What is the relationship between adherence to dietary guidelines and recommendations or specific dietary patterns, assessed using an index or score, and risk of type 2 diabetes?
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
(CVD). 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 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.
There is limited evidence that adherence to a dietary pattern
rich in fruits, vegetables, legumes, cereals and 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
. (DGAC Grade: III-Limited
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 two years 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)
- Published in English in peer-reviewed journals
- Unlimited date range
- 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.
- 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 U.S. 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 Healthy Eating Index (AHEI) was associated with decreased risk of T2D in women in the U.S.
- Adherence to a DASH score was associated with reduced risk of T2D in Whites, but not in the Blacks and Hispanics in the U.S.
- 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 U.S.
- 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.
It was challenging to synthesize the results because of the number of indices examined, including Mediterranean Diet Score (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.