Dietary factors may have role in development of CRC
Factors related to diet, including fiber and alcohol intake, were associated with the development or prevention of colorectal cancer, according to study results.
“Several systematic reviews with meta-analysis of prospective observational studies have summarized evidence for the associations between dietary factors and the incidence of [colorectal cancer (CRC)],” Nathorn Chaiyakunapruk, Pharm D, PhD, from the department of pharmacotherapy at The University of Utah, and colleagues wrote. “However, to date, there has been little synthesis of the strength, precision and quality of this evidence in aggregate.”
Investigators searched the literature for studies that explored the association of dietary patterns, specific foods, food groups, beverages, macronutrients and micronutrients with the incidence of CRC. They included only meta-analyses of prospective observational studies with a cohort study design. Then, they graded the evidence of the association as convincing, highly suggestive, suggestive, weak or not significant.
Researchers identified 45 meta-analyses comprising 109 associations between dietary factors and CRC in their study. Of those studies, 35 were nominally statistically significant, whereas 17 associations demonstrated large heterogeneity between studies, and 11 had small study effects.
Chaiyakunapruk and colleagues determined that five (4.6%) associations had convincing evidence, two (1.8%) were highly suggestive, 10 (9.2%) were suggestive, 18 (16.5%) were weak and 74 (67.9%) had no evidence for an association.
Researchers found convincing evidence for an association between intake of red meat (high vs. low) and alcohol (four or more drinks per day vs. zero or occasional drinks) with the incidence of CRC. Additionally, they found an inverse association between higher vs. lower intake of dietary fiber, calcium and yogurt with CRC risk. These associations remained after sensitivity analyses.
“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 met and alcohol intake,” Chaiyakunapruk and colleagues wrote. “More research is needed on specific foods for which evidence remains suggestive, including other diary products, whole grains, processed meat and specific dietary patterns.”
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Associations with diet and CRC risk have been noted dating back to the 1980s, when it was widely hypothesized that dietary factors contributed to the stark difference of high rates of colorectal cancer in North America and Northern Europe compared with low rates in Asia and Africa. The “Western Diet” — or diets high in processed foods, red meat, added sugar, and refined carbohydrates — have been associated with increased risks for certain types of cancers including colon, prostate and breast cancer.
This study’s strength is that it looked at meta-analyses of prospective observational studies with a cohort study design, and graded the strength of the evidence, rather than looking at just a few studies. The consensus was convincing evidence for increased risk for colorectal cancer with red meat and alcohol, and a decreased risk for a high fiber diet and intake of calcium and yogurt. These findings are in-line with the association of the Mediterranean Diet on reduced risk for cancer, including colon cancer. The Mediterranean Diet focuses on a diet low in red and processed meats, processed foods, and added sugars, and a diet high in fruits, vegetables, nuts, seeds, olive oil, legumes, and whole grains. This study further supports the potential importance of life-style factors on reducing the incidence of colorectal cancer and supports the recommendation for the Mediterranean Diet in prevention.
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In this manuscript, Veettil and others conducted a meta-analysis looking into the role of dietary factors on the onset of CRC. They specifically combined data from previously published cohort studies where large groups of individuals completed surveys about their diet and then were followed for extended periods of time for the onset of diseases like CRC. By compiling data from 222 articles and 45 prior meta-analyses, the authors identified 109 relationships between dietary factors and CRC incidence. Using statistical models and adjusting for factors, including the quality of these studies, they concluded that five of the 109 relationships for high red meat intake consumption, high alcohol consumption, low fiber intake (low vs. high), and high calcium and yogurt consumption were most statistically significant and held the strongest relationships with CRC risk.
These factors are consistent with other guidelines and expert consensus such as the most recent American Institute for Cancer Research/World Cancer Research Fund cancer prevention and CRC prevention guidelines and the recently published American Cancer Society guideline for diet and physical activity for cancer prevention. This data absolutely add to the growing literature supporting a strong role of dietary factors in modulating CRC risk. Ongoing efforts to educate the public about these risks and to identify creative and sustainable strategies to improve dietary habits are urgently needed.
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