Protein quality matters for muscle building, says review

By Annie Harrison-Dunn

- Last updated on GMT

Proteins with a high leucine content are 'advantageous' in triggering a rise in muscle protein synthesis, says review. ©iStock/marekuliasz
Proteins with a high leucine content are 'advantageous' in triggering a rise in muscle protein synthesis, says review. ©iStock/marekuliasz

Related tags Muscle protein synthesis Metabolism Protein functional beverage beverage

The quality of protein and its leucine content has a significant influence on muscle building with resistance training, a review has found.

When it comes to the protein market, whey is king, expected to be worth about €2.47bn globally by 2020.

Yet up-and-coming sources like pea and rice and even more niche sources like algae, hemp and insects have also been catching consumer eyes for their animal-free and sustainability credentials​.

Despite this interest, there is science and industry disagreement on the quality of these different proteins. 

Now a paper – part funded by the Whey Protein Research Consortium (WPRC) – has sought to clarify how these different kinds of proteins drive resistance training-induced hypertrophy, or muscle building.

The review concluded a protein’s leucine content was the “strongest determinant” ​of its capacity to affect muscle protein synthesis and likely hypertrophy.

The building block and trigger 

“As such, ingested proteins with a high leucine content would be advantageous in triggering a rise in MPS [muscle protein synthesis],”​ said the review published in Nutrition & Metabolism.​ 

Whey is particularly high in the amino acid. 

"The higher protein/leucine needed to stimulate MPS in the elderly would be obtained at lower protein doses with higher quality proteins such as whey, which may be advantageous from both an energy intake and potential appetite suppression standpoint."

Author of the paper and executive director of the McMaster Physical Activity Centre of Excellence at McMaster University in Canada, Professor Stuart Phillips, said digestibility of leucine should also be taken into greater consideration.

"Leucine is not only a building block for protein, but a trigger for working muscles to synthesise more protein,” ​he said in a release. 

“In essence, it turns on muscle protein synthesis like a light switch so that over time, there could be greater gains in lean body mass and strength, and subsequently, body composition improvements." 

Comparing proteins

Suzane Leser, head of nutrition for dairy firm and WPRC member Volac, said this review was spurred by the circulation of “two conflicting messages”.

“Protein quality is considered essential by the FAO [UN’s Food and Agriculture Organisation] for muscle growth and maintenance, but a number of new studies suggest that low quality proteins such as rice, pea, and wheat are as good as high quality whey protein, confusing the scientific space,”​ she told us.

What's the difference?

DIAAS measures the oro-ileal nitrogen balance by calculating the digestibility of individual amino acids in a section of the small intestine called the ileum. Meanwhile PDCAAS uses crude faecal digestibility values to measure the oro-faecal nitrogen balance.

A fundamental criticism of PDCAAS is that it uses fecal rather than ileal digestibility as well as nitrogen digestibility rather than the digestibility of individual amino acids to correct amino acid scores, which can lead to an under or overestimate of protein quality. 

Last month a study funded by French ingredients supplier Tereos suggested wheat protein may rival whey for muscle growth​.

Leser has been calling for protein quality to be recognised in EU legislation, and for a particular method called DIAAS (digestible indispensable amino acid score) to be used to measure that. 

The Food and Agriculture Organisation (FAO) has called the DIAAS method "preferable​" to the traditionally used PDCAAS (protein digestibility-corrected amino acid score) and called for more research to be conducted. 

Past research has shown the higher quality of dairy proteins using DIAAS.

Dairy players like Volac have backed DIAAS and called for it to replace PDCAAS, which was established 20 years ago and they say is obsolete. 

Method in the madness

This latest review also compared the two methods, revealing differing quality results.

“While there are few studies that have actually derived the DIAAS of proteins this variable is something that needs to be considered moving forward,”​ the review said. 

Assessing alternatives

The review called for emerging alternative proteins from sources like hemp and insects to be assessed in this way. 

“It is important that these proteins now be assessed and their DIAAS scores estimated so that we can make a true assessment of their quality when compared to more commonly-used isolated proteins,” ​Phillips said in his review. 

Ageing population  ​ 

He said the results had implications beyond the gym. 

"As we age, muscle loss becomes prevalent if we don't thwart the decline. Leucine-rich whey protein supplementation, combined with resistance exercise, may be one way to help preserve muscle mass throughout the lifespan."​ 

This public health potential to tackle muscle wasting in the elderly and bed bound has been highlighted in the past​, but researchers have warned that if individuals are already getting enough protein and leucine, supplementation may not have much impact. 

Source: Nutrition & Metabolism​ 

“The impact of protein quality on the promotion of resistance exercise-induced changes in muscle mass”

2016 13:64, doi: 10.1186/s12986-016-0124

Author: S. M. Phillips

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