiji. Researchers came from its Food Science Research Labs R&D division, as well as researchers from Ritsumeikan University. The capsule of phenylalanine came from ingredient manufacturer Kyowa Hakko, which is owned by the beverage giant Kirin Holdings.

The researchers wrote that effects of a single amino acid combined with exercise on fat oxidation is still unclear, thus the research was to investigate hormone secretion induced by phenylalanine and exercise.

Supplementation + Exercise

Six healthy, active men between the ages of 20 and 40 were recruited for the study. At baseline, the average body mass index of all participants was 22.7 (average height 172.6 cm, average weight 67.7 kg).

After all baseline measurements were recorded, the participants were randomized to ingest either the phenylalanine capsules or a placebo—an empty cellulose capsule made by Matsutani—with a cup of tap water.

The study was placebo-controlled, double blind, randomized, and crossover. After the participants ingested their assigned capsules, they exercised for an hour. Once completed, the participants rested for 60 minutes in supine position.

Blood samples were collected before ingestion of the supplement or placebo, and at 30, 60, 90, and 150 minutes after ingestion.

Results: Potential fat oxidation benefit

Researchers measured multiple parameters that have been correlated to fat oxidation, such as blood glucose and lactate concentrations, as well as exhaled oxygen and carbon dioxide concentrations. “Evaluation of the respiratory exchange ratio is regarded as the gold standard for evaluating whole body fat oxidation,” ​they argued.

They found that the respiratory exchange ratio—the amount of carbon dioxide produced in metabolism per oxygen used—decreased significantly following ingestion of phenylalanine compared to placebo. This suggests that body lipid oxidation increased when supplementation was taken before exercise.

Additionally, the participants had increased glucagon and glycerol concentration after supplementation compared to after taking the placebo. This led the researchers to hypothesize that glucagon secretion following phenylalanine supplementation may lead to fat oxidation.

Strengths in the study included its design and the fact that it administered only 3g of the amino acid, an amount that could be used easily elsewhere. But the study sample was small, only included males, and lasted a short period of time.

“Further studies are needed to investigate whether this acute response induced by the administration of phenylalanine is sustained if the supplement is ingested over several weeks,” ​the researchers wrote.

Source: ​Journal of the International Society of Sports Nutrition

Published online,

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

Authors:​ K. Ueda, et al

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