- Colorectal cancer is the third most common cancer in the United States.
- The risk of developing colorectal cancer is increased by overweight or obesity, smoking, and a diet high in red or processed meats.
- Including plenty of whole grains, fresh fruit, and vegetables in one’s diet can reduce this risk, existing research has shown.
- A large study has now found that, in men, a diet that is high in healthy plant-based foods is associated with lower colorectal cancer risk.
Colorectal cancer, also known as bowel, colon, or rectal cancer, is the
Most people who receive a colorectal cancer diagnosis are over the age of 50, although it can affect younger people, too.
In recent years, cases in older people have started to decline, but the incidence among younger people
The risk of colorectal cancer increases with age. Other risk factors people cannot influence are a family history of colorectal cancer, inflammatory bowel diseases — such as Crohn’s disease — and certain genetic syndromes.
There are, however, many lifestyle factors that also influence a person’s risk of colorectal cancer. Factors that are likely to increase the risk
- a diet low in fiber, fruit, and vegetables
- lack of physical activity
- a diet high in fat and red or processed meat
- overweight and obesity
- tobacco use and heavy alcohol consumption.
Reducing these foods and increasing foods high in dietary fiber is associated with a reduction in risk.
Plant-based foods tend to be high in dietary fiber, but only in an unprocessed state.
Now, a study that appears in
Unhealthy plant-based foods — refined grains, fruit juices, and added sugars — had no beneficial effect on cancer risk.
“This American study adds to lots of existing evidence on the benefits of eating a balanced diet high in fruit, vegetables and fiber for both men and women.”
– Beth Vincent, health information manager, Cancer Research UK (CRUK)
The study group included 79,952 men and 93,475 women who were followed up for an average of 19.2 years. All participants were from Hawaii or the Los Angeles area and were aged between 45 and 75 years at enrolment. The group included people of African American, Japanese American, Native Hawaiian, Latinx, and white volunteers.
At the start of the study, researchers assessed participants’ usual diet with a self-reported questionnaire.
Participants had to report how often and how much they ate out of more than 180 different foods and beverages. They chose from four portion size options, and frequencies ranging from never to four times a day.
From the responses, the researchers calculated daily energy and nutrient intakes, then calculated three plant-based diet indices — overall (PDI), healthful (hPDI), and unhealthful (uPDI).
The researchers defined whole grains, fruits, vegetables, vegetable oils, nuts, legumes, tea, and coffee as healthy plant-based foods. Less healthy plant-based foods included refined grains, fruit juices, potatoes, and added sugars.
To achieve a high hPDI score, participants had to have a high intake of healthy plant-based foods and a low intake of less healthy plant-based foods.
Overall, plant-based diets, particularly healthy plant-based diets, were associated with a reduced risk of colorectal cancer in men, but not in women. Unhealthy plant-based diets did not appear to reduce the risk.
For healthy plant-based diets, the association was stronger in Japanese American, Native Hawaiian, and white men than in those from other groups.
The researchers suggest that “the benefits from plant-based diets may vary by sex, race and ethnicity, and anatomic subsite of tumor.”
The study had a large sample size, long follow-up time, and racial and ethnic diversity in the study population. However, the authors acknowledge some limitations of the study, including possible selection bias in who responded to the questionnaires and the negative scoring of all animal-based foods.
Beth Vincent argued that the study findings should be viewed with caution:
“The research tried to compare ‘healthy plant foods’ and ‘unhealthy plant foods’ and found a link with bowel cancer in men. But because of the design of the study, the authors themselves acknowledge we can’t read too much into their results. The study relied on people remembering what they had eaten up to a year ago. It also made the assumptions that participants’ diets stayed the same over many years, and that all meat and animal products were unhealthy — which isn’t the case.”
This study adds to the growing evidence that diet and lifestyle play
Vincent agreed, giving the following advice: “Eating a well-balanced diet can help with maintaining a healthy weight, which reduces the risk of cancer. Not smoking, cutting down on alcohol, and staying safe in the sun are other important ways to reduce your cancer risk.”
Prof. Jihye Kim, from Kyung Hee University, who is one of the study authors, says that:
“We speculate that the antioxidants found in foods such as fruits, vegetables, and whole grains could contribute to lowering colorectal cancer risk by suppressing chronic inflammation, which can lead to cancer. As men tend to have a higher risk of colorectal cancer than women, we propose that this could help explain why eating greater amounts of healthy plant-based foods was associated with reduced colorectal cancer risk in men but not women.”
The authors’ conclusion that “improving the quality of plant foods and reducing animal food consumption can help prevent colorectal cancer” may be a little optimistic, but their study certainly adds to the evidence that a healthy diet can help to reduce overall cancer risk.