By Katie Scarvey
It might be tempting to think of cancer as something we have little control over, but in fact, what we eat — and how much we eat — can be important factors in whether we get cancer or not.
The American Institute of Cancer Research estimates that one out of three cases of cancer is preventable through changes in lifestyle.
Diet, says Dr. Steven H. Zeisel, “is an important component in whether you get cancer or not.” A poor diet imparts about the same risk of cancer as smoking does, Zeisel said.
Zeisel, the director of the UNC Nutrition Research Institute, recently delivered the first in the Appetite for Life series of lectures at the N.C. Research Campus.
Diet can be a source of carcinogens, or cancer-causing agents, Zeisel said. We take in carcinogens when we eat blackened meat, for example. “You don’t want to eat meats that are burned to a crisp,” Zeisel warned. Eating processed meat like salami and ham also leads to an increased risk of cancer.
Fiber in the diet , however, has a protective effect, because it binds to dangerous chemicals and speeds them through the body, lessening the chances of absorption. Getting adequate fiber, Zeisel said, can reduce cancer risk by about 10 percent.
Good sources of fiber are whole grains or the skins of vegetables and fruits, he added.
Certain vitamins can also serve to counter the effects of carcinogens. Vitamin C can prevent a potent carcinogen, nitrosamine, from forming.
Sometimes the liver, which gets rid the body of poisons, will convert an “innocent compound” into something dangerous. Those compounds can be addressed by Phase II enzymes, which are like a back-up protective system, Zeisel said. Foods like broccoli, cabbage, onions and garlic — cruciferous vegetables —can turn on the Phase II enzymes in your liver. Eating these foods regularly can reduce cancer risk by 10 percent, he said.
Free radicals, Zeisel explained, are agents that can cause DNA damage. Every time we exercise, we leak free radicals into our tissues, since they are products of oxygen metabolism. Those could be damaging to us, but antioxidant systems protect us. Vitamin E is an antioxidant that is “willing to take the damage for us,” instead of our DNA taking the damage, Zeisel said.
When Vitamin E is depleted, Vitamin C can restore it so it can accept the damage again. “You need both E and C,” Zeisel said. Eating citrus fruits, then, can be protective, and the skins or peels are especially valuable. Vitamin supplements are also effective.
Free radicals are not always bad. “Nature has used the free radical as a signal to say, ‘something’s wrong with this cell; kill it off,’” Zeisel said.
Once a cell is damaged, then we don’t want antioxidants to protect it, or keep it from dying off, Zeisel explained. In a study of mice with brain cancer, researchers looked at how low doses of antioxidants versus high doses worked. With weaker antioxidant protection, the tumors were more likely to be killed off, he said.
In a human study, heavy smokers who got high doses of antioxidants got cancer at such alarming rates that the study had to be stopped. If DNA is already damaged by something like long-term smoking or radiation, Zeisel explained, then high doses of antioxidants can be harmful, ty protecting damaged DNA.
In people with no DNA damage, antioxidants would not be a problem. But in people who have cancer or who have survived cancer, taking huge doses of antioxidants (like Vitamin E or C, beta carotene, lycopene or selenium) is probably not a good idea.
“A little is good,” Zeisel said. “A lot, don’t do.”
The same goes for Vitamin D. The amounts you get from moderate sun exposure are beneficial, but large doses, like 800 or 1200 IU, can be counterproductive.
Soybeans are also a food that can help protect people from cancer, Zeisel said. They contain a chemical called genistein, which can stop damaged cells from replicating themselves. Other compounds that act similarly are found in cherries, strawberries and blueberries, he says.
Maintaining a healthy body weight is also important in protecting ourselves from cancer, Zeisel said. “Body weight is an important risk factor,” he said. “High body weight, which means high calorie intake, is associated with more cancer,” he said.
The World Health Organization estimates that 15-20 percent of cancers are due to obesity, which drives cell growth. At a BMI of 30 or more, “you pick up a lot of risk,” Zeisel said. Colorectal cancer is one type of cancer associated with higher BMIs.
Breast cancer is also associated with higher BMIs. In particular, chances of breast cancer recurring are increased in obese women, who have a 78 percent greater chance of recurrence than normal weight breast cancer survivors. Zeisel recommended the American Institute for Cancer Research website, www. AICR.org, for more information about diet and cancer.
On Feb. 28, Dr. Andrew Swick will present “Obesity: It’s Not Easy Being Lean” at the meeting room of the David H. Murdock Core Laboratory Building, 201 North Main Street in Kannapolis. The director of Obesity and Eating Disorders at the Nutrition Research Institute, Swick is an expert on how the gut controls food intake and the regulation of energy expenditure. Swick will talk about why it’s difficult for some to lose and maintain a reduced weight, as well as potential causes of obesity, including environment, and the importance of energy balance.
The following is a list of cancer-fighting foods on the AICR website (www.aicr.org), and you can find discussions of some of them there.
- broccoli and cruciferous vegetables, like Brussels sprouts, rapini, cabbage, caluflower, turnips
- dark leafy green vegetables (spinach, kale, romaine lettuce, leaf lettuce, mustard greens, collard greens, chicory, Swiss chard)
- flaxseed and flaxseed oil
- grapes, grape juice
- green tea
- winter squash (acorn, butternut, spaghetti, hubbard)
- whole grains
- acai berries
- blackberries and raspberries
- chili peppers
- citrus fruits (oranges/lemons)
- legumes (dry beans, peas and lentils)
- sweet potatoes
- watermelon and other melons