Soy is sometimes used to reduce high levels of cholesterol, a major risk factor for heart disease. Available in supplement form, soy is rich in isoflavones (a type of phytoestrogen). Although research on soy supplements and cholesterol has yielded mixed results, some studies suggest that soy may help keep your cholesterol in check.
Including soy protein in your diet may help cut your cholesterol levels, according to a 2007 report from the American Journal of Clinical Nutrition. In their review of 11 studies on soy intake and cholesterol, the report's authors found that soy isoflavones significantly reduced total cholesterol and LDL ("bad") cholesterol but failed to affect HDL ("good") cholesterol. What's more, the authors of a 2006 report from the American Journal of Cardiology analyzed 41 clinical trials and concluded that "replacing foods high in saturated fat, trans-saturated fat, and cholesterol with soy protein may have a beneficial effect on coronary risk factors" (including high cholesterol).
On the other hand, several studies suggest that soy supplements may not fight high cholesterol. In a 2010 report from the journal Menopause, for instance, scientists found that one year of soy supplementation did not significantly change cholesterol levels in participants. (The study included 62 postmenopausal women, all of whom had moderately elevated cholesterol levels.) Published in the European Journal of Clinical Nutrition, a 2005 study of 100 people with high cholesterol showed that those who took a soy supplement for 24 weeks had no greater improvement in cholesterol levels than those who took a placebo for the same time period.
When Should You Use Soy to Lower Cholesterol?
There's not enough scientific evidence to support the use of soy supplements for lowering cholesterol, according to the National Institutes of Health (NIH).
In some cases, soy may cause side effects like nausea, bloating, and constipation.
Although consuming soy from food may help reduce your heart disease risk, soy also has been shown to have an effect on thyroid hormone status. People who have thyroid conditions and those who are taking Synthroid or other thyroid replacement medication should be particularly cautious. Choosing soy products that are fermented, such as tempeh, natto, and miso, may reduce this effect.
Since the safety of long-term use of soy supplements has not been established, it's important to consult your doctor before using soy supplements to lower your cholesterol.
Campbell SC, Khalil DA, Payton ME, Arjmandi BH. "One-year soy protein supplementation does not improve lipid profile in postmenopausal women." Menopause. 2010 May-Jun;17(3):587-93.
Hermansen K, Hansen B, Jacobsen R, Clausen P, Dalgaard M, Dinesen B, Holst JJ, Pedersen E, Astrup A. "Effects of soy supplementation on blood lipids and arterial function in hypercholesterolaemic subjects." Eur J Clin Nutr. 2005 Jul;59(7):843-50.
Ho SC, Chen YM, Ho SS, Woo JL. "Soy isoflavone supplementation and fasting serum glucose and lipid profile among postmenopausal Chinese women: a double-blind, randomized, placebo-controlled trial." Menopause. 2007 Sep-Oct;14(5):905-12.
National Center for Complementary and Alternative Medicine. "Soy [NCCAM Herbs at a Glance]". NCCAM Publication No. D399. Created October 2007. Updated March 2008.
National Institutes of Health. "Soy: MedlinePlus Medical Encyclopedia". February 2011.
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 Sep 1;98(5):633-40.
Taku K, Umegaki K, Sato Y, Taki Y, Endoh K, Watanabe S. "Soy isoflavones lower serum total and LDL cholesterol in humans: a meta-analysis of 11 randomized controlled trials." Am J Clin Nutr. 2007 Apr;85(4):1148-56.