We regularly see some excellent news stories on breast cancer prevention, detection, and treatment and the lives of women and men who have been affected by breast cancer. We also often come across news stories that fail to accurately explain what we do and don't know about what causes this disease.
One recent offender, “Experts Explain Diet to Reduce Breast Cancer Risk,” has appeared on many news stations and their websites over the past few months. (Special thanks to Celia from Tucson who alerted us to this story by writing in a question regarding some of the claims it made.)
You might think from the headline that the reporter spoke to many experts. But she didn't. There was just one researcher quoted Clyde Wilson, PhD, a biochemist at the University of California, San Francisco. (The story also included an interview with one woman who had had breast cancer.)
Wilson recommends that women who have had breast cancer enhance their immune system and decrease their risk of reoccurrence by eating more polyunsaturated fats, increasing fiber intake by eating lots of vegetables, reducing calories, and cutting down on alcohol. He also encourages women to not eat corn because “a half a cup of corn per day is shown in research to increase breast cancer risk 25 percent.”
The story ends with “Dr. Wilson's list of foods that reduce breast cancer risk.”
This is the list, as it is printed:
Spinach (1/2 cup cooked) - 39 percent
Brussels sprouts (1/2 cup) - 33 percent
Cabbage (1/2 cups to several cups) - 10-50 percent
Omega-3 fats included in diet - 25 percent
Green tea (1-2 servings / day) - 15 percent
String beans (1/2 cup) - 15 percent
Omega-6 fats included in diet - 15 percent
Broccoli (1/2 cup) - 14 percent
It would be hard to find a worse way to present this information. It appears that as a reader you are supposed to make the assumption that you would have to eat this amount of each food each day to get this benefit. But that's not stated. It also doesn't say how long. Forever? A month? And what does reducing breast cancer risk by 15 percent mean anyway? If you are 50, you have a 28 out of 1000 chance of getting breast cancer in the next 10 years. That is a 2.8 percent risk. So, if it were true that eating say, 1/2 cup of string beans were to reduce risk by 15 percent, that would mean your risk would now be 2.38 percent instead of 2.8. Doesn't sound quite as interesting, does it? Also, it would be easy to assume that if you ate spinach, Brussels sprouts, string beans, and broccoli, you could reduce your risk completely, since 39+33+15+14 is more than 100 percent. But there is absolutely no evidence that these risk reductions add up in this way.
More importantly, if the reporter had actually talked to more than one expert, she might have learned that there is actually a great deal of controversy over—and very little data on—the relationship between food and cancer risk. Some of the first studies to explore the relationship between breast cancer and foods found that women who ate lots of fruits and vegetables had a decreased risk of breast cancer. But now it appears that it's probably the vegetables that matter, not the fruit, and if they do matter, it's nowhere near to the extent that we thought they might. And while there have been some studies that have found that eating a lot of vegetables might reduce the risk of a breast cancer recurrence, how much you should eat and what the risk reduction would be is far from clear.
It's also not clear where Dr. Wilson's statistics came from. We could find no data whatsoever to support the recommendation of not eating corn. And while there have been some studies conducted on the benefits of the vegetables on Dr. Wilson's list, most have been done in the lab on cells or animals. And we know all too well that what happens in the lab doesn't always happen in human. (We emailed Dr. Wilson about his sources and he said he would supply references, but he never did.)
