Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies

Summary & key facts

Researchers looked at studies up to May 2018 that measured how closely people followed healthy diets and whether they later had symptoms of depression or a diagnosis. They found that people who most closely followed a healthy diet — especially a traditional Mediterranean diet or a diet low in inflammatory foods — tended to have a lower chance of developing depression. These findings come from observational studies, which can show links but cannot prove that the diet caused the change. The authors say the evidence is strong enough to justify testing dietary changes in future prevention studies.

Key facts:

• The review searched major medical databases up to May 31, 2018 and included about 20 studies that followed people over time and about 21 studies that looked at people at one point in time.
• Studies used several ways to score diet quality, including the Mediterranean diet, the Healthy Eating Index and its alternative, the DASH diet, and a Dietary Inflammatory Index that ranks how likely foods are to cause inflammation.
• When researchers combined four studies that followed people over time, those who most closely followed a Mediterranean diet had about a one-third lower risk of developing depression compared with those who followed it least closely.
• When four longitudinal studies were combined, a lower (less inflammatory) Dietary Inflammatory Index was linked with about a one-quarter lower risk of new depression cases.
• Evidence for the Healthy Eating Index and its alternative also suggested a lower risk of depression, with pooled results indicating roughly a one-third lower risk, though there were fewer long-term studies for some diet scores.
• All the results come from observational studies. That means the studies found associations but cannot prove that changing diet will prevent depression. The review notes more research, including intervention trials, is needed to test cause a

Abstract

With depression being the psychiatric disorder incurring the largest societal costs in developed countries, there is a need to gather evidence on the role of nutrition in depression, to help develop recommendations and guide future psychiatric health care. The aim of this systematic review was to synthesize the link between diet quality, measured using a range of predefined indices, and depressive outcomes. Medline, Embase and PsychInfo were searched up to 31st May 2018 for studies that examined adherence to a healthy diet in relation to depressive symptoms or clinical depression. Where possible, estimates were pooled using random effect meta-analysis with stratification by observational study design and dietary score. A total of 20 longitudinal and 21 cross-sectional studies were included. These studies utilized an array of dietary measures, including: different measures of adherence to the Mediterranean diet, the Healthy Eating Index (HEI) and Alternative HEI (AHEI), the Dietary Approaches to Stop Hypertension, and the Dietary Inflammatory Index. The most compelling evidence was found for the Mediterranean diet and incident depression, with a combined relative risk estimate of highest vs. lowest adherence category from four longitudinal studies of 0.67 (95% CI 0.55-0.82). A lower Dietary Inflammatory Index was also associated with lower depression incidence in four longitudinal studies (relative risk 0.76; 95% CI: 0.63-0.92). There were fewer longitudinal studies using other indices, but they and cross-sectional evidence also suggest an inverse association between healthy diet and depression (e.g., relative risk 0.65; 95% CI 0.50-0.84 for HEI/AHEI). To conclude, adhering to a healthy diet, in particular a traditional Mediterranean diet, or avoiding a pro-inflammatory diet appears to confer some protection against depression in observational studies. This provides a reasonable evidence base to assess the role of dietary interventions to prevent depression. This systematic review was registered in the PROSPERO International Prospective Register of Systematic Reviews under the number CRD42017080579.

Topics

Diet and metabolism studies Nutritional Studies and Diet Obesity, Physical Activity, Diet

Categories

Health Sciences Medicine Public Health, Environmental and Occupational Health

Tags

Biochemistry Biology Clinical psychology Gerontology Internal medicine Medicine MEDLINE Meta-analysis Observational study Psychology Systematic review

Conditions & symptoms

Depression Lack of energy or motivation Poor appetite or overeating Poor sleep Sadness or low mood