The cholesterol-lowering effect of soy protein is well established,1-8 but there is also intriguing evidence that independent of cholesterol, soy favorably affects coronary heart disease (CHD) risk factors.
CHD is the leading cause of mortality among Americans according to newly published data by He et al.9 It accounts for about one out of every five deaths. CHD remains the number one killer even though blood cholesterol levels have come down dramatically over the past 20 years. Over this period, mean serum total cholesterol levels decreased from 203.3 mg/dL to 188.5 mg/dL.10 Does this mean elevated cholesterol isn’t a major CHD risk factor? Of course not, but it does mean that it is only one among many such factors.
In 2020, projections are that of the 3.3 million deaths in the U.S., 690,882 were due to CHD (20.6%). Followed closely by cancer, which is thought to be responsible for 598,932 deaths (17.8%). For year 2020, it is worth mentioning that 345,323 Americans died of COVID-19, so there is a large jump in total deaths compared to recent years.
The good news is that cholesterol levels have come down, as has the prevalence of smoking, although 18.1% of Americans still smoke.10 Depending on age and gender, people who smoke are anywhere from two to four times more likely to die from CHD.11 In contrast to smoking and cholesterol, where improvements were noted, from 1999-2000 to 2017-2018, age- and sex-adjusted mean body mass index increased from 28.0 to 29.8. There are several dietary hypotheses about the increasing prevalence of overweight and obesity,12 but it isn’t clear that any particular dietary approach aids in weight loss more than another.13 However, if higher protein diets aid in weight loss, as some but not all evidence indicates,14 then the higher protein content of soybeans compared to other legumes is notable.15
Another risk factor examined by He et al. is blood pressure.10 Mean systolic blood pressure decreased from 123.5mmHg in 1999-2000 to 120.5mmHg in 2009-2010, then increased to 122.8mmHg in 2017-2018.10 So, what is known about the effect of soy on blood pressure?
Several meta-analyses of clinical studies have examined the effects of soy on this outcome. For example, in 2011, Dong et al.16 found that soy protein lowered both systolic blood pressure (SBP) and diastolic blood pressure (DBP) in both normotensive and hypertensive individuals, although the effect was greater in the latter. One year later, Liu et al.17 found that soy isoflavones lowered blood pressure in hypertensive subjects, but not in normotensive subjects. In 2017, Kou et al.18 found that both soy protein and isoflavones lowered blood pressure in postmenopausal women, but only in response to an intake of at least 25g/d soy protein or at least 100mg/d isoflavones. Also, Mosallanezhad et al.19 found that soy significantly lowered SBP and DBP; however, subgroup analysis showed a reduction in both SBP and DBP only in younger participants with lower baseline DBP and intervention durations of <16 weeks. Overall, there is suggestive evidence that one or more components of soy lowers blood pressure, but it would be premature to definitively conclude this is the case.
Finally, mean hemoglobin A1c increased from 5.4% to 5.7% between 1999-2000 and 2017-2018. 10 In 2021, Mohammadifard et al.20 found that in patients with the metabolic syndrome soy products lowered fasting blood sugar and insulin levels and decreased insulin resistance. Also, in 2021, Asbaghi et al.21 found in patients with diabetes, there was a reduction in fasting blood glucose levels but only in individuals with elevated fasting blood glucose levels at baseline and who consumed more than 30g/d soy protein. These two analyses suggest that soy might help control A1c levels.
In conclusion, there is intriguing evidence that soy consumption favorably affects multiple risk factors for CHD, the leading cause of death among Americans.
- Jenkins DJ, Mirrahimi A, Srichaikul K, Berryman CE, Wang L, Carleton A, Abdulnour S, Sievenpiper JL, Kendall CW, Kris-Etherton PM. Soy protein reduces serum cholesterol by both intrinsic and food displacement mechanisms. J Nutr 2010;140:2302S-11S.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Blanco Mejia S, Messina M, Li SS, Viguiliouk E, Chiavaroli L, Khan TA, Srichaikul K, Mirrahimi A, Sievenpiper JL, Kris-Etherton P, et al. A meta-analysis of 46 studies identified by the FDA demonstrates that soy protein decreases circulating LDL and total cholesterol concentrations in adults. J Nutr 2019;149:968-81.
- Ahmad FB, Anderson RN. The leading causes of death in the US for 2020. JAMA 2021;325:1829-30.
- He J, Zhu Z, Bundy JD, Dorans KS, Chen J, Hamm LL. Trends in cardiovascular risk factors in US adults by race and ethnicity and socioeconomic status, 1999-2018. JAMA 2021;326:1286-98.
- Capewell S, Ford ES, Croft JB, Critchley JA, Greenlund KJ, Labarthe DR. Cardiovascular risk factor trends and potential for reducing coronary heart disease mortality in the United States of America. Bull World Health Organ 2010;88:120-30.
- Ludwig DS, Aronne LJ, Astrup A, de Cabo R, Cantley LC, Friedman MI, Heymsfield SB, Johnson JD, King JC, Krauss RM, et al. The carbohydrate-insulin model: a physiological perspective on the obesity pandemic. Am J Clin Nutr 2021.
- Gardner CD, Trepanowski JF, Del Gobbo LC, Hauser ME, Rigdon J, Ioannidis JPA, Desai M, King AC. Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: The DIETFITS randomized clinical trial. JAMA 2018;319:667-79.
- Magkos F. The role of dietary protein in obesity. Rev Endocr Metab Disord 2020;21:329-40.
- Messina MJ. Legumes and soybeans: overview of their nutritional profiles and health effects. Am J Clin Nutr 1999;70:439S-50S.
- Dong JY, Tong X, Wu ZW, Xun PC, He K, Qin LQ. Effect of soya protein on blood pressure: a meta-analysis of randomised controlled trials. Br J Nutr 2011;106:317-26.
- Liu XX, Li SH, Chen JZ, Sun K, Wang XJ, Wang XG, Hui RT. Effect of soy isoflavones on blood pressure: A meta-analysis of randomized controlled trials. Nutrition, metabolism, and cardiovascular diseases : NMCD 2012;22:463-70.
- Kou T, Wang Q, Cai J, Song J, Du B, Zhao K, Ma Y, Geng B, Zhang Y, Han X, et al. Effect of soybean protein on blood pressure in postmenopausal women: a meta-analysis of randomized controlled trials. Food & function 2017;8:2663-71.
- Mosallanezhad Z, Mahmoodi M, Ranjbar S, Hosseini R, Clark CCT, Carson-Chahhoud K, Norouzi Z, Abbasian A, Sohrabi Z, Jalali M. Soy intake is associated with lowering blood pressure in adults: A systematic review and meta-analysis of randomized double-blind placebo-controlled trials. Complement Thr Med 2021;59:102692.
- Mohammadifard N, Sajjadi F, Haghighatdoost F. Effects of soy consumption on metabolic parameters in patients with metabolic syndrome: A systematic review and meta-analysis. EXCLI journal 2021;20:665-85.
- Asbaghi O, Ashtary-Larky D, Mousa A, Kelishadi MR, Moosavian SP. The effects of soy products on cardiovascular risk factors in patients with Type 2 diabetes: A systematic review and meta-analysis of clinical trials. Adv Nutr 2021.
This blog sponsored by SNI Global and the United Soybean Board.