MAILBAG:
"I Heard that a Study Showed that Soy Didn't Prevent Breast Cancer"

by Michael Greger, M.D.

Back in February, there was this Dutch study published that followed thousands of women for a few years and found that those who ate the most phytoestrogens did not have lower rates of breast cancer, as might be expected. So a reader wrote me and asked why I didn't mention that study in any of my newsletters.

Sometimes you have to really dig to discover flaws in experimental design; other times it's a bit more obvious. Phytoestrogen intake in the Netherlands? To study a nutrient you need a good range of intake levels. How much soy do Dutch women eat? Not much, it turns out.

The group with the highest intake was eating 0.5mg of isoflavones a day; the group with the lowest intake was eating 0.3mg a day. That means they were comparing people who drank like a single spoonful of soy milk a day to people who drank like half a spoonful. Or comparing people who ate like 1.5 grams of tofu to people who only ate1 gram of tofu a day (a gram is the weight of a paper clip ). And they're surprised they didn't find any difference in breast cancer rates?

Listen to how this study was described in the press, though: "Dietary Isoflavones Not Linked to Breast Cancer" "High intake of isoflavones does not increase risk of breast cancer"[15] Study Shows Reduction in Breast Cancer Risk Not Seen Even if Started at Early Age" "You may have heard that diets rich in soy that contain phytoestrogen help protect against breast cancer. Now, new research from The Netherlands indicates... [no] protective effect."[16]

So always take media reports of studies with a grain of salt, or, at the very least shoot me an email and I'd be happy to check it out.

REFERENCES

[15] http://www.medscape.com/viewarticle/468113
[16] http://content.health.msn.com/content/article/81/96999.htm