The risk of bowel cancer in men can be reduced by more than a fifth if a plant-based diet of vegetables, whole grains, nuts, and legumes is followed - according to research published in the journal BMC Medicine.

The research called the "Multiethnic Cohort Study," which included 79,952 American men, discovered that those who consumed a majority of healthy plant-based foods had a 22% lower risk of bowel cancer.

However, that percentage was not found to be linked to women of whom 93,475 were included in the research. Jihye Kim, one of the research's authors from Kyung Hee University in South Korea, said, “Colorectal cancer is the third most common cancer worldwide and the risk of developing colorectal cancer over a lifetime is one in 23 for men and one in 25 for women.” 

“Although previous research has suggested that plant-based diets may play a role in preventing colorectal cancer, the impact of plant foods’ nutritional quality on this association has been unclear. Our findings suggest that eating a healthy plant-based diet is associated with a reduced risk of colorectal cancer.” Kim stated.

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Methodology  

Participants were asked about how frequently they ate certain foods from a list of more than 180 items, in addition to being asked about portion size. The options they could select on the list of each food item were “never or hardly ever” up until “two or more times a day."

The listed categories included healthy plant foods involving whole grains, fruits, vegetables, vegetable oils, nuts, legumes, like lentils and chickpeas, and drinks like tea and coffee.

Other categories included less healthy plant foods such as refined grains, fruit juices, potatoes, added sugars, and animal-based foods, including animal fat, dairy, eggs, fish or seafood, and meat.

“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,” said Kim.

He continued, “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.”

On average, men involved in the study were 60 years old at the start while women were 59. It is worth noting that most patients diagnosed with bowel cancer are over 60.

Race and ethnicity also played a role in the link among men. 20% reduced risk, for example, was among Japanese American men, but it was 24% for white men. In light of that, the team stated that more research was needed to define and analyze the differences. 

“We suggest that the association between plant-based diets and colorectal cancer risk may have been strongest in Japanese, American and white men due to differences in other colorectal cancer risk factors between racial and ethnic groups,” said Kim. “However, further research is needed to confirm this.”

Aspects such as obesity were taken into consideration as factors that influenced the results during the study. However, quite significantly, the research team warned that the study meant no direct causal relationship yet between plant-based food intake and colorectal cancer risk.