Mediterranean Diet Improves Depression

Christine Lehmann, MA

December 22, 2017

Diet matters when it comes to mental health. When people with severe depression followed the Mediterranean diet, they experienced a significant reduction in symptom severity that lasted up to 6 months.

In one of the first randomized controlled trials to examine the effect of the Mediterranean diet supplemented with fish oil in people with severe depression, researchers found the diet to be associated with a reduction in depression symptoms.

Dr Natalie Parletta

"While both the intervention and control groups experienced significant mental health improvements, participants eating the Mediterranean diet experienced a greater reduction (45%) in the severity of their depression compared with the control group (27%)," study investigator Natalie Parletta, PhD, told Medscape Medical News. Dr Parletta is a senior research fellow from the Center for Population Health Research, University South Australia, in Adelaide.

The study was published online December 18 in Nutritional Neuroscience.

No Impact of Supplemental Fish Oil

Population research has shown a link between diet and depression. The current study, the authors note, is only the second randomized controlled trial to use a Mediterranean dietary intervention in people with severe depression. The first trial, published earlier this year in BMC Medicine, was also conducted in patients with moderate to severe depression.

In that study, following the Mediterranean diet was found to be associated with significant improvements in depression scores. However, in contrast to the latest study, it ended at 3 months, used buddies for the social control group, and did not supplement the diet with fish oil.

To further investigate the impact of the Mediterranean diet on mental health and quality of life in people with severe depression, the researchers recruited 152 adults aged 18 to 65 years (105 women and 47 men). Thirty-eight percent of participants reported a diagnosis of depression, and 36% reported taking an antidepressant.

Participants were randomly assigned to receive a traditional Mediterranean diet supplemented with fish oil (n = 75) or a control intervention (n = 77).

The Mediterranean diet intervention included an initial nutritional consultation, biweekly group cooking workshops, easy, inexpensive recipes, and take-home food hampers for making the recipes.

The control intervention involved biweekly meetings that included social activities such as board games, book clubs, and photo sharing. Participants were provided with light snacks, such as biscuits, dips, cheese, crackers, coffee, tea, juice, or water.

Participants were assessed at baseline, 3 months, and 6 months using validated, reliable instruments. Primary mental health outcomes were assessed with the Depression, Anxiety and Stress Scale and the Assessment of Quality of Life.

Secondary outcomes were assessed with the Positive and Negative Assessment Scale, the Mediterranean Diet questionnaire, and the Simple Dietary Questionnaire. To measure the impact of the fish oil supplements on mental health, erythrocyte blood samples were taken and analyzed for polyunsaturated fatty acids (omega 3 and 6).

The investigators found that the Mediterranean diet was significantly associated with lower anxiety, negative affect, and better coping and overall quality of life. Dr Parletta said she was "surprised" that the fish oil supplements did not have a significant effect on depression.

"We wanted to boost those levels because previous research showed that people with depression had very low levels of omega 3s compared with the national average," she said.

Diet's Role in Mental Health Underappreciated

The researchers also found associations between food groups and mental health outcomes. For example, eating more vegetables was associated with less stress and more positive emotions, and eating more fruit was associated with less anxiety and more positive emotions and relationships.

Eating a wide range of vegetables and fruits also improved mental health outcomes. Eating a traditional Mediterranean diet also decreased the amount of take-out food and unhealthy snacks the participants ate.

Social interaction also played an important role in improving participants' mental health.

"The Mediterranean diet is more than just food, it's a lifestyle. Participants cooked and ate meals together every 2 weeks. The cooking workshops were the most popular of all the workshops in our pilot studies," said Dr Parletta. She noted that the control group also met every 2 weeks for social activities.

The main limitations of the study were that it used self-reported assessments, there was a high dropout rate, and that single-blinding was used. Participants were not blinded to their treatment allocation, which contributed to the dropout rate.

"Some people joined the study for the nutrition education and cooking classes and were disappointed when they didn't receive that," said Dr Parletta. Of the 152 eligible participants, 95 completed 3-month assessments, and 85 completed 6-month assessments.

Dr Parletta said the medical community has been slow to recognize the role dietary interventions can play, especially in improving mental health. "I would like mental health professionals to take this seriously and start looking at people's diets when they go for counseling."

Dr Parletta and a colleague are writing a paper on the cost-effectiveness of the dietary interventions used in the study. The data look promising, she said.

Exciting Findings

Commenting on the findings for Medscape Medical News, Drew Ramsey, MD, assistant clinical professor of psychiatry from Columbia University in New York City and a practicing nutritional psychiatrist, said, "2017 has been an exciting year for nutritional psychiatry. We now have two randomized controlled trials showing significant efficacy for the treatment of clinical depression with dietary and nutritional interventions."

This study builds on the "groundswell of science connecting nutritional intake and mood disorders, especially depression," said Dr Ramsey. "We have known for decades that certain nutritional deficiencies, such as B12 and folate, can cause clinical depression. These exciting findings show that that diet can work as a clinical intervention with depression."

"This is exciting news for mental health professionals. Medications take up to 6 weeks to work, and the benefits of psychotherapy can take months. Nutritional interventions give patients something they can work on today," he added.

The two randomized controlled trials demonstrated that even people with severe depression can learn and benefit from dietary interventions, dispelling the notion that only people with mild depression can benefit, said Dr Ramsey.

"We also know that nutritional interventions work well with other treatments."

Dr Ramsey said clinicians who want to be on the cutting edge of evidence-based medicine should include dietary interventions in the treatment of clinical depression.

"Great interventions don't have to be complicated. It can be just getting people to eat more leafy greens, anchovies, or lentils or learning how to make delicious vegetables so they will eat them," he said.

He challenged clinicians to offer nutrition services.

"There are many ways to do this, including learning basic nutrition, using simple food assessments, and prescribing healthy food. Another option is to partner with registered dieticians, nutritional health coaches, or local chefs. The challenge for medicine is to change how we think about nutritional interventions."

The study was supported by the National Health and Medical Research Council. Dr Parletta has disclosed no relevant financial relationships. Dr Ramsey serves on the editorial board of Medscape Psychiatry.

Nutr Neurosci. Published online December 7, 2017. Full text

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