Half of us will experience a mental health problem at some point during our lives. Science now confirms that a healthy diet can reduce this risk.
In a paper published last year in The Lancet Psychiatry, an international group of leading academics argued that diet is as important to mental health as it is physical health.
“Depression is the leading cause of disability in the world,” says Dr Drew Ramsey, an integrative psychiatrist at Columbia University and a co-author of the study. “As someone who treats depression, it’s of great interest when we see data that suggests we can treat it by focusing on nutrition and what we eat.”
The President of the International Society for Nutritional Psychiatry Research, Associate Professor Felice Jacka of Deakin University, Melbourne, is one of the world’s leading researchers on the link between diet and mental illness. It was her groundbreaking study, published in the American Journal of Psychiatry in 2010, that kick-started the subsequent flood of research.
Jacka’s study, and many others that followed, found a strong relationship between unhealthy dietary patterns (the so-called Western dietary pattern high in processed food, sugar and unhealthy fats) and an increased risk of depression and anxiety.
The most recent review found a relationship between unhealthy dietary patterns and poorer mental health in children and adolescents.
What’s the link?
Even though depression may change a person’s appetite and dietary choices, this doesn’t appear to explain the relationship between diet and depression. So what does?
A number of factors are influential. Diet affects immunity, which appears to play a role in depression. Inflammation and oxidation, although commonly associated with cardiovascular disease, are also present in people with depression and other mental illnesses. Poor diet can trigger both inflammation and oxidation, while a healthy diet is protective.
Then there are brain essential nutrients, including B-group vitamins, omega-3 fats, zinc, iron and magnesium, often in short supply in a poor, Western style diet.
But perhaps the most exciting area of research is the brain-gut connection.
Over 100 trillion microbes live on and in us, most notably in our gut or large intestine, which makes them almost an organ of sorts.
“The main pathway by which diet exerts its impact on mental health is via the microbiota,” says Dr Jacka.
Your microbiota is sensitive to the type of food you consume. Fibre, probiotics (think yoghurt) and prebiotics (certain carbohydrates that fuel good bacteria) will all positively impact on the makeup of the bugs in your gut. Excessive fat and animal food products, on the other hand, can have a negative impact.
The evidence that gut bacteria can influence anxiety and depression comes from both animal and human studies.
One intriguing study transplanted bacteria collected from a strain of mice prone to anxious behaviour into other mice inclined to be calm. The result? The calmer mice became more anxious.
In humans, probiotics were found to reduce psychological distress and cortisol levels (a key stress hormone) in healthy volunteers. Another group of volunteers given certain prebiotics (carbs that bacteria love) subsequently showed lower levels of cortisol.
It’s not clear how your gut microbiota affects your brain, but it’s likely to be through a number of channels.
What we do know is that the gut microbiota affect many areas relevant to mental disorder – the stress response, neurotransmitter levels, brain plasticity, and the immune system.
And if all of these things are affected by the gut microbiota, then they are all influenced by diet.