The Olive Wellness Institute is a science repository on the nutrition,
health and wellness benefits of olives and olive products, which is
all subject to extensive peer review.

Sign-Up to our Newsletter
Depression and Mental Health Systematic Literature Review

Depression and Mental Health Systematic Literature Review

Depression and Mental Health

Click here to download a summary infographic

Reference: Molendijk, M., et al., Diet quality and depression risk: A systematic review and dose-response meta-analysis of prospective studies. J Affect Disord, 2018. 226: p. 346-354.

One-sentence summary: Any high diet quality, including a Mediterranean diet specifically, was associated with a reduction in the incidence of depressive symptoms, but a causal relationship is not yet established.

Study type: A systematic literature review and meta-analysis of 29 studies from 24 different prospective cohorts.

Diet: Any dietary pattern or food group, including the Mediterranean diet.

Outcomes measured: The incidence of depression or changes in depressive symptoms.

Population: 13 European countries, 7 from North America, 7 from Australia and 2 Asian countries (Japan and Taiwan).

Key results: 

  • The highest category of adherence to any high quality diet was associated with a lower depression incidence:
  • Healthy/prudent diet was associated with a 23% reduced depression incidence (OR = 0.77; 95% CI 0.69, 0.84; P < 0.001) (12 studies)
  • Mediterranean diet was associated with a 25% reduced depression incidence (OR = 0.75; 95% CI 0.67, 0.84; P < 0.001) (5 studies)
  • Pro-vegetarian diet was associated with a 22% reduced depression incidence (OR = 0.78; 95% CI 0.64, 0.93; P < 0.001) (1 study)
  • Tuscan diet was associated with a 36% reduced depression incidence (OR = 0.64; 95% CI 0.51, 0.77; P < 0.05) (1 study)
  • There was a linear dose-response relationship between adherence to any high quality diet (e.g. Healthy/prudent, Mediterranean, pro-vegetarian, Tuscan) and depression risk (P < 0.01).
  • An estimated 47 individuals (95% CI = 34–80) would need to change their dietary patterns from the lowest to the highest quality category in order to prevent 1 case of depression.
  • Protective associations were found for the food group ‘fish’ (OR = 0.86; 95% CI 0.78, 0.95; P < 0.01) (n = 16 studies) and ‘vegetables’ (OR = 0.82; 95% CI 0.70, 0.97; P < 0.01) (n = 7 studies), but no significant association was found for fruit, legumes/pulses, nuts/seeds/soy, or whole grains.
  • Five studies reported on the association between the dietary inflammatory index and depression, with the lowest dietary inflammation index associated with a 19% lower depression incidence compared to the highest category (OR = 0.81, 95% CI = 0.71–0.92, P < 0.01).
  • There were no associations between unhealthy dietary patterns (e.g. Western) or less healthy food groups (e.g. fast/junk food, meat, refined grains) and depression.

Quality assessment: The methodological quality was assessed against standardised criteria including study population, assessment of risk factor and outcome, study design and statistical analysis. The studies on the Mediterranean diet received a quality assessment score ranging from 6 to 10, whilst the quality assessment of all included studies ranged from 4 to 13.

Limitations:

  • There was considerable heterogeneity found.
  • The evidence was from observational studies only, precluding causal relationships.
  • Potential confounders were not always taken into account.
  • Most studies measured dietary habits in a single assessment, while multiple assessments are more accurate over the long-term.
  • Studies used different outcome definitions for depression (e.g. a structured interview vs. antidepressant use).
  • An association between diet and depression was no longer found when the analyses controlled for baseline subclinical depressive symptoms. This may indicate the association is due to reverse causation (i.e. persons with less depression are more likely to follow a healthy diet) but, on the other hand, correcting for baseline depressive symptoms could also be an overcorrection, since it may result in cancelling out the effects that the persons diet had in the years before the study started.

The bottom line: Adherence to high quality diets – regardless whether it was a healthy/prudent, Mediterranean, pro-vegetarian, or Tuscan diet – was associated with a lower incidence of depressive symptoms in a linear, dose-response fashion. Adherence to a diet with a low inflammatory index was associated with a lower incidence of depression, suggesting that this may be an important mechanism of action. Adherence to low quality diets and food groups was not associated with higher depression incidence.  Further research is needed to establish if these relationships are causal.

Other reviews:

Rahe, C., M. Unrath, and K. Berger, Dietary patterns and the risk of depression in adults: a systematic review of observational studies. Eur J Nutr, 2014. 53(4): p. 997-1013.

Psaltopoulou, T., et al., Mediterranean diet, stroke, cognitive impairment, and depression: A meta-analysis. Ann Neurol, 2013. 74(4): p. 580-91.

Sanhueza, C., L. Ryan, and D.R. Foxcroft, Diet and the risk of unipolar depression in adults: systematic review of cohort studies. J Hum Nutr Diet, 2013. 26(1): p. 56-70.

Quirk, S.E., et al., The association between diet quality, dietary patterns and depression in adults: a systematic review. BMC Psychiatry, 2013. 13: p. 175.

Roman, B., et al., Effectiveness of the Mediterranean diet in the elderly. Clin Interv Aging, 2008. 3(1): p. 97-109.