Tofu (soybean curd) is made by taking soybeans, soaking them in water, boiling, mashing, and straining them to make soymilk. This milk then has a coagulant added to it and it is pressed into a cloth-lined mold (Wang, 1984). It originated in East Asia and is an important source of protein in the diet of people from those countries (Kweon, Ryu, & Moon, 1993). Soybeans have a protein content of 40%, which is far higher than that of other legumes (Kweon et al., 1993). It is also a source of oil, with oil and protein making up 60% of the content of dry soybeans (with carbohydrates at 35% and ash at 5%). Tofu, and other soybean products, have become more and more popular in Western diets, especially with the rise in popularity of plant-based foods (McCue & Shetty, 2004). It is important, therefore, to understand the benefits of tofu nutrition, as well as the possible disadvantages of eating it. The preparation and heating process when creating tofu from soybeans has not been found to eliminate any of the health benefits from eating soybeans alone (Eze et al., 2018), so the health benefits of soybean can also be gained from eating tofu. The fermentation of tofu, however, can also lend its own health benefits beyond those of soybean alone (Sanjukta & Rai, 2016).
Soybeans are one of the leading sources of plant-based protein and many people use plant-based proteins exclusively. Protein is an important part of the diet. It is formed from amino acids and is a vital structural component for muscles as well as other body tissues. It also helps in hormone, enzyme, and hemoglobin production, and can be used as a source of energy (Hoffman & Falvo, 2004). There are 20 amino acids, with 12 of them classed as nonessential (they can be produced by the body) and eight as essential (they have to be obtained from food), and being deficient in any of them can cause health problems related to the growth, repair, and maintenance of tissue (Hoffman & Falvo, 2004).
While soybeans are 60% protein (Kweon et al., 1993), they are not an ideal form of protein because they do not contain the essential amino acid methionine (Friedman & Brandon, 2001). In comparison, animal protein produces all of the essential amino acids. Soybean’s level of another essential amino acid, lysine, is also low when compared with cow’s milk. As well as this, raw soybeans are not easily digestible and can cause digestive and nutritional issues because they contain enzyme inhibitors, flatulence factors, and off-flavor producing lipoxygenases (Kumar, Rani, & Chauhan, 2010). While most of these inhibitors are destroyed by heat, 20% remain (Friedman & Brandon, 2001).
Having said that, eating a diet rich in soybeans can have other health benefits. Most notably, soybeans are a good source of vitamin B9 (folate or folic acid). Folic acid is a vitamin that is important for the proper functioning of the nervous system, and it is also involved in cell reproduction. Being deficient in folic acid can lead to folate deficiency anemia (Reynolds, 2014). Folic acid is vital for neural tube development, and maternal folic acid deficiency can result in birth defects such as spina bifida in the fetus (Reynolds, 2014). The effects of folic acid deficiency on the fetus happen so early on in pregnancy that it is advised for women to take folic acid supplements from before they become pregnant up until they are 12 weeks pregnant (NHS.co.uk).
Soybeans are a source of isoflavones. These are an estrogenic substance (Mo et al., 2013) that partially bind to estrogen receptors (McCue & Shetty, 2004), and are sometimes referred to as phyto-estrogenes because of this. This similarity to estrogen means that isoflavones can help treat some symptoms of the menopause such as osteoporosis and hot flushes (McCue & Shetty, 2004). They can help to lower the risk of cardiovascular disease (Mo et al., 2013), and, because of their antioxidant enzyme activities, they can reduce the risk of endometrial, prostate, and breast cancer (McCue & Shetty, 2004).
If tofu is used to replace meat protein sources in the diet, it can reduce the risk of metabolic syndrome. It can also reduce the amount of “bad” cholesterol (LDL), increase the amount of “good” cholesterol (HDL), and reduce the amount of triglyceride in the blood (van Nielen, Feskens, Rietman, Siebelin, & Mensinnk, 2014). Eating tofu instead of meat could, therefore, also reduce the risk of heart disease.
Further, the fermentation process of converting soybean into tofu can give it health benefits over and above those of soybean alone. Soybean is fermented using bacteria and fungi, and this processe results in the production of bioactive peptides (Sanjukta & Rai, 2016). Sanjukta and Rai (2016) conducted a review on these peptides. They found that they act like regulatory compounds and can have several health benefits. They can be protective against hypertension, which is a severe increase in blood pressure that can lead to a stroke. They also have antimicrobial properties, which can protect against infection by destroying microorganisms, as well as antioxidant properties. Antioxidants disrupt the oxidation process that can result in free radicals. These free radicals can lead to heart disease and cancer, so tofu is also protective against these diseases. As well as this, they can lower the risk of diabetes. Eating soybean in tofu form, therefore, will result in both the health benefits of soybean as well as the health benefits resulting from the bioactive peptides released during the tofu fermentation process.
In conclusion, tofu nutrition (soybean curd) can have several health benefits. Some of these are due to the soybean itself, such as improving muscle repair and growth and reducing the risk of folate deficiency anemia and spina bifida. Soybean is also protective against cardiovascular disease, some hormonal cancers, heart disease, and metabolic syndrome. The fermentation process of tofu does lead to health benefits beyond those of soybean, such as being protective against hypertension, helping to fight infection, being protective against cancer and heart disease, and lowering the risk of diabetes. It is lacking in some essential amino acids, however, and is not easily digested, so it may be unsuitable as a complete protein replacement unless the missing essential amino acids are supplemented in another way.
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