Research Updates: Soy Intake Early in Life

Soy Intake Early in Life

Not surprisingly, most clinical research involving soyfoods or soybean constituents such as isoflavones has been conducted on adults, and in particular, postmenopausal women. However, there is a need to understand the impact of soyfood/ isoflavone intake on the nutritional and health status of children and to understand the role of traditional soyfoods in the diets of young Asians. Two recent studies provide some insight in this regard. One provides a very detailed look at the soy/isoflavone intake of young children in Korea.  Many studies are available on the isoflavone intake of adult Asians, but few are available on the isoflavone intake of children. The other study, which has thus far only been presented, examines the relationship between soy intake during childhood and adolescence, and adult breast cancer risk among U.S. Asians.

Korean Isoflavone Intake

Isoflavone intake results were derived from the daily food intake collected by the 1998 National Nutrition Survey. Intake was expressed on an absolute basis and per kilogram (kg) body-weight (bw) for different age groups, using the average weight for each group according to previously published data. As Figure 1 on page 5 shows, on a body-weight basis, soy (as assessed by isoflavone exposure) intake plays as big a role among children ages 1-12, as it does for adults. Peak soy intake occurred during the 30- 49 year period,  but on a body-weight basis that was only slightly higher than age 3-6 years. For comparison purposes, the maximal intake of 33.6 mg isoflavones is the amount found in about 1½ servings of traditional soyfoods. Note, there is a wide range of intake among  any given age group and the mean intake is not necessarily ideal.

The possibility that early soy intake reduces breast cancer incidence later in life is arguably one of the most exciting hypotheses in the entire diet-cancer field. The first animal study in support of this hypothesis was published in 1995 and the first epidemiologic study in 2001. A recent epidemiologic study presented at the American Association for Cancer Research meeting in Washington, DC, late last year provides additional support as well as new insight into the critical period of exposure to soy for protection against breast cancer to occur. This study involved 99 cases and 156 controls. The women were interviewed about their soy intake during childhood (5 – 11 years of age) and adolescence (12 – 19 years of age). Women who were in the third tertile for soy intake during these two periods of life were 58% and 23%, respectively, less likely to have developed breast cancer during adulthood as were women in the first intake tertile. One proposed mechanism for the observed protection against breast cancer is that the isoflavones in soy stimulate differentiation of breast cells making them permanently more resistant to becoming cancer cells. Am Assoc Cancer Res Annual Meeting (abstract - 06-AB-667-AACRCPR) 2006.