Depression: You Are What You Eat!

4. April 2017

The results of the SMILES study offer hope: the first randomised controlled study examined whether a change in diet can have a positive impact on the development of depression. The authors see great potential in this simple form of therapy.

In recent years, there has been growing evidence that the quality of food and the mood of the people could somehow be linked to each another. Depending on the country and culture, there is variation in the idea as to what constitutes healthy nutrition. Observational studies have however shown that first and foremost a low-fat plant-based diet with proteins and fish is coupled with a lower risk of depression. Processed foods and heavily sweetened foods and drinks, on the other hand, have been repeatedly linked to a higher risk of disease.

Depression is a complex mental illness. Treatment through diet initially therefore seems absurd. DocCheck has taken a look at the current situation in terms of studies.

Earliest published data from prospective study

In 2013 a study1 was published in BMC Medicine which concluded that a Mediterranean diet combined with nuts lowered the risk of falling ill with depression three years later.

In order to find out whether a change in diet can also be used to treat depression, scientists in Australia launched the “SMILES” study (Supporting the Modification of Lifestyle In Lowered Emotional States). Now the data from the first randomised control study on depression treatment through diet has been published.


Director of Studies of the SMILES Study: Felice Jacka from the University of Melbourne © University of Melbourne

Participants poorly nourished and severely depressed

The scientists took 67 adult patients who suffered from severe depression into their 12-week study. One of the inclusion criteria was a value of at least 18 out of 60 possible points on the Montgomery Åsberg Depression Scale. 55 of these patients were already receiving treatment: 21 patients received psychotherapy in combination with antidepressants, 9 exclusively received psychotherapy, 25 exclusively antidepressants.

All participants involved also ate poorly. They all had 75 or fewer points from 104 points in a best-possible nutrition assessment. According to their own data, they took in too little fibre, low-fat proteins, fruits and vegetables each day, but plenty of sweets, processed meat and salty snacks.

Diet settings versus social support

The participants were randomly divided into two groups: in one group, patients received seven individual counselling sessions with a trained nutrition assistant. The first four sessions were conducted weekly, the remaining ones every 2 weeks. The focus of nutrition counselling was on improving the quality of food choice. The participants were indeed allowed to eat their fill, but were encouraged to adhere to the following consumption recommendations:

  • whole grain cereals (5-8 servings per day)
  • vegetables (6 servings per day)
  • fruit (3 servings a day)
  • legumes (3-4 servings per week)
  • low-fat and unsweetened dairy products (2-3 servings per day)
  • raw and unsalted nuts (1 serving per day)
  • fish (at least 2 times per week)
  • low-fat, red meat (3-4 servings per week)
  • chicken (2-3 servings per week)
  • eggs (up to 6 per week)
  • olive oil (3 tablespoons per day)
  • extra foods such as sweets, white flour products, fried foods, fast food, processed meat and sugary drinks (maximum 3 per week)

In order to facilitate the cooperation of the study participants, they were provided with the main foods for their new style of diet, as well as recipes and a written diet plan for future reference in the course of consultations.

The control group received social support over the same time period. This consisted of individual conversations on topics which interested the participants. Anybody who did not want to talk could spend their time playing card or board games.

Study results: one-third experienced remission

After 12 weeks, those in the group with the diet adjustment recorded a larger decline in depressive symptoms than those in the social support group. 32 percent of patients in the diet group were able after the 3-month study phase to record a remission; for the socially supervised group this figure was only 8 percent. The statistically significant difference between the two groups was 7.1 points on the Montgomery Åsberg Depression Scale.

For the study director Felice Jacka the reasons are obvious: “The study results relate to the extent of the change in diet, not on sports or body weight. The stricter the diet followed by the participants, the greater their success”. For Jacka, president of the International Society for Nutritional Psychiatry Research, the study results open new doors in the treatment of depression. This is because only about half of those affected can be helped with currently available therapies such as antidepressants and/or psychotherapy. “Therefore, we urgently need new treatment options”, says Jacka.

Gut-brain connection also apparent in animal studies

A relationship between the intestine and brain was also present in other recently published studies – although these were animal experiments. In these, mice not given intestinal bacteria behaved less anxiously than did their counterparts with normal bacterial intestinal colonisation; they did not retreat into protective areas of their cage.

The same was shown by aseptic mice which had received intestinal bacteria transfers from more bold animals. These mice adjusted their behaviour after a short time to match that of their bacterial donors. The fact that intestinal bacteria and brain chemistry are related to each other somehow seems an obvious one. Whether the data from animal experiments can be transferred to understanding humans, and how this could be so, is however something which still needs to be clarified through further studies.

Gut flora affects depression via inflammatory responses

In a review article from 20123 microbiologists already speculated that dysfunctional intestinal flora represents a risk factor for depression. “The intestinal flora regulates inflammatory processes in the body. An altered intestinal flora in susceptible individuals is able to lead to persistent inflammatory reactions – and can thus also affect their mood”, study author Graham Rook, Professor at University College London, tells Spectrum during the course of the study. This is because depression traces back – as do obesity, asthma and irritable bowel syndrome – to inflammatory processes in the body. These inflammatory diseases have increased dramatically in industrialised countries since the mid-20th century.

Killing two birds with one stone

These connections illuminate a theory: a poor diet promotes the growth of pro-inflammatory bacteria in the gut. “Depression increases the risk of obesity, type 2 diabetes and heart disease. Conversely, these diseases also increase the risk of suffering from depression. Improving the nutritional lifestyle would “positively influence the comorbidities”, says Jacka. Depressed patients would perhaps first need support in the implementation of a healthy diet. This is because shopping and preparing healthy food requires basic motivation which is no longer present with depressed patients due to illness.

Therapy: low risk and low cost

A change in diet which influences the composition of the intestinal flora seems, in comparison with the other interventions for depression, to be comparatively easy, and in particular to be virtually free of side effects. Another positive side effect of a healthy diet: patients save money. An analysis of 20 study participants in the SMILES study showed: the unhealthy diet cost the Australian patients an average of $AU138, the healthy version only $AU112. An attempt to achieve this would be worthwhile.

Original publications:

Mediterranean dietary pattern and depression: the PREDIMED randomized trial
Almudena Sánchez-Villegas et al.; BMC Med, doi: 10.1186/1741-7015-11-208; 2013

A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial)
Felice N. Jacka et al.; BMC Med, doi: 10.1186/s12916-017-0791-y; 2017

Can we vaccinate against depression?
Graham A.W. Rook et al; Drug Discovery Today, doi: 10.1016/j.drudis.2012.03.018; 2012

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