Soybean (US) or Soya beans (UK) is the highest source of plant protein; it contains more than 40% protein compared to other legumes which contain 20 to 25% protein. Soy protein is also of the highest quality among all the legumes. The quality of soy protein is equal to that of meat and milk proteins.
Most plant proteins are considered incomplete proteins because they are low in one or more essential amino acids. The levels of one amino acid or another found in some grains are insufficient for human needs. Grains are generally low in lysine; beans are typically low in the sulfur amino acids, methionine and cysteine. However, the level of sulfur amino acids in soybean is higher than in other beans, this makes it equivalent to animal protein in quality. Soybean is the only vegetable that contains all 8 essential amino acids. It is used to substitute animal proteins which contain all the essential amino acids, lacking in pulse protein, in individual diet.
Products into which soybean are made include: soy flour, soy milk, cottage cheese like tofu, tempeh, textured vegetable protein which is made into a wide variety of vegetarian foods, some of them intended to imitate meat, soy lecithin and miso. Soybean are also the primary ingredient in the production of soy sauce. Soy vegetable oil is another product of processing soy bean crop. It’s said that 85% of the world’s soybean crop is processed into soybean meal and vegetable oil.
It can also be used as infant formula. Soy-based infant formula (SBIF) is sometimes given to infants who are not being strictly breastfed; it can be used for infants who are allergic to pasteurized cow milk proteins or who are being fed a vegetarian diet. It is usually sold in powdered, ready-to-feed and concentrated liquid forms.
Soy milk has numerous health benefits:
Soya contains phytoestrogens, chemicals found in plant foods. The type of phytoestrogens found in soybean product are called isoflavones. Some studies suggest that women with a soya-rich diet may have a lower risk of breast cancer because of their intake of soyaisoflavones (daidzein and genistein).
It has been discovered that phytoestrogens help to block the effects of excess oestrogen in the body, evening out any imbalance in the ratio between oestrogen and progesterone. They appear to work by locking into the oestrogen-receptor sites on cells and in doing so they block out the stronger natural oestrogens. They can therefore be helpful in improving symptoms of oestrogen dominance such as PMS and endometriosis.
Due to the phytoestrogen content of soya, many women decide to include it in their diet as they enter the menopause. During the menopause, the body’s natural production of oestrogen stops and symptoms may ensue. As phytoestrogens act as a weak oestrogen, they may help relieve symptoms by boosting levels slightly.
As stated earlier, soybean is the richest plant source of protein. Soya is regarded as equal to animal foods in protein quality yet it is thought that plant proteins are processed differently to animal proteins. Studies show that soya protein isolates tend to lower cholesterol levels while protein from animal sources can raise cholesterol levels. This is a clear advantage over animal protein.
Soybean also contains compounds called phytosterols. These plant compounds are structurally similar to cholesterol and steroid hormones. They function to inhibit the absorption of cholesterol by blocking absorption sites. The cholesterol lowering effects of phytosterols are well documented. This makes soybean a good alternative to meat and other animal proteins and is especially good for vegans.
Soybean contains fat, the good news is that these fats are mostly unsaturated and beneficial. Other legumes (except peanuts) mostly contain between 2 to 14% fat, whereas soybean contains 19% fat. Polyunsaturated, monounsaturated and saturated fats make up 63%, 23%, and 14% respectively of the fat in soybean with saturated fat being the lowest. The polyunsaturated fat content of soybean includes linolenic acid or Omega-3 fatty acid. The presence of omega–3 fats makes it special as soybean is one of the very few plant sources of this essential fatty acid. Omega-3 fatty acids form an essential nutrient which helps to reduce risk of both heart disease and cancer. Omega-3 fatty acids can be found in soybean oil, which is used for cooking.
A serving of soybean provides approximately eight grams of dietary fibre. However, some soy foods are processed in ways that decrease the fibre content significantly. Tofu and soymilk contain very little fibre, while soy foods that utilize the whole bean such as tempeh, soy flour and textured soy protein are high in fibre.
It is advisable to incorporate soybean into your diet from time to time.