A study published in The Journal of Nutrition has shown that increasing physical activity through walking may be sufficient to increase the rate of making new muscle – muscle protein synthesis – in older women, regardless of whether dietary protein intake is increased beyond the recommended intake values.
Age-related loss of skeletal muscle mass and strength can increase the risk of premature death in older adults. The rate of muscle loss in older adults is influenced primarily by physical activity and dietary protein, both of which stimulate muscle protein synthesis. Therefore, optimizing dietary protein intake and physical activity may help improve muscle mass and functional integrity in older populations. Dairy as milk is a high-quality, nutrient-dense, cost-efficient protein source. Studies have demonstrated that whole milk may stimulate muscle protein synthesis to a greater extent than other foods equal in protein and energy. Whether whole milk enhances muscle protein synthesis rates to a greater degree than skim milk in older adults is unknown.
To better understand the effects of protein intake and physical activity on muscle protein synthesis, researcher Tanner Stokes working with Professor Stuart Phillips (McMaster University) and colleagues (McMaster University and Queens’s University), randomly assigned twenty-two older women to 1 of 3 dietary groups: whole milk, skim milk or an almond beverage. During phase 1 of the study, participants consumed a standardized diet (0.8 g protein per kilogram of body weight per day) and performed their habitual physical activity. During phase 2 of the study, participants continued to perform habitual physical activity but consumed an intervention diet consisting of the standardized diet plus twice-daily beverages of either whole milk, skim milk, or almond milk. Finally, during phase 3, the intervention diet was consumed, and physical activity was increased to 150% of habitual daily steps. Participants recorded their daily steps using a pedometer, and diets were personalized to meet each participant’s energy requirements and macronutrient distribution (% of total calories).
Daily muscle protein synthesis rates were not differentially affected by increased intake of whole milk, skim milk or almond milk to a standardized diet. However, increasing daily steps enhanced muscle protein synthesis independent of dietary protein consumption. This study demonstrated that increasing physical activity through walking was sufficient to increase daily muscle protein synthesis rates in older women, regardless of whether dietary protein intake is increased beyond the recommended intake of 0.8 g protein per kg of body weight.
Tanner Stokes, Yixue Mei, Freddie Seo, James McKendry, Chris McGlory, Stuart M Phillips, Dairy and Dairy Alternative Supplementation Increase Integrated Myofibrillar Protein Synthesis Rates, and Are Further Increased when Combined with Walking in Healthy Older Women, The Journal of Nutrition, Volume 152, Issue 1, January 2022, Pages 68–77, https://doi.org/10.1093/jn/nxab358.
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