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Daily Nutrition & Health

Soy Facts Everyone Should Know

Susan Bowerman 23 October 2023

Soy foods have long been recognised as good sources of protein, and in some parts of the world, soy has been part of the diet for thousands for years. In fact, there is a growing body of research to support the many health benefits of soy. And yet, there is still some confusion about this versatile food source.

Fact 1: Plant Estrogens Are Not the Same as Natural Estrogen

Many myths and misconceptions concerning soy foods stem from the fact that soy contains natural plant compounds called isoflavones. Isoflavones are “phytoestrogens,” which are also known as dietary estrogens. Isoflavones have a chemical structure that’s similar, but not identical to natural estrogen, the hormone produced by your body. Therefore, plant-derived phytoestrogens in soy do not exert the same effects as the estrogen that the body produces. When some people hear “soy contains phytoestrogens,” they assume that consuming soy will expose their body to too much estrogen, but that is not the case.

Fact 2: Soy Isoflavones Do Not Increase Breast Cancer Risk

Some people shun soy foods in the mistaken belief that these plant estrogens will increase their body’s exposure to estrogen, and increase their risk for breast cancer. It turns out, that the opposite may be true. In the case of breast cancer, concerns about soy increasing natural estrogen levels are unfounded. In fact, the incidence of breast cancer is lower in countries where soy is consumed regularly. In Asian epidemiologic studies, a higher consumption of soy in early life is associated with a 25 to 60 percent reduction in breast cancer risk. Similarly, the North American Menopause Society has concluded that soy-based isoflavones do not increase the risk of breast or endometrial cancer.

Fact 3: Soy Does Not Have Feminising Effects on Males

This myth has caused some men to avoid soy products completely. While it certainly makes headlines, this has been reported in only one study, which documented the “feminising” effects in a 60-year old man who drank nearly three litres of soy milk daily. It was estimated that the subject was taking nine times (360mg) the amount of isoflavones than typically consumed by older Japanese men, whose soy intake is higher than the worldwide average. The subject’s high soy intake was also part of an unbalanced and nutrient-deficient diet. In numerous clinical trials, there has been no report of feminising effects in men who were exposed to as much as 150mg/day of soy isoflavones.

Fact 4: Soy Protein Supports Muscle Building

When people think of muscle-building protein, they usually think of whey protein. Soy protein is effective for promoting muscle growth, too, but the confusion about phytoestrogens has led to the myth that these plant compounds may lower testosterone levels and interfere with muscle development.

This myth is false. According to a meta-analysis of studies related to soy protein and isoflavones, it was concluded that neither soy foods nor isoflavone supplements had any significant effects on testosterone concentrations in men. Soy is a great source of protein and is also rich in arginine, the amino acid that the body uses to produce nitric oxide. Nitric oxide increases blood flow to the muscles, which helps deliver nutrients and oxygen during your workouts.

Fuel Your Workout with Soy Protein

Soy protein is rich in genistein and arginine

Genistein and arginine support nitric oxide production and blood flow to the muscles

Supports growth and repair of muscle tissue

Fact 5: Soy Is a Healthy, Environmentally-Friendly Alternative to Animal Protein

Moving away from myths, let’s consider the impressive nutritional profile of soy. Soy is a complete plant protein: it contains all the essential amino acid building blocks used to manufacture all kinds of specialised protein structures our body needs. Soy is also low in saturated fat and naturally cholesterol-free. Adding soy foods to your diet could boost your intake of vitamins, such as folate and Vitamin K, as well as minerals like calcium, magnesium, and iron. You can increase your intake of fibre if you eat whole soybeans – and you can’t get fibre from animal proteins. Finally, you can also help the planet by consuming more plant-based protein like soy. When compared to the environmental impact of raising farm animals, soy production uses less water and land, and produces fewer greenhouse gases.



Senior Director, Worldwide Nutrition Education and Training, Herbalife Nutrition.