Whole grain intake lowers risk of colorectal cancer
Higher consumption of whole grains and fibre from grains, but not total intake of dietary fibre, may reduce the risk of colorectal cancer (CRC), a recent study has shown.
“[O]ur study is the largest prospective cohort to date to examine intake of whole grains and dietary fibre in relation to CRC,” the researchers said. “Our findings suggest that dietary guidance for CRC prevention should focus on increasing whole grain intake as a nutrient-dense source of fibre.”
Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95 percent confidence intervals (CIs) for the risk of CRC related to whole grain and dietary fibre intake among 478,994 adults aged 50–71 years in the US.
The researchers assessed diet using a self-administered food frequency questionnaire at baseline (1995–1996). A total of 10,200 incident CRC cases occurred over 16 years and 6,464,527 person-years of follow-up. Finally, 24-hour dietary recall data were collected on a subset of participants and used to examine the impact of measurement error on risk estimates.
Intake of whole grains (quintile 5 vs quintile 1: HR, 0.84, 95 percent CI, 0.79–0.90; ptrend<0.001), but not dietary fibre (HR, 0.96, 95 percent CI, 0.88–1.04; ptrend=0.40) was inversely correlated with CRC incidence after multivariable adjustment for potential confounders, including folate. Whole grain intake was also inversely correlated with all CRC cancer subsites, particularly rectal cancer (HR, 0.76, 95 percent CI, 0.67–0.87; ptrend<0.001). [Am J Clin Nutr 2020;112:603-612]
Moreover, fibre from grains, but not other sources, correlated with a lower CRC incidence (HR, 0.89, 95 percent CI, 0.83–0.96; ptrend<0.001), particularly distal colon (HR, 0.84, 95 percent CI, 0.73–0.96; ptrend=0.005) and rectal cancer (HR, 0.77, 95 percent CI, 0.66–0.88; ptrend<0.001).
These findings were consistent with those from prior studies, which also found an inverse association between whole grain intake and CRC, with the magnitude of associations ranging from an 8-percent to a 20-percent risk reduction, according to the researchers. [Nutr Cancer 1998;30:85-96; Br J Cancer 2010;103:730-734]
Prior literature on dietary fibre intake, however, was inconsistent. Some studies had found associations, while others had not. [BMJ 2011;343:d6617; Int J Cancer 2019;145:3040-3051; Br J Nutr 2015;114:959-969; Am J Clin Nutr 2007;85:1353-1360; Int J Cancer 2012;131:469-478; PLoS One 2012;7:e39361; Lancet 2003;361:1496-1501; JAMA 2005;294:2849-2857]
“Whole grains contain numerous micronutrients and bioactive components such as B vitamins, minerals, phenols, antioxidants, and phytoestrogens, which may protect against CRC,” the researchers said. [Am J Clin Nutr 1999;70(3 Suppl):459S-463S; Nutr Res Rev 2010;23:65-134]
“In addition, whole grains, which are a good source of fibre, increase stool bulk, dilute possible carcinogens, decrease stool transit time through the bowel, and produce short chain fatty acids, which are hypothesized to protect against CRC risk,” they noted. [Am J Clin Nutr 1999;70(3 Suppl):459S-463S; Annu Rev Nutr 1999;19:545-586]
Whole grains and fibre also help in reducing weight gain and type 2 diabetes, which are both risk factors for CRC. [PLoS Med 2007;4:e261; Arch Intern Med 2007;167:956-965]
“Taken together, our results suggest the importance of considering whole foods for cancer prevention rather than individual constituents, such as fibre supplements,” the researchers.