There's significant evidence that diets high in red meat and fatty foods increase the risk of colon cancer. Now, research published in this week's Journal of the American Medical Association provides evidence that this type of diet may also increase the risk of recurrence once colon cancer has been diagnosed.
Researchers from the Dana Farber Cancer Institute in Boston analyzed the diets of more than 1,000 patients with stage 3 colon cancer, meaning the cancer had spread to nearby lymph nodes. The patients had surgery to remove the cancer, followed by chemotherapy.
Oncologist Jeffrey Meyerhardt headed the study, which asked patients about their diet during, and six months after, chemotherapy.
"We looked at a whole variety of fruits," he says. "Apples, oranges, grapefruit, vegetables, broccoli, Brussels sprouts, carrots, multiple types of meats including processed foods like cold cuts, turkey, fish, breakfast cereals, cooking oils, supplements people add to their coffee, and then a whole variety of desserts."
The critical question, Meyerhardt says, was exactly how much high fat, sugary food people ate.
"Do they have ice cream?" he says. "One serving? A half a cup? Do you never have it? Do you have it once a month, three times a month, once a week, once a day, two times a day and so forth."
Once patients are diagnosed with stage 3 colon cancer, even if they follow recommended treatment (surgery to remove the cancer, followed by chemotherapy), after five years about 30 percent can be expected to have a recurrence of cancer.
In his study, Meyerhardt found that, indeed, did happen. But he also found another, more dramatic result: Compared with patients who ate relatively little fat, meat and sugar, patients who consumed high-fat, high-sugar diets were three and a half times more likely to see a recurrence of cancer.
"High-fat, high-sugar diets," Meyerhardt says, "included people who had five to seven servings of red meat per week; one to two sugary desserts per day; and one or two servings of high-fat foods per day." He says this type of diet clearly put patients "in the category of Western-pattern diet."
Scientists know that high-fat, high-sugar diets increase cardiovascular risk. Meyerhardt says it makes sense they could also increase colon cancer risk.
Extra fat and sugar may increase insulin and insulin-like growth factors. And if there's more of that circulating around colon cancer cells, it will help the cell grow, divide and spread.
These hormonal changes might also interfere with cancer treatment.
Dr. Stephen Forman is an oncologist at the City of Hope Cancer Center. He says the changes that the body undergoes when it is processing these foods should be addressed in future studies.
"We need to know what impact these changes have on the growth of the cancer itself, as well as the impact on drugs used in treatment of the cancer," Forman says. "Could it be that we are undermining our therapies by the diet we maintain? I think that's the important question this study raises, and it's an important question to answer."
The link between cancer and diet is not entirely clear. But one thing is, according to Forman: People undergoing these very difficult treatments need to maintain a healthy diet.