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Is adherence to dietary guidelines or specific dietary patterns, assessed by a predetermined score, related to the likelihood of developing type 2 diabetes?

In the past, researchers looked at the relationship between individual foods and nutrients and health. Today, there is interest in looking at how combinations of foods and beverages, or dietary patterns, impact health. Many researchers use a score to measure how well individuals follow specific dietary guidance or a healthy diet. These are numeric scores of foods, food components, and/or nutrients and the individual components are summed to derive a total score for a dietary pattern. This summary of a NEL review presents what we know about dietary patterns, assessed using a score, and the likelihood of developing type 2 diabetes.

Conclusion
There is limited evidence that adherence to a dietary pattern rich in fruits, vegetables, legumes, cereals/whole grains, nuts, fish, and unsaturated oils, and low in meat and high-fat dairy, assessed using an index or score, is associated with decreased risk of type 2 diabetes.

What the Research Says
  • Among included studies there was variation in the types of indices or scores used, without a preponderance of studies with any one index related to risk of type 2 diabetes, making it difficult to draw overarching conclusions related to a specific dietary pattern
In European populations, consumption of a Mediteranean-style diet was associated with reduced incidence of type 2 diabetes

Technical Abstract

Background
The goal of this systematic review project was to identify dietary patterns of food and beverage intake that promote health and prevent disease. Historically, most dietary guidance has been based on research conducted on individual food components or nutrients. Dietary patterns are 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. The objective of this systematic review was to assess the relationship between adherence to an a priori score and risk of cardiovascular disease. An a priori score measures the degree of adherence to specific dietary guidelines or adherence to a healthy diet defined by scientific evidence on diet and disease. A priori scores are composite numeric scores of foods, food components, and/or nutrients that are assessed as dichotomous variables (with predefined cut-points), ordinal variables such as quintiles, or as continuous variables. The individual components are summed to derive a total score. 
 
Conclusion Statement
There is limited evidence that adherence to a dietary pattern rich in fruits, vegetables, legumes, cereals/whole grains, nuts, fish, and unsaturated oils and low in meat and high-fat dairy assessed using an index or score, is associated with decreased risk of type 2 diabetes. (Grade: III-Limited)
 
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 (using an a priori index or score) and risk of obesity. Studies that met the following criteria were included in the review: randomized controlled trials, non-randomized controlled trials, or prospective cohort studies; subjects aged 2 to 18 years; subjects who were healthy or at elevated chronic disease risk; subjects from countries with high or very high human development (2011 Human Development Index); and published in English in peer-reviewed journals. The date range was unlimited. Diet exposure was assessed by adherence to a hypothesis-based dietary pattern, defined using a numerical scoring system.
 
A group of technical experts were involved in a qualitative synthesis of the body of evidence, development of a conclusion statement, and assessment of the strength of the evidence (grade) using pre-established criteria including evaluation of the quality, quantity, consistency, magnitude of effect, and generalizability of available evidence. 
 
Findings
  • A total of 11 studies met the inclusion criteria for this systematic review and the body of evidence consisted primarily of large prospective cohort studies.
  • The studies identified two major categories of dietary pattern scores and their association with incident T2D was mixed.
  • Mediterranean style dietary pattern:
    • European studies (Spain and Greece) found a favorable association between a Mediterranean diet and risk of T2D
    • A study in the United States found no association between a Mediterranean diet and T2D incidence in the total population, in men or women, or in racial/ethnic subgroups
  • Dietary guidelines-related pattern (each study used a different score or index):
    • Adherence to the alternate HEI (AHEI) was associated with decreased risk of T2D in women in the United States
    • Adherence to a DASH score was associated with reduced risk of T2D in Whites, but not in the Blacks and Hispanics in the United States
    • Adherence to the DQI-2005 was not associated with risk of T2D in young adults in the total population or in Black or White young adults in the United States
    • European studies ( Australia and Germany) found no association between their dietary guidelines scores and incident T2D
  • Studies that assessed intermediate outcomes including glucose tolerance and insulin resistance showed there was some agreement that a Mediterranean style diet was protective.
 
Discussion
It was challenging to synthesize the results because of the number of indices examined, including MDS, variations on MDS, and a large number of unique dietary guidelines-related scores. Overall, there were not a compelling number of studies with any one index. Of the eight studies that examined diabetes incidence, seven different scores were used and only the MDS was used in two studies. Of the five studies that assessed glucose tolerance and insulin resistance, all used different scores.