Health Benefits of Soy - Part 2

This is the second part of the post:  Health benefits of soy


Carbohydrates

Carbohydrates in soy, though present in only low levels, consist primarily of fiber and the oligosaccharides raffinose and stachyose. The presence of the oligosaccharides can lead to flatulence in human beings due to their lack of alpha-galactosidase, the enzyme necessary for oligosaccharide digestion. However, the low level of carbohydrates in soybeans and their poor digestibility is responsible for the low glycemic index of soybeans and many soy products. Furthermore, research has suggested that the oligosaccharides in soybeans may support intestinal health by acting as a probiotic and stimulating the growth of beneficial bacteria.

Vitamins and Minerals

Soybeans are a quality source of several vitamins and minerals including folate, calcium, zinc, and iron. Folate, an essential B-vitamin, is present in raw, green soybeans at a level of 165 llgll 00 g of soybeans. A 100 g portion of raw soybeans also contains 197 mg calcium (-20% of the RDA), 3.55 mg iron (-20% of the RDA for women and -40% of the RDA for men), and 0.99 mg zinc (-10% of the RDA). The bioavailability of these minerals from soy is an area of increasing research interest. Recent studies indicate that calcium-fortified soymilk is an excellent source of calcium and that soybean ferritin, a source of iron, is readily bioavailable. Additionally, zinc absorption has been reported to be similar between meat and soy proteins. In contrast, it has been reported that non-heme iron and zinc are more poorly absorbed from soy protein than from beef protein and that there is a decline in calcium bioavailability when meat protein is replaced by isoflavone-free soy protein.

Saponins

Saponins are glycoside compounds with a triterpenoid or steroid structure attached to water-soluble mono-or oligosaccharides found in a wide variety of plants. The saponins present in soy, called soyasaponins, are found in a variety of concentrations ranging from 0.6-6.5% dry weight depending on soy variety, growing conditions, and degree of maturity. Soyasaponins have been classified into two main groups, Group A and Group B, based on their aglycone structure. Though soyasaponins are generally considered to have a low bioavailability, they have been shown to have a multitude of biological actions and potential health benefits.

Soy Isoflavones

Though soy has been shown to have a variety of health benefits related to both the protein and isoflavone components of the soybean, it is generally thought that most of the beneficial effects of soy are due to its isoflavones.

Metabolism

It is generally accepted that the glycoside forms of the soy isoftavones are poorly absorbed intact. Therefore, after consumption, the soy isoftavone glycosides must undergo metabolism in the intestinal tract prior to absorption. The soy isoftavones may either be absorbed or further metabolized by intestinal bacteria to such metabolites as p-ethyl phenol, O-desmethylangolensin, and equol. Equol production is of particular interest because it has been implicated in a variety of health benefits; however, only about 30% of the population produces equol. The bioavailability of the isoftavones is highly variable and may depend upon a number of factors including form of soy intake, intestinal microftora populations, and inter-individual differences. The metabolism, absorption, and bioavailability of soy isoftavones are thoroughly reviewed elsewhere.

Posted in: Nutrition,Vitamins and Minerals