Few men will ever come close to matching the muscular physique of Arnold Schwarzenegger and few women will ever achieve the toned body type of Olympic gold medal gymnast Aly Raisman. But there is good reason to aim in that direction. Muscles not only look good, but engaging in exercises that increase muscle mass can lead to a healthier metabolism, reduce risk of chronic disease, and help to maintain a higher quality of life. Diet alone may not get you where you want to be, but the right diet can help you on your way. And several recent studies highlight the utility of making soy part of that diet.
The statistics are sobering. Muscle mass decreases approximately 3–8% per decade after the age of 30 and this rate of decline is even higher after the age of 60. The loss in strength as we age can be even greater. This loss has significant consequences for our overall health and well-being. Advanced aging is associated with an increased risk of sarcopenia which is characterized by a progressive loss of skeletal muscle mass and strength and/or physical performance. However, studies consistently show that by engaging in resistance exercise training (RET), muscle mass and strength can be increased, even in the elderly.
While RET is the key to building muscle and strength, diet, and in particular protein, plays a key role as well. There is universal agreement that people engaged in RET require more protein than the recommended dietary allowance (RDA). Estimates range from 50% to 250% more. Most Americans consume more protein that the RDA, so getting the additional amount of protein needed by individuals newly engaged in RET may not as much of a challenge as it may seem. That may be less true for older folks because they tend to consume less protein and may need more than younger folks to build muscle.
While there is general agreement about the need for more protein, there has been quite a bit of debate about whether certain types of proteins are more conducive for building muscle than others. For a long time, whey protein was viewed as the gold standard in this regard. That would be obvious to anyone shopping around for protein powders online or in stores. Whey represents about 20% of milk protein, casein being the other 80%.
Whey is high in leucine, an amino acid that is heavily involved in triggering muscle protein synthesis. Nevertheless, in 2018, a statistical analysis of 9 clinical studies concluded that soy protein led to similar gains in muscle mass and strength as whey protein and other types of animal protein. Two newly published studies further our understanding of the benefits of soy for building muscle.[11,12]
One of these studies involved two groups of younger men, one group was comprised of vegans (vegans do not eat any animal protein) and the other group of omnivores. Both groups engaged in RET twice per week for 12 weeks. The vegans consumed a daily soy protein supplement, and the omnivores consumed a whey protein supplement every day. The study was designed so that each group of men would consume about 0.7 grams of protein per pound of body weight, or about twice the protein RDA. At study completion, both groups experienced gains in strength and muscle mass, but there were no differences between groups. This novel study design shows that even in the context of a completely plant-based diet, soy protein supplementation can lead to gains in performance.
The second study involved 4 groups of older Chinese men and women who had low lean body (muscle) mass. At study enrollment, protein intake was slightly above the protein RDA. One group continued to consume their usual diet, the other groups consumed their usual diet for 6 months but in addition consumed daily 16 grams of soy protein, or the same amount of whey protein or a blend of whey and soy.
At study conclusion, in comparison to the group that consumed their usual diet, all three groups experienced gains in muscle mass and strength, but there were no differences among the 3 protein-supplemented groups. This study shows that even without RET, adding more protein can help to build strength and muscle mass, and that soy performs as well as whey. Furthermore, just 16 grams of additional protein was sufficient to see pronounced benefits. Depending upon the soyfood in question, those 16 grams can be obtained from either one or two servings of soyfoods. Given the wide array of soyfoods, adding one or two servings of soy daily to diet can easily be done.
 McPherron AC, Guo T, Bond ND, et al. Increasing muscle mass to improve metabolism. Adipocyte. 2013;2:92-8.
 McLeod JC, Stokes T, Phillips SM. Resistance Exercise Training as a Primary Countermeasure to Age-Related Chronic Disease. Front Physiol. 2019;10:645.
 Liao CD, Chen HC, Huang SW, et al. The role of muscle mass gain following protein supplementation plus exercise therapy in older adults with sarcopenia and frailty fisks: A systematic review and meta-regression analysis of randomized trials. Nutrients. 2019;11.
 Volpi E, Nazemi R, Fujita S. Muscle tissue changes with aging. Current opinion in clinical nutrition and metabolic care. 2004;7:405-10.
 Phillips SM, Martinson W. Nutrient-rich, high-quality, protein-containing dairy foods in combination with exercise in aging persons to mitigate sarcopenia. Nutr Rev. 2019;77:216-29.
 Chen LK, Woo J, Assantachai P, et al. Asian working group for sarcopenia: 2019 consensus update on sarcopenia diagnosis and treatment. J Am Med Dir Assoc. 2020;21:300-7 e2.
 Fragala MS, Cadore EL, Dorgo S, et al. Resistance training for older adults: Position statement from the National Strength and Conditioning Association. Journal of strength and conditioning research. 2019;33:2019-52.
 Berryman CE, Lieberman HR, Fulgoni VL, 3rd, et al. Protein intake trends and conformity with the Dietary Reference Intakes in the United States: analysis of the National Health and Nutrition Examination Survey, 2001-2014. Am J Clin Nutr. 2018;108:405-13.
 Devries MC, Phillips SM. Supplemental protein in support of muscle mass and health: advantage whey. J Food Sci. 2015;80 Suppl 1:A8-A15.
 Messina M, Lynch H, Dickinson JM, et al. No difference between the effects of supplementing with soy protein versus animal protein on gains in muscle mass and strength in response to resistance exercise. International journal of sport nutrition and exercise metabolism. 2018;28:674-85.
 Hevia-Larrain V, Gualano B, Longobardi I, et al. High-protein plant-based diet versus a protein-matched omnivorous diet to support resistance training adaptations: A comparison between habitual vegans and omnivores. Sports Med. 2021.
 Li C, Meng H, Wu S, et al. Daily supplementation with whey, soy, or whey-soy blended protein for 6 months maintained lean muscle mass and physical performance in older adults with low lean mass. Journal of the Academy of Nutrition and Dietetics. 2021.