Soybean nutritional properties: The good and the bad about soy foods consumption - A review.

Abstract

Consumption of soy foods is increasing worldwide mainly due to their acclaimed health benefits. However, nutritional demerits associated with soy foods consumption exist. Proteins and lipids, some vitamins and minerals, are major nutritionallyimportant components of soybeans; carbohydrates are major constituents quantitatively. Whole soy foods are also good sources of dietary fibre, B-vitamins, calcium, and omega-3 essential fatty acids. This review examines the merits and demerits of consuming soy foods. The amino acid composition of soybean protein complements that of cereals. Also, the high biological value of soy proteins increases their value as feedstuff. Processing generally increases digestibility of soybean protein; soy protein concentrate and isolate have higher digestibility than soy flours. Trypsin and chymotrypsin inhibitors in flours lower protein digestibility. However, despite demonstrated growth inhibition in animals, due to antinutrients, methionine supplementation in infants is useful only when dietary protein intake is marginal. Although processing considerably reduces antinutrient levels, care must be taken not to reduce protein nutritional value by excessive heating, which can result in loss of thermolabile amino acids. Significant lowering of plasma cholesterol has been reported in hypercholesterolemic subjects with hyperlipoproteinemia, when soy protein replaced animal protein in diets. Also, a dose-response relationship has been shown with isoflavones, particularly genistein, in lowering low-density lipoprotein cholesterol in human kinetic studies. However, questions are being raised about soy isoflavones, especially when consumed as concentrated supplements by segments of the population. Data suggest that genistein may prompt growth of breast tissue in male mice, while other data suggest the opposite effect. Studies also showed that infants consuming soy formula had higher blood levels of isoflavones than women receiving soy supplements who show menstrual cycle disturbances. Also, some animal and human study results have linked soy isoflavones to goitre. Nevertheless, data linking soy consumption to reduced risk of osteoporosis, prostate, breast and colon cancers exists, despite the data being inadequate to make definitive conclusions. Despite concerns on soy isoflavones, the FDA-sanctioned claim on soy protein, covers a component generally accepted as heart-healthy. Nevertheless, the need for more research is emerging as well as caution on soy foods inappropriate consumption. As Africa produces small but increasing amount of soybeans, it will continue relying on imports to meet demand. As demand for soy products increases worldwide, due to its health benefits, African consumers are advised to take note of emerging unhealthy side effects of consumption of large amounts of soy products.

Key words: Soybean, nutrients, health benefits, demerits