New research shows that differences in protein synthesis between older and younger adults means that as we age, we must double our protein RDA to remain active
It is well known that we need to consume protein to enable our body to build and repair muscle. As we get older, the body becomes less efficient in this process at a time when fitness affects our quality of life and strong muscles can help protect our joints from osteoarthritis.
Research published in January in the American Journal of Physiology — Endocrinology and Metabolism suggests the amount of protein consumed by older adults affects the body’s net protein balance due to differences in the way they synthesise protein compared to younger adults.
The U.S. recommended dietary allowance (RDA) for protein is 0.8 g per kilogram of bodyweight per day. Previous research has shown that to encourage maximum protein synthesis, older adults need to eat at least 0.4 g of protein per kg of bodyweight at each meal, which is 1.2 g per kg of bodyweight per day.
Based on this new study looking at whole body as well as muscle protein synthesis, older adults can maximise their body’s muscle-building efficiency by eating at least 1.5 g of protein per kg of bodyweight per day.
The researchers, from the Center for Translational Research in Aging and Longevity, the Donald W. Reynolds Institute on Aging, and the University of Arkansas for Medical Sciences, measure whether protein intake that exceeds the protein RDA results in greater net protein balance in older adults. They also measure whether the timing of protein consumption impacts the net protein balance for the day.
The 20 healthy adult volunteers, 52 to 75 years old, were divided into four groups. One group consumed the protein RDA of 0.8 g/kg of bodyweight per day, evenly distributed across breakfast, lunch and dinner, another group consumed the protein RDA with 65% of the protein eaten at dinner, and two further groups consumed almost double the protein RDA (1.5 g/kg), one group with even and the other with uneven distribution. To reflect people’s normal eating habits, protein was consumed in mixed meals, where previous studies have used high-quality protein sources.
The researchers found the whole body net protein balance was greater with protein intake above the protein RDA (in the context of mixed meals), mainly due to higher rates of protein synthesis at whole body and muscle levels. Contrary to previous research on adults that found protein synthesis was increased by even distribution, this study on older adults found no clear effects of protein intake timing.
If we want to remain active well into old age, this study shows the key role of protein in building and maintaining the muscle mass required to keep us healthy.
First published on Science Nutshell February 9, 2015
References
I.-Y. Kim, S. Schutzler, A. Schrader, H. Spencer, P. Kortebein, N. E. P. Deutz, R. R. Wolfe, A. A. Ferrando. (2014). Quantity of dietary protein intake, but not pattern of intake, affects net protein balance primarily through differences in protein synthesis in older adults. AJP: Endocrinology and Metabolism, 308 (1), E21-E28. DOI: 10.1152/ajpendo.00382.2014
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