A study finding that a diet high in total carbohydrates can increase the risk of cancer recurrence and mortality doesn’t mean that patients need to totally avoid carbohydrates, any more than previous findings about increased risk from a Western pattern diet means patients can’t eat any red meat. What the findings do mean, according to lead author Jeffrey Meyerhardt, MD, MPH, Associate Professor of Medicine at Dana-Farber Cancer Institute in Boston, is that “a healthy balanced diet is probably reasonable” for patients to reduce their risk of recurrence and improve their opportunities for survival.
That diet should involve foods with a lower glycemic load, a measure of how much eating a specified serving size of a particular food raises blood glucose levels. For example, patients can be advised to choose fresh fruits like apples, oranges, and cantaloupes, which have much lower glycemic loads than do dried fruits like dates or raisins. Substituting whole grains for refined grains and choosing brown rather than white rice can also lower the glycemic load.
Complex Issues
Dr. Meyerhardt said that when the study was first published in the Journal of the National Cancer Institute and then reported by the media, he was concerned that it might be misinterpreted as meaning that carbohydrates, and particularly sugar, were to be strictly avoided. “It is a little more complex than simply saying sugar makes cancer grow. It is the body’s response to a more starchy type of diet and the impact on glycemic load. It is not that you have to totally avoid sugar, or totally avoid carbohydrates; it has more to do with maintaining lower levels.”
The patients participating in the study had stage III colon cancer and regional lymph node metastases but no evidence of distant metastases, and all had complete resection and adjuvant chemotherapy. While following a healthy balanced diet is reasonable, “it is not a substitute” for treatment,” Dr. Meyerhardt stressed.
“Another consideration for colon cancer survivors is that even if they don’t experience a cancer recurrence, they may have a risk for other diseases down the line, including heart disease and diabetes. These dietary measures have also been shown to be preventive against heart disease, diabetes, and other potential comorbidities,” Dr. Meyerhardt noted.
Prediagnosis Diet
“Given that patients who consume high glycemic loads or carbohydrates after cancer diagnosis may have consumed a similar diet before diagnosis, we cannot exclude the possibility that individuals with these dietary exposures acquire tumors that are biologically more aggressive,” Dr. Meyerhardt and his colleagues stated in the published study.
“When you ask patients questions about their diet and lifestyle and other host factors after diagnosis, you could also ask them what they did beforehand, but you would obviously have issues with recall bias. So we chose not to do that.” It is possible, he said, that patients reporting very high carbohydrate diets in the study also had a history of very high carbohydrate diets before diagnosis, and that may have affected their risk of developing colorectal cancer and of having more aggressive cancer with a higher risk of recurrence.
That distinction is relevant, Dr. Meyerhardt noted, because if risk of recurrence is related to the diet patients followed before first developing colorectal cancer, “it is not an actionable item.” Patients can’t retroactively change their diet before diagnosis. “So you hope that you can find recommendations for patients to improve their outcome once they already have the diagnosis,” he added. ■
