"Will eating a diet high in soy protect me from breast cancer?" That's a question I hear frequently. And it's a good question. Study after study has shown that the chance of getting breast cancer in countries where soy is a major part of the diet is dramatically less than it is in countries where the people eat very little soy. So soy is protective against breast cancer. But the problem is how much soy do you need to eat to get the anti-cancer benefits? A recent study indicates that it's probably a lot more than you are going to eat.
Researchers followed 84,450 women for 13 years to find out how much soy they had to eat to prevent breast cancer. The group of women was quite varied. It included Japanese Americans, whites, Latinos, African Americans, and Native Hawaiians. And they were also very different in their dietary intake of soy-based foods.
The researchers divided the women into five groups depending on how much soy they ate. The ones in the lowest group hardly ate any soy at all – less than two tablespoons per day on average. And the ones in the highest group ate about 16 ounces per day on average. That's a lot more than most people eat. Over the 13 years, 3,873 women developed breast cancer and 896 women develop a precancerous condition known as carcinoma in situ.
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When the researchers went to compare the chance of getting cancer to the amount of soy in the diet, they found no difference at all between any of the groups. Their conclusion was that although soy does decrease the chance of getting breast cancer, the amount per day has to be a lot more than just 16 ounces. And that's a lot more than most anybody – other than a vegan – is likely to eat.
So if you are looking for strategies to prevent breast cancer, eating more soy does not look like your best option. You can eat as much as you want, but unless you eat more than 16 ounces daily, it won't prevent the disease. Instead, I recommend to my patients that they do the following:
- Take 12.5 mg of iodine in the form of Lugol's solution or Lugol's tablets each day.
- Take 3 mg of melatonin at bedtime.
- Take enough vitamin D3 to get your blood levels between 65-75 ng/ml (usually about 5,000 IU daily).
- If you are over 45, use progesterone cream under the supervision of a doctor.
- Eat plenty of cruciferous vegetables (broccoli, cauliflower, kale, collard greens, bok choy, cabbage, and Brussels sprouts).
Based on available studies, I estimate that simply doing this will lower your overall cancer risk from 1 in 7 to about 1 in 35. Those are much better odds – without any side effects.
Yours for better health,
Frank Shallenberger, MD
Morimoto Y, Maskarinec G, Park SY, et al. Dietary isoflavone intake is not statistically significantly associated with breast cancer risk in the Multiethnic Cohort. Br J Nutr. 2014 Sep 28;112(6):976-83.