Soyfoods and Brain Health, Part 2

Linda Funk

Linda Funk

Flavorful Insight

The U.S. Soybean Export Council (USSEC) tracks trends that may represent global market opportunities for U.S.-grown soy. As evolving consumer priorities elevate health, wellness and nutrition considerations, soyfoods may gain additional traction globally. Research on soyfoods and depression is an emerging area of interest.

This is part two of a two-part series.

Scientists have been motivated to study the effects of soyfoods on depression because soybeans are a rich source of isoflavones. Isoflavones are naturally occurring compounds. They are different from the hormone estrogen, but they do share some properties in common.[1]

Currently, 73 percent of global consumers rate mental health and depression as having a moderate or severe impact on their everyday life.[2] Everyone experiences mood fluctuations –the normal emotional ups and downs of everyday life. But globally, more than 264 million people suffer from depression[3] that goes beyond a bout of the blues.

Depression is a mood disorder that causes a persistent feeling of sadness and loss of interest. When depression is long-lasting with moderate or severe intensity, it may become a serious health condition. Its effects cause people to suffer greatly and function poorly at work, school and at home.

Researching the role of diet in decreasing risk of depression: Despite the fact that there are effective treatments available for mental disorders, between 76 percent and 85 percent of people in low-income and middle-income countries receive no treatment for their disorder.[4]  Women are more likely to be affected by depression than men[5], which suggests there may be a hormonal component to depression. It is known that depression results from a complex interaction of social, psychological, and biological factors.

Food is one factor that may affect the odds of having depression. A group of academics suggests that “diet is as important to psychiatry as it is to cardiology, endocrinology, and gastroenterology.”[6]

Two recent analyses suggest that a healthy dietary pattern may decrease the risk of depression, whereas a western-style diet may increase risk of this disease.[7] [8]  Much of the research showing that soyfoods reduce risk of depression has been conducted in postmenopausal women.

Examining the anti-depressive effects of soybean isoflavones: A logical question to ask is whether soy is protective against depression, given that it alleviates hot flashes and night sweats.[9] After all, poor sleeping habits can lead to depression and there is a link between menopausal symptoms and depression. While that is an interesting hypothesis, research indicates the anti-depressive effects of soy are unrelated to its effect on hot flashes. For example, a Japanese study found that isoflavones in soybeans alleviated depression in postmenopausal women without affecting hot flashes.[10]

One intriguing study to evaluate the anti-depressive effects of isoflavones involved women suffering from depression living in the Dominican Republic who were enrolled into one of four groups.[11]  One group received isoflavones alone, two groups received common drugs (fluoxetine or sertraline) used to treat depression, and one group received isoflavones plus one of the drugs. Isoflavones on their own performed as well as the established drugs, and the combination treatment performed better than each of the other three groups.

How much soy is enough? Studies have used a variety of different amounts of soy, but generally two servings per day of the traditional soyfoods appears sufficient to alleviate depression. A serving is a cup of soymilk or a half cup of tofu or edamame.

While it isn’t possible to say for certain that soy will benefit people with depression, it is a nutritious, high-protein food, so there are plenty of reasons to add it to the diet. Soyfoods from U.S.-grown soybeans provide high-quality protein, healthy fat and a variety of vitamins and minerals.

[1] Harvard T.H. Chan School of Public Health, Straight Talk About Soy. The Nutrition Source.

[2] Westbrook, G and Angus, A.  Euromonitor International, Top 10 global consumer trends 2021, p. 32.

[3] World Health Organization. “Depression.” Fact Sheet, January 30, 2020.

[4] World Health Organization. “Depression.” Fact Sheet, January 30, 2020.

[5] Albert, PR. Why is depression more prevalent in women? J Psychiatry Neurosci, July 2015; 40 (4); 219-221.

[6] Sarris J, Logan AC, Akbaraly TN, et al. Nutritional medicine as mainstream in psychiatry. Lancet Psychiatry. 2015;2:271-4.

[7] Wu PY, Chen KM, Belcastro F. Dietary patterns and depression risk in older adults: systematic review and meta-analysis. Nutr Rev. 2020.

[8] Li Y, Lv MR, Wei YJ, et al. Dietary patterns and depression risk: A meta-analysis. Psychiatry Res. 2017;253:373-82.

[9] Taku, K, Melby MK, Kronenberg F, et al. Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials. Menopause. 2012; 19:776-90.

[10] Hirose A. Terauchi M, Akiyoshi M, et al. Low-dose isoflavone aglycone alleviates psychological symptoms of menopause in Japanese women: a randomized, double-blind, placebo-controlled study. Arch Gynecol Obstet. 2016; 293:609-15.

[11] Estrella RE, Landa AI, Lafuente JV, et al. Effects of antidepressants and soybean association in depressive menopausal women. Acta Pol Pharm. 2014; 71:323-7.