A new study on 79,952 men in the United States has found that a diet rich in vegetables, fruits, whole grains, legumes, nuts, and seeds is associated with a 22 percent lower risk of developing colorectal cancer compared to those who eat the least amount of plant-based food.

The research is only observational, which means scientists still don’t know why some foods are linked to better bowel health, though they have a few ideas.

That said, the findings do suggest that generally reducing the consumption of animal-based foods, refined grains, and sugars could provide lifetime benefits.

Interestingly, researchers did not find a link between plant-based diets and colorectal cancers among 93,475 women
in the U.S.

“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,” explains Jihye Kim, who researches nutrition and dietetics at Kyung Hee University in South Korea.

“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.”

Women also consume more plant foods than men in general, so eating more fruits and veggies might not necessarily increase protection from cancer in any discernable way. This particular cohort of women might have already maxed out the health benefits of a plant-based diet.

Previous studies in other nations have also noticed similar sex discrepancies.

In a United Kingdom Biobank study, for instance, men who ate relatively little meat were 9 percent less likely to develop colorectal cancer than typical meat-eaters.

Similar benefits were not observed among women.

As a population-level study the research was highly comprehensive, but it’s focus was on levels of meat in the diet, not the intake of specific plant-based foods. A reduction in meat consumption doesn’t necessarily coincide with an increase in healthier options.

Some plant-based foods come with a bigger nutritional boost than others. Prior studies, for instance, have shown that whole grains, vegetables, and cereal fibres can reduce cancer risk, whereas refined grains have health downsides.

Unfortunately, the current study did not differentiate between different types of animal-based foods, which is a bit limiting given that some foods, like fish and dairy, might actually be good for you.

What’s more, participants in the long-term study had their diets assessed using a questionnaire, which doesn’t encompass lifelong food intake.

Where this study does excel, however, is in incorporating a multi-ethnic cohort from Hawaii and Los Angeles.

Worldwide, colorectal cancer is the third most common cancer, and yet not everyone is equally at risk. Researchers found that a plant-based diet is associated with the biggest improvements in colorectal cancer risk among Japanese American and White men as opposed to African Americans.

Among White men, those who ate the most healthy plant-based foods were 24 percent less likely to develop colorectal cancer later in life than those at the other end of the dietary spectrum. Among Japanese American men, risk was lowered by 20 percent.

“This pattern of association may be attributable to the differences in non-dietary lifestyle risk factors among racial and ethnic groups,” the authors write.

“In the [multiethnic cohort], African American men had higher rates of obesity and smoking and less physical activity than did Japanese American and White men.”

More research is needed to explore the different genetic and environmental factors that might be playing into colorectal cancer rates, and where diet might fit into the mix.

The study was published BMC Medicine.