There is new evidence that just saying no to fast foods — especially hamburgers, French fries and shakes — may reduce the risk of developing colon cancer.

Moreover, the benefit may be even greater if a switch to healthy eating is part of a lifestyle plan that includes increased physical activity.

Those are some of the findings of a large study of colon cancer. The research is reported in the June issue of Cancer Epidemiology, Biomarkers & Prevention (Vol. 11: 541-548).

Researchers asked 1,458 colon cancer patients and 2,410 healthy adults in the same age range very detailed questions about the types of food they normally ate and how often they ate them.

"The cancer patients were asked about their diets during the year before they were diagnosed with cancer, while the controls were asked about diet at the time they were enrolled in the study," said co-author, Karen Curtin, MSTAT, research associate at the health research center, department of family and preventive medicine, University of Utah, Salt Lake City.

The researchers found that the so-called "Western diet"— a diet high in red meats and fast foods — was linked with colon cancer.

But the risk was greatest for those who ate diets that were especially high in red meats, "for example eating one or two quarter-pound cheeseburgers a week along with one to two 3-ounce slices of beef, pork, or lamb every day," said Curtin.

Martha L. Slattery, PhD, and colleagues were able to analyze tissue taken from the tumors that were removed from the colon cancer patients.

Using DNA analysis, they were able to identify different genetic mutations in the tumors, specifically in the p53 tumor suppressor gene.

The p53 gene normally helps cells to die at the right time. When it works well, it prevents tumor growth, but if it is damaged or mutated, tumors can form. About half of all cancers have tumors that have p53 mutations.

In this study, 47% of patients had tumors with p53 mutations. Those who ate Western diets were slightly more likely to have p53 mutations than those who did not. Diets high in sugar, red meat, fast food, and trans-fatty acids were all more often linked to p53 mutations.

A diet high in sugar had a stronger link with p53 mutations in colon cancers in women than in men.

Age was also a factor. While diets high in red meat, fast food, and trans-fatty acids were linked with p53 mutations in both men and women of any age, it was seen more strongly with those at age 65 or older.

Charles S. Fuchs, MD, MPH, associate professor of medicine at Harvard Medical School, and a cancer researcher at Dana-Farber Cancer Institute, Boston, said the new study shows the importance of lifestyle in cancer prevention.

He said it was interesting that the researchers found a link between high sugar intake and p53 mutations.

High sugar diets elevate levels of sugar in the blood, which then triggers increased insulin production.

"Insulin is a growth factor that is known to promote the growth of cancer cells," said Fuchs. He noted that in lab studies researchers often add insulin to cancer cells to speed their growth.

Ann Chao, PhD, an American Cancer Society research scholar in epidemiology and surveillance, said that the study reinforces the ACS position on the relationship between diet and cancer risk.

But beyond the link with p53 mutations, Chao said the researchers clearly connected the dots between a fast food, couch-potato lifestyle, and the overall risk for colon cancer.

"This diet was associated with increased risk for all colon cancers, regardless of p53 status," she said.

Finally, Curtin said that the results of the new study "advance our understanding of how diet is associated with disease."

She said that making some dietary changes now — cutting back on hamburgers and passing up the super-sized shakes — may reduce the risk of developing colon cancer in the future.

And making those changes may be doubly worth the effort because the same changes are also linked to a reduced risk for heart attacks and diabetes.

For more information about diet and cancer prevention, see the new ACS nutrition and physical exercise guidelines.