A Varied Diet May Help Protect from Colorectal Cancer

Source: Tufts University
September 7, 2000 (Reviewed: January 2, 2003)

Sweet potato or broccoli or red pepper or carrot: which of these vegetables should you eat to lower your risk for colorectal cancer? How about some of each. A study recently published in the journal Preventive Medicine showed that people who ate the greatest variety of foods, and specifically vegetables, had the lowest risk of developing cancer of the colon or rectum (colorectal cancer).

A team of scientists in Italy compared the dietary habits of 1900 people with colorectal cancer to those of 4100 people without the disease. Researchers asked each volunteer how many times per week they ate each of 79 different foods over the 2-year period before they were diagnosed or, for the healthy control group, over the 2 years before entering the study. From these data, they tallied the average number of different foods eaten over the course of a week and called this number the "total food diversity score." Similar calculations were done for each of the five major food groups yielding a "vegetable diversity score," a "meat diversity score," etc.

The results showed that people with the highest vegetable diversity scores-defined as eating 10 or more different vegetables per week-were about 30% less likely to have colorectal cancer than those who ate less than seven kinds. Based on the total food diversity score, all volunteers in the study who ate more than 30 (compared with 21) different foods per week were less likely to have colon cancer, with the strongest association seen for men.

In this study, the only food group to show a significant positive association between eating habits and incidence of colorectal cancer was vegetables. This is likely due to the phytochemicals that are plentiful in peppers, tomatoes, cauliflower, and all other plant foods. Plants produce these chemicals as a natural defense against infection and disease, and they are believed to protect people from chronic diseases as well. Carotenoids, flavonoids, and isoflavones are just a few of the hundreds of phytochemicals that have been identified so far and scientists believe there are many more to be found. Since each plant has a unique collection of chemicals, eating a variety is essential for optimal health.

The effects of specific dietary factors, such as phytochemicals, on the incidence and development of colorectal cancer have been examined by many researchers. Unfortunately, findings are inconsistent. One such example is a study recently published in the prestigious New England Journal of Medicine. Here, scientists reported that four years of a produce-rich, low-fat, high-fiber diet offered no protection against the recurrence of colorectal adenomas (a potent risk factor for colorectal cancer) in a group of volunteers with a history of adenomas. This study contradicts the widely held belief that such a diet can in fact reduce the chances of developing colorectal cancer. To reconcile these findings, the scientists point out that cancer development is a very long process and that the healthful components of a low-fat, high-fiber, fruit and vegetable-rich diet may be effective at keeping intestinal cells healthy rather than promoting healing after an adenoma has been formed.

Hopefully, further study will tease out a more precise understanding of how dietary habits affect colorectal cancer risk. For now, though, plenty of solid research has shown that plant-based foods-fruits, grains, and vegetables-can help to lower the risk for certain types of cancer as well as other chronic diseases. So on your next stroll through the produce aisle, pick up a new fruit or vegetable to add to your diet.

Note to Readers: Colorectal cancer is the fourth most common cancer and cause of death from cancer throughout the world. However, according to the American Cancer Society, it is also a disease that can, to some degree, be controlled. First, you can decrease your chance of developing this cancer by eating a diet high in fruits, vegetables, and grains, and low in fat, particularly fat from animal products (meats, bacon, full-fat dairy products); and exercising regularly. Second, proper screening can detect colorectal cancer early, when it is highly curable.

Sources

• Diet diversity and colorectal cancer. E. Fernandez, A. Schatzkin,  et al., Preventive Medicine., 2000, vol. 31, pp. 11--14



• Lack of effect of a low-fat, high-fiber diet on the recurrence of colorectal adenomas. E. Fernandez, A. Schatzkin,  et al., The New England Journal of Medicine, 2000, vol. 342, pp. 1149--1155

Related Links
The Colon and Rectum Cancer Resource Center, American Cancer Society
Colon and Rectal Cancer, National Cancer Institute
Tufts University's Nutrition

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