Health professionals and consumers are seeking guidance regarding appropriate soy intake levels. Several different types of evidence that support of our recommendation that adults should consume 15 g (range 10-25 g) soy protein and 50 mg isoflavones (range 30-100 mg)/day are presented.
There are many reasons for the growing popularity of soy foods, but the much discussed health effects are the main reason that increased numbers of consumers are including soy in their diets. Hypothesized health benefits include, but are not limited to, protection against osteoporosis, coronary heart disease (CHD), and certain forms of cancer, especially breast and prostate cancers. The two soybean constituents that most experts consider responsible for disease prevention are protein and isoflavones.
As soy foods make their way into the mainstream food market (Figures 1, 2, and 3), it is important that dietitians and nutritionists can advise the public regarding appropriate intake levels for soy protein and isoflavones. Guidelines are especially needed because it is increasingly easy for consumers to ingest large amounts of both of these soybean components. Isoflavones are now sold as dietary supplements and are used as food fortificants, being added to both nonsoy foods and soy foods. Also, many Western soy foods, such as energy bars, burgers, and soy protein-based beverages, are more concentrated in soy protein than the traditional soy foods, some providing as much as 20 g protein per serving.
In 1999, the US Food and Drug Administration (FDA) approved a health claim, intended primarily for those with hypercholesterolemia, for the cholesterol-lowering properties of soy protein and set 25 g per day as the intake necessary for cholesterol reduction. However, the health claim does not address soy protein's effects other than cholesterol reduction; nor does it address health effects of isoflavones unrelated to serum cholesterol. Therefore, the purpose of this article is to present a brief rationale for recommending that healthy adults strive to consume approximately 15 g (range 10-25) soy protein and 50 mg isoflavones (range 30-100) per day. As noted in Table 1, traditional soy foods have an isoflavone (mg):protein (g) ratio of 3-3.5:1. This rationale is based on four types of evidence or considerations: (1) Asian soy intake, (2) efficacy, (3) safety, and 4) practical considerations.