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Soy contains antioxidants and phytonutrients that are linked to health benefits, but it can have adverse effects.

Александр Пономарев image by Pixabay

Soy , scientifically called Glycine max, is a type of bean belonging to the botanical family Fabaceae. Originally from China and Japan, it can be consumed cooked and in the formats of soy oil, tofu, soy sauce, soy milk, fmiso, soy mite, soy protein, among others. Soy is rich in protein and minerals with calcium and magnesium, but there is controversy as to whether it is beneficial to health. Understand:

• What is tofu and what are its benefits

Nutritional information

Soy is mostly made up of protein, but it also contains good amounts of carbohydrates and fats. Every 100 grams of cooked soy contains:

• Calories: 173
• Water: 63%
• Protein: 16.6 grams
• Carbohydrates: 9.9 grams
• Sugar: 3 grams
• Fiber: 6 grams
• Fats: 9 grams
• Saturated: 1.3 grams
• Monounsaturated: 1.98 grams
• Polyunsaturated: 5.06 grams
• Omega-3: 0.6 grams
• Omega-6: 4.47 g

• Foods rich in omega 3, 6 and 9: examples and benefits

Protein

Soy is among the best sources of vegetable-based proteins, having from 36 to 56% of its dry weight made up of protein (see studies about it here: 1, 2, 3).

A 172 gram cup of cooked soy has about 29 grams of protein. The amount of protein present in soy is considered good. However, it lacks all nine essential amino acids (proteins) like other foods like quinoa. Learn more about this topic in the articles: "What are amino acids and what they are for" and "Quinoa: benefits, how to make them and what they are for".

The main types of protein in soy are glycinin and conglycinin, which represent approximately 80% of the total protein content. However, these proteins can trigger allergic reactions in some people (see studies about it here: 4, 5).

Soy protein consumption was associated with a decrease in cholesterol levels (see studies on this: 6, 7, 8).

Fat

Soy is an oil seed used in the production of soy oil. Its fat content is approximately 18% of dry weight - consisting mainly of polyunsaturated and monounsaturated fatty acids, with small amounts of saturated fat (see study about it: 9).

• Saturated, unsaturated and trans fat: what's the difference?
• What is saturated fat? Its make bad?

The predominant type of fat in soy is linoleic acid, which accounts for approximately 50% of the total fat content.

Carbohydrates

Because it is low in carbohydrates, whole soy has a low glycemic index (GI), which is a measure of how foods affect the increase in blood sugar after eating. This means it is suitable for people with diabetes.

• What is the Glycemic Index?

Fiber

Soy contains a fair amount of soluble and insoluble fiber. Insoluble fibers are mainly alpha-galactosides, which can cause flatulence and diarrhea in sensitive individuals (see studies on this here: 10, 11).

Alpha-galactosides belong to a class of fibers called FODMAPs (acronym for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols), which can worsen the symptoms of irritable bowel syndrome (IBS) (see study on this: 12).

Although it can cause unpleasant side effects in some people, soluble soy fibers are generally considered healthy. They are fermented by bacteria in the intestine, leading to the formation of short-chain fatty acids, which can improve intestinal health and reduce the risk of colon cancer (see studies here: 13, 14).

• What are probiotic foods?
• What are prebiotic foods?

Vitamins and minerals

Soy is a good source of vitamins and minerals, including:

• Molybdenum: an essential trace element found mainly in seeds, grains and legumes (15);
• Vitamin K1: plays an important role in blood clotting (16);
• Folate: Also known as vitamin B9, folate has several functions in the body and is considered particularly important during pregnancy (17);
• Copper: its intake is low in Western populations. Deficiency can have adverse effects on heart health (18);
• Manganese: a trace element found in most foods and drinking water. Manganese is poorly absorbed from soybeans due to its high phytic acid content (19);
• Phosphorus: Soy is a good source of phosphorus, an essential mineral abundant in the Western diet;
• Thiamine: Also known as vitamin B1, thiamine plays an important role in many bodily functions.

• What is Phytic Acid and How to Eliminate It from Food

Other plant compounds

Soy is rich in several bioactive plant compounds (see studies about it here: 19, 20, 21, 22):

• Isoflavones: As a type of antioxidant polyphenol, isoflavones have a variety of health effects;
• Phytic Acid: Found in all seeds, phytic acid (phytate) impairs the absorption of minerals such as zinc and iron. Levels of this acid can be reduced by boiling, sprouting or fermenting the beans. Learn more in the article: "What is phytic acid and how to eliminate it from food";
• Saponins: One of the main classes of plant compounds in soy, saponins reduce cholesterol.

• Does altered cholesterol have symptoms? Know what it is and how to prevent it

Isoflavones

Soy is one of the foods with the highest amount of isoflavones (see study about it here: 23). Isoflavones are unique phytonutrients that resemble the female sex hormone estrogen. In fact, they belong to a family of substances called phytoestrogens (plant estrogens).

The main types of isoflavones in soy are genistein (50%), daidzein (40%) and glycitein (10%) (see study about it here: 23). Some people have a special type of intestinal bacteria that can convert daidzein to equol, a substance thought to be responsible for many of the health benefits of soy consumption. These people benefit much more from soy consumption than those whose organisms are unable to convert daidzein (see study about it here: 24).

The percentage of equol producers is higher in Asian populations and among vegetarians than in the general Western population (see studies on this here: 25, 26).

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health benefits

Like most whole foods, soy has several beneficial health effects.

May reduce cancer risk

Cancer is one of the leading causes of death in modern society. Intake of soy products is linked to increased breast tissue in women, hypothetically increasing the risk of breast cancer (see studies about it here: 27, 28, 29).

However, most observational studies indicate that consumption of soy products can reduce the risk of breast cancer (see studies on this: 30, 31).

Studies also indicate a protective effect against prostate cancer in men (see studies about it here: 32, 33, 34).

Several soy compounds - including isoflavones and lunasin - may be responsible for the potential cancer preventive effects (see studies on this here: 35, 36). Exposure to isoflavones early in life may be particularly protective against breast cancer later in life (see studies on this here: 37, 38).

However, it must be taken into account that these conclusions were drawn from observational studies, which only indicate the correlation between soy consumption and cancer prevention, and do not prove the cause. In addition, it is necessary to take into account that soy, mainly in Brazil, has high levels of pesticides, including glyphosate. Studies correlate glyphosate consumption with the onset of diseases such as cancer, obesity, diabetes, heart disease, depression, autism, infertility, Alzheimer's disease, Parkinson's disease, microcephaly, gluten intolerance, hormonal changes, Non-Hodgkin's Lymphoma, cancer of bone, colon cancer, kidney cancer, liver cancer, melanoma, pancreatic cancer, thyroid cancer, among others. Learn more about this topic in the article: "Glyphosate: a widely used herbicide can cause fatal diseases".

Therefore, whether you are consuming soy beans, in the form of tofu, soy protein or any other, always opt for organic soy. Learn more about this topic in the article: "What are organic foods?".

Menopause Symptoms Relief

Menopause is the period in a woman's life when menstruation stops. Learn more about this topic in the article: "Menopause: symptoms, effects and causes". Menopause usually comes with unpleasant symptoms - such as sweating, hot flashes and mood swings - which are brought on by a reduction in estrogen levels.

Interestingly, Asian women—especially Japanese women—are less likely to experience menopausal symptoms than Western women. Eating habits, such as the increased consumption of soy-based foods in Asia, may explain this difference.

Studies indicate that isoflavones, a family of phytoestrogens found in soybeans, can alleviate these symptoms (see studies on this here: 39, 40).

• Menopause Remedy: Seven Natural Options

However, soy products do not affect all women equally. Soy only appears to be effective in organisms that are capable of producing equol - due to the presence of a type of intestinal bacteria capable of converting isoflavones into equol.

Equol may account for many of the benefits of soy. One study showed that daily intake of 135 mg of isoflavones for a week - 68 grams of soy per day - reduced menopausal symptoms only in people able to produce equol.

Although hormonal therapies have traditionally been used as a treatment for menopausal symptoms, isoflavone supplements are widely used as a complementary treatment (see study on this: 41).

bone health

Osteoporosis is characterized by reduced bone density, which increases the risk of fractures, especially in older women. The consumption of soy-based products can reduce the risk of osteoporosis in women who have gone through menopause (see studies about it here: 42, 43).

These beneficial effects seem to be caused by isoflavones (see studies about it here: 44, 45, 46, 47).

Concerns and adverse effects

While soy has many health benefits, some people need to limit their consumption of soy products - or avoid them altogether.

Suppression of thyroid function

High intake of soy products can suppress thyroid function in some people and contribute to hypothyroidism - a condition characterized by low production of thyroid hormones (see study on this: 48).

• Hyperthyroidism: what it is, symptoms and treatment
• Hyperthyroidism and hypothyroidism: what's the difference?

The thyroid is a large gland that regulates growth and controls the rate at which the body expends energy. Animal and human studies indicate that isoflavones found in soy can suppress the formation of thyroid hormones (see studies on this here: 49, 50).

A study of 37 Japanese adults showed that eating 30 grams of soy a day for three months caused symptoms related to suppressed thyroid function. Symptoms included discomfort, drowsiness, constipation and thyroid enlargement - all disappearing after the study ended.

Another study in adults with mild hypothyroidism found that ingesting 16 mg of isoflavones every day for two months suppressed thyroid function in 10% of participants. The amount of isoflavones consumed was quite small - equivalent to eating 8 grams of soy per day.

However, most studies in healthy adults found no significant link between soy consumption and changes in thyroid function (see studies here: 51, 52, 53).

An analysis of 14 studies found that there are no significant adverse effects of soy consumption on thyroid function in healthy adults, while infants born with thyroid hormone deficiency were considered to be at risk.

In summary, regular consumption of soy products or isoflavone supplements can lead to hypothyroidism in sensitive individuals, especially those who have an underactive thyroid gland.

flatulence and diarrhea

Like most other grains, soy contains insoluble fiber, which can cause flatulence and diarrhea in sensitive individuals (see studies on this here: 54, 55). While not harmful to your health, these side effects can be unpleasant.

• Diarrhea Remedy: Six Home-Style Tips

Belonging to the FODMAPs class of fibers, raffinose and stachyose fibers can worsen the symptoms of IBS (see study about it here: 56).

Allergy

Food allergy is a common condition caused by a harmful immune reaction to certain food components. Soy allergy is triggered by soy proteins - glycinin and conglycinin - found in most soy-based products (see study about it here: 57).

Although soy is one of the most common allergenic foods, allergy is relatively uncommon in children and adults (see studies about it here: 58, 59).