Sound Familiar? Eat Right and Get Exercise

For most Americans, the key to preventing colon cancer can be found in those two little words Americans hate to hear: diet and exercise.

Scientists have known for years that a diet rich in vegetables, fruits and fiber, and low in fat, can greatly reduce--or eliminate--the chances of developing colon cancer. Researchers have also found that regular physical activity also is protective, possibly because it speeds digestion and decreases the time carcinogens stay in the gastrointestinal tract.

Despite the link to diet, scientists don’t know precisely why foods ward off cancer or which chemicals in them are responsible.

“One of the problems is that it’s hard to separate nutrients,” said Arthur Schatzkin, a senior investigator at the National Cancer Institute who is studying whether diet can reduce the formation of new polyps that typically are a precursor to cancer.

Even though researchers have concluded that at least 40% of colon cancer cases could be prevented by adhering to a prudent diet, engaging in regular physical activity and avoiding obesity, many people fail to do so.

Americans are fatter than ever--one-third of adults are at least 20 pounds overweight--and only about half of the population consumes enough vegetables and fruits to ward off colon cancer, numerous studies have shown.

“Colon cancer is the second-most common fatal cancer in the United States, and after lung cancer it’s the most preventable,” said Michael Thun, director of analytic epidemiology at the American Cancer Society. “But think about the attempts to reduce cigarette smoking. Here we are almost 40 years after the Surgeon General’s report [the landmark 1964 document that said cigarettes cause lung cancer], and 25% of Americans still smoke. Well, when you talk about food, it’s a much more complicated pattern to change.”

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One of the patterns health officials most would like to change is the paucity of fruits and vegetables and the abundance of fat in the typical American diet.

Seven years ago the National Institutes of Health launched its “Five a Day for Better Health” program, a public education campaign designed to persuade Americans to eat a minimum of five servings of fruit or vegetables per day to ward off cancer.

A diet high in fiber and vegetables, especially green leafy vegetables such as broccoli, and low in fat also reduces the risk of a host of other cancers, as well as stroke, heart disease and diabetes.

Why five?

“Five a day was chosen as a lower limit, not because it’s a magic number,” Thun noted.

Thun said that some members of the committee that promulgated the recommendation wanted to advocate nine servings per day. That number was rejected because public health officials feared that many Americans would regard the number as unattainable and would tune out the message.

While five servings may sound like a lot, nutritionists say it is not. Six ounces of fruit or vegetable juice counts as one serving, as do a quarter-cup of raisins or other dried fruit or one cup of lettuce.

“If people realized how small the serving sizes were, they’d be amazed,” said Colleen Doyle, director of nutrition and physical activity for the ACS. “A typical dinner salad, which is not very big, contains 2 1/2 cups.”

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Although Americans are eating more fruit and vegetables than they were a decade ago, they still aren’t eating enough, health officials say.

A study by the U.S. Department of Agriculture released last month found that Americans eat an average of about four servings per day, and about 12 to 15 grams of fiber, less than the 20 to 30 grams recommended by the NCI.

“We’re making some progress, but we’re not nearly there yet,” said Bonnie Liebman, a nutritionist at the Center for Science in the Public Interest. “The main point is, we’ve got a long way to go.”

Time pressures are a factor, Thun noted.

“If one is chopping things up and cooking them, that takes longer than putting something in a microwave or eating in a fast-food restaurant,” he said.

Although there is evidence that proper diet protects against colon cancer, there is little proof that dietary supplements can make up for an inadequate diet.

“Most research shows no protection against cancer from supplements,” Doyle said.

But the evidence that regular physical activity protects people against colon cancer is stronger than the relationship between regular activity and all other cancers, she added.

Doyle noted that while many people mistakenly believe that vigorous exercise is required, studies show that moderate levels of physical activity appear to be sufficient.