Leucine intake from a supplement may be better for muscle protein synthesis than leucine from a meal

By Adi Menayang

- Last updated on GMT

Getty Images / Dragon Images
Getty Images / Dragon Images
Researchers in Japan and the UK found that plasma concentrations of leucine were higher after 10 young healthy men took leucine as a liquid supplement than when their intake came from a meal — even when both had the same amount of leucine.

“The observation that rapid elevations in plasma leucine concentrations are suppressed when leucine is ingested at the same time as a meal suggests that the timing of its intake must be considered to maximize the anabolic response,”​ the researchers wrote in their report, published this week​ in the open-access journal Nutrients.

These results have implications for our understanding of supplementation timing as well as sports nutrition formulation, they argued, because plasma amino acid concentrations increase with protein intake, and increases in muscle protein synthesis are dependent on concentrations of leucine, an essential amino acid.

They also found that maximum levels of leucine in the blood was suppressed when participants ingested leucine immediately after a meal, even when the total leucine content was doubled.

This may be because of how our stomach digests food. “With respect to the rate of discharge from the stomach—referred to as gastric emptying—food rheology (i.e., liquid vs. solid food) has been shown to influence the gastric emptying, with solid food slower than liquid meal,”​ they argued.

“Based on these findings, it is presumed that compared to the intake of protein alone or free amino acids alone, the intake of dietary protein from mixed meals may result in a lower maximum plasma leucine concentration.”

It’s important to keep in mind, however, that the only outcomes the researchers focused on was how much leucine showed up in blood plasma. Hence, it wasn’t the strongest indicator of how much amino acid was actually absorbed and metabolized.

But the results still make the case that when free amino acids are ingested with the purpose of increasing plasma amino acid concentrations, the timing in relation to the mixed meal intake needs to be considered.

Study details

Ten healthy Japanese men with the average age of 25 underwent four different conditions in this crossover-design study.

The first condition was intake of 2 g of leucine alone with 200 g of water; the second was intake of a mixed meal that had 2.15 g of leucine without additional supplementation; the third was intake of 2 g of leucine immediately after a meal; and finally intake of 2 g of leucine 180 minutes after a meal.

Between each condition, participants went through a ‘washout period’ of one week.

All meals during testing days were Japanese style, consisting of egg, fish, and milk for protein, along with other ingredients such as rice and vegetables.

On these days, researchers drew the participants’ blood to analyze plasma concentrations of leucine.

Source: Nutrients
Published online; doi:10.3390/nu10101543
“Effect of Mixed Meal and Leucine Intake on Plasma Amino Acid Concentrations in Young Men”
Authors: Naomi Yoshii, et al.

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