Higher fiber consumption after colorectal cancer diagnosis linked to better survival

Eating more fiber was associated with better survival among patients with nonmetastatic colorectal cancer (CRC), a recent study found.

The prospective cohort study included 1,575 health professionals from the Nurses' Health Study and Health Professionals Follow-up Study who had been diagnosed with stage I to III CRC. The study was conducted from Dec. 23, 2016, to Aug. 23, 2017. Most participants (61.1%) were women, and their mean age was 68.6 years. During a median of eight years of follow-up, 773 participants died, including 174 of CRC. Results were published online Nov. 2 by JAMA Oncology.

Higher intake of fiber (assessed by a validated food frequency questionnaire six months to four years after cancer diagnosis) was associated with lower all-cause and CRC-specific mortality. For every 5-g increase in fiber consumption per day, the multivariable hazard ratio (HR) was 0.86 for all-cause mortality (95% CI, 0.79 to 0.93; P<0.001) and 0.78 for CRC-specific mortality (95% CI, 0.65 to 0.93; P=0.006). Patients who ate more fiber after their cancer diagnosis than they had before had lower mortality, and each 5-g/d increase was associated with 18% lower CRC-specific mortality (95% CI, 7% to 28%; P=0.002) and 14% lower all-cause mortality (95% CI, 8% to 19%; P<0.001).

Consumption of cereal fiber was particularly associated with reduced mortality: Higher cereal consumption was associated with both CRC and all-cause mortality, while vegetable fiber was associated only with all-cause mortality and fruit fiber showed no association. Consumption of whole grains was associated with lower CRC mortality (HR per 20-g/d increment, 0.72; 95% CI, 0.59 to 0.88; P=0.002), and the association was attenuated after adjustment for fiber intake.

“Our findings provide novel evidence for the potential benefit of increasing fiber and whole grain consumption among patients with CRC,” the study authors said. They noted that fiber had been shown to help prevent CRC in other studies. Possible explanations for the findings include that fiber consumption may mitigate hyperinsulinemia and inflammation or that butyrate, produced by bacterial fermentation of fiber, may modulate the tumor microenvironment. The particular benefit of cereals may be due to their high fiber content or other ingredients with favorable effects, the authors speculated.

The study was limited by its size and the risk of residual confounding, among other factors, and large-scale trials are needed, the study authors said. However, the current results support nutritional recommendations for sufficient fiber intake among patients with CRC.