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Diet changes highly effective in reducing clinical depression


The world’s first dietary intervention study for severe to moderate clinical depression showed diet has a powerful impact on mood.

We have known from epidemiological studies that poor diet is associated with depression, however, this does not prove diet causes it, or a good diet treats it. To prove that diet is an effective treatment you need an intervention trial with a control, that is a group that is not following the diet but also has clinical depression.

A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial)

Sixty-seven participants took part in this trial, one group ate a prescribed diet with dietary support, the other had social support of the same duration.  The goal was to assess whether eating a modified Mediterranean diet that included foods known to improve mental health and removed foods known to be detrimental would affect people who had clinical depression.

Participants were randomised, 31 completed the diet support and 25 the social support.

Diet intervention

The diet was ad libitum, meaning eat to appetite.

Participants were counselled to eat the following 12 key food groups:

  • Whole grains (5 – 8 serves a day)
  • Vegetables (6 per day)
  • Fruit (3 per day)
  • Legumes ( 3 – 4 per week)
  • Low fat and unsweetened dairy foods (2 -3 per day)
  • Raw and unsalted nuts (1 per day)
  • Fish 9 (at least 2 per week)
  • Lean red meats (3-4 per week)
  • Chicken (2 – 3 per week)
  • Eggs (up to 6 per week)
  • Olive oil ( 3 tablespoons per day)

Foods to reduce – termed “extras”

  • Sweets, refined cereals, processed meats, suargary drinks (3 maximum per week), fast food, fried food,
  • All alcohol except red or white wine up to 2 standard drinks per day, ideally red wine with meals only

Each person received 7 support sessions of 1 hour each, either dietary support or social support or befriending, but no therapy. A food hamper, recipes and meal plans were also given at the beginning to diet group.

The following assessments were done at baseline and 12 weeks:

  • Montgomery-Åsberg Depression Rating Scale (MADRS) to assess depressive symptomology
  • Hospital Anxiety and depression scale (HADS)
  • Profile of Mood states (POMS)
  • Clinical Global Impression – Improvement (CGI-I) scale
  • World Health Organisation well-being scale (WHO-5)
  • Generalised Self-Efficacy Scale
  • Clinical data -BMI, plasma fatty acids, fasting glucose, total, HDL, LDL cholesterol and triglycerides.


The diet intervention group improved their diet, particularly in decreasing ‘extras’ food by 22 serves per week, while recommended foods increased.

The dietary support group demonstrated significantly greater improvement in MADRS scores from baseline to 12 weeks. Weight did not change indicating this was not a factor.

In the diet group 10 people (32.3%)of the diet group, and 2 (8.0%) of the social support group achieved remission of a score less than 10 on the MADRS. The data showed a 2.2 score improvement in MADRS with every 10% increase in dietary adherence.

Based on this data the numbers needed to treat (NNT) is 4.1.

The HADS depression and anxiety subscales and the CGI-I improved significantly in the diet group.

Only one biomarker showed a difference at 12 weeks, total polyunsaturated fatty acids decreased in the social support group.

Food costs

It was estimated that participants spent AU$138.00 per week on food and beverages at baseline while the recommended diet cost AU$112.00 per week for an individual.

One participant was interviewed for ABC news in Australia and reported feeling happier, clearer in her mind, balanced. Mediterranean diet can help in fight against depression, Australian study finds.

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