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Complementary and Alternative Medicine: Fair and Balanced

Concentrations of isoflavones in food

If you were raised on meat and potatoes, a significant (but often pleasant) change in cuisine will be needed to increase isoflavones in your diet.

By John Russo Jr./

VICUS.COM (27 June 2000) -- Isoflavones, one of the families of phytoestrogens, appear to make a positive contribution to health, and soy foods offer the best source of isoflavones.

Soy also provides high-quality protein, as well as being low in saturated fat, and is a good source of essential fatty acids.

Although there is no recommended daily intake for soy or isoflavones, for those who want to increase their consumption of soy-containing foods, here are some guidelines to consider.

How much is enough?

A summary of the daily amounts of soy and isoflavones that have or are being studied to prevent a range of diseases is provided in Table 1. 

Table 1. Daily amounts of soy and isoflavones studied or being studied to prevent a range of diseases.

Objective Daily dose
Lowering cholesterol 25-50 grams of soy protein
Cancer (breast, prostate, colon) prevention 20-40 grams of soy protein
Hot flashes, reduction 45 g of soy flour/day
80-160 mg of isoflavones  
Osteoporosis, post-menopausal women 40 grams of soy protein per day containing 90 mg total isoflavones/day for six months had a positive effect on bone density  

Source: University of Illinois at Urbana-Champaign, College of Agricultural, Consumer and Environmental Sciences

Sources of soy and isoflavones

Isoflavones are available in tablets, but these are not recommended as the primary source of phytoestrogens. This is because it is not known if the beneficial effects of isoflavones are due to the body's response to isoflavones alone or a combined effect of isoflavones with other nutrients.

For example, in addition to isoflavones, soybeans contain protease inhibitors, omega-3 fatty acids and phytosterols, all of which are absent from isoflavones tablets. In addition, soybeans contain other beneficial nutrients such as iron, protein and calcium, as well as non-nutrients such as fiber. 

What’s so special 
about isoflavones?

Although scientists have known about the existence of isoflavones for 50 years,  only a handful of scientific papers were published on these phytochemicals until the early 1990s. In the past five years, more than 300 papers have been published annually on isoflavones. The proliferation is attributed to a 1990 National Cancer Institute decision to allocate nearly $3 million to study the anti-cancer effects of isoflavones. As interest in the potential anti-cancer effects of isoflavones grew, researchers began to look at effects on other diseases, including heart, disease, osteoporosis and hypertension. 

Source:  Archer Daniels Midland Company

Most manufacturers do not list the isoflavone content of their packaged foods, but here is a partial list (Table 2) developed through a collaborative effort between the U.S. Department of Agriculture and the Department of Food Science and Human Nutrition of Iowa State University (Ames, Iowa). 

The USDA/Iowa State database reflects the isoflavone content of foods produced in 1999. The year and place where the food was grown affects the isoflavone content of soybeans as well as soy foods. 

However, this list and the figures that follow provide guidelines for selecting foods that are rich in isoflavones. 

All soybeans are not equal ... in isoflavones

The average concentration of isoflavones varies according to the source. For example, Taiwan soybeans have only about 40% of the isoflavones found in soybeans from Korea, the richest source of isoflavones from soybeans (figure1). Soy flour is even richer in isoflavones (figure 2). Full fat, roasted soy flour has almost 200 mg of isoflavones per 100 grams compared with defatted soy flour, which has about 40% fewer isoflavones for the same weight. 

Eating soybean seeds as a snack, available in markets and health food stores as soy nuts, is a convenient way to increase soy intake. They can be eaten in place of peanuts (contain 0.26 mg isoflavones/100g) or dried sunflower seed kernels (contain no isoflavones). The concentration of isoflavones in soybean seeds varies (from 12 to 153 mg/100g), depending on the maturity and processing of the seed (figure4). 

Other good sources of isoflavones are beans, although compared with soybeans, their isoflavone content is rather low (figure 3).

Some food processors have attempted to capitalize on the growing interest in soy and isoflavones. The five examples in (figure 5).Figure 5 reveal the wide differences in isoflavone content of franks, links, patties, nuggets and adult formula.

A strategy for increasing dietary isoflavones

In order to reach the daily amounts of isoflavones that researchers suggest are needed for a positive impact on health, it is logical to concentrate on soy-based foods. This might include baking with soy flour (up to 177.9 mg isoflavone/100g), drinking a soy beverage (109.5 mg/100g), or eating defatted soybean flakes (125.8 mg/100g). Other good sources of isoflavones include tofu, such as Mori-Nu silken firm (27.9 mg/100g) or dried-frozen (67.5 mg/100g), and tempeh, either cooked (53.0 mg/100g) or burgers (29.0 mg/100g). 

Not all beans contain isoflavones. Those that do contain modest concentrations of isoflavones and should be eaten to supplement an isoflavone-rich diet. Navy, pinto, red, fava, garbanzo and small white beans contain 0.1 to 0.7 mg/100g. 

For people raised on meat and potatoes, it may require significant (often pleasant) changes in cuisine to achieve the intake reported in clinical studies, including eating misotofu and natto. Contrary to popular belief, soya sauce (shoyu), the most important Japanese condiment, is a relatively poor source of isoflavones (1.6 mg/100g). 

John Russo Jr., PharmD, is senior vice president of medical communications at He is a pharmacist and medical writer with more than 20 years of experience in medical education.



University of Illinois at Urbana-Champaign, College of Agricultural, Consumer and Environmental Sciences. Soy and Human Health. Last modified 2000 March 31. [Cited 2000 May 30] Available from URL:

USDA-Iowa State University Database on the Isoflavone Content of Foods. Released 1999 Jan 1. [cited 2000 May 30] Available from URL: