Evidence that the right food helps maintain a healthy mood continues to grow.
More confirmation now comes from a team that included Australian psychologist Felice N. Jacka, Ph.D., who led the landmark SMILES clinical trial published in 2017.
Before we get to the findings of the new and recent research — one evidence review and three population studies — let’s take a quick look at the SMILES trial.
SMILES trial found big mood benefits from a Mediterranean-style diet
Like the new evidence review, this randomized, controlled clinical trial was led by Felice N. Jacka, Ph.D.
She and her team set out to test the effects of a modified Mediterranean diet on people diagnosed with moderate to severe depression.
As Dr. Jacka’s SMILES team wrote, there’s a good deal of evidence that “… the Mediterranean diet, promotes brain and mental health, and it is made up of fresh fruits, vegetables, whole grains, legumes, nuts, extra virgin olive oil, and fish.” (See Fish Alleviates Women's Anxiety.)
The SMILES trial lasted three months and involved 67 people diagnosed with moderate-to-severe depression who were randomly assigned to one of two groups:
Among the 67 participants, 12 were not being treated and 55 were receiving psychotherapy and/or antidepressant drug treatment.
Eleven of the original recruits dropped out before the end of the trial, leaving 31 in the Modified Mediterranean Diet group and 25 in the control group.
The results of the study showed that participants in the Modified Mediterranean Diet group enjoyed much greater reductions in their depressive symptoms, compared to those in the control group (Jacka FN et al. 2017).
By the end of the three-month trial, 33% of those assigned to the Modified Mediterranean Diet group met the criteria for remission of major depression, versus only 8% of the participants assigned to the control group.
Importantly, the people assigned to the Modified Mediterranean Diet (MMD) group who came closest to following the MMD eating plan experienced the greatest mood lifts.
No single study — even a “gold standard” controlled clinical trial can be taken as proof.
So, it’s important that a new evidence review and three recent studies affirm the validity of the link between healthy diets and healthy mood.
Large evidence review supports diet-mood link
Last month, an international team published the results of their review of the existing evidence concerning links between diet and mood.
The review was conducted by scientists from Britain, France, Spain, Finland, and Australia, and included Felice N. Jacka, Ph.D., who led the SMILES trial (Lassale C et al. 2018).
The team searched the medical literature for studies that had examined the anti-depression effects of adherence to a healthy diet.
That search produced 41 population eligible studies: 20 longitudinal and 21 cross-sectional, which look for links between mood health and adherence to one of four well-known/well-studied diets:
Their analysis calculated that the greatest benefit came from close adherence to the Mediterranean diet, which was linked to a one-third (33%) drop in the risk for depression.
Similarly, diets that ranked low on the Dietary Inflammatory Index — such as Mediterranean-style diets — were associated with a 25% reduced risk for depression.
The team’s analysis also linked closer adherence to the Healthy Eating Index (HEI) with a 35% lower risk, although the statistical strength of that link was weaker.
The authors also calculated that a pro-inflammatory diet — one providing lots of saturated fat, sugar and processed food — raised the risk of depression.
As the review’s authors wrote, “Avoiding pro-inflammatory foods and favoring anti-inflammatory foods rich in plant fiber, vitamins, minerals and polyphenols, such as fruits, vegetables, legumes, fish, olive oil and nuts, may reduce the risk of depressive disorders.”
According to the study’s lead author, University College London researcher Camille Lassale, “A pro-inflammatory diet can induce systemic inflammation, and this can directly increase the risk for depression.”
Three recent studies link healthy diets to reduced anxiety/depression risks
Let’s take a quick look at three recent studies that compared people’s diets to their risk for developing depression or reducing its symptoms.
#1 – French population study
Most prior studies that sought to compare people’s self-reported diets to official healthy eating plans were “retrospective”.
In other words, they asked people to recall what they’d eaten, and then compared their answers to their current mental health status.
So, a team of French researchers set out to conduct a “prospective” study, which would ask people about their current diets and then followed them for several years to compare those diets to the participants risk for developing depressive symptoms.
In August of this year, researchers from the University of Paris published their analysis of data collected during a six-year prospective study (Adjibade M et al. 2018).
The study included 26,225 men and women aged 18-86 years who completed diet surveys during its first two years.
The French team and then compared the participants’ self-reported diets to four healthy eating plans or diet-quality indices:
And the results of their analysis strongly linked the quality people’s diets to their risk for developing symptoms of depression.
Except for the AHEI-2010 index, closer adherence to the healthy eating plans was linked to reductions in risk that ranged from 5% to 9%.
As they wrote “Overall, these findings suggest that diets in accordance with national or international guidelines could have beneficial effects with regard to mental health.”
#2 – British population study
Four years ago, researchers from University College London set out to see whether adherence to a healthy diet would reduce study participants risk for depression over a 5-year period.
They compared people’s self-reported diets to the Alternative Healthy Eating Index (AHEI) and compared those scores to the participants’ risk for developing depression (Akbaraly TN et al. 2013).
The study included 4,215 people who participated in a study called Whitehall II.
After adjusting the results to account for the effects of for potential confounding factors, the British team’s analysis showed that close adherence to the AHEI diet reduced the risk for depressive symptoms among women (but not men) in a convincing "dose-response" fashion.
Women who closely adhered to the AHEI diet or adhered more closely to it over time were 65% and 68% less likely to suffer recurrent depressive symptoms, compared with women whose diets adhered least closely to the AHEI plan.
As the British researchers wrote, “In the current study, there was a suggestion that poor diet is a risk factor for future depression in women.”
#3 – Canadian/Iranian population study
Two years ago, scientists from Canada and Iran published a study that compared participants’ self-reported diets to the Alternative Healthy Eating Index or AHEI-2010.
They then compared relatively close adherence to that plan with the risk for depression, versus relatively poor adherence to that index (Saneei P et al. 2016).
The scientists calculated that the one-quarter of participants whose diets adhered most closely to the AHEI-2010 index were 49% less likely to develop anxiety and 45% less likely to develop depression, compared with the one-quarter of participants whose diets scored lowest on the healthy eating index.
Importantly, they controlled the results to account for the effects of potential “confounding” factors — i.e., other things known to affect the risk for depression.
For unknown reasons, the benefits of adherence to the healthy diet plan were stronger in women than in men, and were stronger in younger people.
Among the participants who were 40 years old or younger, the one-quarter who adhered most closely to the healthy eating plan were 58% and 51% less likely to have anxiety and depression, respectively, compared with those whose diets adhered least closely to the healthy eating plan.
As the study's authors concluded, “Adherence to healthy eating was inversely associated with a lower chance of anxiety and depression in Iranian adults.”
The takaway from these studies is clear: eat an anti-inflammatory diet, such as a Mediterranean-style diet, because inflammation fuels and can trigger depression!
To learn more about research on the links between diet, exercise, and mood, see these recent articles from our Vital Choices newsletter: