BETHESDA, Md--Understanding the complex association of lifestyle and colon cancer risk requires evaluating a number of different behavioral factors, and these may best be studied as clusters rather than individual items, Martha Slattery, PhD, MPH, said at the American Society of Preventive Society (ASPO) meeting.
"These factors dont exist in isolation," she said. Dr. Slattery, of the Department of Oncological Sciences/PHS, University of Utah, reached that conclusion after a study involving 1,993 colon cancer cases and 2,410 controls, age 30 to 79 years, seen from 1991 to 1994. Everything from physical inactivity, obesity, and glycemic index to hormone levels, body size, and a mutated APC gene can affect the onset of colon cancer, she said.
By evaluating clusters of risk factors, rather than single foods or nutrients, Dr. Slattery observed two patterns of diet and behavior that have sharply different effects on a persons risk of developing colon cancer.
The first was the "western" diet, containing processed meats, eggs, fast food, refined grains, added sugar, and potatoes. Those who ate this diet also had a higher body mass index (BMI), lower physical activity, and higher total energy (caloric) intake.
Conversely, those who ate what she termed a "prudent" diet consumed more fresh fruit, legumes, cruciferous vegetables, salad, carrots and tomatoes, other vegetables, fish, and poultry. They also had higher physical activity and higher total energy intake.
Men in the highest quintile of the "western" diet were 1.8 times more likely to get colon cancer than those in the lowest quintile, while the "prudent" diet was protective (odds ratio, 0.7, or, in other words, a 30% reduction in the risk of developing colon cancer for those in the highest vs lowest quintiles). For women, similar figures were 1.5 for the western diet and 0.7 for the prudent diet.
For both men and women, Dr. Slattery said, the effect was stronger in those under age 67, the median age of the controls. Risk factors were adjusted for age, body size, physical activity, aspirin use, family history, and total energy intake.
To lower the risk of colon cancer, Dr. Slattery recommends eating the "prudent" diet; avoiding obesity; and staying active. She noted that some have suggested performing intense physical activity for at least 30 minutes a day, all or most days of the week. Finally, she emphasized the value of screening sigmoidoscopy for early identification of polyps in the colon. [See page 2 for the NCCN guideline on colon cancer screening.]