Meta-analyses of the clinical data consistently show that soy protein lowers circulating LDL-cholesterol (LDL-C) levels. The most recent meta-analysis demonstrating this was published in 2015, while the first appeared in 1995. Four years later, after conducting its own analysis of the literature, the U.S. Food and Drug Administration (FDA) authorized a health claim for soy protein and reduced risk of coronary heart disease. Since 1999, similar claims have been approved in 11 other countries; the most recent being Canada in 2015.


However, the debate over soy’s benefits has raised the question: “Is soy bad for you?” In December 2007, the FDA indicated its intention to reevaluate evidence in support of the soy protein health claim. On October 31, 2017, the FDA proposed revoking the existing heart health claim. The current unqualified claim indicates that rigorous scientific agreement has been met regarding the cholesterol lowering effects of soy protein. If revoked, a qualified claim which requires less scientific consensus could replace it. 

It isn’t entirely clear why the FDA revisited the claim, though a 2006 science advisory from the American Heart Association (AHA) questioning the hypocholesterolemia properties of soy protein isolate may have been a factor.¹⁴ The AHA found only about a 3% LDL-C reduction, however there was never actually any meta-data conducted for this analysis. When a similar analysis was done four years later, Jenkins¹ found that soy protein lowered LDL-C by 4.3%, similar to that of soluble fiber, which also has an unqualified health claim. The 4.3% reduction noted by Jenkins is much lower than the initial estimates reported by Anderson in 1995,¹¹ but Jenkins’ findings still support moderate benefit. 

The FDA cited that the inconsistency of the data was the reason for revoking the existing claim, however slight inconsistencies are to be expected since the clinical topic is understudied. This fact is true even for health claims like the effects of sodium on blood pressure,^16,17 and calcium on bone mineral density.^18,19 Nevertheless, reducing the intake of sodium is routinely recommended by health professionals as a means of reducing the risk of heart disease and increasing calcium intake as a means of preventing osteoporosis.

The FDA found that only 19 of 46 studies showed soy protein statistically significantly lowered LDL-C. However, in nine of those studies, participants consumed less than 25 g of soybean isolate per day, which is below the FDA’s threshold required for making the claim. Because of this, the results of these studies are of questionable relevance. Critics also argue that the FDA’s binary “supportive vs. non-supportive” approach ignores the nuances revealed in meta-analysis.


Regardless of the FDA’s final decision, the question “Is soy bad for you?” needs a balanced answer. From a practical standpoint, adding foods with soy protein isolate or whole soy foods to the diet can assist in decreasing risk of coronary heart disease (CHD). The reduction of cholesterol and CHD risk requires adopting a comprehensive dietary approach. At the very least, soybeans provide high quality protein²⁰ that considerable evidence suggests lowers cholesterol. Soybean oil is also known to contain essential fatty acids that support cardiovascular health²¹ making it one of the dietary approaches that have led to reductions in cholesterol.^22-27

REFERENCES

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2. Zhan S, Ho SC. Meta-analysis of the effects of soy protein containing isoflavones on the lipid profile. Am J Clin Nutr. 2005;81:397-408.

3. Harland JI, Haffner TA. Systematic review, meta-analysis and regression of randomised controlled trials reporting an association between an intake of circa 25 g soya protein per day and blood cholesterol. Atherosclerosis. 2008;200:13-27.

4. Anderson JW, Bush HM. Soy protein effects on serum lipoproteins: A quality assessment and meta-analysis of randomized, controlled studies. J Am Coll Nutr. 2011;30:79-91.

5. Benkhedda K, Boudrault C, Sinclair SE, Marles RJ, Xiao CW, Underhill L. Food Risk Analysis Communication. Issued By Health Canada’s Food Directorate. Health Canada’s Proposal to Accept a Health Claim about Soy Products and Cholesterol Lowering. Int Food Risk Anal J. 2014;4:22 | doi: 10.5772/59411.

6. Tokede OA, Onabanjo TA, Yansane A, Gaziano JM, Djousse L. Soya products and serum lipids: a meta-analysis of randomised controlled trials. Br J Nutr. 2015;114:831-43.

7. Yang B, Chen Y, Xu T, et al. Systematic review and meta-analysis of soy products consumption in patients with type 2 diabetes mellitus. Asia Pacific journal of clinical nutrition. 2011;20:593-602.

8. Hooper L, Kroon PA, Rimm EB, et al. Flavonoids, flavonoid-rich foods, and cardiovascular risk: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2008;88:38-50.

9. Reynolds K, Chin A, Lees KA, Nguyen A, Bujnowski D, He J. A meta-analysis of the effect of soy protein supplementation on serum lipids. Am J Cardiol. 2006;98:633-40.

10. Weggemans RM, Trautwein EA. Relation between soy-associated isoflavones and LDL and HDL cholesterol concentrations in humans: a meta-analysis. Eur J Clin Nutr. 2003;57:940-6.

11. Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soy protein intake on serum lipids. N Engl J Med. 1995;333:276-82.

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13. Summary of Health Canada's Assessment of a Health Claim about Soy Protein and Cholesterol Lowering. Bureau of Nutritional Sciences Food Directorate Health Products and Food Branch. https://www.canada.ca/en/health-canada/services/food-nutrition/food-labelling/healthclaims/assessments/summary-assessment-health-claim-about-protein-cholesterollowering.html.

14. Sacks FM, Lichtenstein A, Van Horn L, Harris W, Kris-Etherton P, Winston M. Soy protein, isoflavones, and cardiovascular health: an American Heart Association Science Advisory for professionals from the Nutrition Committee. Circulation. 2006;113:1034-44.

15. Messina M. Potential public health implications of the hypocholesterolemic effects of soy protein. Nutr. 2003;19:280-1.

16. Graudal NA, Hubeck-Graudal T, Jurgens G. Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride. The Cochrane database of systematic reviews. 2011:CD004022.

17. Lelong H, Galan P, Kesse-Guyot E, Fezeu L, Hercberg S, Blacher J. Relationship between nutrition and blood pressure: a cross-sectional analysis from the NutriNet-Sante Study, a French webbased cohort study. Am J Hypertens. 2015;28:362-71.

18. Lanou AJ, Berkow SE, Barnard ND. Calcium, dairy products, and bone health in children and young adults: a reevaluation of the evidence. Pediatrics. 2005;115:736-43.

19. Tai V, Leung W, Grey A, Reid IR, Bolland MJ. Calcium intake and bone mineral density: systematic review and meta-analysis. BMJ. 2015;351:h4183.

20. Hughes GJ, Ryan DJ, Mukherjea R, Schasteen CS. Protein digestibility-corrected amino acid scores (PDCAAS) for soy protein isolates and concentrate: Criteria for evaluation. J Agric Food Chem. 2011;59:12707-12.

21. Petersen KS, Maki KC, Calder PC, Belury MA, Messina M, Kirkpatrick CF, Harris WS. Perspective on the health effects of unsaturated fatty acids and commonly consumed plant oils high in unsaturated fat. Br J Nutr. 2024 Oct 28;132(8):1039-1050. doi: 10.1017/S0007114524002459. Epub 2024 Oct 30. PMID: 39475012; PMCID: PMC11600290.

22. Jenkins DJ, Jones PJ, Frohlich J, et al. The effect of a dietary portfolio compared to a DASH-type diet on blood pressure. Nutrition, metabolism, and cardiovascular diseases: NMCD. 2015;25:1132-9.

23. Jenkins DJ, Jones PJ, 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: a randomized controlled trial. JAMA. 2011;306:831-9.

24. Jenkins DJ, Kendall CW, Faulkner D, et al. A dietary portfolio approach to cholesterol reduction: combined effects of plant sterols, vegetable proteins, and viscous fibers in hypercholesterolemia. Metabolism. 2002;51:1596-604.

25. Jenkins DJ, Kendall CW, Faulkner DA, et al. Long-term effects of a plant-based dietary portfolio of cholesterol-lowering foods on blood pressure. Eur J Clin Nutr. 2008;62:781-8.

26. Jenkins DJ, Kendall CW, Marchie A, et al. Effects of a dietary portfolio of cholesterol-lowering foods vs lovastatin on serum lipids and C-reactive protein. JAMA. 2003;290:502-10.

27. Jenkins DJ, Kendall CW, Marchie A, et al. Direct comparison of a dietary portfolio of cholesterollowering foods with a statin in hypercholesterolemic participants. Am J Clin Nutr. 2005;81:380-7.