The good and bad of Soybean (Nung hawai) consumption

Keithellakpam Sanatombi *

Soybean (Nung hawai) :: Pix - manipursfac.com

Soybeans are leguminous plants that originated in East Asia, but are now being cultivated in all parts of the world. Soybeans are consumed as whole or after processing. It is commonly used in tofu, soy milk and various other dairy and other meat substitutes, including infant formulas.

In some Asian countries, it is also commonly consumed as fermented foods like miso, natto, tempeh and the indigenous hawaijar, etc. In western countries, whole soybeans are rarely consumed and processed soy products are mostly consumed. Most of the soy produced in US is used to produce soybean oil and the soybean meal which remains after extraction of oil is a good source of protein.

Soybean meal is used to feed livestock and also in other processed foods. About 100 grams of mature, boiled whole soybeans contain 173 calories, 9 grams of fat, 10 grams of carbohydrates (6 of which are fiber), 17 grams of protein and other nutrients like Manganese, Selenium, Copper, Potassium, Phosphorus, Magnesium, Iron, Calcium, Vitamin B6, Folate, Riboflavin (B2), Thiamin (B1) and Vitamin K.

Soybean has also been shown to have many health benefits including cholesterol lowering effects, decreasing risk of heart disease, type 2 diabetes, asthma, reducing the risk of prostate cancer in old age, lung cancer, endometrial cancer, and thyroid cancer, as well as preventing weak bones and slowing the progression of kidney disease.etc.

Other uses of soybean in different parts of the world include consumption for treating constipation and diarrhea and treating muscle soreness caused by exercise. Soybean has also been reportedly used by women for breast pain, preventing breast cancer, preventing hot flashes after breast cancer, menopausal symptoms, and premenstrual syndrome (PMS).

Although soybeans are a good source of protein and are generally considered a good food item, there are many health risks of soybean consumption. Whole soybeans also contain phytates, which bind minerals and reduce their absorption. Therefore, soybeans are best when cooked. Soybeans are a good source of plant proteins.

However, processing at high temperatures may denature the proteins and reduce the quality of proteins. The fatty acids in soybeans are mostly Omega-6 polyunsaturated fats. Since consumption of large amount of Omega-6s can lead to inflammation, consumption of soybean oil and other processed foods should be avoided.

Soybeans also contain large amounts of compounds called isoflavones, which function as phytoestrogens or plant-based compounds that can activate estrogen receptors in the human body. Estrogens are hormones which play a role in sexual development and reproductive cycle in females. However, the phytoestrogens, with weak estrogenic effects, have been shown to influence many cancers in the lab.

The key isoflavones in soy are genistein, daidzein and glycitein. They can cause reduced estrogen activity by blocking the actual isoflavones or they can increase estrogen activity when isoflavones activate the receptors. Due to the estrogenic activity, these isoflavones are used as a natural alternative to relieve symptoms of menopause as well as reduce the risk of bone loss in elderly women.

However, many believe that the risks of soybean outweigh any potential benefit and its use is mostly controversial. Many studies in animal models have shown that soy isoflavones can cause breast cancer. The influence of soybean on breast cancer has long been a source of concern. Studies with humans have further shown that soy isoflavones stimulate the proliferation and activity of breasts cells that were likely to develop breast cancer. These indicate an increased risk of breast cancer.

Soy has also been shown to cause mild disruptions of menstrual cycle leading to delayed menses and prolonged menstruation. It is believed that drinking just two glasses of soymilk daily provides enough isoflavones to alter a woman’s menstrual cycle. Although some observational studies have shown that consumption of soybean may reduce the risk of breast cancer in women, the biological changes observed in the breasts cells and the studies showing the development of breast cancer in rodents fed wit soybean are a major cause for concern.

Men also have some amount of estrogen in their body, but increased estrogen activity from soy isoflavones may produce adverse effects in men. In rodents, exposure of male embryos to soybean isoflavones in the womb has been shown to affect development adversely.

Further, in one human study involving men attending an infertility clinic, those men who consumed most soybean products during the 3 months before the study had the lowest sperm counts. Soybeans can also reduce testosterone levels in men. However, another study showed that 40 milligrams per day of soy isoflavones for a period of 4 months had no effect on semen quality or testosterone levels.

The soybean isoflavones also functions as goitrogens, which can inhibit the function of the enzyme thyroid peroxidise required for the production of thyroid hormones. In a study with 37 Japanese adults, consumption of 30 grams of soybeans for 3 months increased the level of Thyroid Stimulating hormone (TSH) and many experienced symptoms of hypothyroidism, including malaise, constipation, sleepiness and thyroid enlargement, which disappeared after they stopped consuming soybeans.

However, there are other studies which show that soybean has either no effect or only a mild effect on thyroid function in humans. Soybeans also contain high amount of aluminum. Since excessive presence of aluminum is known to be the primary cause of various renal diseases, consumption of large amounts of soybean may be harmful for the kidneys. Moreover, the oxalates present in soybean are difficult to be degraded by our digestive system and they accumulate within the kidneys turning into kidney stones.

Therefore, it is advisable for people with a history of renal failure or other renal disorders to stay away from soy protein. Soy proteins are commonly used in infant formula, but exposing infants to isoflavones can produce harmful effects.

A study with infant girls showed that infant girls that were fed with soy formula had significantly more breast tissue at 2 years of age than those who were fed with dairy-based formula or breast milk. Girls fed with soy formula were also shown to go through puberty at a younger age by another study. Feeding soy formula during infancy has also been shown to associate with lengthening of the menstrual cycle and increased pain during menses in adulthood.

Since soybean contain much higher amount of manganese than breast milk, consumption of soy infant formula may lead to neurological problems and attention deficit hyperactivity disorder (ADHD). Also, high levels of aluminium in soy may be toxic to the nervous system and kidneys of infants. It is true that many Asian populations have been consuming soy products since ages without much problem. The reason may due to the consumption of soybean mostly as fermented products like natto, miso, tempeh and the hawaijar, etc.

Fermenting of soybean leads to degradation of phytic acid, but does not degrade the isoflavones. Although fermented products are also rich in other nutrients, the dosage of phytoestrogens poses a problem. Consumption of fermented soy products may be the best way to consume soy since they are also a good source of probiotics.

However, only small amounts are recommended to control the dose of phytoestrogens. Thus, although most of the studied harmful effects of soybean are contradicted by other showing beneficial effects, it is also interesting to note that most of the studies showing beneficial effects were either sponsored by soy industries or were linked to them in one way or the other.

Therefore, it is important to consider the health risks of soybean before consuming it in large amounts, especially for pregnant women and breastfeeding women as well as in the use of soy infant formula.