Cancer physician and researcher Kimmie Ng of Harvard-affiliated Dana-Farber Cancer Institute was senior author of a recent study linking a low-insulin-load diet—fruits, vegetables, whole grains, and healthy protein and fats to a dramatic drop in colorectal cancer recurrence.

With the incidence of colorectal cancer rising among younger adults, the American Cancer Society has lowered its recommended age for first screening from 50 to 45.

Diet and lifestyle are prime suspects in the rising incidence among under-50 adults, Ng said during a conversation on the American Cancer Society guidelines and how her work seeks to illuminate risk factors in colorectal cancer.

American Cancer Society's decision

"I do think it is a good idea, especially in light of the documented rise in the incidence of colorectal cancer in young patients. We do not have direct clinical evidence yet that this is going to be cost-effective, but we are seeing many more patients under the age of 50 who are getting diagnosed with colorectal cancer. Often it is already metastatic at the time of diagnosis," Ng said.

"The American Cancer Society's main message is that any screening is better than no screening, so they have been cautious in not preferentially recommending one screening method over another. They suggest that as long as you get screened by one of the methods in their guidelines, there could be a benefit," Ng explained.

"We do think there is a birth cohort effect. Colorectal cancer seems to have increased in successive birth cohorts as we go through the years. So we think it is probably some change in behavior or the environment that's causing this," Ng added.

"Our leading hypotheses are the increasing amount of sedentary behavior in younger folks compared with people who grew up in earlier times, the increase in processed foods—and other dietary changes as well—and higher rates of obesity, all of which are linked to the development of colorectal cancer," Ng said.

"We looked at a completed Phase III clinical trial that was run by the National Cancer Institute of 1,023 Stage III colon cancer patients who had their tumors completely resected at surgery and enrolled in this trial to test two different chemotherapy regimens," he said.

"It ended up that those regimens were equally effective, so we were able to pool all those patients and look at their self-reported dietary data, which was collected at two different time points: shortly after starting chemotherapy and then approximately six months after completing chemotherapy," Ng said.

"We averaged the reported dietary intakes from both of those questionnaires for each patient, and we calculated an insulin score—both an insulin load, which takes into account how much of each food you are ingesting, as well as an insulin index, which is the amount of insulin response per kilocalorie. We calculated those scores for each patient," Ng said.