“Higher fiber intake after the diagnosis of nonmetastatic colorectal cancer is associated with lower colorectal cancer–specific and overall mortality.”

— Mingyang Song, MD, ScD

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IN A STUDY reported in JAMA Oncology, Mingyang Song, MD, ScD, of Massachusetts General Hospital and Harvard Medical School, and colleagues found that higher fiber intake after diagnosis of nonmetastatic colorectal cancer is associated with improved colorectal cancer–specific and overall survival.¹ The benefits were also observed for higher intake of whole grains. 

Study Details 

THE STUDY INCLUDED 1,575 health-care professionals with stage I to III colorectal cancer from the prospective Nurses’ Health Study (n = 963) and Health Professionals Follow-up Study (n = 612) cohorts. The Nurses’ Health Study enrolled 121,700 registered female nurses aged 30 to 55 years in 1976. The Health Professionals Follow-up Study enrolled 51,529 male health-care professionals aged 40 to 75 years in 1986. 

Participants received a questionnaire regarding medical history and lifestyle factors at baseline and every 2 years thereafter. Dietary data were collected and updated every 4 years, with validated food frequency questionnaires. The current analysis used data from 1980 for the Nurses’ Health Study and from 1986 for the Health Professionals Follow-up Study as baselines on fiber intake. Follow-up rates were 95.4% in the Nurses’ Health Study cohort and 95.9% in the Health Professionals Follow-up Study cohort for each of the questionnaires through 2010. Consumption of total fiber and different sources of fiber and whole grains was assessed between 6 months and 4 years after colorectal cancer diagnosis. The current analysis was performed between December 2016 and August 2017. 

Multivariate analysis for colorectal cancer–specific and overall mortality included stratification by age group at diagnosis; sex; cancer stage and adjustment for age at diagnosis; year of diagnosis; tumor grade of differentiation; cancer subsite; prediagnostic fiber intake; postdiagnostic alcohol consumption; pack-years of smoking; body mass index; physical activity (metabolic-equivalent hr/wk); regular use of aspirin; glycemic load; and consumption of total fat, folate, calcium, and vitamin D. 

Association of Survival With Fiber Intake 

AMONG THE 1,575 patients, the mean age was 68.6 years at diagnosis, and 61% were women. Over a median follow-up of 8 years, a total of 773 deaths were documented, with 174 (22.5%) due to colorectal cancer. 

On a multivariate analysis, among all patients, higher fiber intake was associated with significantly better colorectal cancer–specific and overall survival, with hazard ratios (HRs) of 0.78 (P = .006) and 0.86 (P < .001) per each 5-g increment in intake per day, respectively. Patients who increased fiber intake after diagnosis from prediagnosis levels also had significantly improved colorectal cancer–specific and overall survival, with hazard ratios of 0.82 (P = .002) and 0.86 (P <.001) per each 5-g/d increase in intake, respectively. 

By source of fiber, higher cereal fiber intake was associated with lower colorectal cancer–specific mortality (HR per 5-g/d increment = 0.67, P = .007) and all-cause mortality (HR per 5-g/d increment = 0.78, P < .001). Higher intake of vegetable fiber was associated with lower all-cause mortality (HR per 5-g/d increment = 0.83, P = .009) but not colorectal cancer–specific mortality (HR per 5-g/d increment = 0.82, P = .22). Associations with higher intake of fruit fiber were not significant for colorectal cancer–specific mortality (HR per 5-g/d increment = 0.91, P =.58) or all-cause mortality (HR per 5-g/d increment = 0.92, P = .29). 

Whole Grain Intake 

INCREASED WHOLE grain intake was associated with lower colorectal cancer–specific mortality (HR per 20-g/d increment = 0.72, P = .002); the risk reduction was attenuated after adjustment for fiber intake in a multivariate analysis (HR = 0.77, P = .02). Higher intake was also associated with lower all-cause mortality (HR per 20-g/d increment = 0.88, P = .008), with the risk reduction being attenuated after adjustment for fiber intake (HR = 0.91, P = .08). 

The investigators concluded: “Higher fiber intake after the diagnosis of nonmetastatic colorectal cancer is associated with lower colorectal cancer-specific and overall mortality. Increasing fiber consumption after diagnosis may confer additional benefits to patients with colorectal cancer.” 

The study was supported by National Institutes of Health grants; an American Association for Cancer Research-AstraZeneca Fellowship in Immuno-oncology research grant; and grants from the American Institute for Cancer Research, Project P Fund for Colorectal Cancer Research, The Friends of the Dana-Farber Cancer Institute, Bennett Family Fund, and the Entertainment Industry Foundation through the National Colorectal Cancer Research Alliance. ■

DISCLOSURE: For full disclosures of the study authors, visit www.jama.jamanetwork.com. 

REFERENCE 

1. Song M, Wu K, Meyerhardt JA, et al: Fiber intake and survival after colorectal cancer diagnosis. JAMA Oncol. November 2, 2017 (early release online).