Health Benefits of Soy - Part 1

Dietary soy consumption has been shown to have beneficial effects on several aspects of human health. Soy consumption has been reported to modestly improve plasma lipid profiles, improve bone health, reduce menopausal symptoms, enhance cognitive function, and potentially reduces the risk of breast and prostate cancers. The health benefits of dietary soy have been attributed to its isoflavones as well as to the biological actions of its constituent proteins. The amount of soy to consume in order to achieve appreciable health benefits has long been a topic of debate. Initial estimates were based on Asian population intakes because the incidences of breast and prostate cancer have been historically lower in Asian populations compared to the United States and Europe; however, determining soy protein and isoflavone intake was problematic. Recently, it has been determined that typical soy intake by older Japanese adults is approximately 6-11 g soy protein and 25-50 mg soy isoflavones, though it is uncertain if this amount provides maximum health benefits.

The potential health benefits of soy have led to its inclusion in an ever-growing number of cosmetic products. The vast majority of these products are designed for topical application; however, it is becoming clearer that proper nutrition and a variety of dietary ingredients impact dermatological health. This chapter will discuss some basic information on soy and its biological actions and will elucidate the evidence regarding the potential benefits of soy and soy isoflavones for dermatological health. Additionally, we will discuss our own studies designed to explore the potential benefits of dietary soy for skin, hair, and nail appearance.

Nutritional Components of Soy

Soy is rich in macronutrients like protein, fat, and carbohydrates, and it contains a variety of micronutrients such as calcium, iron, zinc, riboflavin, and folate. These will be discussed briefly below; however, more detailed reviews are available.

Protein

Soybeans are best known as a rich source of nonanimal protein. The nutritional quality of soy protein has been extensively studied and reviewed. Metabolic studies of nitrogen balance have been used to assess protein quality. When nitrogen balance, digestibility, and net protein utilization were examined, no differences were found between beef and soy proteins. Additionally, these investigators found no differences between these protein sources in the amount of nitrogen intake needed to maintain nitrogen equilibrium. Other studies have reported that both soy protein concentrate and isolated soy protein are capable of maintaining nitrogen balance.

Fat

Soybeans typically contain more dietary fat than other legumes; however, the fats in soybeans are of the healthy varieties. Raw and mature soybeans contain approximately 20 g of fat in a 100 g portion. Of the fat present in soybeans, approximately 15% is saturated, 24% is mono- unsaturated, and 61% is polyunsaturated; therefore, approximately 85% of the fat in soy is of the healthy, unsaturated kind. The predominant unsaturated fats found in soy include linoleic acid and alpha-linolenic acid, two essential fatty acids. Together with the monounsaturated oleic acid, these fatty acids make up nearly all of the unsaturated fat in soybeans. Alpha-linolenic acid is an essential omega-3 fatty acid that is metabolized in the body to form eicosapentaenoic acid and docosahexaenoic acid, two fatty acids with numerous reported health benefits.

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