Changes in dietary pattern quality and risk cardiometabolic disease in adults: a systematic review and meta-analysis of cohort studies

Review question Among adults, is a change in dietary pattern quality over time (improvement or decline in a diet quality index score) associated with incident hypertension, cardiovascular disease, and type 2 diabetes, compared with stable diet quality? Background and purpose Most evidence linking dietary patterns to cardiometabolic disease relies on a single baseline dietary assessment, which assumes diet is stable over years or decades of follow-up. In reality, dietary habits change across adulthood, and a single measurement may misclassify long-term exposure and cannot show whether changing one’s diet alters disease risk. A growing number of cohort studies have repeated dietary assessments and examined changes in validated diet quality indices (for example, the Healthy Eating Index, Alternative Healthy Eating Index, DASH score, and Mediterranean diet scores) in relation to cardiometabolic outcomes. However, these findings have not been systematically synthesized. The purpose of this review is to systematically identify, appraise, and quantitatively synthesize observational evidence on the association between changes in dietary pattern quality and blood pressure, cardiovascular disease, and type 2 diabetes in adults. Specifically, we will compare adults whose diet quality improved, worsened, or remained unchanged over time, and examine whether associations differ by diet index, magnitude and duration of change, baseline diet quality, and population characteristics. Findings will help clarify whether dietary improvement later in life is associated with meaningful risk reduction, informing public health recommendations and clinical counseling. Expected outcomes Primary outcomes Incident cardiovascular disease (total CVD, coronary heart disease, stroke, and CVD mortality as reported) Incident type 2 diabetes Incident hypertension and/or change in systolic and diastolic blood pressure (mmHg) Measures of effect Hazard ratios, risk ratios, or odds ratios for incident outcomes, comparing improved vs. unchanged and worsened vs. unchanged diet quality (or per standardized unit increase in index score) Mean differences for continuous blood pressure outcomes We anticipate that improvement in diet quality will be associated with lower risk of incident CVD, type 2 diabetes, and hypertension, and that declines in diet quality will be associated with higher risk, relative to stable diet quality.