Nutritional psychiatry: how what we eat affects our mental health

More and more people say they are taking an active approach to their health. According to NielsenIQ, 70% of consumers worldwide consider themselves proactive about their health. However, mental health problems continue to increase, and a significant proportion of the world's population does not meet basic dietary recommendations. Cases of anxiety and depression have doubled in recent decades, and nearly 40% of the population in low- and middle-income countries does not follow national dietary recommendations, according to the GBD 2023 study by the Institute for Health Metrics and Evaluation. Eating a healthy diet remains a challenge for a large part of the population. And although doctors prescribe a balanced diet to treat many of the most common conditions, such as cardiovascular disease, obesity, and diabetes, relatively few specialists still view nutrition as a foundation for or therapeutic support in treating mental health conditions.

“We have developed a healthcare system that often asks what medication someone should take before considering whether their brain has the nutrients it needs to function properly,” explains Julia Rucklidge. “If someone came in with symptoms of scurvy, we wouldn't prescribe an antidepressant; we would treat the vitamin C deficiency. However, in mental health, nutrition is still overlooked far too often.”

Thanks to researchers such as Felice Jacka, director of the Food & Mood Centre at Deakin University, and other psychiatrists and psychologists such as Dr. Rucklidge, author of The Better Brain, this trend is beginning to change.

Jacka, one of the pioneers of nutritional psychiatry, published her doctoral thesis in 2010, the first paper to establish a link between diet and depressive and anxiety disorders in a large sample of women. “Those with a higher-quality diet were less likely to have a common mental disorder, regardless of their income, education level, body weight, or other health habits,” the doctor says.

But the real turning point came in 2017 with the SMILES trial. Led by Jacka herself, it showed that a dietary intervention could significantly help improve depressive symptoms in certain patients. For the study, researchers recruited adults with moderate to severe major depression. “Most were already receiving some other form of treatment — psychotherapy, antidepressants, or both — but they were still very unwell,” she adds. Participants were divided into two groups: one received structured social support (befriending), while the other attended sessions with a dietitian to implement a traditional Mediterranean diet.

The results after 12 weeks transformed the landscape. “By the end of the intervention, we saw that people who received dietary support had a much greater improvement in their depression. A full third of them achieved complete remission,” Jacka says. “The extent to which their depression improved was closely linked to the extent to which their diet improved.” The study also revealed three key findings: the improvement was not dependent on weight loss, the prescribed diet was less expensive than their original diet, and the intervention generated savings for the public healthcare system.

Since then, various studies have been conducted that reinforce the same evidence. “Regardless of where in the world we live, if our diet more closely resembles a traditional diet — rich in plant-based foods and whole foods, and low in ultra-processed foods — our risk of developing depression is approximately one-third lower,” Jacka says.

Some research is also examining the relationship between maternal diet, child neurodevelopment, and certain subsequent risks, including ADHD and autism spectrum disorders.

But how can what we eat affect our minds? One of the keys lies in the gut-brain axis, the complex communication network that connects the two organs. The gut is also home to a vast community of microorganisms involved in processes related to metabolism, the immune system, and the inflammatory response. “We evolved alongside them; we can't live without them, and they can't live without us,” notes Jacka.

The microbiota also plays a role in producing compounds and signals involved in communication between the gut and brain. “The microbes that inhabit our digestive tract influence processes such as inflammation, immune function, the stress response, neurotransmitter production, and even how we respond emotionally to the world,” explains Julia Rucklidge.

To understand this, the researcher suggests thinking of the microbiota as an ecosystem: “Just as a healthy forest sustains life, a healthy microbiome supports brain function. Feed it well and it will help regulate mood and resilience; feed it poorly and you'll start to see consequences that go far beyond digestion.”

The health of our microbiome and our minds depends on a balanced diet. But few people today meet recommended nutritional standards. In the United States and Europe, various studies show that only a small proportion of the population meets daily recommendations for fruit and vegetable intake.

“One of the paradoxes of modern life is that we can be overfed and undernourished at the same time,” warns Rucklidge. This is because the ultra-processed foods that are so prevalent in our diets “are loaded with calories but stripped of nutrients; they were designed to be convenient and tasty, not to support brain function.”

These foods have a direct impact on both our hippocampus and our gut. As Jacka explains, some common ingredients in ultra-processed foods are being studied for their potential impact on health; emulsifiers damage the intestinal lining, while high sugar intake causes blood sugar spikes and inflammation, both of which are closely linked to depression. 

So the message is clear. To maintain a healthy gut microbiome that supports our mental health, we need to move away from ultra-processed foods and opt for a diet rich in a variety of plant foods. “The foods that stand out as the most protective of mental health are exactly the same as those that protect our physical health,” Jacka explains. “Whole grains (oats, barley, rye, corn, polenta); fiber-rich foods such as onions and leeks. Legumes (chickpeas, lentils, beans) are also wonderful. They are rich in protein, filling, packed with fiber, and they also benefit the soil and the planet by fixing nitrogen. And if you eat meat or fish, choose unprocessed varieties.”

Beyond the nutritional aspect, eating well has a social impact that goes beyond our mental health. “Food is never just about nutrition: it's also about culture, connection, family, belonging, and identity,” Rucklidge reflects. “Throughout history, meals have been social occasions. Today, many people eat alone or in front of a screen. I'm not suggesting that sharing a meal is the ultimate solution to the mental health crisis, but I do think we've underestimated the psychological value of eating together. Human beings need nutrients, but they also need connection.”

For Jacka, the solution lies in “returning to local food production, bringing back community gardens, and cooking at home.” In Julia Rucklidge's words, “food isn't just fuel: it's one of the most powerful tools we have to simultaneously support biological, psychological, and social well-being.”