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Press Release from the Journal of Nutrition:
New study finds meal distribution of protein may be important for adult muscle mass
Adequate amounts of dietary protein are needed throughout the lifespan, and requirements depend on a variety of factors including age, sex, physiologic state (e.g., pregnancy), and the amount of muscle mass a person has. However, not all proteins are similar in terms of their quality, with animal-source proteins having higher “values” than plant-source proteins. This is because animal-source foods, such as meat, dairy, and eggs, contain all the needed amino acids in the appropriate ratios, whereas their plant-source counterparts, such as wheat and soy, do not. As such, lower amounts of the former – as compared to the latter – may be sufficient to support optimal health. In addition, some evidence suggests that timing of protein intake throughout the day might impact its ability to be incorporated into muscles. Consequently, scientists continue to study protein quality, quantity, and daily distribution in their quest to understand better optimal protein intake throughout life. Helping to explore some of these research questions, Drs. Layne Norton and Donald Layman, both at the University of Illinois at Urbana-Champaign, conducted 2 studies in which adult rats were fed various types and timing of dietary protein. Their results, which are summarized below, can be found in the February 2017 issue of The Journal of Nutrition.
In study 1, rats were randomly assigned to consume experimental diets providing protein obtained from either dairy whey, egg white, soy, or wheat gluten. All diet types provided 16% of their calories from protein, but differed in their amino acid profiles. For instance, leucine contents were ~11, 9, 8, or 7%, respectively. Rats were trained to consume 3 meals per day, each one providing 4-6 grams of food and mimicking typical American eating habits. In study 2, all animals were fed a high-quality, whey-based diet, but some were provided with similar amounts of protein in each meal (“balanced” distribution) while others were given increasing amounts of protein from morning until evening (“unbalanced” distribution). Outcomes such as body composition and muscle protein synthesis were monitored in both studies.
The researchers found that consumption of whey or egg proteins increased muscle synthesis more than consumption of wheat or soy, and animals fed the wheat-based diet had 20% more body fat than those consuming soy, egg, or whey. In study 2, animals consuming the “balanced” distribution of protein over the course of the day had greater muscle mass than those consuming the “unbalanced” distribution. Collective results from these studies suggest that both meal distribution and amino acid content of the diet can influence muscle protein synthesis and long-term changes in muscle mass. Of course, follow-up studies in men and women will be required to determine if these effects are also seen in humans.