What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns (assessed using methods other than index/score, cluster or factor, or reduced rank regression analyses) and risk of cardiovascular disease?
The goal of this systematic review project is to identify 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 (when available) in diets, and the frequency with which they are habitually consumed. Different methods of analyses are used to assess dietary patterns including index or score, cluster or factor, reduced rank regression, in addition to other methods, to exam the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns of a population and outcomes of public health concern. The objective of this systematic review was to assess the relationship between patterns of food and beverage intake identified using methods other than index or score, factor or cluster, or reduced rank analyses, and risk of cardiovascular disease.
There is strong and consistent evidence that consumption of a DASH diet results in reduced blood pressure in adults with above optimal blood pressure, up to and including stage 1 hypertension. A dietary pattern consistent with the DASH diet is rich in fruits, vegetables, low-fat dairy, fish, whole grains, fiber, potassium, and other minerals at recommended levels and low in red and processed meat, sugar-sweetened foods and drinks, saturated fat, cholesterol, and sodium. There is limited evidence that adherence to vegetarian diets is associated with decreased death from ischemic heart disease, with the association being stronger in men than in women. (Grade: I-Strong - DASH and Blood Pressure; Grade: III-Limited – Vegetarian and Ischemic Heart Disease)
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 defined using methods other than index factor or cluster analysis and body weight status. Studies that met the following criteria were included in the review: conducted in subjects aged 2 to18 years; randomized controlled trials, non-randomized controlled trials, or quasi-experimental studies; subjects from countries with high or very high human development (based on the 2011 Human Development Index); subjects who were healthy or at elevated chronic disease risk; published in English in a peer-reviewed journal. The date range was unlimited.
The results of each included study were summarized in evidence worksheets (including a study quality rating) and an evidence table. A group of subject matter 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.
- Two types of dietary patterns were identified using other methods of assessing dietary exposure related to cardiovascular disease (CVD) risk: (1) a DASH dietary pattern and (2) a vegetarian-style dietary pattern.
- Evidence from RCTs showed a DASH diet resulted in reduced blood pressure (BP) including systolic BP (SBP) and/or diastolic BP (BP) in adults with above optimal blood pressure, up to and including stage 1 hypertension, with further reductions with the low sodium DASH modification and the DASH high protein or DASH high unsaturated fat modifications (OmniHeart). Addition of a behavioral intervention or weight management intervention together with the DASH diet was more effective in reducing BP than DASH diet alone (PREMIER, ENCORE). Approximately two-thirds of the U.S. population has pre-hypertension or hypertension.
- Evidence from prospective cohort studies showed a vegetarian diet was associated with reduced ischemic heart disease (IHD) or cardiovascular disease (CVD) mortality in four out of six studies. In studies that showed a favorable association for the vegetarian diet, the risk reduction for men was greater than that for women. The association between vegetarian diets and BP was less clear.
- Studies that examined cerebrovascular disease or stroke mortality did not find differences between vegetarians and non-vegetarians.
- The results of either a DASH diet or vegetarian diet on blood lipids were mixed regarding effects on total-, LDL-, and HDL-cholesterol and triglycerides.
- The DASH diet is high in fruits, vegetables, low-fat diary, whole grains, fish, fiber, potassium, and other minerals at recommended levels and low in red and processed meat, sugar-sweetened foods and drinks, saturated fat, cholesterol, and sodium. Vegetarian diets include vegan (no meat, fish, eggs, or dairy); lacto-ovo vegetarian (includes eggs and dairy, but no fish or meat), and pesco vegetarian (includes fish, but no meat) diets.
There were limitations of the evidence in this review. In the DASH trials, including the original DASH and DASH-sodium, the feeding phases were relatively brief (4-8 wks) and the trial outcomes were CVD risk factors, not clinical events. In DASH trials with free-living populations, including PREMIER and ENCORE, there was the potential for selection bias, as participants may have been more motivated toward behavior modifications.
The studies on vegetarian diets were all prospective cohort studies and there was the potential for vegetarian cohorts to be relatively health conscious in other lifestyle components, in addition to diet. Additionally, in these studies, analyses relied on single baseline measurements of diet, without further dietary intake assessment over the time course of prospective studies. Related to the specific systematic review question on dietary patterns, vegetarian diets including vegan, lacto-ovo vegetarian, and pesco vegetarian, were most often described by what was excluded from the diet rather than a full dietary pattern including all foods and beverages consumed. Overall, the definition of vegetarian diets has not been standardized.