Not all proteins are equal: Leucine triggers muscle protein synthesis more effectively than others – study

Dr Stuart Phillips, a professor from McMaster University’s Department of Kinesiology, was speaking at the event “Building towards Sustainable Physical Activity Behaviour” ​organised by International Life Sciences Institute South East Asia (ILSI-SEA) recently.

In his presentation, he highlighted that the amino acid leucine was more effective in triggering muscle protein synthesis as compared to the others.

“Of all the amino acids, leucine has taken on the role of prominence… This is the branched-chain amino acid that triggers the response of muscle protein synthesis,” ​he said.

Citing a number of scientific studies, he said that compared to adding branched-chain amino acids (BCAA) to whey protein, or increasing the consumption of whey protein, adding leucine was more effective in augmenting muscle protein synthesis.

A study involving elderly women also showed that leucine consumption helped to stimulate muscle protein synthesis during both rest and exercise.

“It is not just an added response, it is actually synergistic and it is driven by a single amino acid,” ​he said when explaining the impact of leucine.

Supplements with good scientific evidence ​

As part of the International Olympic Committee (IOC), Philips pointed out that only a few sports supplements have shown good evidence for enhancing muscle protein synthesis. 

The IOC issued a consensus statement​ in March last year, stating that only a few supplements, such as caffeine, creatine, bicarbonate, nitrate, beta-alanine, and CHO drinks have shown good evidence of benefits.

Philips pointed out that others such as omega-3, vitamin D, and probiotics could be categorised as “B grade hopefuls” while he argued BCAA, HMB, glutamine, arginine, and zinc need more evidence.

He also said that there has been “no evidence”​ to show that protein supplements are better than real food, except that supplements provided an ease of convenience.

Intervening factors ​

There are a number of factors that will intervene with the amount of protein intake required for muscle protein synthesis.

These factors included mobility, amount of exercise, and age, Philips said.

For instance, while protein supplement could help to gain muscles, the impact is not as significant when compared to the benefits gained by going to the gym.

“​​When you are physically active, the amount of leucine needed to trigger muscle protein synthesis drops. You can actually get away with lower doses of leucine but its transient. In other words, you have to keep exercising,” ​Philips said.

This therefore means that when one is immobile or confined to bed rest, more leucine intake will be required to trigger muscle protein synthesis.

How much and when? ​

Besides the right type of protein, there is also the issue of consuming the right amount of protein at the right time.

Philips pointed out that the ideal amount of protein intake was 0.3 – 0.5g/ kg for per meal dose, with the optimal intake per day ranging from 1.6g/kg to 2.2g/kg.

Since the rate of muscle protein synthesis is lower in elderly than in young people, the elderly had to consume a higher amount of protein.

On the other hand, protein supplementation needs to take place throughout the day, ideally four times in a day, instead of consuming it once per day. 

Source: The American Journal of Clinical Nutrition

Leucine supplementation of a low-protein mixed macronutrient beverage enhances myofibrillar protein synthesis in young men: a double-blind, randomized trial​

https://doi.org/10.3945/ajcn.113.068775​

Authors: Tyler A Churchward-Venne et al ​