Diet and Breast Cancer – Is There a Link?

My friend Jan was recently diagnosed with breast cancer.  Fortunately, Jan’s doctor detected the cancer in the very early stages and Jan’s going to be fine.  Nonetheless, it’s been a very difficult and scary time.  Last week, Jan asked me for advice on how she might change her diet to reduce her risk of recurrence.  Given how common breast cancer is, this is something every woman should think about.

Although diet plays a role in the development and progression of breast cancer, it’s a fairly secondary one. Still, it’s the factor that we have the most control over.  Even though no diet or food can prevent breast cancer, if certain habits can reduce our risk, why wouldn’t we adopt them?  Let’s just make sure that we’re basing our decisions on sound science.

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Does Dairy Cause Breast Cancer?

There’s a popular book called The China Study by T. Colin Campbell, which argues that consuming dairy products increases your risk of breast cancer.  Although Campbell’s book has convinced many readers that dairy causes cancer, there are significant criticisms of his methodology, statistical analysis, and conclusions.

Over the last ten years, dozens of studies—several of them involving thousands of subjects—have investigated the possible relationship between dairy consumption and breast cancer.  Researchers have failed to turn up any link between dairy and breast cancer risk.  (In a few of the studies, dairy consumption was actually linked to a slight reduction of risk.)

As I’ve said many times before, dairy is not essential to a healthy diet and I support anyone who chooses not to consume dairy products. However, if you want to include dairy in your diet, I think you can do so without any concern about it increasing your risk of cancer.

Does Soy Promote or Prevent Cancer?

There’s also a fair amount of controversy about soy for breast cancer survivors. As I explained in my previous articles on soy, it contains compounds that are shaped very similarly to the human hormone estrogen. In fact, they’re close enough that they can actually fit into estrogen receptors in human cells. 

Soy consumption appears to reduce the risk of breast cancer in the general population, but researchers worried that the estrogen-like compounds in soy could promote the growth of estrogen-sensitive cancer cells in people who already had cancer.  Several recent studies have put this concern to rest. Eating soy appears to have no adverse effect on breast cancer survivors—and may even slightly reduce the risk of recurrence.

Given this latest evidence, my advice on soy for breast cancer survivors is the same as for everyone else:  Enjoy soy foods in moderation (no more than 2-3 servings per day) and choose soy products that are minimally processed, such as edamame, tofu, miso, tempeh, and unsweetened soy milk.

Does Sugar Feed Cancer Cells?

Another common myth about cancer and nutrition is that cancer cells “feed on sugar.”  This is simply not true.  All cells use glucose (or sugar) for fuel. But sugar does not make cancer cells grow faster—and a lack of sugar does not stop them from growing. Studies have not found a consistent link between a high glycemic diet and breast cancer. That said, there are a lot of other good reasons to limit the amount of sugar in your diet, whether or not you have cancer.  What’s most important is to avoid chronically high blood sugar—and I have some tips on how to do that in What is High Glucose?

The 3 Most Important Things You Can Do to Reduce Your Risk of Breast Cancer

If you or a loved one has had a brush with cancer, it may give you some extra motivation to clean up your diet, avoid foods you know are bad for you, and eat more healthfully. You’ll find plenty of ideas on how to make your diet healthier in the Nutrition Diva archives. But if you’re trying to reduce your risk of breast cancer, be sure you’re not overlooking the things that will have the biggest impact:

1. Lose Weight (If You Need To)
   Being overweight is one of the strongest and most consistent risk factors for breast cancer—particularly in women who have gone through menopause.  Obesity increases circulating estrogen levels, which contribute to cancer risk.   Check out my tips on how to take off extra weight and how to find a diet that will work for you.

2. Exercise Regularly
   Even if you can maintain a healthy weight without exercising, regular exercise further reduces your risk of breast cancer by lowering the levels of circulating estrogen in your body.  Among cancer survivors, regular exercise has been shown to cut mortality risk in half.  I’m not talking about ironman competitions or 100-mile bike rides.  You can substantially reduce your risk of breast cancer by taking a brisk 30-minute walk every day.

3. Drink Moderately or Not at All
   Although it’s not completely clear how or why alcohol increases cancer risk, the evidence of a link between drinking and breast cancer is quite convincing.  Even one drink a day is linked to a slight increase in risk. Higher consumptions levels bump your risk up dramatically.  If you regularly consume alcohol and you’re at all concerned about breast cancer, this is one habit you may want to give serious thought to.

I wish I had a magic bullet—a special diet, a superfood, a cancer-killing recipe—that would ensure that none of us would ever have to worry about breast cancer (or any cancer) again. Short of that, let’s do the best we can to take good care of ourselves and take some comfort in the fact that, while there are no guarantees, the same habits that lower our cancer risks also reduce the risk of lots of other diseases and help us enjoy life to the fullest.