Soy-based nutrition with sources of isoflavones such as miso, natto or tofu is the basic diet for a major part of the world’s population. Approximately 1.5 billion humans have a life-long exposure to high quantities of soy. A survey over 50 years in 20,000 citizens of all age groups was published by the Japanese Ministry of Health (Kobayashi 1992). Typical soy consumption is approximately 65 g/day, with higher consumption in the elderly (60-69 years). Calculated as isoflavones the daily intake corresponded to 26-54 mg, with higher values in Japan as compared with the more westernized dietary habits in Hong Kong or Singapore. In certain regions of China the daily intake reaches 76 mg, which correlates with a reduced risk of prostate cancer (Kobayashi 1992; Lee et al. 2003). A subpopulation of up to 10 % of soy consumers – approximately 150 million – consume 100 mg of isoflavones daily, calculated as aglycones (Kobayashi 1992). This range of up to 100 mg of isoflavones daily must be considered absolutely safe by experience – and in addition beneficial for human health.
Soyfood, and soy and red clover supplements are the only relevant dietary sources of isoflavones. Since soyfood does not play an important role in European dietary habits, the exposure to isoflavones is usually very low, with intakes of less than 1 mg of isoflavones per day being rather the rule than the exception (Wu et al. 2008). In Western countries nutritional isoflavone exposure is mostly due to milk products, with the animals grazing on pastures with red clover. The concentration of equol in cow milk can reach 3 to 4.5 µg/100 ml in summer, and at the time of the flowering of red clover even more than 29µg/ml (Antignac et al. 2003; King et al. 1998). The quantities ingested by animals grazing on pastures with red clover are passed on through the food chain, and are one of the major reasons for the background exposure to isoflavones even in societies with no dietary habit for soy consumption. Other contributors to the background exposure are the use of soy preparations as excipients or protein source in food manufacturing.
References
Kobayashi, S. (1992). Trends in national nutritional survey of Japan. Nutr. Health 8 (2-3): 91-96.
