Introduction:
Soy protein comes from soybeans and offers multiple health benefits. Benefits of soy protein include improved cardiovascular status, potentially improved survival for certain cancers, and more options for food variety. Consumption of soy protein has been found to reduce concentrations of total cholesterol and LDL. Soy protein has also been found to improve lean muscle after exercise.
Soy protein and cholesterol:
FDA statement on soy protein: The Food and Drug Administration (FDA) has approved a statement on food labels that soy protein may reduce the risk of coronary artery disease by lowering cholesterol levels when included in a diet low in saturated fat and cholesterol (1).
Soy protein, LDL, HDL, and triglycerides:
A double-blind randomized parallel trial of 156 healthy men and women with LDL cholesterol levels between 3.62 mmol/L (140 mg/dL) and 5.17 mmol/L (200 mg/dL) were studied to identify the link between isoflavones together with soy protein or soy protein itself and cholesterol. Participants were randomly assigned to one of 5 daily diets: 25 g of casein [for isoflavone-free comparison] or 25 g of isolated soy protein containing 3, 27, 37, or 62 mg of isoflavones. Crouse et al found that subjects on a National Cholesterol Education Program Step I diet plus taking isolated soy protein with 62 mg isoflavones per 25 grams for 9 weeks lowered total cholesterol by about 4% and LDL cholesterol by about 6% compared to casein. A greater benefit was seen in subjects with higher LDL levels. The soy protein did not affect plasma concentrations of triglycerides or HDL cholesterol. (2)
Soy protein, cholesterol, and resistance training:
Overweight hypercholesterolemic men with serum cholesterol >200 mg/dl were randomly divided into 3 groups (placebo (n = 9), soy (n = 9) or whey (n = 10) supplementation) and participated in supervised resistance training for 12 weeks. Total serum cholesterol decreased significantly (average=5.8%) for all groups (mean reduction = 12.6 mg/dL), with no differences among groups. Specifically, total cholesterol reduction was 10.4 mg/dL for placebo, 11.2 mg/dL for soy, and 15.9 mg/dL for whey. Participation in a 12 week resistance exercise training program significantly reduced serum cholesterol, increased strength, and improved body composition in overweight, hypercholesterolemic men. Whey protein improved cholesterol a small amount more than placebo or soy protein but additional added benefit from protein (soy or whey) supplementation was not otherwise seen in this study group. (3)
Soy protein and resistance training:
Researchers studied whey protein or soy protein in combination with resistance exercise in 27 untrained healthy subjects (18 female, 9 male) age 18 to 35 years. Participants were randomly assigned (double blind) to supplement with whey protein, soy protein or placebo for 6 weeks. Lean tissue mass, strength, and an indicator of myofibrillar protein catabolism were measured before and after training. Results showed that both soy and whey protein supplementation during resistance training increased lean tissue mass and strength over placebo with equal calorie diet and resistance training (P < 0.05). (4)
Soy protein and breast cancer:
Research suggests that soy lowers the risk of breast cancer recurrence and increases the chances for survival in women. Findings from the Shanghai Breast Cancer Survival Study of 5,033 Chinese women diagnosed with breast cancer found a high soy diet (compared to a diet with little or no soy) lowered the risk of breast cancer death and recurrence by 29% and 32%, respectively. Among women with high soy intake (top 25%) 4-year mortality was 7.4% compared to 10.3% for low soy intake (bottom 25%). Recurrence rates were 8.0% for high soy intake and 11.2% for low soy intake. (5)
Assessment and Plan: Soy Protein
- Benefits of soy protein include improved cardiovascular status, potentially improved survival for breast cancer, reduction of total cholesterol/LDL, and enhancement of lean muscle mass with training.
- Soy protein and cholesterol: The Food and Drug Administration (FDA) has approved a statement on food labels that soy protein may reduce the risk of coronary artery disease by lowering cholesterol levels when included in a diet low in saturated fat and cholesterol (1).
- Subjects on a National Cholesterol Education Program Step I diet plus taking isolated soy protein with 62 mg isoflavones per 25 grams for 9 weeks lowered total cholesterol by about 4% and LDL cholesterol by about 6% compared to casein. A greater benefit was seen in subjects with higher LDL levels. The soy protein did not affect plasma concentrations of triglycerides or HDL cholesterol. (2)
- Soy protein, whey protein, resistance training, and cholesterol: Whey protein may have a greater benefit than soy protein in controlling cholesterol. A study showed that overweight men with hyperlipidemia performing resistance training for 12 weeks showed total cholesterol reductions of 10.4 mg/dL for placebo, 11.2 mg/dL for soy protein, and 15.9 mg/dL for whey protein (3).
- Soy protein and resistance training: Researchers found that both soy and whey protein supplementation during resistance training increased lean tissue mass and strength over placebo with equal calorie diet and resistance training (4).
- Soy protein and breast cancer: Findings from the Shanghai Breast Cancer Survival Study of 5,033 Chinese women diagnosed with breast cancer found (5):
- High soy diet compared to a diet with little or no soy lowered the risk of breast cancer death and recurrence by 29% and 32%, respectively.
- 4-year mortality was 7.4% for high soy intake vs. 10.3% for low soy intake.
- Recurrence rates of breast cancer were 8.0% for high soy intake and 11.2% for low soy intake.
References:
1.Food labeling: health claims; soy protein and coronary heart disease. Food and Drug Administration, HHS. Final rule. Fed Regist.1999 Oct 26;64(206):57700-33. http://www.ncbi.nlm.nih.gov/pubmed/11010706
2.Crouse JR III, Morgan T, Terry JG, Ellis J, Vitolins M, Burke GL. A randomized trial comparing the effect of casein with that of soy protein containing varying amounts of isoflavones on plasma concentrations of lipids and lipoproteins. Arch Intern Med 1999;159:2070–6. http://archinte.jamanetwork.com/article.aspx?articleid=485126
3.Denysschen CA, Burton HW, Horvath PJ, Leddy JJ, Browne RW. Resistance training with soy vs whey protein supplements in hyperlipidemic males. J Int Soc Sports Nutr. 2009 Mar 11;6:8. http://www.ncbi.nlm.nih.gov/pubmed/19284589
4.Candow DG, Burke NC, Smith-Palmer T, Burke DG, Candow DG, Burke NC, Burke DG. Effect of whey and soy protein supplementation combined with resistance training in young adults. Int J Sport Nutr Exerc Metab 2006 June; 16(3):233-244. http://www.ncbi.nlm.nih.gov/pubmed/16948480
5.Shu XO, Zheng Y, Cai H, et al. Soy food intake and breast cancer survival. JAMA. 302(22):2437-43, 2009. http://www.ncbi.nlm.nih.gov/pubmed/19996398