As mentioned in a previous blog, soybeans are a nutrient-rich legume.  While soybeans, and other legumes, are best known as excellent plant sources of protein, they also have a healthier fat profile (over 80% of the fats found naturally in soybeans are mono- or polyunsaturated) compared to many other foods and are a good source of a number of essential micronutrients. Despite this, soy consumption in the U.S. is extremely low compared to countries like Japan and China.  A new soy nutrition research paper reviewed current soy consumption levels and estimated the nutritional impact of increasing soy consumption [1].

To determine current levels of dietary soy consumption, the soy nutrition researchers analyzed dietary habit information from the 2003-2004 National Health and Nutrition Examination Survey (NHANES).  The information was collected from over 5,500 men, women, and children.  Analysis of their dietary habits showed that not counting soy sauce, consumption of soy products was mentioned only 226 times with the most common soy foods consumed being meat replacement soy foods, soy drinks, soy energy bars, soy milk, and tofu.  Overall, soy consumption was about 100-150 times less than the amount of meat consumed by adult men and women.  This analysis also showed that as a population, Americans were consuming too few servings of fruits, vegetables and dairy and too many calories from solid fats and added sugars.

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Soybeans are rich in macronutrients like protein, fat, and carbohydrates and contain a variety of micronutrients such as calcium, iron, zinc, riboflavin, and folate [1].  Some of these are discussed briefly below.

Protein. Soybeans are best known as a rich source of non-animal protein.  In fact, about 37% of the raw soybean consists of protein according to the USDA National Nutrient Database for Standard Reference, Release 22 [2]. The amino acid pattern of soy protein provides adequate levels of each indispensable amino acid for normal growth and development. The high digestibility of properly processed soy protein and the bioavailability of its amino acids and nitrogen content make soy protein a high quality protein.  The Protein Digestibility Corrected Amino Acid Score (PDCAAS) of soy protein is 1.0, the highest possible score and similar to other high quality proteins.   Therefore, the addition of soy to the diet is a great way to meet all of one’s protein nutritional requirements.

Fat. Soybeans typically contain more dietary fat than other legumes; however, the fats in soybeans are mainly of the healthier varieties.  According to the USDA National Nutrient Database for Standard Reference, Release 22, raw, mature soybeans contain approximately 20 grams of fat in a 100-gram portion [2].  Of the fat present in soybeans, ~15% is saturated, ~24% is monounsaturated, and ~60% is polyunsaturated; therefore, over 80% of the fat in soy is of the healthier, unsaturated kind.  The predominant unsaturated fats found in soy include linoleic acid and alpha-linolenic acid, two essential fatty acids. Alpha-linolenic acid is an essential omega-3 fatty acid that is metabolized in the body to form eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in small amounts.

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