Latest on Fruits and Vegetables and Colon Cancer
Martin Root, Ph.D.
November 14, 2000

A recent report from the Nurses Health Study and the Health Professionals’ Follow-up Study in a back-handed way supports the conclusion of my recent article that generally healthy lifestyle patterns have generally healthy outcomes and that we should not spend lots of time trying to figure out which part of the pattern prevents which disease.

The study reports that fruit and vegetable consumption, within the range of the American diet, does not prevent colorectal cancer. The men and women who ate more fruit and vegetable had a generally healthier lifestyle with less smoking and drinking and more physical activity and vitamin supplementation. Despite all of these good habits, they had about the same risk of colon cancer as those with less fruit and vegetable intake. Interestingly, three items that are usually considered healthy where unchanged or increased in the higher fruit and vegetable groups, total caloric intake, body mass index (BMI, a measure of fatness), and meat intake.

This would suggest 3 conclusions. 1) Again, the whole lifestyle package is important. Eating lots of fruit and vegetable while being overweight and eating red meat and too many calories cuts into the expected benefits. 2) Even Americans who meet the recommended guidelines of eating 5 or more fruit and vegetable per day (accounting for about a third of these subjects) may not be getting the benefits seen in other countries with higher fruit and vegetable consumption and much lower colon cancer risk. 3) A healthy diet may not be uniformly healthy for every disease. These results suggest that the level of fruit and vegetable that have previously been shown to prevent other diseases like heart disease and diabetes may not help prevent colon cancer.

At a recent gathering on vegetarian diets, Walter Willet, the principal investigator of the Nurses Health Study, commented on the health benefits that are measurable among vegetarians. He asked what part of the vegetarian lifestyle, including less meat, more fruit and vegetable, or more exercise, was the most beneficial part. His answer was, all of the above. In reports on meat and colon cancer from these same research groups, it was clear that red meat consumption promoted colon cancer. Their group and others have concluded that sustained physical exercise is also protective against colon cancer. So while the fruit and vegetable part of a healthy lifestyle may not be active against this specific disease (and this point is still in debate) other parts of the lifestyle are measurably protective.

In fact, a report from the Health Professionals’ Follow-up Study earlier this year calculates the proportion of colon cancer that could be prevented by changing various practices to healthier choices. They considered 6 practices that they had previously shown to cause colon cancer: obesity, physical inactivity, alcohol consumption, early adulthood cigarette smoking, red meat consumption, and low intake of folic acid supplements. While we might not agree with this exact list, they concluded that if the study subjects had improved their lifestyle in all of these practices to that of the healthiest 8% of the population, then about half of the colon cancer could have been avoided. This seemingly elite group of 8% is not that hard to get into. The reason this healthy group is so small is that they meet not just one of two of the healthy goals but they reach all six of the rather modest goals.

We should continue to eat a great variety of fruit and vegetable every day at the same time as we do everything else that is part of a healthy lifestyle, eschew meat, exercise regularly, maintain a healthy weight, quit smoking, and minimize drinking. The pattern of a healthy lifestyle will give a pattern of healthy outcomes. We will enjoy ourselves at both ends of the bargain and not have to worry about side effects.

Discuss this aritcle on the VegScience board.

Marty Root has a PhD in Nutrition from Cornell University, and works as a Senior Research Scientist at BioSignia, Inc. in Chapel Hill, NC. His work involves making statistical models that predict the onset of chronic diseases such as heart disease and the cancers, and he is a frequent contributor to VegSource.