Certain Dietary Patterns May Be Associated with Lower Risk of Colorectal Cancer

There is an association between a lower risk for colorectal cancer (CRC) and higher intakes of dietary fiber, dietary calcium and yogurt as well as lower intakes of alcohol and red meat, according to study results published in JAMA Oncology.

“The etiology of CRC is multifactorial, with both genetic and environmental factors playing a role,” the study authors wrote. “Evidence suggests that modifiable lifestyle factors, including excess adiposity, poor diet, and physical inactivity, play an important role in the occurrence and progression of this disease.”

Past studies have shown evidence for the association of dietary factors and incidence of CRC, but there had not been a full synthesis of the strength, precision and quality of this evidence in aggregate, according to the authors.

To strengthen the data around this correlation, researchers identified 9,954 publications and evaluated 222 full-text articles and 45 meta-analyses that described 109 associations between dietary factors and CRC incidence. The methodological quality of the meta-analyses was evaluated using A Measurement Tool to Assess Systematic Reviews (AMSTAR-2), which is a critical appraisal tool that identifies the quality of a systematic review as high, moderate, low or critically low.

Of the 109 associations between diet and CRC incidence, five (4.6%) were supported by convincing evidence. Red meat intake (AMSTAR-2, high quality) and heavy alcohol intake (AMSTAR-2, moderate quality), defined as more than four drinks per day, were both associated with an increased risk of CRC.

Conversely, inverse associations in which dietary patterns were associated with reduced CRC incidence included higher intake of dietary fiber (AMSTAR-2, high quality), calcium (AMSTAR-2 moderate quality) and yogurt (AMSTAR-2, moderate quality).

Two associations (1.8%) were supported by highly suggestive evidence. A higher intake of dairy products such as milk, cheese and yogurt (AMSTAR-2, high quality) was associated with CRC risk reduction, while a moderate intake of alcohol (AMSTAR-2, moderate quality), defined as less than 1-3 drinks per day, was associated with an increase in incidence of CRC.

Eight associations (7.3%) were supported by suggestive evidence. Adherence to a Mediterranean diet, a pesco-vegetarian diet or a semivegetarian diet and the intake of whole grains, nonfermented milk and supplemental calcium were all associated with a reduced risk of CRC, while adherence to a Western diet and the intake of processed meat were both associated with an increased risk of CRC in adults. The remaining associations had either weak evidence (16.5%) or no evidence (67.9%).

A possible limitation to the review, according to the authors, is that randomized clinical trials are often scarce in research on associations between diet and cancer. Self-reported diets could also be reported incorrectly, making it hard to consider them completely accurate.

According to the authors, these findings widen the scope of information on dietary associations with risk for CRC and support existing cancer prevention dietary guidance which emphasize higher intakes of dietary fiber, calcium and yogurt as well as lower intakes of red meat and alcohol, however, “More research is needed on specific foods for which evidence remains suggestive, including other dairy products, whole grains, processed meat, and specific dietary patterns.”

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