5 myths about soy protein


Soy is a high quality source of protein 100% vegetable that contains all the essential amino acids. It is high in vitamins and minerals, fibers, omega-3 and omega-6, it doesn’t contain cholesterol and has a low tenor of fat when compared with meat. This protein source contains a high tenor of arginine and glutamine, nutrients that contribute to elevate the levels of nitric oxide and to a higher release of growth hormone, which improves performance, recovery and muscle growth.

Even though there’s plenty of information available, there are still many doubts regarding soy protein that must be clarified. What are the myths and truths about soy protein? We unveil and explain five of them.

Myth 1. Soy protein lowers the levels of testosterone and boosts estrogen production.

Some studies have been developed throughout the years on professional masculine athletes, from different sports, that consume high quantities of soy protein and do not show any changes on testosterone nor fertility levels. What is more, these athletes even gained lean muscle mass and improved their performance.

READ ALSO: 12 tips to increase the production of testosterone and to build muscle mass

Myth 2. Soy contains estrogen and it is a protein that must be consumed only by women.

Soy doesn’t contain estrogen but it contains isoflavones. Isoflavones are present in soy and may also be called phytoestrogens that despite having a similar structure to estrogen is not the same as the feminine hormone. Two of its main functions consists of diminishing LDL cholesterol and fighting osteoporosis. There is no scientific evidence that shows that using soy protein alters the hormone levels or affects muscle development.

For example, in 2010 a publication of the international newspaper Fertility and Sterility declared that neither isoflavones supplements, nor soy high in isoflavones affected the levels of free or total testosterone. It also stated, based on the nine studies that have been made on the subject, that there is no concrete evidence that isoflavones affects the levels of estrogen in men.

Myth 3. Soy protein is difficult to digest, it causes stomach irritation and intestinal discomfort.

Isolate soy protein is easy to digest. Its digestibility values vary from 95% to 98% which is higher than most of the animal proteins usually consumed. Some forms of soy, as soy flour, containing protein and carbohydrates may be difficult to digest. However, most of sports nutrition supplements are made of isolate soy protein, a safe and easy to digest form of consuming it.

Myth 4. All soy products are made from GMO (Genetically modified organisms).

Some varieties of soy are modified to be able to tolerate certain herbicides, allowing farmers to use huge amounts of herbicides to kill invasive species without damaging crops. However, most of the manufacturers use soy ingredients which haven’t been genetically modified and that are also certified by the regulations that don’t allow such procedures. Due to the importance of this matter and in order to make you feel 100% safe about buying and consuming soy supplements, you can check the labels of these products which must include information stating that the products wasn’t made using GMO.

Myth 5. Soy phytoestrogens inhibit the normal functioning of the thyroid.

The defenders of the non-consumption of soy, state that phytoestrogens are very powerful anti-thyroid agents that cause hypothyroidism. In fact, in May 2011, one study of Clinical Thyroidology detected 6 from 60 women with subclinical hypothyroidism (a condition that has no symptoms) converted in clinic hypothyroidism, after 8 weeks of supplementation with soy protein, containing 16mg of phytoestrogens per day. To imitate the typical occidental diet, researchers gave women soy protein supplements containing 2mg of phytoestrogens per day. The group of women that took the lower dose didn’t suffer any alteration on thyroid function. It was concluded that only high doses of phytoestrogens in soy supplements may cause clinical hypothyroidism in a short group of patients with subclinical hypothyroidism.

Curiously, in the same study made by Sathyapalan, the highest dose of phytoestrogens reduced significantly the resistance to insulin, blood pressure and inflammation markers.

Soy protein is a safe alternative to other types of protein for athletes who intend to increase and/or maintain muscle mass and can (must) be consumed by men and women as a diet complement as long as they do not exceed the recommended daily values (approximately 25g, equivalent to 1,2-2g of protein for each kilogram of body weight). Change the sources of protein; add meat, fish, eggs, dairy products and vegetables.

Note 1: Soy can be used by turns or simultaneously with other sources of protein (casein, albumin or whey, to prevent muscle mass loss.

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Judith C. Thalheimer, RD, LDN, The Top 5 Soy Myths, Today’s Dietitian, Vol. 16 No. 4 P. 52, April 2014, adaptation from the original version

Bianca Bassoto, Mitos e verdades sobre a proteína de soja, March 2013, adaptation from the original version


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