Soy matches casein for muscle protein synthesis: Study

By Stephen Daniells

- Last updated on GMT

Related tags Amino acid Metabolism

Protein from soy or casein both benefit the synthesis of muscle protein at the same rate, suggests a new study that supports both sources for muscle health.

Previous studies have suggested that casein is more effective at raising body protein levels than the equivalent level of soy protein in healthy young people, leading scientists from the US, the Netherlands and France to hypothesize that a casein protein/carbohydrate meal would result in higher protein accumulation in muscle, compared with soy.

However, according to findings published in Clinical Nutrition​ there were no differences between the protein sources in terms of acute muscle protein metabolism.

There were differences observed between the proteins for the uptake of amino acids in the leg, added researchers from the University of Arkansas for Medical Sciences, Maastricht University and University Hospital, and the University Hospital of Clermont-Ferrand.

The study involved 22 healthy 22 year olds randomly assigned to receive moderate-nitrogen and carbohydrate casein and soy meals.

While there were no differences in the synthesis of muscle protein between the groups, the researchers did note differences in changes in levels of glutamate, glutamine, serine, histidine, isoleucine and branched chain amino acids.

‘Interesting’ results

Commenting on the study’s findings, Mark Cope, clinical research scientist at Solae told NutraIngredients-USA: “This study shows that both soy and casein decrease muscle protein breakdown, which is important for maintaining muscle.

“It is interesting to note that muscle protein synthesis rates were the same for soy and casein at the end of the four hours of protein intake. A challenge in applying these results is that the proteins were not ingested under normal eating conditions, but rather through tube-feeding.”

Indeed, Nicolaas Deutz and his international collaborators write in Clinical Nutrition​ that there is a possibility that “more profound differential effects on muscle protein kinetics” ​would be observed if the subjects had been fed the meals rather than via tube-feeding.

“Previous studies have shown soy is superior to casein for muscle protein synthesis in exercising individuals.” ​added Soale’s Cope.

Sports nutrition

The link between protein and muscles is well established, with protein a key player in sports nutrition products. The main sources of protein are whey from dairy and soy proteins. Solae’s Gregory Paul recently outlined the rationale for a blend of proteins from animal and vegetal sources (Journal of the American College of Nutrition​, 2009, Vol. 28, No. 4, 464S-472S).

Concerns have been raised over excessive protein intakes, however, with some linking this to calcium wasting or extreme pressure on the kidneys. A position paper by the International Society of Sports Nutrition supported the intake of protein by exercising individuals, with recommendations of between 1.4 and 2 grams per kilograms of body weight per day (that’s 98 grams per day for a 70 kg person).

“When part of a balanced, nutrient-dense diet, protein intakes at this level are not detrimental to kidney function or bone metabolism in healthy, active persons,”​ states the position paper. “While it is possible for physically active individuals to obtain their daily protein requirements through a varied, regular diet, supplemental protein in various forms are a practical way of ensuring adequate and quality protein intake for athletes.”​ (Journal of the International Society of Sports Nutrition​, 2007, 4, 8)

Source: Clinical Nutrition
Published online ahead of print, doi: 10.1016/j.clnu.2010.06.012
“Differential metabolic effects of casein and soy protein meals on skeletal muscle in healthy volunteers”
Authors: Y.C. Luiking, M.P.K.J. Engelen, P.B. Soeters, Y. Boirie, N.E.P. Deutz

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