According to the American Cancer Society (ACS), around 95,520 new cases of colon cancer and 39,910 cases of rectal cancer will be diagnosed in the U.S. this year, and more than 50,000 people are expected to die from the disease.
A wealth of research has suggested that a diet rich in fiber and whole grains may protect against the development of colorectal cancer, but how does high fiber consumption affect those who have already been diagnosed with the disease?
This is what Dr. Andrew Chan — of Massachusetts General Hospital and Harvard Medical School in Boston, MA — and colleagues sought to find out with their new research.
Colorectal cancer and fiber intake
The study included the data of 1,575 individuals who were part of either the Nurses' Health Study or the Health Professionals Follow-Up Study.
All subjects had been diagnosed with stage 1, 2, or 3 colorectal cancer. These are non-metastatic stages, wherein the cancer has not spread to distant sites.
As part of their studies, the participants regularly completed food frequency questionnaires. The team used information from these questionnaires to calculate the subjects' total fiber intake and whole grain consumption, as well as their intake of fiber from individual food sources.
Participants were followed for an average of 8 years after diagnosis, during which time a total of 773 deaths occurred. Of these deaths, 174 were directly related to colorectal cancer.
The researchers found that colorectal cancer patients who had a high total fiber intake had a lower risk of death than those with a low total fiber intake.
Each 5-gram increase in fiber per day was associated with a 22 percent reduction in colorectal cancer-specific mortality and a 14 percent reduction in all-cause mortality, the team reports.
The team also found that every 20-gram increase in whole grain consumption per day was linked with a 28 percent decrease in colorectal cancer death, while the risk of all-cause mortality was reduced by 12 percent.
Cereal fiber most beneficial
On looking at the sources of fiber, the researchers found that cereal fiber posed the greatest benefit; every 5-gram daily increase in cereal fiber was linked to a 33 percent reduction in colorectal cancer death and a 22 percent reduction in all-cause mortality.
A 17 percent reduction in all-cause mortality was identified with every 5-gram daily increase in vegetable fiber, but this type of fiber appeared to have no impact on colorectal cancer-specific mortality.
Fruit fiber was found to have no influence on colorectal cancer death or all-cause mortality.
Dr. Chan and team caution that their study is observational, so it cannot prove cause and effect. There are also a number of limitations to consider — for example, the intake of fiber and whole grains among participants was self-reported, thereby leaving room for error.
"Our findings," write the authors, "need to be validated by further studies, including possible clinical trials."
Still, the researchers are confident that an increase in fiber intake could benefit patients in the non-metastatic stages of colorectal cancer. The team concludes:
"Higher intake of fiber and whole grains after CRC [colorectal cancer] diagnosis is associated with a lower rate of death from that disease and other causes. Our findings provide support for the nutritional recommendations of maintaining sufficient fiber intake among CRC survivors."