Belief that diet affects our mental health must be more than just gut feeling
THERE is “increasing evidence” that what we eat can worsen anxiety, depression and accelerate cognitive decline in old age, researchers have said.
A study of existing evidence found that a diet rich in fruit, vegetables, fish and whole grains, including the so-called Mediterranean diet which also includes olive oil and moderate wine consumption, were repeatedly linked to dozens of studies with a lower risk of depression.
However, the scientists stressed that at present the findings are based on correlation, and further work is needed on causality amid growing diagnoses of depression, anxiety and mood disorders in the developed world.
Professor Suzanne Dickson, a Scottish expert in neuroendocrinology, which looks at how hormones affect the brain, led the study at the Gothenburg University in Sweden.
Professor Dickson, who is also an honorary professor at Edinburgh University, said: “We have found that there is increasing evidence of a link between a poor diet and the worsening of mood disorders, including anxiety and depression.
“However, many common beliefs about the health effects of certain foods are not supported by solid evidence.”
The study, published in the journal European Neuropsychopharmacology, noted that some studies had also linked a diet high in refined sugar and saturated fat to ADHD or hyperactivity, while eating large amounts of fruit and vegetables appeared to show some protective benefit.
However, Prof Dickson said the evidence for this was “mixed”.
“There are comparatively few studies, and many of them don’t last long enough to show long-term effects,” she said.
However, the Swedish study found that existing evidence shows “clear associations between diet and cognitive and mental health in adulthood” and concluded that “nutritional interventions could be helpful in reducing the impact of ageing”. Again, however, it is unclear exactly how diet has this effect.
The study comes amid growing interest in nutritional psychiatry, which explores how food and supplements could be used to treat or prevent mental health problems. The relationship between the brain, gut, diet and mental health is one of the most hotly debated issues in biological psychiatry at present.
One of the leading theories is an interplay between diet, gut health and hormone-signalling between the gut and brain. For example, a correlation has been found between more diverse microbiota – the bacteria in the human gut – and a lower risk of psychiatric disorders.
The study adds: “An involvement of the gut microbiome in other disorders such as ADHD, autism spectrum disorders and anorexia nervosa also appears possible. In addition, stress can affect and disturb the gut microbiota and negatively impact on digestive health.
“A high-quality diet may therefore help to regulate the gut microbiota and reduce stress and inflammation in the brain and subsequently maintain proper cognitive function throughout life.”
High-fibre diets, Mediterranean diets and diets high in fermented foods such as pickled gherkins or sauerkraut are known to promote diverse gut microbiota, and are associated with a reduced likelihood of depression.
The study added that being able to prove which dietary habits lead to better mental health and how this happens
“will improve sustainability in our healthcare systems and reduce the economic costs associated with poor mental health and cognitive decline”.
Prof Dickson added: “Nutritional psychiatry is a new field. The message of this paper is that the effects of diet on mental health are real, but that we need to be careful about jumping to conclusions on the base of provisional evidence. We need more studies on the long-term effects of everyday diets”.
Professor Andreas Reif, chair of the European College of Neuropsychopharmacology, said a current shortage of clinical research studies in humans “leaves room for speculation and flawed science”.
He added: “As the potential societal impact of this rapidly developing field is enormous, we must be scientifically sound in making our recommendations.”