Healthy Plant-based Diet Found to Lower Colorectal Cancer Risk in Men

A diet high in plant-based foods and low in refined grains, fruit juices, and additional sugar was found to lower the risk of colorectal cancer in men, according to a study published in BMC Medicine. Colorectal cancer is the third most common type of cancer worldwide, with 1 in 23 men and 1 in 25 women at risk for developing the disease over their lifespan.

“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,” said corresponding author Jihye Kim, in a press release. “Our findings suggest that eating a healthy plant-based diet is associated with a reduced risk of colorectal cancer.”

To evaluate the potential association between plant-based diets and the risk of colorectal cancer, the investigators reviewed data from adults who were recruited for the Multiethnic Cohort Study between 1993 and 1996. Male participants had an average age of 60 years and female participants had an average age of 59 years at the start of the study.

The participants recorded their typical food and drink consumption over the previous year, which the study authors assessed for the amount of healthy plant-based foods or unhealthy foods consumed to compare with the other participants. Investigators then calculated the rate of new colorectal cancer cases until 2017 with data obtained from cancer registries.

They accounted for age, familial history of colorectal cancer, body mass index, smoking history, physical activity levels, alcohol consumption, multivitamin use and treatment, and daily energy intake. They also accounted for use of hormone replacement therapy among the female participants.

Among 79,952 American men, the investigators found that individuals consuming the highest average daily amounts of healthy plant-based foods had a 22% lower risk of colorectal cancer vs individuals who consumed the lowest amount of plant-based foods, which include whole grains, vegetables, and legumes.

Notably, the investigators did not find a significant link between the nutritional quality of plant-based diets and the risk for colorectal cancer among 93,475 American women.

“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,” Kim said. “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 investigators said that the link between diet quality and colorectal cancer risk among men varied by race and ethnicity. Among Japanese American men, the risk for colorectal cancer was 20% lower in individuals who consumed the greatest amount of healthy plant foods per day vs individuals who consumed the lowest amount.

Among white males, individuals who consumed the greatest amount of healthy plant foods had a 24% lesser risk of colorectal cancer compared with individuals consuming the lowest amount. The investigators did not find a significant association between plant-based diets and the risk of colorectal cancer among African American, Latino, or native Hawaiian men.

“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,” Kim said in the release. “However, further research is needed to confirm this.”

Among the entire study population, 4976 individuals (2.9%) developed colorectal cancer during the study period. The authors said that the observational nature of the study limited any conclusions regarding a causal relationship between intake of plant-based food and the risk of colorectal cancer.

The study also did not account for the beneficial dietary impact of foods such as fish, which they said may have helped reduce the risk of colorectal cancer in their study. Further, because the diets were recorded only at the start of the study, the findings may not be representative of participants’ dietary health over their full lifespan.

The authors said that additional research is needed to evaluate the genetic and environmental factors that may impact the association between plant-based food intake and the risk of colorectal cancer between racial and ethnic groups.

Reference

Kim, J., Boushey, C.J., Wilkens, L.R. et al. Plant-based dietary patterns defined by a priori indices and colorectal cancer risk by sex and race/ethnicity: the Multiethnic Cohort Study. BMC Med 20, 430 (2022). https://doi.org/10.1186/s12916-022-02623-7