Convincing evidence exists to support an association between a decreased risk of colorectal cancer (CRC) and an increased intake of dietary fiber, dietary calcium, and yogurt, as well as a decreased intake of alcohol and red meat, according to the results of a study published in JAMA Network Open.
Researchers conducted an umbrella review of meta-analyses of prospective observational studies to grade the evidence supporting an association between dietary patterns, specific foods, food groups, beverages, macronutrients, and micronutrients and the incidence of CRC. The study authors searched MEDLINE, Embase, and the Cochrane Library through September 2019 and graded the evidence of an association as convincing, highly suggestive, suggestive, weak, or not significant.
The investigators identified 9954 publications, evaluated 222 full-text articles (2.2%), and included 45 meta-analyses (20.3%) that described 109 associations. A total of 35 associations (32.1%) were found to be nominally statistically significant (P ≤.05). Of these, 7 associations (20.0%) reached statistical significance at P ≤1 × 10−6.
Overall, 24 significant associations (68.6%) suggested potential protective effects of dietary factors or dietary patterns associated with CRC risk, including adherence to a healthy diet, a Mediterranean diet, a pesco-vegetarian diet, or a semivegetarian diet and higher intakes of dietary fiber, whole grains, legumes, dairy products including yogurt and nonfermented milk, fruits and vegetables, and micronutrients (ie, supplemental and dietary calcium, zinc, magnesium, vitamin A, vitamin B6, folic acid, vitamin D, and vitamin E). The other significant associations (31.4%) suggested a higher risk of CRC with adherence to an unhealthy diet or Western diet and increased intake of alcohol, red meat, processed meat, pork, eggs, and haem iron.
Of these 109 associations, 5 (4.6%) were supported by convincing evidence, and 2 of these associations — higher vs lower red meat intake (high quality) and heavy alcohol intake (defined as >4 drinks/d compared with those who did not drink or occasionally drank) (moderate quality) — were linked with an increased risk of CRC. Convincing evidence was observed for 3 inverse associations; higher vs lower intake of total dietary fiber (high quality), calcium (moderate quality), and yogurt (moderate quality) was linked with reduced CRC incidence.
“We found that few of the 35 statistically significant associations (ie, positive associations of 4 drinks/d and red meat with the incidence of CRC and inverse associations of higher intake of dietary fiber, calcium, and yogurt with the incidence of CRC) were supported by convincing evidence in the main and sensitivity analyses,” stated the study authors.
A possible limitation to the findings is the exclusion of dose-response meta-analyses, according to the researchers, because the data needed for predictive interval estimation and assessment of small study and excess significant bias effects were not available.
“The findings of this study support existing recommendations for diet in the primary prevention of CRC, emphasizing higher intakes of dietary fiber, calcium, and yogurt and lower intakes of red meat and alcohol,” the researchers commented. “Emerging evidence supports a possible role for overall dietary patterns that, in totality, emphasize habitually consuming fruits, vegetables, grains, and low-fat dairy and reducing red meat and alcohol intake. More research is needed on specific foods for which evidence remains suggestive, including other dairy products, whole grains, processed meat, and specific dietary patterns.”
Veettil SK, Wong TY, Loo YS, et al. Role of diet in colorectal cancer incidence: umbrella review of meta-analyses of prospective observational studies. JAMA Netw Open. 2021;4(2):e2037341. doi:10.1001/jamanetworkopen.2020.37341