What Is the Best Colorectal Cancer-Fighting Diet?: A Dana-Farber Q&A
In 2014 approximately 136,830 people are expected to be diagnosed with colorectal cancer, and about 50,310 are predicted to die from the disease, according to the American Cancer Society. Colorectal cancer, which occurs when tumors form in the lining of the large intestine, is the third most commonly diagnosed cancer and the third leading cause of cancer death in the U.S.
Still, significant progress has been made over the past few decades in terms of colorectal cancer incidence and survival rates. Scientists have developed better treatments, while doctors have also seen increased uptake for cancer screenings such as colonoscopies. The numbers below reflect how progress in research and increased awareness has led to improved outcomes.
While researchers continue to conduct trials on more effective treatments for colorectal cancer, patients are increasingly looking for ways to take matters into their own hands—both in terms of how they can decrease their risk of developing cancer and, if they’ve already been diagnosed, what they can do beyond surgery or radiation to try to improve their outcome. Lifestyle choices—diet in particular—are important in that they are factors patients can control.
To find out more about the best diet for colorectal cancer prevention and treatment, HealthCentral interviewed Dr. Kimmie Ng, a medical oncologist at the Center for Gastrointestinal Oncology at Dana-Farber Cancer Institute and assistant professor of medicine at Harvard Medical School.
[An edited transcript of the interview follows.]
Why is research in diet and cancer particularly important now?
Obesity is increasing at alarming rates and there’s evidence that obesity increases your risk of getting colorectal cancer, as well as doing more poorly once you’re diagnosed.
Vitamin D levels have also been decreasing over the years—due to a number of factors, including spending less time outside and increased use of sunscreen to prevent skin cancer, which blocks the UVB rays from penetrating the skin to synthesize vitamin D. Higher rates of obesity are linked to low vitamin D levels, so that’s another important trend to mention
Why has research in diet and cancer increased in recent years?
It could be because people are becoming more aware of the environment and the potential toxins out there. It may also be because our techniques in the laboratory and our ability to study diet and cancer have improved over the years as well.
Specifically, it makes sense that colon cancer is the type of cancer that may be the most affected by diet and lifestyle because anything you ingest through the environment comes into direct contact with the lining of the colon. So it is plausible that many environmental factors may potentially influence the development of cancer.
Is there a specific diet recommended for people with colon cancer?
In terms of people who currently have colon cancer, we’ve studied dietary patterns—a Western dietary pattern versus a prudent pattern. A Western pattern consists of red meat, processed meat, sugary sweets and desserts and a high-fat diet, while a prudent pattern has more vegetables, fruits, whole grains, fish and poultry. We found that colon cancer patients who consumed a Western pattern diet had significantly worse survival. We don’t know what component of the Western pattern diet is responsible for that or whether it’s the interaction of multiple dietary components—but that pattern of a diet seems to be detrimental.
We also found a slight benefit in colon cancer patients who followed a prudent pattern diet. The risk of death didn’t go up when you had a prudent diet, but with the Western diet, there was almost three times worse survival.
HealthCentral discussed the following list of foods with Dr. Ng and their role in fighting colorectal cancer.
[Hover over the image below to read about each food item’s role in treating and/or preventing colorectal cancer.]
Besides following a more prudent diet pattern, are there other dietary guidelines that people should follow?
Well, in one study done a few years ago in middle-aged men, researchers calculated that if a typical middle-aged man had a normal body mass index, exercised at least 15 hours per week—I think walking 30 minutes per day—took a daily multivitamin containing folate, had less than a drink of alcohol a day, did not smoke and ate less than two servings of red meat per week, that 71 percent of colon cancers could be prevented. This is based on calculations and simulations, but it gives you an idea of how important all these things might be in combination.
Do these dietary guidelines apply more or less to a specific demographic?
Regarding the findings we’re discussing today, most of the studies and cohorts we have access to have included white males and females. It’s not that these dietary guidelines apply only to white people; it’s just a lot of what we’re studying comes from studies where it’s mainly white. So that is an important thing to mention.
We do have evidence where black people have a much higher incidence of developing colon cancer; they also have a worse mortality after they get diagnosed with colon cancer. And it’s unclear why—it’s unclear whether it’s due to economic status, access to health care—we think there’s more to it than just those social factors. And it may be that differences in diet and lifestyle habits and also vitamin D levels may be contributing.
Does it make a difference at what age people begin following these guidelines?
We are looking at body mass index at early life versus later life, and whether that has any effect on developing cancer. I don’t think those timelines have been teased out yet, but it is probably best to start practicing healthy habits at an early age. The American Institute for Cancer Research did publish general recommendations for cancer prevention, which say to maintain a healthy weight, be physically active for 30 minutes a day, avoid sugary drinks, eat vegetables, fruits whole grains, legumes, limit consumption of red meat and processed meat, limit alcoholic drinks to two for men and one for women, limit consumption of salty foods and foods processed with salt, don’t use supplements to protect against cancer, don’t smoke or use tobacco, and cancer survivors should follow the same guidelines.
What about the effects of exercise on colon cancer?
There is promising epidemiologic evidence and support of higher levels of physical activity being helpful both for prevention as well as for treatment of colon cancer.
There are no randomized clinical trials, which are a standard for establishing cause and effect, but there have been lots of observational studies looking at physical activity and development of colon cancer. In one meta-analysis published in 2012, there was a 27 percent decrease in the incidence of getting a proximal, or the right side of colon cancer, with higher levels of physical activity. There was a 26 percent decrease in developing a distal, or the left side of colon cancer, with higher levels as well. And these are statistically significant results.
How much exercise do people need to get in order for it to affect cancer risk?
The American Institute for Cancer Research has put out general guidelines for diet and lifestyle for people to follow, and they recommend at least 30 minutes of walking per day, or 15 MET hours per week. (METs, short for metabolic equivalents, are used by researchers as a measurement by which they can assess physical activity levels.)
What are good resources for finding more information about diet and lifestyle factors?
The American Cancer Society is a good, trusted resource. The National Cancer Institute also has a lot of information on its website. I would urge people to check with their doctors for recommendations on where they can get more information.
What is the biggest takeaway for patients and researchers?
For patients, it is important that they know that there aren’t randomized clinical trials or the same level of evidence that we would need to, say, approve a drug for treatment of colon cancer. But a lot of these things are modifiable and are within a patient’s control. Altering diet to a more prudent pattern and exercising more certainly have no downsides and can potentially help with survival as well as decreasing risk of cancer.
For researchers, this is a very important area of research and could potentially have a significant impact on both the incidence of developing cancer as well as treating cancer. And that should be a high priority for research funding so we can more rigorously study these questions. This type of research has been difficult to fund through traditional grant mechanisms but should be an important area for funding.