Healthy plant-based diets linked to lower colorectal cancer risk in men

Diets high in healthy plant foods and low in unhealthy plant foods were associated with a lower colorectal cancer risk in men, a recent study published in BMC Medicine found.

“Although screening and treatment for colorectal cancer have improved, new preventive strategies to lower risk remain a priority,” Jihye Kim, a professor in the College of Life and Sciences at Kyung Hee University in South Korea, and colleagues wrote. “Accumulating evidence indicates that diet is an important modifiable risk factor for colorectal cancer.”

According to the researchers, three plant-based diet indices have recently been developed to assess the quality of food intake: overall plant-based diet index (PDI), healthful plant-based diet index (hPDI) and unhealthful plant-based diet index (uPDI).

Previous studies have shown that PDI and hPDI can lower the risk for CVD, type 2 diabetes and related conditions, while uPDI increases the risk for these outcomes, Kim and colleagues noted. However, “it remains unknown whether these indices are associated with colorectal cancer risk, especially in racially and ethnically diverse populations,” they wrote.

To examine the association between colorectal cancer (CRC) risk with the indices, the researchers utilized data from the Multiethnic Cohort study, which involved more than 215,000 participants enrolled between 1993 to 1996.

Their analysis was limited to 79,952 men and 93,475 women aged 45 to 75 years who did not have CRC or tumor registry information prior to baseline, or an implausible diet. Eligible participants also belonged to one of five racial and ethnic groups: African American, white, Native Hawaiian, Japanese American and Latino.

Diet was assessed at baseline with a food frequency questionnaire containing more than 180 food items. The respondents reported both the frequency of food consumption and portion sizes of food consumption within the last year. Follow-up surveys were continued until patient diagnosis, death or the study’s closure on Dec. 31, 2017.

Using questionnaire data, Kim and colleagues calculated the three indices based on 16 food groups, which were classified as healthy plant foods, less healthy plant foods and animal foods. Grains, vegetables, vegetable oils and nuts were among healthy plant foods, while less healthy plant foods included refined grains, fruit, juices and potatoes.

During the mean follow-up duration of 19.2 years, the researchers identified 4,976 CRC cases within the eligible study population. In a multivariable-adjusted analysis, the risk for CRC was lower among men with the highest PDI and hPDI indices vs. those with the lowest indices:

• 0.77 (95% CI, 0.67-0.88) for PDI; and
• 0.8 (95% CI, 0.7-0.91) for hPDI.

There was no significant association between CRC risk in men and uPDI, according to the researchers.

A stronger inverse association with PDI was observed in Japanese American, white and Native Hawaiian men compared with Latino and African American men (P = 0.01), as well as for left and rectal tumors than right tumors (P = 0.005).

While none of the indices were associated with CRC risk in women, an inverse association of hPDI was found in women who had ever smoked (HR=0.8; 95% CI, 0.65-0.98) compared with those who never smoked.

When examining individual food components, Kim and colleagues noted that higher intakes of whole grains (HR per SD=0.95; 95% CI, 0.91-0.995) and legumes (HR per SD=0.91, 95% CI: 0.87-0.96) were associated with a lower CRC risk.

Further CRC risk reductions were also reported in substation analyses, which included drops of:

• 9% (HR=0.91; 95% CI, 0.84-0.995) when whole grains replaced added sugars;
• 8% (HR=0.92; 95% CI, 0.84-1) when fruits replaced added sugars;
• 8% (HR=0.93; 95% CI, 0.85-1.01) when vegetables replaced added sugars; and
• 12% (HR=0.88; 95% CI, 0.8-0.96) when legumes replaced added sugars.

The researchers offered several reasons why healthy plant-based diets resulted in lower CRC risks, one being that fruits, vegetables and whole grains “are rich in dietary fiber, polyphenols or carotenoids with antioxidant and antiinflammatory features.”

“It is also postulated that gut microbiota may play a mediating role for decreasing risk of colorectal cancer by healthy plant foods,” they wrote.

Meanwhile, the lack of association between women and indices could be attributed to dietary habits between genders, Kim and colleagues pointed out, due to women generally consuming more plant foods and less animal foods compared with men.

Kim and colleagues concluded their findings “support that improving the quality of plant foods and reducing animal food consumption can help prevent colorectal cancer.”

References:

• Health: Healthy plant-based diets associated with lower colorectal cancer risk in men. https://www.eurekalert.org/news-releases/971859. Published Nov. 28, 2022.
• Kim J, et al. BMC Med. 2022;doi:10.1186/s12916-022-02623-7.