Fiber Intake and Survival After Colorectal Cancer Diagnosis

Abstract

Importance: Although high dietary fiber intake has been associated with a lower risk of colorectal cancer (CRC), it remains unknown whether fiber benefits CRC survivors.

Objective: To assess the association of postdiagnostic fiber intake with mortality.

Design, setting, and participants: A total of 1575 health care professionals with stage I to III CRC were evaluated in 2 prospective cohorts, Nurses' Health Study and Health Professionals Follow-up Study. Colorectal cancer-specific and overall mortality were determined after adjusting for other potential predictors for cancer survival. The study was conducted from December 23, 2016, to August 23, 2017.

Exposures: Consumption of total fiber and different sources of fiber and whole grains assessed by a validated food frequency questionnaire between 6 months and 4 years after CRC diagnosis.

Main outcomes and measures: Hazard ratios (HRs) and 95% CIs of CRC-specific and overall mortality after adjusting for other potential predictors for cancer survival.

Results: Of the 1575 participants, 963 (61.1%) were women; mean (SD) age was 68.6 (8.9) years. During a median of 8 years of follow-up, 773 deaths were documented, including 174 from CRC. High intake of total fiber after diagnosis was associated with lower mortality. The multivariable HR per each 5-g increment in intake per day was 0.78 (95% CI, 0.65-0.93; P = .006) for CRC-specific mortality and 0.86 (95% CI, 0.79-0.93; P < .001) for all-cause mortality. Patients who increased their fiber intake after diagnosis from levels before diagnosis had a lower mortality, and each 5-g/d increase in intake was associated with 18% lower CRC-specific mortality (95% CI, 7%-28%; P = .002) and 14% lower all-cause mortality (95% CI, 8%-19%; P < .001). According to the source of fiber, cereal fiber was associated with lower CRC-specific mortality (HR per 5-g/d increment, 0.67; 95% CI, 0.50-0.90; P = .007) and all-cause mortality (HR, 0.78; 95% CI, 0.68-0.90; P < .001); vegetable fiber was associated with lower all-cause mortality (HR, 0.83; 95% CI, 0.72-0.96; P = .009) but not CRC-specific mortality (HR, 0.82; 95% CI, 0.60-1.13; P = .22); no association was found for fruit fiber. Whole grain intake was associated with lower CRC-specific mortality (HR per 20-g/d increment, 0.72; 95% CI, 0.59-0.88; P = .002), and this beneficial association was attenuated after adjusting for fiber intake (HR, 0.77; 95% CI, 0.62-0.96; P = .02).

Conclusions and relevance: Higher fiber intake after the diagnosis of nonmetastatic CRC is associated with lower CRC-specific and overall mortality. Increasing fiber consumption after diagnosis may confer additional benefits to patients with CRC.

Figure 1

Dose-response relationship between post-diagnostic fiber intake and colorectal cancer-specific mortality (A) and all-cause mortality (B) among colorectal cancer patients. Dashed lines represent the 95% confidence intervals of the hazard ratio (HR). Multivariable model was adjusted for the same set of covariates as in Table 1. For colorectal cancer-specific mortality, no spline variable was selected and P for linearity = 0.004; for all-cause mortality, there was a non-linear relationship with P = 0.007 for non-linearity and P<0.001 for the overall significance. Sample size within each interval of fiber intake (containing the lower limit but not the upper limit) is shown below the X-axis in panel (A). For example, there are 67 patients with fiber intake of ≤10 and >12.5 g/day. Twenty-five and 61 patients with fiber intake of <10 and ≥35 g/day are not shown, respectively.

Figure 1

Dose-response relationship between post-diagnostic fiber intake and colorectal cancer-specific mortality (A) and all-cause mortality (B) among colorectal cancer patients. Dashed lines represent the 95% confidence intervals of the hazard ratio (HR). Multivariable model was adjusted for the same set of covariates as in Table 1. For colorectal cancer-specific mortality, no spline variable was selected and P for linearity = 0.004; for all-cause mortality, there was a non-linear relationship with P = 0.007 for non-linearity and P<0.001 for the overall significance. Sample size within each interval of fiber intake (containing the lower limit but not the upper limit) is shown below the X-axis in panel (A). For example, there are 67 patients with fiber intake of ≤10 and >12.5 g/day. Twenty-five and 61 patients with fiber intake of <10 and ≥35 g/day are not shown, respectively.