Until recently, “the idea that what you put in your mouth could affect your mental health was met with great skepticism,” says researcher Felice Jacka. (Bigstock)

Jodi Corbitt had been battling depression for decades and by 2010 had resigned herself to taking antidepressant medication for the rest of her life. Then she decided to start a dietary experiment.

To lose weight, the 47-year-old Catonsville, Md., mother stopped eating gluten, a protein found in wheat and related grains. Within a month she had shed several pounds — and her lifelong depression.

“It was like a veil lifted and I could see life more clearly,” she recalled. “It changed everything.”

Corbitt had stumbled into an area that scientists have recently begun to investigate: whether food can have as powerful an impact on the mind as it does on the body.

Research exploring the link between diet and mental health “is a very new field; the first papers only came out a few years ago,” said Michael Berk, a professor of psychiatry at the Deakin University School of Medicine in Australia. “But the results are unusually consistent, and they show a link between diet quality and mental health.”

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“Diet quality” refers to the kinds of foods that people eat, how often they eat them and how much of them they eat. In several studies, including a 2011 analysis of more than 5,000 Norwegians, Berk and his collaborators have found lower rates of depression, anxiety and bipolar disorder among those who consumed a traditional diet of meat and vegetables than among people who followed a modern Western diet heavy with processed and fast foods or even a health-food diet of tofu and salads.

“Traditional diets — the kinds of foods your grandmother would have recognized — have been associated with a lower risk of mental health issues,” Berk said. Interestingly, that traditional diet may vary widely across cultures, including wheat for some people but not for others; the common element seems to be whole, unprocessed, nutrient-dense foods.

“There’s lots of hype about the Mediterranean diet [fruits, vegetables, whole grains, olive oil, nuts, fish] but the traditional Norwegian diet [fish, shellfish, game, root vegetables, dairy products, whole-wheat bread] and the traditional Japanese diet [fish, tofu, rice] appear to be just as protective” of mental health, he said.

The association between diet and mental well-being may start even before birth. A 2013 study of more than 23,000 mothers and their children, led by Berk’s frequent collaborator and Deakin colleague Felice Jacka, suggests a link between a mother’s consumption of sweets and processed foods during pregnancy and behavioral and mental health issues in her child at age 5.

Not clear how it works

It’s unclear how diet relates to mental health, said Rif El-Mallakh, a professor of psychiatry at the University of Louisville School of Medicine. “There seems to be a clear link, but it’s an association — it doesn’t tell you cause and effect,” he said. “We don’t know which is the chicken and which is the egg.”

It could be, he said, that mood disorders change how and what people choose to eat.

But an alternate theory is that the relationship works the other way: Certain foods, or their absence, may contribute to poor mental health. For example, studies in people and rats have linked zinc deficiency to depression. Also, illnesses that cause deficiencies — including celiac disease, an autoimmune disease in which the body reacts to gluten — have shown associations with mood disorders.

“There’s a two-way street between what’s going on in the gut and what’s going on in the brain,” said Linda A. Lee, director of the Johns Hopkins Integrative Medicine and Digestive Center — and recent research points to bacteria as possible middlemen in this back-and-forth. Gut bacteria are known to make most of the body’s serotonin, one of several chemicals that regulate mood, and the bugs may even have a hand in shaping behavior. A 2011 study in mice for example, showed that swapping the gut bacteria of two strains of mice — one known for its daring behavior, the other for its fearfulness and shyness — could make the timid mice more willing to explore and the bold mice more anxious and hesitant.

Gut bacteria

Of course, mice are not men, but changing diet has been shown to change human gut bacteria, and fairly quickly. That suggests it’s possible that dietary choices can alter well-being and behavior, Lee said, but researchers aren’t yet sure if this complex interplay means that swapping food in or out of one’s diet can ease or cure a mental illness.

“We’re not at the point where we can use diet as therapy, especially when we’re dealing with someone whose mental health issues render them very disabled, because we just don’t know enough,” Lee said. “I think we’re just on the new frontier, and five or 10 years from now we’ll know more.”

Jacka, president of the International Society for Nutritional Psychiatry Research, echoes these reservations. She notes that nearly all research on the connection between diet and mental health has been limited to animal studies and observational studies in humans.

“We can’t say [that] if we improve your diet, you’ll feel better,” she said. “We have circumstantial evidence that suggests this could be true, but we can’t say for sure.”

The lack of strong evidence and well-designed studies has led to some resistance to Berk’s and Jacka’s work. Until recently, “the idea that what you put in your mouth could affect your mental health was met with great skepticism,” said Jacka, who recalled colleagues’ dismissing the idea as “rubbish.” With more studies, though, the research community is beginning to come around, she said.

Even as scientists struggle to understand the link between food and mood, some patients, such as Corbitt, seem to tap into it without intending to.

She saw a link

“I changed my diet because I had gastrointestinal issues,” said a 32-year-old woman with bipolar disorder who lives in San Francisco and asked not to be named because she worries about being stigmatized. Three years ago, at her gastroenterologist’s urging, she tried the Atkins diet and found relief — not just from her digestive issues but also from her mental illness, which had at one point nearly derailed her life.

“I noticed within a day or two the marked difference in my head,” she recalled. “It felt clear for the first time in years and years.”

That may seem like a surprisingly quick turnaround, but Jacka said it is not out of the question. “We know from animal studies and a human study that a poor diet can impair memory and attention within a week,” she said.

The woman no longer takes the medication prescribed to treat her bipolar disorder, and she said she has remained stable for the past three years. She said she has sought out psychiatric and neurological researchers across the country, hoping to share her experience and to learn what they know, but has found little interest and few studies.

“It surprised me how little information was out there, because for me it was life-changing,” she said. “I wanted to validate the experience I was having, and to make sure that everything I was doing was safe. That’s how I found Dr. El-Mallakh.”

El-Mallakh had hypothesized in 2001 that a ketogenic diet — a high-fat, moderate-protein and low-carbohydrate diet often used to control epileptic seizures and nearly identical to the diet adopted by the 32-year-old woman — could be helpful for bipolar disorder, because many of the medications that work for bipolar disorder have anti-

seizure properties.

After being contacted by the woman, El-Mallakh found several other people with bipolar disorder who said they were benefiting from a ketogenic diet. Last year,he published two case studies of its apparent effectiveness. His report drew interest from people with the mental illness, but efforts at Stanford University to test the diet with a controlled trial failed to recruit enough participants.

Without such studies, El-Mallakh acknowledged that no one can say how the diet might quell the symptoms of bipolar disorder. With his own patients, herecommends it only alongside mood-stabilizing medications. Despite his own willingness to supplement mental health treatment with dietary changes, El-Mallakh remains skeptical that diet alone can heal the mind.

“There are a lot of people out there who call themselves depressed who aren’t actually depressed,” he said. “I think people confuse low energy with depression, or sugar crashes with mood swings, but they probably don’t have a mental illness. And those people may do better with dietary interventions alone.”

And even if diet can do the trick, providers don’t yet know how to use it effectively or safely. The problem, El-Mallakh said, is that mental illness is still poorly understood. Eventually, he hopes, the connection between food and mental health could benefit researchers who study mental illness as well as those who live with it.

Experimenting with change

Berk and Jacka areconducting the most comprehensive controlled study yet, involving 176 people, of whether dietary intervention can help ease depression, but they don’t yet have results. For now, Berk advocates an integrative approach to treating mental illness that includes experimenting with changes in diet and exercise along with more traditional treatments.

“For a mood disorder like depression, there are hundreds if not thousands of risk pathways that all contribute to the disorder,” Berk said. “Targeting one factor doesn’t target all the factors that cause someone to develop depression. That’s why you need to develop an integrated package of care as the norm.”

That time can’t come soon enough for Corbitt.

“This was such a simple solution,” she said. “I could have saved myself a lot of money and a lot of misery if someone had asked about my diet 15 years ago. My life could have been different.”

Telis is a freelance science and health writer.