The Role of Soy in the Performance of Active and Athletic Americans
Optimal nutrition is imperative for physical activity, athletic performance, strength training, and recovery. In general, nutrient needs vary by individual, sport or activity, body composition, weight, and fitness or performance goals. Of course, an individual’s age, training status, and the intensity and duration of exercise should also be taken into account. Regardless of these variables, physically-active individuals should consume diets that follow the 2015 Dietary Guidelines for Americans and adjust intake to address specific calorie and protein needs.
Soyfoods provide essential fatty acids, dietary fiber, iron, and other nutrients. For recreational and non-elite athletes, little evidence exists to support protein intake greater than amounts recommended for the general population.1,2 But for elite athletes, the joint Position Statement by the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance suggests that protein needs range from 1.2-1.4 g per kg body weight/day for endurance athletes to 1.2-1.7 g/kg body weight/day for strength athletes.3 Although optimal protein intake levels for athletes are not totally clear, research suggests intake between 1.2 and 1.7 g/kg body weight would be adequate.1,4 The high quality of soy protein means that it is uniquely suited among plant proteins because it is an excellent source of all essential amino acids.
Along with adequate protein, athletes need adequate calorie and carbohydrate intakes to replenish glycogen stores and repair and build tissue. Moreover, selection of the right amount and type of fat is important to provide energy, essential fatty acids, and fat soluble vitamins without raising blood cholesterol.
Antioxidants in Soy
The antioxidants in soy are known to have a positive impact on antioxidant status and other aspects of health. Soy-based foods may improve an individual’s oxidative state by supplying antioxidants to the body, helping to protect against free radicals. Research has shown that antioxidants may play a role in preventing various chronic diseases associated with oxidative stress such as cancer, cardiovascular disease, and diabetes.5
Exercise can increase free radical production and oxidative stress, thus increasing lipid peroxides.6 Consumption of soy protein before moderate-intensity, weight-resistance exercise has been shown to decrease serum lipid peroxides post-exercise.6 In addition, antioxidant intake may improve antioxidant status in the body. In a study involving participants who followed a strength training protocol, after 9 weeks the group assigned to 33 g of soy protein daily experienced a favorable effect on radical scavenging capacities, positively affecting oxidative status, compared with the control and whey groups.7 Soy can be beneficial in an oxidative capacity, which may also be beneficial in relation to the muscle.
Soy in Muscle Growth and Recovery
Skeletal muscles are essential to coordination, balance, speed, and strength. Dietary protein provides both the essential amino acids and calories necessary to help build and repair muscles, organs, and tissues in the body. Through physical activity and daily body functions, muscles are constantly broken down into amino acids and new muscle proteins are being made. Consumption of protein is not directly responsible for building muscle, but protein does have an anabolic effect on muscle tissue. After resistance exercise, muscles are in a catabolic state and although carbohydrate intake following exercise will refuel glycogen stores and delay the rate at which muscle protein catabolizes, protein intake is very much needed for protein synthesis. The intake of complete protein is key to providing the necessary amino acids for muscle building and repair, and soy-based foods provide the high-quality protein necessary for protein synthesis.
Moreover, by combining soy with other proteins, such as whey and casein, an added benefit to supporting muscle growth and recovery may be achieved. Soy protein isolate, whey protein, and casein seem to have different amino acid absorption rates (whey protein is considered “fast,”8 casein is considered “slow“8 and soy protein isolate is more “intermediate”9). Because of this variability in absorption, the availability of amino acids in the blood is extended, and the absorption of these amino acids by muscle may increase. In summarizing the research and rationale for consuming protein blends, Paul concluded that phasing the release of amino acids into circulation may be associated with greater rates of skeletal muscle protein synthesis and increases in lean body mass.9
Many studies also have shown that soy protein, like other high-quality protein, can support increased muscle mass during resistance-type training.10-13 A 9-week study of young male bodybuilders supplemented with 33 g of soy or whey protein while strength training found a significant increase in lean body mass with either type of protein supplementation compared with the control group.7 Another study found a significant increase in lean mass in males aged 18 to 40 years who supplemented their diets with 50 g of protein, regardless of whether it was soy, whey, or a blend.14 Likewise, in postmenopausal women, adding 25 g of soy protein per day to a weight-training program significantly increased resting energy expenditure15 and muscle mass11,16 compared with a placebo group with no exercise or protein supplementation. Therefore, soy may be as effective as other forms of protein in increasing strength and improving body composition.17,18
Soy protein is highly digestible and is comparable to beef, milk, fish, and egg protein in terms of protein quality.19 The internationally accepted standard method for assessing protein quality is the Protein Digestibility Corrected Amino Acid Score (PDCAAS). Soy protein has a PDCAAS of 1.00.20 Haub and colleagues compared the effect of beef versus soy-based textured vegetable protein during resistance training in older men, and found similar improvements in strength in both the beef and soy groups. The muscle area of the vastus lateralis, the largest part of the quadriceps, increased in both groups.17 A high-protein diet has been shown to improve body composition in overweight and obese people by enabling the loss of fat without significant loss of fat-free tissue.16 By consuming soy-based foods as a source of protein, athletes can keep intake of cholesterol and saturated fat to a minimum.
A High-Quality, Heart-Healthy Protein
Cardiovascular disease (CVD) risk factors are a concern among some elite athletes, especially large professional football players. In a cross-sectional study, the prevalence of CVD among veteran football players was compared men of the same age in the general U.S. population. Hypertension and prehypertension were more prevalent among the National Football League (NFL) players with a larger body mass index (BMI). Large BMIs in either group were associated with increased levels of low-density lipoprotein cholesterol, triglycerides, and fasting glucose, and decreased levels of high-density lipoprotein cholesterol. Both groups had similar occurrences of dyslipidemia.21
Based on a review of more than 50 studies that found soy protein reduced blood cholesterol about 3% to 5%,22 the U.S. Food and Drug Administration (FDA) authorized a health claim for products containing at least 6.25 g of soy protein per serving. The claim recognizes that 25 g of soy protein a day (or four servings of foods with 6.25 g of soy protein), as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. Since 1999, numerous meta-analyses and significant examination of peer-reviewed data have appeared that support the initial FDA health claim.23 The cholesterol-lowering effect of soy protein may be enhanced to a 13% to 14% reduction when combined with other foods such as plant sterols, viscous fibers, and nuts.24
Although some reports in the press have cautioned use of soy protein, research over the past 20 years involving both men and women has not found negative impacts on breast cancer, testosterone, or semen quality, motility, or quantity. A study by Kalman and colleagues found that after 12 weeks of supplementation with 50 g soy protein, no significant differences occurred in levels of total and free testosterone or sex hormone binding globulin (SHBG).14 An extensive review found no effects of soy protein or isoflavones intake on testosterone or SHBG in men.25 The National Cancer Institute and the American Cancer Society recommend that breast cancer survivors can safely consume moderate amounts of soyfoods–anywhere from a few servings a week to three servings a day.26,27 The evidence has shown that intake of soyfoods is not associated with breast cancer risk and may actually provide protective effects against breast cancer,28 especially if consumed during childhood and adolescence.29
Re-Set the Plate with Soyfoods
Soyfoods can make great training meals for individuals of all ages and levels. MyPlate recognizes soy-based meat alternatives and tofu in the protein food group; fortified soymilk in the dairy food group; and edamame and soybeans in the vegetable food group. With the variety of soyfoods products available, soyfoods can be incorporated into any breakfast, lunch, dinner, or snack plate.
- Consumers can try soy burgers or marinated tofu for lunch or dinner; steamed edamame for on-the-go eating or added to a favorite stir fry; and soy yogurts, whole soy nutrition bars, and soy nuts with dried fruit make great snacks.
- Soynut butter provides a nutritious alternative to peanut butter for pre- or post-workout fuel.
- Fortified soymilk, over cereal or in a smoothie, packs protein into the diet after a workout. For added benefits, soymilk or soy protein can be blended with other protein powders.
Although soyfoods are generally low in calories, athletes and fitness buffs should always adjust portion sizes to caloric needs. Soyfoods are simple, healthful choices to help anyone stay fueled, meet performance goals, and maintain a healthy heart.
- Tarnopolsy M. Protein requirements for endurance athletes. Nutrition. 2004;20:662-668.
- Phillips SM. Protein requirements and supplementation in strength sports. Nutrition. 2004;20:689-695.
- Rodriguez NR, DiMarco NM, Langley S. American Dietetic Association; Dietitians of Canada; American College of Sports Medicine. Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. J Am Diet Assoc. 2009;109:509-527.
- Phillips SM, Moore DR, Tang JE. A critical examination of dietary protein requirements, benefits, and excesses in athletes. Int J Sport Nutr Exerc Metab. 2007;17(suppl):S58-S76.
- Wilcox JK, Ash SL, Catignani GL. Antioxidants and prevention of chronic disease. Crit Rev Food Sci Nutr. 2004;44:275-295.
- Hill S, Box W, DiSilvestro RA. Moderate intensity resistance exercise, plus or minus soy intake: effects on serum lipid peroxides in young adult males. Int J Sport Nutr Exerc Metab. 2004;14:125-132.
- Brown EC, DiSilvestro RA, Babaknia A, et al. Soy versus whey protein bars: effects on exercise training impact on lean body mass and antioxidant status. Nutr J. 2004;8:22-26.
- Boirie Y, Dangin M, Gachon P, et al. Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci U S A. 1997;94:14930–14935.
- Paul GL. The rationale for consuming protein blends in sports nutrition. J Am Coll Nutr. 2009;28(suppl):S464-S472.
- Candow DG, Burke NC, Smith-Palmer T, et al. Effect of whey and soy protein supplementation combined with resistance training in young adults. Int J Sport Nutr Exerc Metab. 2006;16:233-244.
- Dr?gan I, Stroescu V, Stoian I, et al. Studies regarding the efficiency of Supro isolated soy protein in Olympic athletes. Rev Roum Physiol. 1992;29:63-70.
- Wilkinson SB, Tarnopolsky MA, Macdonald MJ, et al. Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. Am J Clin Nutr. 2007;85:1031-1040.
- Hartman JW, Tang JE, Wilkinson SB, et al. Consumption of fat-free fluid milk after resistance exercise promotes greater lean mass accretion than does consumption of soy or carbohydrate in young, novice, male weightlifters. Am J Clin Nutr. 2007;86:373-381.
- Kalman D, Feldman S, Martinez M, et al. Effect of protein source and resistance training on body composition and sex hormones. J Int Soc Sports Nutr. 2007;4:4-11.
- Trevisan MC, Souza JM, Marucci Mde F. Influence of soy protein intake and weight training on the resting energy expenditure of postmenopausal women. Rev Assoc Med Bras. 2010;56:572-578.
- Maesta N, Nahas EA, Nahas-Neto J, et al. Effects of soy protein and resistance exercise on body composition and blood lipids in postmenopausal women. Maturitas. 2007;56:350-358.
- Haub MD, Wells AM, Tarnopolsky MA, et al. Effect of protein source on resistive-training-induced changes in body composition and muscle size in older men. Am J Clin Nutr. 2002;76:511-517.
- Deibert P, Solleder F, König D, et al. Soy protein based supplementation supports metabolic effects of resistance training in previously untrained middle aged males. Aging Male. 2011;14:273-279.
- Hughes GJ, Ryan DJ, Mukherjea R, et al. Protein digestibility-corrected amino acid scores (PDCAAS) for soy protein isolates and concentrate: criteria for evaluation. J Agric Food Chem. 2011;59:12707-12712.
- Food and Agricultural Organization/World Health Organization. Protein Quality Evaluation: Report of the Joint FAO/WHO Expert Consultation, FAO Food and Nutrition Paper No. 51. FAO, Rome, Italy, 1991.
- Tucker AM, Vogel RA, Lincoln AE, et al. Prevalence of cardiovascular disease risk factors among National Football League players. JAMA. 2009;301:2111-2119.
- United States Food and Drug Administration. Federal Register 64 FR 57699 October 26, 1999-food labeling: health claims; soy protein and coronary heart disease; final rule. Page 57699-57733. Available at http://www.fda.gov/food/labelingnutrition/labelclaims/healthclaimsmeetingsignificantscientificagreementssa/ucm074740.htm. Accessed December 28, 2011.
- Anderson JA, Bush HM. Soy protein effects on serum lipoproteins: a quality assessment and meta-analysis of randomized, controlled studies J Am Col of Nutr. 2011;30:79–91.
- Jenkins D, Jones P, Lamarche B, et al. Effect of a dietary portfolio of cholesterol-lowering foods given at 2 levels of intensity of dietary advice on serum lipids in hyperlipidemia. JAMA. 2011;306:831-839.
- Hamilton-Reeves JM, Vazquez G, Duval SJ, et al. Clinical studies show no effects of soy proteins or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil Steril. 2010;94:997-1007.
- American Institute of Cancer Research. Foods that fight cancer. Available at: http://www.aicr.org/foods-that-fight-cancer/foodsthatfightcancer_soy.html. Accessed January 9, 2012.
- American Cancer Society. Nutrition and physical activity during and after cancer treatment: answers to common questions. Available at: http://www.cancer.org/Treatment/SurvivorshipDuringandAfterTreatment/NutritionforPeoplewithCancer/nutrition-and-physical-activity-during-and-after-cancer-treatment-answers-to-common-questions?sitearea=MH. Accessed January 9, 2012.
- Wu AH, Yu MC, Tseng C-C, et al. Epidemiology of soy exposures and breast cancer risk. Br J Cancer. 2008;98:9-14.
- Shu, X, Zheng, Y, Cai H, et al. Soy food intake and breast cancer survival. JAMA. 2009;302:2437-2443.