Future research needed to investigate link between plant-based food intake, CRC
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A plant-based diet rich in whole grains, vegetable and legumes was associated with a reduced risk for colorectal cancer in a multiethnic cohort of men but varied by race, ethnicity and site of tumor, according to research in BMC Medicine.
“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,” Jihye Kim, of the department of genetics and biotechnology at Kyung Hee University in South Korea, told Healio. “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.
“We aimed to investigate whether the quality and healthiness of plant-based diet would affect the incidence of colorectal cancer and also whether the associations would differ between racial and ethnic populations.”
To estimate the incidence of invasive CRC, Kim and colleagues analyzed 79,952 men (mean age, 60 years) and 93,475 women (mean age, 59.3 years) from the Multiethnic Cohort Study, of whom 13% and 18.5% were African American, 30.2% and 28.1% were Japanese American, 7% and 7.4% were Native Hawaiian, 24% and 20.7% were Latino and 25.8% and 25.3% were white, respectively.
Participants completed qualitative food frequency questionnaires at baseline and reported food consumption frequency and portion size from the previous year. Cox models estimated risk across quintile scores of an overall plant-based diet index (PDI), healthful plant-based diet index (hPDI) and unhealthful plant-based diet index (uPDI).
During a mean follow-up of 19.2 years, researchers reported 4,976 incident cases of CRC. The highest mean scores for PDI and hPDI were among Japanese American participants (49.2 and 49 in men, 49.7 and 49.6 in women) and lowest among Native Hawaiian participants (46.7 and 46.8 and 47 and 46.8, respectively). Native Hawaiian men (49.3) and women (49.4) had the highest mean uPDI, while African American men (47.9) and white women (48.3) had the lowest mean uPDI.
Further, results showed plant-based diet indices “significantly” inversely associated with the risk for CRC among men, with those in the highest quintile of PDI and hPDI groups having a 24% (HR = 0.76; 95% CI, 0.67-0.87) and 21% (HR = 0.79; 95% CI, 0.69-0.91) lower risk, respectively, compared with those in the lowest quintile of each index. These results remained similar following sensitivity analysis.
For individual foods, higher intake of whole grains (HR = 0.95; 95% CI, 0.91-0.995) and legumes (HR = 0.91; 95% CI, 0.87-0.96) associated with a lower risk for CRC, while higher intake of added sugar was linked with a higher risk for CRC (HR = 1.03; 95% CI, 0.99-1.08), although researchers noted this association did not reach significance.
Race- and ethnicity-specific analyses yielded a significant inverse association among Japanese American and white men in the PDI group compared with African American or Latino men. Further, anatomic subsite-specific analysis revealed the inverse association for PDI was stronger for left colon and rectal tumors while the risk reduction with hPDI was significant for all subsites. Researchers noted uPDI was linked with an increased risk for rectal cancer but not right or left colon cancer.
“Eating a plant-based diet rich in healthy plant foods — whole grains, vegetables and legumes — and low in unhealthy plant foods — refined grains, fruit juices and added sugars — which improve the nutritional quality of plant-based diet, could help prevent colorectal cancer risk,” Kim said.
“Future research is needed to investigate the genetic and environmental factors that could influence the association between plant-based food intake and colorectal cancer risk between racial and ethnic groups, because it is not clear yet what causes the racial and ethnic differences.”
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