Are soy products good or bad?

Food is a miracle which enriches our nutrition requirement daily. While it positively correlates with our health, an overconsumption would tend to affect our health negatively. Therefore, maintenance of a better health is a big challenge since the food market is constantly invaded by junk food. As a country with a history of robust agriculture, there’s still time to save our health by consuming fresh fruits and vegetables. However, due to the inadequate consumption of nutrients, our lives tend to depend on medicine as we contract various non-communicable diseases. According to the World Health Organization, 75% of total deaths in Sri Lanka have occurred due to non-communicable diseases. Therefore, this week the Mirror Health Capsule takes a look at consumption and overconsumption of soy foods. 

Soybeans (Glycine max) belong to the legume family, which includes dried beans, peas and lentils. They have  a good nutritional value. Soy has been consumed for centuries in Asian countries while Sri Lanka was the pioneer in soy consumption in the third world.  Soy is a good alternative to animal based products such as dairy and meat. This is because it has good nutritional value and soy is the only plant protein which is equal to animal protein. 

Soy is an excellent source of minerals such as calcium, iron and potassium. Also soy is rich in vitamin B.  Calcium is essential to build and maintains strong bones and teeth whereas iron is used to carry oxygen to tissue and muscle cells

Nutritional value
Soy foods are rich in quality protein, for example, 175 ml of cooked soybeans contains as much protein as 75 g (125 ml of cooked meat, chicken or fish). Soybeans contain all the essential amino acids; same as in meat and which are in amounts that we need for our growth. Apart from that Soy is higher in good fat mainly, monounsaturated and polyunsaturated fats, including omega-3 fatty acids compared to other legumes, which are generally almost fat-free. And soy does not contain cholesterol. Furthermore, Soy is an excellent source of minerals such as calcium, iron and potassium. Also soy is rich in vitamin B.  Calcium is essential to build and maintains strong bones and teeth whereas iron is used to carry oxygen to tissue and muscle cells. Soy contains isoflavones, which are antioxidants that may have a bunch of health benefits.

Common Soy Foods - 
There are many kinds of soy foods made of soybeans. 
Tofu – Use firm or extra-firm tofu in vegetable stir-fries, soups and pasta sauces. 
Soybeans – Whole soybeans can be found fresh, dried, canned, frozen (green soy bean)  or roasted. 
Soy beverages – Soy beverages are ground-up soybeans made into a liquid that looks like milk. Fortified soy beverages have just as much calcium, vitamin D, A and zinc as milk. Soy beverages also provide an average of 8 to 14% of the recommended daily iron intake.

Soya cooking sauces
Soya flour- used for samaposha, short eats, soy snacks, tempeh, 
Soy dairy frozen dessert- Ice Cream, dairy free soya yogurt 

• Soy meat
• Soy nut butter
• Health benefits 

Cardiovascular Disease
Soyfoods potentially reduce the risk of cardiovascular disease through multiple mechanisms as followed.  Elevated low-density lipoprotein (LDL)-cholesterol is a well-established risk factor for coronary heart disease. The Food and Drug Administration established 25 g/day soy protein as the threshold intake for cholesterol reduction. And also American Heart Association concluded that soy protein only lowers LDL-cholesterol 3%.  Soy’s cardio-protective effects results from the inhibition of LDL oxidation by the anthocyanins found in color seed coat of soy and reduction of the formation of plaque in the arteries. In addition to lowering LDL-cholesterol by enhancing serum LDL uptake by the liver’s LDL receptors, soy protein also lowers circulating triglyceride levels (~5%) and raises high-density-lipoprotein (HDL)-cholesterol levels (~1%–3%) as discovered by research studies. The clinical and population levels as epidemiologic and intervention data suggest that for every 1% reduction in LDL-cholesterol there is a corresponding 1%–2% reduction incardiovascular diseases and for every 2%–3% increase in HDL-cholesterol there is a reduction in cardiovascular diseases by 2%–4%. Some clinical data suggesting soy protein in particular is hypotensive due to soy food being rich in protein. Moreover, studies revealed that soybean isoflavones improved endothelial function and the arterial stiffness in postmenopausal women. 

Bone health
Isoflavones in soy foods promote bone health and bone mineral density in postmenopausal women since declining estrogen levels will be lose substantial amounts of bone mass of women in the decade following menopause, which markedly increases bone fracture risk. Research studies found that among postmenopausal women, soymilk consumption was associated with a significantly lower risk of developing osteoporosis due to its richness of calcium content rather than isoflavone content.

Prevention of  obesity-related metabolic syndrome
Soy consumption controls the obesity and related complications by regulating formation of fat cells from stem cells through the binding to estrogen receptors, thus decreasing lipoprotein lipase activity. According to the research studies, improvements in blood lipids and insulin resistance was observed in soy food rich diet. 

Anticancer properties 
Soy food has potential to reduce the risk of many types of cancer specially breast and prostate cancers due to their sensitivity to sex steroid hormones. Mechanisms of soy’s cancer prevention effects are attributable to presence of the isoflavones in soy foods and this cancer preventive mechanism of isoflavones is described by previous research studies and according to that there are multiple mechanisms of action may be responsible. Isoflavones have been shown to affect the cell cycle, cell death, differentiation, production, growth, along with effects on cell signaling. Isoflavones also have antioxidant capacity. Therefore they are well-known scavengers for reactive oxygen species, but recent research is suggestive of additional antioxidant activity beyond direct scavenging of radicals. Genistein, is an isoflavones in particular, has been shown to activate transcription factors (protein that control the rate of transcription of genetic information from DNA to messenger RNA) such as estrogen receptor and stimulate gene expression ( the process by which information from gene is used in synthesis of a functional gene products) in breast cancer cells.

Kidney function
Soy protein places less stress on the kidneys in comparison to other high-quality proteins, which could reduce the risk of developing renal disease in susceptible individuals, such as those with diabetes. More specifically, some studies has been proposed that replacing animal protein with soy protein which leads to a decrease in hyper-filtration and glomerular hypertension, with resultant protection from diabetic nephropathy. 

Mental health
“Diet is as important to psychiatry as it is to cardiology, endocrinology and gastroenterology”.  With this background in mind the emerging evidence suggesting that isoflavones in soy foods may function as antidepressants. Depression is a commonly occurring disorder associated with weakened quality of life and increased morbidity and mortality while the higher prevalence of depression could be seen among women compared to men suggests that reproductive hormones maybe involved in the etiology of this disease.

Skin health
Soy has a positive impact on skin health including wrinkles and overall skin health such as skin elasticity, water-holding capacity, pigmentation and vascularity due to presence of phytoestrogen (plant based estrogen). Moreover, skin appendages, such as hair follicles, are influenced by estrogens presence in soy foods. 

Developmental effect
Healthy eating habits in early life is important since childhood eating habits track into adulthood, and changing adult dietary behaviour is very difficult and also healthy behaviour during childhood and adolescence can affect the risk of developing certain chronic diseases later in life. Normally there is an impact of the diet on pubertal development because pubertal characteristics occur at an earlier age. Clinical studies have found that both total and animal protein intake are associated with earlier first occurrence of menstruation and the development of early pubertal characteristics.

Fertility in women
In women, soyfoods appear to increase the length of the menstrual cycle although ovulation is not prevented. According to research evidence,this minor effect on menstrual cycle length could help to decrease breast cancer risk and there is actually some evidence that isoflavones aid fertility in women. 

(Next article will focus on the harmful effects of soy foods)
The writer is a medical laboratory technologist at a private hospital and holds a MSc. Degree in Industrial and Environmental Chemistry from the University of Kelaniya and a BSc in Food Production and a Technology Management degree from the Wayamba University of Sri Lanka.