My friend Kate recently asked what I thought about the fact that her granddaughter drinks a lot of soymilk. I said I thought it was great!

There are plenty of reasons—mostly from ethical and environmental standpoints—to avoid cow’s milk. Whether there are important health risks associated with dairy consumption is still a question of debate. But there is little to suggest that dairy has any protective benefits that you can’t get elsewhere. Soy, on the other hand, may have some unique and long-lasting benefits for young girls.

Interest in a cancer-protective effect of soyfoods comes, in part, from the fact that breast cancer is much lower in Japan, where soyfoods are commonly consumed, than in western countries. Scientists have been speculating for decades that the anti-estrogen effects of isoflavones—compounds that are unique to soyfoods—are responsible for this difference.

Unfortunately, there is no clear consensus that adding soyfoods to your diet in adulthood will lower cancer risk. But some very interesting studies suggest that when young girls consume soyfoods, their risk for breast cancer later in life is much lower.

A National Cancer Institute study found that risk for breast cancer was 58% lower for women who had consumed soyfoods between the ages of 5 and 11 years. A study in China—where soy consumption differs greatly across different regions—had a similar result. Consuming soy between the ages of 13 and 15 was associated with a 49% reduction in breast cancer risk.

Why soy might provide this long term protection isn’t known, but it may have something to do with effects of isoflavones on breast tissue during development. And according to the data, as little as one serving of soy per day might be protective.

While the studies aren’t conclusive, it clearly makes sense for young girls to consume soyfoods that are rich in isoflavones. Best choices are tofu, tempeh and soymilk (many commercial soy burgers are not rich in isoflavones). Soymilk is probably the easiest food to include in a child’s diet. Choose a brand that is fortified with calcium and vitamin D, and use it just as you would cow’s milk–over cereal, in baking, and in milk shakes.