The research is among the first to look at the impact that specific nutrients have on the likelihood of disease recurrence in people with colon cancer, one of the leading causes of cancer death in the United States. It found that people treated for Stage 3 disease, in which tumor cells have spread to lymph nodes, had greatly increased chances of dying of it or experiencing a recurrence if their diets were heavy in carbohydrate-rich foods that cause spikes in blood sugar and insulin.A new study suggests that what you eat may affect your chances of surviving colon cancer.
The patients who consumed the most carbohydrates and foods with high glycemic loads — a measure of the extent to which a serving of food will raise blood sugar — had an 80 percent greater chance of dying or having a recurrence during the roughly seven-year study period than those who had the lowest levels. Stage 3 colon cancer patients typically have a five-year survival rate of about 50 to 65 percent.
The study, however, was observational, meaning it could only highlight an association between carbohydrates and cancer outcomes without proving direct cause and effect. The researchers also obtained some of their data from food questionnaires that required patients to recall details about their diets, a method that can be unreliable.
Still, the researchers, who published their findings in The Journal of the National Cancer Institute, believe insulin may play a critical role in colon cancer recurrence. Chronically high insulin levels have been linked to cancer recurrence and mortality in previous research, and people with a history of Type 2 diabetes or elevated plasma C-peptide, a marker of long-term insulin production, have also been found to have an increased risk of colon cancer. One hypothesis is that insulin may fuel the growth of cancer cells and prevent cell death, or apoptosis, in cancer cells that have spread.
“It’s not simply that all carbs are bad or that you should avoid all sugar,” said Dr. Jeffrey A. Meyerhardt, the lead author of the study and an associate professor of medicine at the Dana-Farber Cancer Institute in Boston. It’s not as simple as ‘sugar causes cancer to grow.’”
He added: “Different carbs and sugar lead to different responses in your body. I think people should focus on a well-balanced diet” and substitute foods associated with lower glycemic loads or carbs for foods that have higher levels.
Earlier research published by Dr. Meyerhardt’s group showed that Stage 3 colon cancer patients who most closely followed a Western-style diet — with high intakes of meat, fat, refined grains and sugary desserts — had a threefold increase in recurrence and death from the disease compared with those who most strongly deviated from Western patterns of eating.
For this study, Dr. Meyerhardt and his team wanted to see to what extent carbohydrate intake could influence the progression of the disease, so they followed about 1,000 Stage 3 colon cancer patients taking part in a clinical trial sponsored by the National Cancer Institute. The patients, who had all had surgery and chemotherapy as part of their treatments, provided information on their diets and lifestyle habits. But the researchers went beyond just carbohydrate and sugar intake, taking into account glycemic measures.
The glycemic index, an increasingly popular nutritional measure, looks at the rate at which carbohydrate-containing foods raise a person’s fasting level of blood sugar and subsequent need for insulin. Sugary drinks, white bread and other highly processed carbohydrates rank higher on the index, while those that are digested more slowly, like brown rice, many vegetables, unrefined grains and legumes, have a lower index value.
Another barometer, however, is the glycemic load, which refers to the blood sugar effect of a standard serving of a food. A glycemic load of 10 or less for a food is generally considered low, while 20 or more is high. The latest study showed that glycemic load and total carbohydrate intake were the best predictors of cancer recurrence and mortality, and the link was strongest in people who were overweight or obese.
Dr. Meyerhardt said the findings suggest that colon cancer patients would be wise to keep glycemic load in mind while making food decisions, looking for ways to work into their diets foods that rank lower on the scale.
“So if you think about beverages, most juices and certainly sodas have a higher glycemic load than flavored waters and tomato juice and things like that,” he said. “Fruits like a date or raisins have very high glycemic loads, whereas fresh fruits like an apple, orange or cantaloupe all have sugar but have a very low glycemic load. Substitute brown rice for white, whole grains instead of white bread, and instead of having a starchy potato as your side dish, substitute beans and vegetables.”
One expert who was not involved in the research, Somdat Mahabir, a nutritional epidemiologist with the National Cancer Institute’s division of cancer control and population sciences, said the findings from the latest study must be borne out in further research. But in the meantime, making dietary changes that reduce glycemic load is a reasonable recommendation for colon cancer patients, he said, since it can only be helpful, not harmful.
“The results of the current study need to be confirmed, but the current indications are that diet is important to colon cancer survival,” Dr. Mahabir said.