What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns, assessed using an index or score, and risk of cardiovascular disease?
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.
There is strong and consistent evidence that in healthy adults increased adherence to dietary patterns scoring high in fruits, vegetables, whole grains, nuts, legumes, unsaturated oils, low-fat dairy, poultry and fish; low in red and processed meat, high-fat dairy, and added sugars; and moderate in alcohol is associated with decreased risk of fatal and non-fatal cardiovascular diseases, including coronary heart disease and stroke. (Grade I: Strong)
Literature searches were conducted using PubMed, Embase, (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 cardiovascular disease. 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.
- A total of 55 studies met the inclusion criteria for this systematic review and the body of evidence consisted primarily of large prospective cohort studies. These studies had large, relatively homogeneous populations of generally healthy adults, with long follow-up times.
- The majority of studies that assessed CVD incidence or mortality reported a favorable association between increased adherence to a dietary pattern and risk of CVD. The decrease in risk of CVD ranged from 22 to 59 percent for increased adherence to a Mediterranean dietary pattern and from 20 to 44 percent for increased adherence to a dietary guidelines-related pattern.
- In studies that examined CVD mortality secondary to total mortality, there were mixed results for favorable and null associations.
- The majority of studies that assessed CHD incidence or mortality reported a favorable association between adherence to a dietary pattern and CHD risk. The decreased risk of CHD ranged from 29 to 61 percent for increased adherence to a Mediterranean dietary pattern, from 24 to 31 percent for increased adherence to a dietary guidelines-related pattern, and from 14 to 27 percent for adherence to DASH.
- The majority of studies that assessed stroke incidence or mortality reported a favorable association between adherence to a dietary pattern and stroke risk. The decreased risk of stroke ranged from 13 to 53 percent for increased adherence to a Mediterranean dietary pattern and from 14 to 60 percent for increased adherence to a dietary guidelines-related pattern.
- A smaller number of studies examined intermediate, secondary outcomes, and other individual clinical endpoint outcomes with mixed results.
The preponderance of evidence from studies carried out in large, well-characterized prospective cohorts from the United States, Europe, Japan, and Australia showed that an increase in a Mediterranean diet score or dietary guidelines-related score was associated with decreased risk of fatal and non-fatal CVD, defined as coronary heart disease (CHD) and stroke, as well as decreased risk of CHD and stroke as individual clinical outcomes. Scores that were most frequently associated with decreased risk of CVD, CHD, or stroke were the original Mediterranean Diet Score (MDS), the Alternate Mediterranean Diet Score (aMed), the Healthy Eating Index (HEI)-2005, the Alternate HEI (AHEI) and updated AHEI-2010, the Recommended Food Score (RFS), and a DASH score. Positive food components of scores that were associated with decreased CVD risk were fruits, vegetables, whole grains, nuts, legumes, unsaturated fats, and fish. Alcohol was included as a positive component when consumed in moderation, but not in all scores. Red and processed meats were negative components in the Mediterranean scores, AHEI scores, and DASH; whereas, poultry was included as a positive component in the original AHEI and RFS scores. Total high-fat dairy was a negative component in the MDS, but dairy was a positive component when meeting recommended intakes for the HEI-2005 or as low-fat dairy in the RFS and DASH scores. Certain scores also included sugars or sugar-sweetened beverages as negative components.
Limitations in this body of evidence were the use of different scores and differences between scores based on median population intakes versus recommended intakes. However, in this relatively large body of evidence, a limited number of scores were predictive of risk, oftentimes less complicated versions of these scores, and in some studies different scores were tested in the same cohorts, making comparisons across these scores feasible.