Expert Q&A: The Anti-Cancer Diet

An interview with Karen Collins, MS, RD.

Reviewed by Louise Chang, MD on November 25, 2008

Keeping track of the foods that prevent – or cause – cancer can get pretty confusing. So to lower your risk, what should you really be doing? Filling up on fiber? Shunning nitrates? Stocking your fridge with only organic vegetables?

We got some concrete answers from Karen Collins, MS, RD, CDN, nutrition advisor for the American Institute for Cancer Research (AICR) in Washington, D.C.

Do preservatives, nitrates, food additives, and other food chemicals cause cancer?

You know, we hear a lot of news stories linking various additives and chemicals and food colorings with cancer risk. It’s certainly possible. But at this point, the evidence hasn’t shown any real connection. In fact, some preservatives seem to be antioxidants, which could mean they’re actually protecting us.

I think people can get a little too preoccupied with these theoretical connections when they would be better off focusing on better established ways of reducing their risk of cancer -- weight loss, exercise, and a healthier diet.

Why do fruits, vegetables, and plant foods seem to protect against cancer?

Plant foods probably offer protection in a number of ways. They provide thousands of phytochemicals, which are natural plant compounds. Many are antioxidants, which seem to protect and repair our DNA. Some antioxidants appear to affect cancer cells, controlling how they grow or spread. The vitamins and minerals in vegetables, fruits, whole grains, and beans also help produce and repair DNA and control cell growth.

Some foods can have a more direct effect on specific types of cancer. For instance, plant foods contain fiber, which seems to lower the risk of colon cancer.

There’s also an indirect benefit to eating whole foods that are low in fat. They tend to be less calorically dense, so we can fill up on them without getting so many calories.

Are organic foods the best defense against cancer?

Eating organic foods is fine as an option, but it’s not necessarily preferable in terms of lowering cancer risk. You can find studies showing that organic foods are higher in nutrients and protective phytochemicals, but you can find just as many showing they're not. Although people worry about pesticide residues, not all conventionally grown, nonorganic crops contain them. Of those that do, less than 1% have them in amounts above the current strict tolerance levels.

If you prefer organic, that’s fine. But organic fruits and vegetables do cost more. So if you’re eating fewer fruits and vegetables just so you can afford buying them organic, that’s not a good idea. People shouldn’t feel like they’re putting themselves at risk if they’re eating conventionally grown foods.

Why is keeping a normal body weight so important to cancer prevention?

We know that being overweight or obese is strongly linked to an increased risk of several common cancers – like cancers of the colon, breast, kidneys, esophagus, endometrium, and pancreas to name a few. We think there could be several reasons why.

Excess body fat, especially around the waist, is linked with insulin resistance and high insulin levels. Although people associate insulin with blood sugar and diabetes, researchers think that high levels of insulin may promote the growth of cancer cells. Excess fat also seems to trigger inflammation throughout the body, which seems to encourage cancer growth.

Excess body fat can pose a specific risk to older women. After menopause, excess weight is associated with higher levels of estrogen. That can promote the development and growth of estrogen-sensitive cancers of the breast and endometrium.

How does physical activity affect a person’s cancer risk?

We now think that physical activity has a vital role in lowering cancer risk. It can directly reduce insulin resistance, inflammation, and the levels of reproductive hormones. Indirectly, it can help achieve and maintain weight loss, as well as prevent the weight gain that many adults experience as they get older.

The current recommendations from the American Institute for Cancer Research are at least 30 minutes a day of moderate physical activity. And if you can, you should aim for 60 minutes a day – or 30 minutes of more vigorous activity. You’ll achieve even better cancer protection and weight control.

Does meat or any other type of food contribute to the risk of cancer?

There’s a pretty convincing link between red meats and colon cancer, and possibly other cancers as well. It’s not just the fat. Although choosing lean meat is good for nutrition, it’s not enough to reduce the cancer risk.

However, you don’t have to give it up completely. Eating up to 18 ounces of red meat a week seems to be safe. You just want to make meat an occasional food instead of one that you eat daily.

Eating processed meat -- which is salted, cured, smoked, or treated with preservatives -- seems to have an even greater risk of colon cancer. So you should try to limit that as much as you can.

You should also be careful of how much sodium you get – more than 2,400 milligrams a day seems to increase the risk of stomach cancer. Eating fewer processed foods can help with that. Alcohol also increases the risk of several cancers, so from a cancer perspective, the less you drink the better. Women should have no more than one drink a day and men no more than two.

Should cancer survivors follow any specific diet? Are there any foods, nutrients, or supplements that they should avoid?

In general, cancer survivors don't seem to be any different from anyone else in terms of what they should eat. One exception would be those taking anti-estrogen medications -- like tamoxifen or aromatase inhibitors – who may need to avoid soy foods. Soy contains a plant form of estrogen, so it could work against these medications.

If you’re a cancer survivor and the effects of your cancer – or its treatment – are making it hard to eat well, see a registered dietitian. Together you can figure out ways to get the nutrients you need.

Could you describe the ideal diet for cancer prevention?

There is no one specific ideal diet that is perfect for all of us. So we can each come up with a diet that's protective and still works with our lifestyles and food preferences.

But here’s an easy way to picture a healthy, protective diet. Every time you eat, aim to have two-thirds of your plate made up of healthy plant foods, like vegetables, fruits, whole grains and beans. Then have the remaining one-third, or less, made up of animal foods, preferably lean poultry, seafood, and very limited amounts of red meat. To add flavor, use moderate amounts of healthy oils, herbs, spices, citrus, and vinegars.

A protective diet can still fit in occasional treats, but you’d get most of your sweets from fruits instead of candy and cookies. For drinks, you’d want to emphasize water, some tea and coffee, and maybe modest amounts of fruit juice. You’d want to stay away from sugary drinks, because their high calorie content makes it hard to control weight.

Adopting this approach to diet will have big benefits. A 2007 expert report from the American Institute for Cancer Research found that eating like this -- combined with physical activity and weight control -- could prevent one-third of all cancers.

Some people could find that diet hard to follow. What would you say to them?

Even if that ideal diet doesn’t seem possible to you, don’t be discouraged from taking small steps. It’s not all or nothing. Working any of the recommendations into your lifestyle can help.

For instance, if you could just cut out 200 calories a day – calories you eat out of habit, not hunger – you will lose weight, and that will lower your risk. If the idea of working out 30 to 60 minutes a day seems ridiculous, just try to add in 10-minute walks twice a day.

Now, you won’t get as much cancer protection benefit by making small steps as you would if you followed the full recommendations. But you can still make a difference. You’re much better off doing something to lower your risk of cancer than doing nothing.

Has eating a healthy diet always come naturally for you? Are there any foods that you find hard to resist?

I actually grew up a vegetable and fruit hater. As a kid, the only ones I’d eat were applesauce, potatoes, bananas, corn, and iceberg lettuce. And even as a teenager, it didn’t get much better than that. But as I got older, the more nutrition I studied, the more I came to realize how important vegetables and fruits are. I just made up my mind that it was important to eat more of them, but decided I wasn't going to suffer. So I set about experimenting, making all kinds of vegetables in a wide variety of ethnic and other flavorful styles. Now the vegetables are usually my favorite food in the meal. Change is possible!

I do have a sweet tooth, and I especially love chocolate. But I don't try to make it "forbidden,” since I know I'd just crave it more and go overboard. For me the solution comes down to the obvious -- I don't keep sweets around the house. So I get something sweet occasionally when we're entertaining or when I know I will really sit and enjoy it. Or I might order a dessert when we eat out. But strangely, when something's not here in the home, I rarely crave it.

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Karen Collins, MS, RD, CDN, nutrition advisor, American Institute for Cancer Research, Washington, D.C.

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