A recent US-based study assessed the association between high fiber intake after colorectal cancer diagnosis and survival of patients.
Colorectal cancer is the third leading cause of cancer death in the United States. Past studies suggest that dietary risk factors play an important role in the cause of this cancer. There is evidence to suggest that dietary fiber decreases the risk of several diseases including colorectal cancer. Several mechanisms have been proposed to explain the association of fiber intake and risk of this type of cancer cancer, including dilution of carcinogens in the colon, increased stool bulk, and reduced transit time. Additionally, gut bacteria ferment fiber into short chain fatty acids, such as butyrate that has been shown to help control the growth of cells lining the gut and has anti-inflammatory effects, thus protecting against colorectal cancer.
Even though many studies have demonstrated a protective role of dietary fiber, there is little evidence to determine the association between fiber intake and survival of patients with this type of cancer. A recent prospective cohort study tested whether high consumption of fiber after diagnosis of colorectal cancer is associated with lower mortality. The study, published in the Journal of American Medical Association Oncology, included a total of 1,575 healthcare professionals with stage l, ll and lll colorectal cancer.
The participants from two large prospective cohorts, the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS) were evaluated for their medical history and lifestyle factors. The study was conducted from December 2016 to August 2017. Researchers collected dietary data using food frequency questionnaires at baseline and updated every four years. They evaluated fiber intake from different food components including cereals, vegetables, and fruits separately and also assessed consumption of whole grains. The study physicians confirmed a colorectal cancer diagnosis, followed up participants for a median of eight years, and identified deaths through review of National Death Index. During the follow-up period, there were a total of 773 deaths, including 174 from colorectal cancer.
Pre- and Post-Diagnosis of Fiber Intake and Patient Survival
Statistical analysis showed a linear relationship between post-diagnostic fiber intake and colorectal cancer-specific mortality. The association between fiber intake and all-cause mortality was found to be statistically significant. The results showed that this association was positive for up to a fiber intake of 24 g/day, beyond which there was no further reduction in mortality observed. Interestingly, patients who increased their fiber intake after diagnosis compared with their fiber intake before diagnosis had a reduced rate of mortality. The researchers observed an 18% lower colorectal cancer-specific mortality and 14% lower all-cause mortality with each 5 g/day increase in post-diagnostic fiber intake.
Significance of the Dietary Source of Fiber
The study also analyzed the major dietary sources of fiber such as cereals, vegetables, and fruits. The results showed a decrease in the rate of mortality with an increased intake of fiber from cereals. Each 5g/day increase of cereal fiber was linked to 33% lower risk of colorectal cancer mortality and a 22% lower risk of all-cause mortality. Fiber from vegetables showed a 17% reduction in all-cause mortality but no significant reduction was observed for colorectal cancer mortality. Fiber from fruits did not show any association with colorectal or all-cause mortality. Furthermore, whole grain consumption was associated with a lower colorectal cancer-specific mortality.
Relevance for Colorectal Cancer Patients
The study puts forward evidence to support the protective effect of high fiber intake for prevention of colorectal cancer as well as better prognosis after diagnosis. Colorectal cancer patients who increased their fiber intake after diagnosis experienced a reduced risk of mortality. The researchers found that better survival rates were associated with consumption of cereals and whole grains compared with the fiber from fruits and vegetables.
The main strengths of the study are its prospective nature, detailed collection of pre- and post-diagnostic data, and long follow up period. The study has certain limitations such as unavailability of detailed treatment data and data on recurrence of cancer, and a relatively small number of colorectal cancer-related deaths. In addition, the authors caution about the observational nature of this study and expressed the need for validation of results by future studies.
In conclusion, findings of the study suggest that a diet with high levels of fiber and whole grains after diagnosis lowers the risk of mortality in patients with non-metastatic colorectal cancer. Eating high fiber foods such as brown rice, oatmeal, wholegrain bread, and cereals can not only lower the risk of getting the cancer but also reduce the risk of death from the disease. The authors suggest that these findings may assist in making nutritional recommendations for fiber intake in colorectal cancer survivors.
Written by Preeti Paul, MS Biochemistry
Reference: Mingyang Song et al., Fiber Intake and Survival After Colorectal Cancer Diagnosis. JAMA Oncology, 2 November 2017.