Why GPs should include diet in mental health care

Deputy Director of the Deakin University Food and Mood Centre Associate Professor Wolfgang Marx says the link between food quality and depression is particularly strong and is no longer based on just observational research.

“Randomised controlled trials have shown that improving diet quality can reduce depressive symptoms, including in people with clinically diagnosed depression,” Associate Professor Marx said.

“I would like to see mental health care routinely consider diet, physical activity, sleep and other modifiable lifestyle factors alongside psychological and pharmacological treatments.”

“There are also now resources to help clinicians translate this evidence into practice.”

However, Associate Professor Marx clarifies that GPs do not need to become dieticians.”

“We have published international clinical guidelines on lifestyle-based mental health care for major depressive disorder, which include recommendations around diet, and our Food & Mood Academy provides online training in nutritional psychiatry and lifestyle-based mental health care,” he said.

Reviewing diet as a routine part of mental health care

Associate Professor Marx said a useful starting point for doctors is to review diet as a routine part of mental health care, alongside questions about sleep, exercise, alcohol and smoking. 

“GPs can identify one or two achievable changes, such as increasing vegetables, legumes and wholegrains, eating fish more regularly, or replacing some highly processed foods with relatively simple whole-food alternatives,” he said.

“The dietary pattern with the strongest evidence is broadly Mediterranean-style, with plenty of vegetables, fruits, wholegrains, legumes, nuts, seeds, olive oil and fish, and less reliance on highly processed foods.”

“Diet can influence inflammation, oxidative stress, mitochondrial function, neuroplasticity, the stress-response system, tryptophan metabolism and the gut microbiome, all of which are relevant to brain health.”

Research shows links between food and mood

Recent studies have highlighted the mental health risks of eating ultra-processed foods, and the importance of fermented food in our diets.

“Our BMJ umbrella review brought together 45 pooled analyses involving almost 10 million people and found that greater exposure to ultra-processed foods was associated with poorer outcomes across a wide range of health domains, including depression, anxiety and other common mental disorders,” he said.

“More recently, our randomised trial published in Cell Reports Medicine compared food-based and supplement-based very-low-energy diets. Despite similar energy intake, the more food-based diet produced more favourable changes in aspects of the gut microbiome, suggesting that the form and processing of food may matter beyond simply its calorie and nutrient content.

“We have also recently published a triple-blind randomised trial in Gut examining a probiotic fermented dairy product. After eight weeks, we observed changes in the gut microbiome alongside preliminary changes in hippocampal neurochemistry and connectivity. 

“This was a small study in healthy women, so it is not evidence that fermented foods treat depression, but it provides interesting proof-of-concept evidence that changing a food can produce measurable changes in both the gut microbiome and brain-related outcomes.”

Diet is about more than weight loss

Associate Professor Marx said the positive effects on mental health are not simply related to weight loss, as trials had shown improvements in depression occurred independently of changes in body weight.

“For people experiencing depression, small and achievable changes are particularly important because motivation, energy and executive functioning may already be impaired,” he said.

“For patients requiring more intensive dietary support, referral to an Accredited Practising Dietitian is ideal. This is particularly important where there are significant medical comorbidities, nutritional deficiencies, food insecurity or concerns around disordered eating.”

He cautioned against doctors framing this as a diet versus medication approach to treating depression.

“Depression is heterogeneous and there is unlikely to be a single treatment that is right for everybody,” Associate Professor Marx said.

“Pharmacotherapy and psychological therapies remain important evidence-based treatments. What nutritional psychiatry adds is another potentially useful component of care, which also has substantial benefits for physical health.

“In fact, most participants in our original SMILES trial were already receiving antidepressant medication, psychotherapy, or both, so dietary treatment was largely being tested as an adjunct rather than a replacement.”