Background

The goal of this systematic review was to determine whether dietary patterns are associated
with risk of colorectal cancer. Dietary patterns were defined as the quantities, proportions,
variety or combination of different foods, drinks and nutrients in diets, and the frequency with
which they are habitually consumed.

Conclusion statement

Moderate evidence indicates an inverse association between dietary patterns that are higher
in vegetables, fruits, legumes, whole grains, lean meats and seafood, low-fat dairy and
moderate alcohol; and low in red and processed meats, saturated fat and sodas and sweets
relative to other dietary patterns and the risk of colon and rectal cancer. Conversely, diets that
are higher in red and processed meats, French fries and potatoes, and sources of sugars
(i.e., sodas, sweets and dessert foods) are associated with a greater colon and rectal cancer
risk. 

2015 DGAC Grade: Moderate 

Methods

Literature searches were conducted using PubMed, Embase, Navigator (BIOSIS, CAB Abstracts and Food Science and Technology Abstracts) and Cochrane databases to identify studies that evaluated the association between dietary patterns and risk of colorectal cancer. Studies that met the following criteria were included in the review: randomized controlled studies (RCTs), non-randomized controlled trials, prospective cohort studies, or nested casecontrol studies; human subjects aged two years and older who were healthy or at elevated chronic disease risk; subjects from countries with high or very high human development (2012 Human Development Index); and published in English in peer-reviewed journals. The date range was from January 2000 to January 2014. The intervention or exposure was adherence to a dietary pattern (e.g., a priori patterns, data-driven patterns, reduced rank regression or patterns derived from other methods, and a description of the dietary pattern(s) (i.e., foods and beverages) consumed by subjects was provided. The outcome was incidence of colorectal cancer.

Data from each included article were extracted, and risk of bias was assessed. The evidence was qualitatively synthesized, a conclusion statement was developed and the strength of the evidence (grade) was assessed using pre-established criteria including evaluation of the quality and risk of bias, quantity, consistency, magnitude of effect and generalizability of available evidence. 

Findings

• This systematic review included 21 articles from prospective cohort studies and one article from an RCT published since 2000 that examined the relationship between dietary patterns and risk of colorectal cancer
• The articles used diverse methodology to assess dietary patterns. Nine articles used indices and scores to assess dietary patterns, 10 articles used data-driven methods and three used other approaches.
• The dietary patterns examined in this systematic review were defined in various ways, making comparisons between articles difficult. However, despite general heterogeneity in this body of evidence, some protective dietary patterns emerged, particularly in articles where patterns were defined by index or score; articles using data-driven methods were less consistent.
  • Patterns emphasizing vegetables, fruits, fish and seafood, legumes, low-fat dairy, and whole grains were generally associated with reduced risk of colorectal cancer
  • Patterns higher in red and processed meats; potatoes and French fries; and sodas, sweets, added sugars were generally associated with increased risk of colorectal cancer.
• The relationship between dietary patterns and colorectal cancer risk often varied by sex and tumor location. Results based on analysis by sex were mixed, while analysis in tumor subgroups seemed to indicate that dietary patterns may be more strongly associated with tumor development in distal regions of the colon and rectum.

Limitations

The ability to draw strong conclusions was limited by the following issues:

• Although most cohort studies make extensive efforts to include participants across a wide range of race/ethnic groups and across the socioeconomic continuum, there still may be some groups for which the association between dietary patterns and colorectal cancer risk cannot be reliably assessed; therefore, conclusions cannot be drawn.