The Link Between Diet Quality and CRC Outcomes

November 12, 2018

A study looks at how dietary patterns impact colorectal cancer outcomes before and after diagnosis.

People who have diets with a higher intake of plants and lower intake of animal products both before and after diagnosis with colorectal cancer survived longer, according to a new study. The results indicate the “importance of diet quality as a potentially modifiable tool to improve prognosis among men and women with colorectal cancer.”

The reduced mortality was seen among participants who had a higher ACS score based on the American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention, which recommends at least five servings per day of fruits and vegetables, a high variety of fruits and vegetables, whole grains over refined grains, and limited red or processed meat.

“The ACS score was the only dietary pattern we evaluated that was derived specifically for cancer prevention, which may explain why its results were more strongly inverse than the other dietary patterns,” Mark A. Guinter, PhD, MPH, of the American Cancer Society, and colleagues wrote in the Journal of Clinical Oncology.

The study is the first of its kind to look at change in dietary quality from pre- to post-diagnosis of colorectal cancer. In the Cancer Prevention Study-II Nutrition Cohort, there was 2,801 participants without cancer in 1992/1993 who were later diagnosed with nonmetastatic colorectal cancer. Pre-diagnosis diet information was available for 2,671 participants and post-diagnosis data for 1,321 participants. The researchers looked at the Dietary Approaches to Stop Hypertension (DASH), ACS-score, prudent, and Western dietary patterns to evaluate diet quality.

Those participants with the highest ACS score prediagnosis had a 22% lower risk for all-cause mortality compared with participants with the lowest ACS score (95% CI, 5%–35%). Inverse trends were found for ACS score and both all-cause mortality and colorectal cancer-specific mortality. Higher Western diet score was associated with higher all-cause mortality compared with those with the lowest Western diet score.

Post-diagnosis, higher scores for DASH, ACS score, and prudent diets were all significantly associated with lower all-cause mortality, leading to 21%, 38%, and 28% lower risk, compared with participants with the lowest scores for those dietary patterns. Reduced colorectal cancer-specific mortality risk was found with higher DASH and ACS-score compared with increased risk with increasing Western diet quartiles.

“Consistently observed inverse associations suggest that prognosis may improve with better post-diagnosis diet, even when prediagnosis diet quality was relatively low,” the researchers wrote. “These results were supported further in postdiagnostic models that identified statistically significant associations between diet quality and mortality that were independent of prediagnosis diet quality.”

Based on these results, the researchers wrote that recommendations should be made in support of high diet quality before and after colorectal cancer diagnosis to improve survival.

“Collectively, the results from all dietary patterns suggest that consumption of a diet high in plant products and fiber while limiting red and processed meat and added sugars both before and after diagnosis may be beneficial,” the researchers wrote.