More evidence links the Mediterranean diet to less depression

A new systematic review and meta-analysis suggest that adherence to a healthy diet, particularly the plant-rich Mediterranean diet and the prevention of sugary processed foods that promote inflammation, are associated with a risk reduces depression.

It's still a confirmation that a healthy diet not only improves physical health but also mental health, said lead author Camille Lassale, PhD, research associate, department of epidemiology and Public Health, University College London, UK. Medscape Medical News.

For mental health professionals, these new findings provide additional support to help patients stay on a healthier diet, Lassale added.

"A bad or unhealthy diet is responsible for so many other diseases, so you can not go wrong by advising patients to reduce processed foods and try to incorporate more fruits and vegetables." vegetables in their diet, "she said.

The results were published online September 26 Molecular Psychiatry.

"Convincing evidence"

After searching the literature for relevant English studies on the influence of diet on depression, researchers studied 41 studies. Most studies have included generally healthy participants.

Of these studies, 20 had a longitudinal design and a transverse design. Among the longitudinal studies, the investigators included only those who had a "correct level of adjustment" to account for lifestyle factors that may affect depression, such as smoking, loneliness and depression. physical inactivity and a high body mass index.

The analysis compared a wide range of dietary scores a priori. Some studies included several of these indices.

Ten analyzes used Mediterranean Diet Scores (MDS), Seven Healthy Eating Index (HEI) or Alternative Healthy Eating Index (AHEI), four DASH (Dietary Approaches to Stop Hypertension) , nine (DII). and 15 used a variety of other scores.

The MDS includes nine items: five considered beneficial (fruits, vegetables, legumes, cereals, fish), two considered harmful (meat, dairy products), one on dietary fat and one on moderate consumption of alcohol.

The three cross-sectional studies that examined the Mediterranean diet yielded inconsistent results. However, results from four longitudinal studies showed that for individuals in the highest category of adherence to the diet, the risk of depressive incidence was lower (overall odds ratio). [OR]0.67; 95% confidence interval [CI], 0.55 – 0.82) compared to those with the lowest degree of compliance.

The Mediterranean diet has provided "the most compelling evidence" of the impact of diet on depression, Lassale said. She added that it is also "the most studied".

Typing associations

The other clue that had a "striking association with depression" was the DII, reported Lassale. This index quantifies the overall effect of diet on inflammatory potential using 45 parameters.

The studies that used this index were "slightly more difficult to interpret" because the DII score is based not only on foods, but also on inflammatory factors such as C-reactive protein, polyphenols and inflammatory cytokines.

She noted that many of the foods included in the Mediterranean diet (fatty fish, fruits, vegetables, nuts, legumes and other unprocessed herbal foods) are anti-inflammatory.

Lassale added that proinflammatory foods include those that are high in trans fat, saturated fat, refined sugar, and "anything that is too processed".

Five cohort studies and four cross-sectional studies used the IID.

Comparing the least inflammatory regimen with the most inflammatory regimen, there was an inverse inverse association with both longitudinal (OR overall, 0.76, 95% CI, 0.63-0.92) and transverse ( Overall OR 0.64, 95% CI 0.45 – 0.91) studies.

"We find that the less likely you are to follow the proinflammatory regimen, the less likely you are to become depressed or develop a depression," Lassale said.

Similar trend

The analysis showed the same general trend for indices assessing adherence to US dietary guidelines, using the IES and similar AHEI. These guidelines focus on fruits and vegetables, but not on the complete elimination of meat and dairy products.

The three longitudinal studies showed a lower risk of incident depression for high vs low scores on the HEI / AHEI regimen (OR 0.76, 95% CI, 0.57 to 1.02). However, the authors note that "this association is significant only on the conventional level". They also note that the estimates for these three studies were very heterogeneous.

Overall, cross-sectional studies have shown an inverse association between some versions of the IES or the HEAI and the prevalence of depression (OR, 0.53, 95% CI, 0). , 38 to 0.75), without apparent heterogeneity.

In addition, four studies used the DASH diet score or a modified version of it. This score has eight components. Negative components include sugary drinks, meat and sodium; and positive components include fruits, vegetables, legumes and nuts, whole grains and low-fat dairy products.

The DASH index was "the least consistent," said Lassale. "Most of the time, there was no association between the DASH diet and depression."

In the only longitudinal study, investigators found a significantly negative association with the incidence of depression (OR, 0.63) only when using a particular DASH scoring system. Other DASH scores were not associated with clinical depression.

In addition, the results of the cross-sectional studies revealed no association except for one study of Iranian adolescents. He showed an inverse association between DASH and depressive symptoms (OR, 0.47).

Lassale has hypothesized that this general lack of association may be due to the fact that dairy products and meat are considered "detrimental" in the Mediterranean diet, but that the DASH diet is not to avoid these foods. "

The DASH diet has been studied and recommended for its usefulness in reducing blood pressure.

Biological Mechanisms

Several biological mechanisms could explain the relationship between diet and depression, said Lassale.

First, unrefined herbal foods, high in fiber, B vitamins and polyphenols, have anti-inflammatory quality and can have a direct impact on brain function, brain structure and neurotransmitters.

"There is a strong inflammatory cause of depression," Lassale noted. "We find that people with depression have higher levels of C-reactive protein and other markers of inflammation."

Most foods in the Mediterranean diet are rich in omega-3 polyunsaturated fatty acids, which are not only anti-inflammatory but can also reduce oxidative stress, she said. "They can have direct effects on the plasticity of brain cells."

The microbiome-intestine-brain axis is another possible route through which diet can affect mood. Healthy foods could modulate the relationship between bacteria in the intestine and the brain, said Lassale.

She noted that this mechanism is of interest to researchers studying depression.

Confirmation of evidence?

Lassale noted that the new analysis summarizes the growing research on diet and depression. "In recent years, people began to think that there was indisputable evidence, and we have just confirmed it."

Although cross-sectional studies "have some value", the focus of the relationship "is not clear". The new meta-analysis also includes longitudinal studies in which the relationship is clearer, she added.

"With this new analysis, we show that there is good evidence not only of cross-sectional but also longitudinal studies that there is a relationship between healthy eating and depression and which opens the door to clinical trials," he said. declared Lassale. I said.

Some of these tests have already been done. One of the co-authors of this new analysis, Felice Jacka, PhD, Deakin University, Food and Mood Center, Geelong, Australia, participated in the SMILES trial. Results published last year showed that depressed patients who followed the Mediterranean diet for 12 weeks improved significantly compared to those who received social support.

"It was the first clinical trial showing very encouraging results, but we need more research," Lassale said.

Once such trials are complete, experts may be able to develop dietary guidelines for mental health professionals, she added.

Strengthen and reassure

Asked a comment by Medscape Medical NewsDrew Ramsey, MD, associate professor of psychiatry at Columbia University in New York, said the new findings "are reassuring in the sense that they are consistent" with previous research.

"They reinforce the idea that food is a tool we can use to improve our health, including our mental health," he said.

Ramsey, who did not participate in this research, founded the Brain Food Clinic, wrote a number of books on nutrition and mental health, and launched the Eat to Beat Depression online course.

"Asking for nutrition in a clinical setting has always been common sense, and now it's common sense based on evidence," he said.

However, he wonders how to use the growing evidence that nutrition plays a key role in mental health, he added.

"Does this mean that psychiatrists have to screen patients for referrals to coaches, nutritionists or dietitians, does this mean that we should expect that a psychiatric evaluation is part of the process?" A nutritional assessment? " He asked.

Ramsey said that he recognizes that a healthy diet is not the complete answer to depression. But the results of this new review "reflect what we have seen, namely that nutrition is a piece of the puzzle, for most patients it's not all."

Laurel Cherian, MD, Department of Neurological Sciences, Rush University Medical Center, Chicago, also commented on the results.

"This study was interesting in that it included longitudinal studies and also examined a variety of healthy diets," Cherian said. Medscape Medical News.

"One of the limitations is the great heterogeneity between the studies with regard to the definition of depression and the comparison of the quality of the diet (tertiles, quintiles, etc.)," ​​he said. she noted.

"Nevertheless, this study builds on a growing body of evidence suggesting that diet could be part of a holistic approach to the treatment and prevention of depression," she concluded. "Medications, therapy and exercise are also beneficial, and people can see the greatest benefit when they use a combination of these approaches.This study further reinforces the argument in favor of 39, a dietary intervention test for depression. "

Dr. Lassale, Dr. Ramsey and Dr. Cherian have not reported any relevant financial relationship.

Mol Psychiatry. Posted online 26 September 2018. Full text

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