Index-based Dietary Patterns and Risk of Colorectal Cancer
The authors compared how four indexes—the Healthy Eating Index-2005, Alternate Healthy Eating Index, Mediterranean Diet Score, and Recommended Food Score—are associated with colorectal cancer in the National Institutes of Health-AARP Diet and Health Study (n = 492,382). To calculate each score, they merged data from a 124-item food frequency questionnaire completed at study entry (1995—1996) with the MyPyramid Equivalents Database (version 1.0). Other variables included energy, nutrients, multivitamins, and alcohol. Models were stratified by sex and adjusted for age, ethnicity, education, body mass index, smoking, physical activity, and menopausal hormone therapy (in women). During 5 years of follow-up, 3,110 incident colorectal cancer cases were ascertained. Although the indexes differ in design, a similarly decreased risk of colorectal cancer was observed across all indexes for men when comparing the highest scores with the lowest: Healthy Eating Index-2005 (relative risk (RR) = 0.72, 95% confidence interval (CI): 0.62, 0.83); Alternate Healthy Eating Index (RR = 0.70, 95% CI: 0.61, 0.81); Mediterranean Diet Score (RR = 0.72, 95% CI: 0.63, 0.83); and Recommended Food Score (RR = 0.75, 95% CI: 0.65, 0.87). For women, a significantly decreased risk was found with the Healthy Eating Index-2005, although Alternate Healthy Eating Index results were similar. Index-based dietary patterns that are consistent with given dietary guidelines are associated with reduced risk.

The development of different diet quality indexes has increased in the last decade, as has interest in understanding how indexes predict health outcomes. Index-based dietary patterns are an appealing method to address the complexity of diet and the likely interaction among multiple dietary components. Use of an index-based method—calculating a numerical score based on a priori knowledge—is one way to comprehensively approach the study of the relation between diet and cancer.

Assessing overall dietary patterns is an important alternative to traditional methods in nutritional epidemiology that have focused only on single nutrients. Although it is important to understand the role of individual dietary constituents, there are inherent statistical limitations with the single-nutrient approach because intakes are often intercorrelated. Diet quality indexes preserve some of the multidimensional aspects of food and allow for the analysis of nonnutrient components without reducing dietary intake to a single nutrient or a series of nutrients.

In this analysis, we examine four indexes—the Healthy Eating Index-2005, Alternate Healthy Eating Index, Mediterranean Diet Score, and Recommended Food Score—in relation to colorectal cancer in the National Institutes of Health (NIH)-AARP Diet and Health Study cohort. These indexes share some similarities, but they differ in philosophy and design. The Healthy Eating Index-2005 replaces the original Healthy Eating Index, aligns with Dietary Guidelines for Americans, 2005, and uses an energy-adjusted density approach. The Alternate Healthy Eating Index is grounded in a different food guide, the Healthy Eating Pyramid. The Mediterranean Diet Score was designed to reflect key components of the Mediterranean diet and is dependent on the distribution of intake within a given population to determine cutpoints for scoring; the components are also energy adjusted. The Recommended Food Score is the simplest approach and counts whether foods were consumed at least weekly from a specified food list defined by dietary guidelines.