CLINICAL RESEARCH

Heart Health

Heart disease remains the leading cause of death for both men and women in the United States.¹ Dietary choices have a significant impact on heart disease risk, and soyfoods can be an important component of a heart-healthy diet. It is well-established that soy protein directly lowers LDL cholesterol levels.^2,3 Soyfoods are often low in saturated fat and high in polyunsaturated fats, potentially further reducing cholesterol when they are used to replace animal protein sources. Soy also contains naturally occurring omega-3 ALA fatty acids. Beyond their effects on cholesterol, evidence indicates that soy protein modestly lowers blood pressure⁴ and that the isoflavones in soybeans enhance endothelial function.⁵

^{1. Heart Disease and Stroke Statistics 2010 Update: A report from the American Heart Association, Circulation. 2010; 121: e46-e214.

2. Jenkins, D.J., et al., Soy protein reduces serum cholesterol by both intrinsic and food displacement mechanisms. J Nutr, 2010. 140(12): p. 2302S-2311S.

3. Anderson, J.W. and H.M. Bush, Soy protein effects on serum lipoproteins: A quality assessment and meta-analysis of randomized, controlled studies. J Am Coll Nutr, 2011. 30(2): p. 79-91.

4. Dong, J.Y., et al., Effect of soya protein on blood pressure: a meta-analysis of randomised controlled trials. Br J Nutr, 2011. 106(3): p. 317-26.

5. Li, S.H., et al., Effect of oral isoflavone supplementation on vascular endothelial function in postmenopausal women: a meta-analysis of randomized placebo-controlled trials. Am J Clin Nutr, 2010. 91(2): p. 480-6.}

^{References:
1. Heart Disease and Stroke Statistics 2010 Update: A report from the American Heart Association, Circulation. 2010; 121: e46-e214.}

Soy & Cholesterol

Elevated cholesterol is one of a number of risk factors in heart disease. Diet and lifestyle can play a role in this component. Along with exercise, reducing intake of saturated fat has been shown to help improve blood cholesterol levels. This includes consuming a plant-based diet rich in fruits, vegetables, whole grains, seeds, nuts and legumes such as soy.

The cholesterol-lowering effects of soy protein have been demonstrated in clinical studies for more than 45 years.¹ In 1999, the US Food and Drug Administration formally recognized the ability of soyfoods to lower cholesterol by approving a health claim for soyfoods and coronary heart disease.² Foods that provide at least 6.25 grams of soy protein per serving may be eligible for the claim. This figure was established by the FDA, as 25 grams per day was considered the threshold intake needed for cholesterol reduction. Four servings per day of soyfoods were considered a reasonable intake for this threshold. A typical serving of soy includes ½ cup edamame, 3 ounces of tofu, or 1 cup of soymilk.

Evidence reveals consuming this amount of soy protein can lower cholesterol by about 4 percent.^3,4,5 This level of reduction can be beneficial, particularly when incorporating soyfoods in a diet that is heart-protective overall. When the effects of healthy fats (poly and mono-unsaturated) along with the effects of soy protein are taken into consideration, it’s possible that replacing other sources of protein with soy could lower cholesterol by as much as 8 percent.⁶ Over time, this could reduce heart disease risk by as much as 16 percent.^7,8

The way in which soy protein lowers cholesterol isn’t well understood, however one theory is that the protein is digested to form peptides that promote degradation of cholesterol in the liver.^9,10 Additionally, soybeans are rich in healthful polyunsaturated fat. When they replace meat and cheese in diets, they automatically lower the saturated fat content of diets.¹¹

While no single food is powerful enough to markedly prevent heart disease, a combination of healthy foods and an active lifestyle can have a significant effect. Using a low-saturated fat diet high in fiber, fruits, vegetables, plant sterols, nuts, and soyfoods, Canadian researchers were able to reduce cholesterol by 30 percent.¹²

Consider adding soy to your diet, and you may be able to reap the benefits as well!

^{1. Hodges RE, Krehl WA, Stone DB, Lopez A. Dietary carbohydrates and low cholesterol diets: effects on serum lipids on man. Am J Clin Nutr 1967;20(2):198-208.

2. Food Labeling: Health Claims; Soy Protein and Coronary Heart Disease. In: Federal Register: (Volume 64, Number 206)]; 1999. p. 57699-57733.

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

4. 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(1):13-27.

5. 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(5):633-40.

6. Jenkins DJ, Mirrahimi A, Srichaikul K, Berryman CE, Wang L, Carleton A, et al. Soy protein reduces serum cholesterol by both intrinsic and food displacement mechanisms. J Nutr 2010.

7. Law MR, Wald NJ, Thompson SG. By how much and how quickly does reduction in serum cholesterol concentration lower risk of ischaemic heart disease? Bmj 1994;308(6925):367-72.

8. Law MR, Wald NJ, Wu T, Hackshaw A, Bailey A. Systematic underestimation of association between serum cholesterol concentration and ischaemic heart disease in observational studies: data from the BUPA study. Bmj 1994;308(6925):363-6.

9. Cho SJ, Juillerat MA, Lee CH. Cholesterol lowering mechanism of soybean protein hydrolysate. J Agric Food Chem 2007;55(26):10599-604.

10. Manzoni C, Duranti M, Eberini I, Scharnag H, Marz W, Castiglioni S, et al. Subcellular Localization of Soybean 7S Globulin in HepG2 Cells and LDL Receptor Up-Regulation by Its alpha’ Constituent Subunit. J Nutr 2003;133(7):2149-55.

11. Slavin M, Kenworthy W, Yu LL. Antioxidant properties, phytochemical composition, and antiproliferative activity of Maryland-grown soybeans with colored seed coats. J Agric Food Chem 2009;57(23):11174-85.

12. 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.}

Soy & Blood Pressure

Coronary heart disease (CHD) includes a number of risk factors. One of the most important is elevated blood pressure. A recent study presented by researchers from Wake Forest University found that the systolic blood pressure (top number) of people consuming the most soy isoflavones was 5 points (mm Hg) lower than that of people who consumed diets low in isoflavones.¹ The effects were especially pronounced in African Americans. Isoflavones are naturally-occurring plant compounds that are found in especially high amounts in soybeans and traditional soyfoods such as soymilk.

Soyfoods can make important contributions to heart-healthy diets. They provide high-quality protein and, in contrast to more traditional sources of protein in Western diets, they are low in saturated fat, high in polyunsaturated fat, and cholesterol free.^2,3 When soyfoods are substituted for animal products, blood cholesterol levels may be reduced.⁴ In addition, soy protein directly lowers LDL blood cholesterol. This benefit of soy protein was formally recognized by the U.S. Food and Drug Administration in 1999 when it approved a health claim for soyfoods and coronary heart disease.⁵

The results from the Wake Forest study by itself do not allow definitive conclusions to be drawn. However, they are consistent with previously published research. To this point, a recently published statistical analysis that included 27 clinical (human intervention) studies found that on average, soy lowered blood pressure about 2 ½ points.⁶

More research into the effects of soy on blood pressure is needed. Given all the advantages of soyfoods, people concerned about reducing their risk of heart disease may want to consider adding soyfoods to their diets.

^{References

1. Richardson S, Smith C, Burke L, Xia Z, Shikany JM, Steffen L, Rodriguez CJ. Dietary isoflavone intake is associated with lower systolic blood pressure: the Coronary Artery Risk Development in Young Adults (CARDIA) Study (Abstract). Am College Cardiol Annual Meeting. 2012.

2. 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.

3. Slavin M, Kenworthy W, Yu LL. Antioxidant properties, phytochemical composition, and antiproliferative activity of Maryland-grown soybeans with colored seed coats. J Agric Food Chem. 2009; 57: 11174-85.

4. Jenkins DJ, Mirrahimi A, Srichaikul K, Berryman CE, Wang L, Carleton A, Abdulnour S, Sievenpiper JL, Kendall CW, et al. Soy protein reduces serum cholesterol by both intrinsic and food displacement mechanisms. J Nutr. 2010; 140: 2302S-2311S.

5. Food labeling: health claims; soy protein and coronary heart disease. Food and Drug Administration, HHS. Final rule. Fed Regist. 1999; 64: 57700-33.

6. 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.}

Research suggests a portfolio diet including soy may be more effective at lowering cholesterol than a low saturated fat diet.

A study showed adults with high cholesterol who followed a “portfolio diet” of cholesterol-lowering foods including soyfoods like soymilk and soy meat alternatives, oats, nuts and plant sterols, lowered LDL cholesterol by 13.8% compared with a decrease of only 3% in those that followed a standard low saturated fat diet. ¹

Link to study

^{References:

1.Jenkins DJ 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 Epidemiology of soy exposures and breast cancer risk. JAMA 2011; 306(8): 831-839.}

Research suggests soy may lower cholesterol in as little as four weeks.

One study compared cholesterol levels between those who drank soymilk and those who drank 1% dairy milk as part of an overall sensible diet. In only four weeks, the soymilk group showed a 5% reduction in LDL cholesterol—a statistically significant advantage over those who consumed dairy milk.¹

Link to Study

^{References:

1. Gardner CD, Messina M, Kiazand A, Morris JL, Franke AA. Effect of two types of soy milk and dairy milk on plasma lipids in hypercholesterolemic adults: a randomized trial. J Am Coll Nutr. 2007 Dec;26(6):669-77.}

Research suggests soy reduces LDL cholesterol by 3% to 5%.

This level of reduction is significant, particularly from a public health perspective, since every 1% reduction in LDL reduces the risk of cardiovascular disease by 2%—5%.¹

In a meta-analysis of 23 studies, soy protein was shown to reduce total cholesterol, LDL cholesterol (by 5.25%) and trigylcerides, and to modestly increase HDL levels.² Other similar meta-analyses have reported LDL reductions of 3% and 4%.^3,4

Link to study

^{References:

1. Law M, Wald NJ, Thompson SG. By how much and how quickly does reduction in serum cholesterol concentration lower risk of ischemic heart disease? BMJ. 1994; 308: 367-72.

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

3. Sacks FM, Lichtenstein A, Van Horn L, Harris W, Kris-Etherton P, Winston M. Soy protein, isoflavones, and cardiovascular health: an AHA Science Advisory for professionals from the Nutrition Committee. Circulation. 2006; 113: 1034-1044.

4. 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: 940-946.}

Soy Facts

Soy may help reduce the risk of heart disease

Healthy Lifestyle