Soy has been one of the most discussed plant foods for several decades. Some consider it a superfood with multiple virtues, while others think it could disrupt the hormonal system. Between these sometimes diametrically opposed views, it can be difficult to find your way. In this article, we will explore the nutritional composition of soy, examine some famous controversies, and especially review the scientific research that supports or nuances these claims. The goal is to help you better understand soy to make an informed decision about the place you want to give it in your diet and lifestyle.

1. The History and Popularity of Soy

Soy (Glycine max) is a legume native to East Asia, cultivated and consumed for over five thousand years. In China, traces of its cultivation date back to antiquity, when it was already considered one of the Five Sacred Grains (alongside wheat, rice, millet, and barley). In other Asian countries, such as Japan, Korea, or Vietnam, soy also holds an important place in traditional gastronomy, in the form of tofu, miso, or natto, to name just a few examples.

With globalization and the growing interest in vegetarian or vegan diets, soy has gained considerable visibility in many regions of the world. Beyond being an alternative to meat, it is also appreciated for its high nutritional value. However, it is precisely this popularity that has contributed to the emergence of many myths about soy, particularly those concerning its supposed effects on hormones and health in general.

2. The Nutritional Composition of Soy

Soy is certainly one of the most nutritionally rich legumes. Here are some elements that help understand what makes it stand out:

1. Complete Proteins: Unlike most other legumes, soy contains all the essential amino acids that the human body needs, making it a high-quality protein source. For people following a vegetarian or vegan diet, it is a food of choice.
2. Dietary Fiber: Soy is rich in fiber that promotes good digestive health, contributes to satiety, and helps control blood sugar levels.
3. Healthy Fats: Its lipids are mainly composed of unsaturated fatty acids (primarily omega-6 and to a lesser extent omega-3).
4. Vitamins and Minerals: Soy is an interesting source of B vitamins (B1, B2, B3, B6…) and also contains important minerals such as magnesium, iron, and potassium.
5. Isoflavones: Isoflavones are often mentioned to describe the phytoestrogens present in soy. These compounds are the subject of many studies due to their potential influence on hormonal and cardiovascular health.

These elements highlight the contributions of soy as a complete plant food. However, it is important to address the controversies surrounding these same constituents, particularly isoflavones, as this is often where concerns about soy consumption arise.

3. Myths Around Phytoestrogens

Isoflavones, often called phytoestrogens, are plant chemical compounds whose structure somewhat resembles that of the human hormone estrogen. This resemblance is why they are named as such. The main isoflavones in soy are genistein, daidzein, and glycitein.

3.1 Understanding What Phytoestrogens Really Are

The main misunderstanding comes from the idea that these phytoestrogens act in the human body in the same way as estrogens produced by the body. However, it’s not that simple. Studies show that isoflavones can, in some cases, bind to estrogen receptors but are much less potent than the human hormone. They can also, under certain conditions, act as anti-estrogens by occupying these receptors without triggering the same hormonal action.

The action of isoflavones therefore depends on the context: age, hormonal status (for example, post-menopause), and the amount consumed. This is why the exact impact of soy differs from person to person, and also why many myths arise around this complexity.

3.2 Soy and Feminization

A common myth is the idea that consuming soy could “feminize” men or heavily disrupt women’s menstrual cycles. Rigorous studies conducted on men do not show a clear masculinization or feminization effect linked to soy consumption. In 2010, a meta-analysis published in Fertility and Sterility examined more than fifteen studies and concluded that soy or isoflavone consumption did not have a negative effect on testosterone levels in men.

Regarding effects on the female cycle, some women experience slight comfort linked to the presence of isoflavones, especially during menopause, as these can partially mimic the effect of estrogen and alleviate some discomforts related to hormonal deficiency. However, studies remain divided on the actual extent of this effect.

3.3 Does Soy Cause Thyroid Problems?

There is also a concern about thyroid problems. Some claim that soy products could inhibit iodine absorption, necessary for the synthesis of thyroid hormones. However, most epidemiological studies have not found a direct link between moderate soy consumption and hypothyroidism in people with normal iodine status. Recommendations include ensuring sufficient iodine intake to avoid any imbalance, especially among vegetarians and vegans who regularly consume soy.

4. Scientific Evidence on Soy Consumption

4.1 Studies on Cardiovascular Health

Some existing studies show that soy consumption can have a positive effect on blood cholesterol levels. The World Health Organization (WHO) and the American Heart Association indicate that replacing animal proteins with soy proteins (not necessarily in supplement form, but through foods containing soy) can help reduce LDL cholesterol (the “bad” cholesterol).

This effect is relatively modest but can add to the other potential benefits of a plant-rich diet, such as reducing the risk of high blood pressure and improving overall cardiovascular health.

4.2 Studies on Cancer and Prevention

Soy isoflavones have been studied for their potential link with different types of cancers, particularly hormone-dependent cancers (breast cancer, prostate cancer).

• Breast Cancer: Several studies conducted in Asia, where soy consumption is widespread, suggest that regular soy consumption from childhood or adolescence could reduce the risk of developing certain types of breast cancer in adulthood. However, caution is needed in extrapolating these results, as cancer prevention is multifactorial (lifestyle, genetic predisposition, environment, etc.).
• Prostate Cancer: Some research indicates a possible link between soy product consumption and a reduced risk of prostate cancer. Isoflavones could play a protective role, similarly to how they interact with hormone receptors for breast cancer.

4.3 Limitations and Nuances

It is important to note that all these studies have methodological limitations. Results are not always reproducible from one population to another, notably due to different dietary approaches (e.g., consuming traditionally fermented soy vs. industrially processed soy). It is also essential to consider the quality of soy-based foods consumed: ultra-processed preparations filled with additives and salt will not have the same beneficial effects as artisanally prepared tofu.

5. Forms of Soy and Their Specificities

There are many soy-based preparations. Some have been used for centuries, while others are more recent products of modern food. Here is an overview of the main forms and their characteristics:

1. Tofu: Probably the most popular soy product outside Asia. It is obtained by curdling soy “milk,” similar to cheese from animal milk. Tofu can be firm, silky, smoked, seasoned with herbs… There are many variations that lend themselves to a multitude of savory or sweet recipes.
2. Tempeh: Originating from Indonesia, it is produced by fermenting whole soybeans with a fungus, Rhizopus oligosporus, resulting in a firm, protein-rich, and flavorful product. It is often considered more digestible than non-fermented soy, thanks to the action of the ferments.
3. Miso: A fermented paste made from soy (sometimes mixed with rice or barley), this Japanese specialty is traditionally used to season soups, sauces, and marinades. Miso is appreciated for its umami flavor and potential benefits on gut flora.
4. Natto: Particularly popular in Japan for breakfast, natto results from the fermentation of soy by the bacterium Bacillus subtilis. It is characterized by a stringy texture and a strong odor. Rich in vitamin K2, it is appreciated for its possible beneficial effects on bone and cardiovascular health.
5. Soy Milk: A beverage obtained after soaking, grinding, and filtering soybeans. It is a popular plant-based alternative to animal milk, especially for people who are lactose intolerant or following a vegan diet.
6. Textured Soy Protein: Frequently used in industrial food to create “meat substitutes” or vegetarian products. In the form of granules or dehydrated pieces, they are then rehydrated and integrated into dishes like chili, stews, or vegetarian Bolognese sauces.

6. Criticisms Around Soy: GMOs and Intensive Agriculture

Beyond health issues, soy raises environmental and ethical concerns. A large amount of soy grown worldwide is intended for animal feed (notably for the meat industry), and this soy is often genetically modified (GMO) to resist herbicides. For human consumption, organic and non-GMO channels exist, but it may be necessary to check labels to ensure the product’s origin and quality.

6.1 Ecological Impact

Soy production is criticized for its impact on deforestation, notably in the Amazon. However, the majority of this production is intended for industrial livestock. Opting for soy from responsible and organic channels helps support more environmentally friendly agricultural practices. In general, adopting a vegetarian or vegan diet already contributes to reducing one’s carbon footprint. However, it is always preferable to choose products whose origin and production method are known.

6.2 Soy Cultivation in Europe

In recent years, several European countries have started cultivating non-GMO soy to meet the growing demand of consumers concerned about food traceability. France, Switzerland, Italy, and Germany are thus increasing their soy acreage, encouraged by the quest for local plant proteins. This helps provide more environmental guarantees and limit the importation of soy from high deforestation risk areas.

7. How Much Soy to Consume?

Each individual is different, and the inclusion of soy in the diet depends on multiple factors: digestive tolerance, nutritional needs, taste preferences, and any specific medical conditions. Some studies suggest that one to two servings of soy per day (one serving equivalent to 100 g of tofu or 250 ml of soy milk) can be beneficial, without showing significant adverse effects in most people.

7.1 General Recommendations

In general, nutritionists estimate that:

• Children: Can consume soy, but it is important to ensure a variety of protein sources for a balanced amino acid intake and to avoid any deficiency.
• Adults: Can include soy in their diet, taking into account their health specifics and needs. It is often advised to diversify protein sources (lentils, chickpeas, beans, nuts, etc.) rather than relying exclusively on soy.
• People with Thyroid Dysfunction: Should consult a healthcare professional to assess their iodine status and adjust, if necessary, their consumption of soy products.

7.2 Variety and Balance

As with any food, the key lies in variety. It is preferable not to rely solely on soy to meet protein needs. Other legumes, nuts, whole grains, and varied plant alternatives also provide essential nutrients for a balanced diet, especially if you are vegetarian or vegan.

8. How to Incorporate Soy into Your Diet

Incorporating soy into your daily cooking is not complicated:

• Add tofu cubes (plain, smoked, or marinated) to your salads, stir-fries, or soups.
• Marinate tempeh and grill it to incorporate into your sandwiches or vegetable dishes.
• Use soy milk for your hot drinks, smoothies, or cake preparations.
• Prepare sauces based on miso or silken tofu to enhance pasta, rice, or even roasted vegetables.
• Try international recipes like Japanese miso soup, Thai pad thai with tofu, or Indian tofu curry.

Varying preparations and cooking methods allows you to fully appreciate the culinary and nutritional potential of soy.

9. Untangling Fact from Fiction: What to Remember?

The controversy around soy often stems from sensationalist headlines in the press or hasty conclusions drawn from certain studies. To sort through, here are some key points to remember:

1. Soy phytoestrogens are not equivalent to human estrogen and their effect on the body depends on many individual factors.
2. Most studies do not validate the idea of feminization in men or major hormonal disruption in women, for moderate soy consumption.
3. Soy appears to have beneficial effects on cardiovascular health, notably through a modest reduction in LDL cholesterol.
4. The link with cancer is complex, but some data suggest potential benefits, especially if soy is consumed long-term and as part of a healthy lifestyle.
5. The quality and origin of soy products are essential. It is preferable to favor organic, non-GMO, and fermented products, with a lower ecological impact and easier to digest.
6. Moderation and variety remain essential. It is recommended to diversify protein sources to avoid any form of overconsumption and to benefit from a wide range of nutrients.

10. Conclusions

Soy is a particularly interesting food, both culinary and nutritionally. It offers an excellent source of complete proteins, fiber, vitamins, and minerals. Concerns about its hormonal effects have led to many debates, but most serious scientific research concludes that there is no reason to demonize soy consumption in a balanced diet. The isoflavones it contains have complex mechanisms of action, which can sometimes be beneficial (for example, for cardiovascular health or the prevention of certain cancers), while not causing most of the feared side effects.

What matters is choosing quality soy, ideally organic and from responsible channels, and integrating it in a varied and moderate way into your diet. And if you want to discover all its flavors, opting for fermented versions like tempeh, natto, or miso can be an excellent way to enjoy their benefits and rich taste.

Ultimately, there is no universal answer to the question “Should you consume soy?” because this decision depends on your health, tastes, and dietary preferences. However, based on current studies, it can be said that reasonable soy consumption, respecting the principles of a varied and balanced plant-based diet, can be an asset to health and well-being. Do not hesitate to consult a nutritionist or doctor if you have specific questions or if you have particular medical conditions. The essential thing is to develop eating habits that suit you, while remaining open to reliable and up-to-date information.