Soy is a herbaceous plant of the legume family. Since time immemorial, it is consumed in Asia as tofu, tempeh, miso and soy sauce. Currently, it is converted to soya drinks and alternative yoghurt or cream, and proteins are included in many vegetarian meat substitutes.Soy provides an important source of protein, potassium, copper, magnesium and manganese. Low in saturated fat, it contains no cholesterol. As for its low calcium, she explains that often flaw add soy beverages during the production process. In addition, it is rich in isoflavones, which are attributed many benefits. All these contributions are arguments for soy defenders.

As for his critics, they just point the finger at these isoflavones, as they are part of phytoestrogen group, molecules with a chemical structure similar to hormones female. And even if their hormonal activity is lighter (1, 2), it is nonetheless present, exposing, according to them, the people who consume to diseases, including hormone-dependent cancers.

Cancers hormone

Some thus fear that soy does not increase the risk of breast cancer. However, scientific studies point out that Asian populations, characterized by a high consumption of soy, have a lower risk of breast cancer; However, this report has not been established in Western populations. The positive effect is indeed likely related to a sufficiently high intake of soy during childhood and adolescence. Based on available data, the AICR (American Institute for Cancer Research) and the Global Fund to research against cancer conclude that soy does not increase the risk of breast cancer and may even have the opposite effect, which must be confirmed by further research (2, 3). Even women who have had breast cancer should therefore no reason to avoid soy. The fear that soy isoflavones do not increase the risk of relapse is unfounded, due to a daily consumption of 1 to 2 soy products (2).

Prostate cancer is other cancer hormone linked with soybeans was investigated. This cancer is more common among Westerners than among Asians, who eat more soy. Research has shown that soy isoflavones have slowed the progression in animals, but these results can not be applied as such to humans … Thus, clinical studies with men who were administered isoflavones Prevention or during prostate cancer treatment do not mention or little positive effect. New clinical studies on the broader role of soy in reducing the risk of this cancer or halt the progression must therefore be carried out (4).

Men, women and hormones

Hot flashes in postmenopausal women and male fertility problems are other hormonal symptoms made contact with soybeans. Due to their estrogenic activity was investigated to what extent soy isoflavones can reduce these problems. In 2012, EFSA, based on the literature available at the time, decided not to approve a statement on the beneficial effect of isoflavones on hot flushes. Again, more research is needed to confirm the limited positive results (5). Since then, several large studies have been conducted, with conflicting conclusions. This is explained in part by the inclusion or not of tests involving patients with breast cancer and the type of isoflavone. It is possible that the positive effects are greater in these patients and in cases of use of genistein, a specific soy isoflavone. Therefore await further studies before drawing conclusions (6, 7).

In the same report, EFSA refused to manufacturers to affix to their products a health claim on the effect positive soy isoflavones on osteoporosis (5).

Because of the estrogenic activity of isoflavones, we sometimes think that soy could have a negative effect on male fertility, which has that is the subject of little research. Most studies were also conducted with men who have had fertility problems. A limited number of studies show that perhaps there is an impact on sperm quality, but these effects are so small they do not exert influence on male fertility (8).

Another negative effect mentioned concerns the activity of the thyroid. Several animal studies have shown that soy isoflavones may have a negative effect on the activity of the thyroid, which would be slowed. The results of several clinical studies are however contradictory. Further research again prove indispensable (4).

Between heart and brain

In 1999, the United States, the FDA (Food and Drug Administration) approved a statement that “25 grams of soy per day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of cardiovascular disease” (9). Proponents of soybeans took the opportunity to erect the soya superfood rank, forgetting their enthusiasm in other parts of the assertion. Subsequent studies have demonstrated that the effect expected positive effect of soya proteins alone on LDL cholesterol (bad cholesterol) is lower than what we originally thought. In 2010, EFSA concluded that there was no established link between soy protein consumption and LDL cholesterol (10). A Cochrane review from 2013 arrived at the same conclusion (11).

Finally, many rumors point to the negative effect of soy isoflavones on memory. These rumors are based on several observational studies that would have established a link between consuming soy (tofu) and memory impairment. These studies, however, not possible to establish a link of cause and effect. Several clinical studies in postmenopausal women have verified the impact of soy on memory and did not detect any negative effects. Instead, soybeans seemed rather have a positive effect. More extensive studies are needed to confirm these findings (12).

It is clear that neither supporters nor opponents soy can claim victory. Soy is not a miracle food and it does not cause either health problems. But it is an excellent food, rich in fiber and protein quality, which deserves a place in a healthy diet. If you regularly place soy products on the menu, the consumption of animal products rich in (bad) saturated fat will give way to (good) unsaturated fats. This will reduce the risk of cardiovascular disease.