Definition of Antinutrient
A naturally occurring substance found in plant derived foods, that interferes with the absorption or proper functioning of nutrients in the body.
What are anti-nutrients in soybeans?
Soybean is one of the best sources of protein in livestock diets, it is highly nutritious as it contains all the essential amino acids needed for plant growth. Soybean contains about 35-40% of crude protein, which is relatively a high quantity for livestock. (1)
A high antinutrient content of soybean is a concern, both to us and to livestock, because antinutrients interfere with the digestion and absorption of protein,vitamins and minerals, but do not reduce the number of amino acids in the soyabean.
Anti- nutrients in soybean are:
- Trypsin inhibitors
- Lectins
- Phytoestrogen
- Tannin
- Saponin
- Oligosaccharides
- Phytic acid
Trypsin inhibitors are the specific proteins present in raw soybean. They reduce protein digestibility, and are one of the most abundant antinutrient factors in soybeans. As the name suggests, it inhibits the activity of enzymes that digest protein in the digestive tract such as trypsin, chymotrypsin and so on.
However trypsin inhibitor antinutrients can be destroyed by heat.
Lectins prevent the breakdown of starch and other complex carbohydrates into simple sugars. Binds to the inner lining of the intestine, thus affecting general absorption of nutrients.
Soybeans contain high concentrations of phytate (also known as phytic acid), one of the most common types of antinutrients found in seeds,nuts, legumes and grains. Phytate impairs the absorption of minerals like iron and zinc. Binds Ca, Mg, Fe, Cu and Zn. Reason why product should be low in fiber; high fiber indicates there are more particles from the hull of the seeds and grains.
However phytates are not harmful unless your diet is severely imbalanced and you rely on soy protein as your main source of iron and zinc. Levels of this acid can be reduced by boiling, sprouting or fermenting the beans.
When soybeans are industrially processed, they are soaked, as it makes it easier to remove fibrous husk. After soaking they are boiled. Soaking (in plain water) and boiling together reduce the levels of Tannins (-100%) and Trypsin inhibitor (-82%), without affecting the levels of phytates. Now after the dehulling and boiling process, tannins are not present in any soy food.
Now, at this point, soybeans are ready to produce various soy foods, also soy flours and protein concentrates.
Finally, for making soy flours and protein powders from the boiled soybeans, they will be ground and roasted. Mainly, roasting reduces the levels of trypsin inhibitors (-98%), phytate (-78%) and tannins (-75%) of the raw bean levels. Those reductions are supported by analysis of soy protein concentrates and isolates.(1)
Summary
Soybean processing methods include soaking, boiling, fermenting and roasting which greatly reduces the anti nutrient content (namely, phytate trypsin inhibitor and tannins) of soy foods.
What are isoflavones?
Isoflavones belong to a family of substances called phytoestrogens (‘phyto’ means plant) which are naturally occurring chemicals found in plants.(2)
Soy contains isoflavones which are changed in the body to phytoestrogens. Phytoestrogen molecules are similar in chemical structure to the hormone estrogen.(3)Isoflavones are very strong anti-oxidants and can mimic the effects of female sex hormone estrogen. Their estrogenic properties affect both men and women but their full physiological effects are still being investigated. (1)
The main types of isoflavones in soy are genistein (50%), daidzein (40%) and glycitein (10%) of the total isoflavone content of soybean.
Following is the soybean phyto-nutrients chart (Phaseolus lunatus. L), Raw, mature seeds, value per 100 gm. (Source: USDA National Nutrient database) (4)
In regard to isoflavone metabolism, a striking difference among individuals is that only about 25% of non Asians and 50% of Asians host the intestinal bacteria (gut flora) that convert daidzein into the isoflavonoid equol.(1) In 2002, in the Journal of Nutrition Setchell et al.proposed that those individuals who host these bacteria are more likely to benefit from soy food consumption. (5)
Soybeans are the most common source of isoflavones in food. However, the amount of isoflavones varies with the type of soy food, preparation method and brand.(2)
Therefore,USDA databases for the isoflavone content of selected foods, can only indicate which foods tend to have low, moderate or high levels of isoflavones.(1)
Each gram of soy protein in soybeans and traditional soy foods is associated with approximately 3.5 mg of isoflavones. Consequently, one serving of traditional soy food, such as 100 gm of tofu or 250 ml soymilk, typically provides about 25 mg isoflavones. In more refined products such as ISP, as much as 80% to 90% of the isoflavone content can be lost as a result of processing.(6)
The average daily intake of isoflavones in Japan and China is 25-50 mg. Compared to less than 1 mg in western countries, this is because Asian diets include more soy foods.(1)
Health effects of soy isoflavones
Some evidence suggests that soy’s health effects depend on how much equol you produce, which depends on the composition of your bacterial gut flora.(1) Equol does appear to offer health benefits over its precursor daidzein in possibly several different areas but especially in the alleviation of hot flashes. People whose bodies can produce equol are expected to benefit much more from soy consumption than those whose bodies cannot. (6)
Isoflavones are considered chemoprotective and can be used as an alternative therapy for a wide range of hormonal disorders, including several cancer types, namely breast cancer and prostate cancer cardiovascular diseases, osteoporosis or menopausal symptoms.
Breast cancer:- Higher isoflavone intake during childhood and/or maturing appears to be the key to the proposed protective effects against breast cancer. (7)
Menopausal symptoms:- Intake of soy isoflavone by the women who are able to produce equol (detected in the urine) noticed a reduction in menopausal symptoms. (8)
Cardiovascular diseases:- In a review of clinical studies it was reported that, people who consume high amounts of soy products, have a lower incidence of cardiovascular diseases. (9)
Bone Health:- Soy isoflavones attenuated bone loss from the lumbar spine in perimenopausal women. (10)
Thyroid Function:- A high isoflavone intake does not seem to increase the risk of hypothyroidism, as long as an appropriate iodine intake is provided: a review of the relevant literature. (11)
Summary
Isoflavones are classified as phytoestrogens- plant derived compounds with estrogenic activity. Soy is rich in isoflavones, considerably genistein and daidzein which are responsible for many of soybeans’ health effects. The content levels of isoflavones of each type of soy food varies greatly, and hence one’s intake level is difficult to ascertain.
Conclusion
Antinutrients:-
- Trypsin inhibitor Prevents digestion and absorption of proteins.
- Lectin Prevents the breakdown of starch and other complex carbohydrates into simple sugars. Binds to the inner lining of the intestine, thus affecting general absorption of nutrients.
- Phytic Acid Found in the hulls of nuts, seeds and grains. Binds Ca, Mg, Fe, Cu and Zn. Reason why product should be low in fiber; high fiber indicates there are more particles from the hull of the seeds and grains.
Isoflavones:-
- Not an antinutrient because they do not interfere in the absorption of nutrients.
- Known to have oestrogenic effects.
- Animal studies indicate risk of lower fertility and higher incidence of cancer in rats given feed high in isoflavones.
- A study found that girls fed soy formula as infants had longer bleeding and discomfort during menstruation.
- Not enough evidence for detrimental effects of isoflavones in infants fed soy based formula.
References:-
-
- Is soy good or bad for you? – Examine
- Soybeans and soy foods – Better Health Channel
- SOY: Overview, Uses, Side Effects, Precautions, Interactions, Dosing and Reviews (webmd.com)
- Top 11 Soybean Nutrition facts and Health benefits (nutrition-and-you.com)
- The clinical importance of the metabolite equol-a clue to the effectiveness of soy and its isoflavones – PubMed (nih.gov)
- Soy and Health Update: Evaluation of the Clinical and Epidemiologic Literature – PMC (nih.gov)
- Early intake appears to be the key to the proposed protective effects of soy intake against breast cancer – PubMed (nih.gov)
- Effect of intestinal production of equol on menopausal symptoms in women treated with soy isoflavones – PubMed (nih.gov)
- Review of clinical studies on cholesterol-lowering response to soy protein – PubMed (nih.gov)
- Isoflavones – PubMed (nih.gov)
- Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature – PubMed (nih.gov)
