Doctors should pay more attention to the link between common mental illness and obesity in patients because the two health problems are closely linked, according to researchers at the University of Adelaide.

In an editorial published today in the British Medical Journal (BMJ), the Adelaide researchers add support to claims of a two-way risk between obesity and common mental disorders.

The editorial makes comments on a new research paper on this topic published in the same issue of the BMJ by Professor Mika Kivimäki from University College London.

A better understanding of the mechanisms for the apparent bi-directional risk between obesity and common mental disorders is needed for effective treatment and prevention, says the lead author of the editorial, Dr Evan Atlantis from the University of Adelaide's School of Medicine.

Although the topic is largely unexplored, several psychosocial, lifestyle and physiological factors may be involved in the complex inter-relationship between obesity and mental illness, he says.

Obese people - especially those who perceive themselves as being overweight - often experience weight-related stigma and discrimination, and consequently present with symptoms of low self esteem, low self worth, and guilt. Obesity is associated with socioeconomic disadvantage and low levels of physical activity, both of which are strong predictors of depression.

Obesity may constitute a chronic stressful state, which in turn can cause significant physiological dysfunction. Such dysfunction would then predispose individuals to depressed mood and associated symptoms, he says.

Dr Atlantis says reduced physical activity and overeating - particularly comfort foods rich in fats and sugars to improve mood - are common among depressed and anxious patients.

Activation of the endocannabinoid system, which increases appetite and may simultaneously alleviate depression, is likely to reinforce this eating behaviour. Socioeconomic disadvantage may further exacerbate the over-consumption of comfort foods because of their low cost, he says.

Dr Atlantis says patients presenting to their doctor with symptoms of common mental disorder should be assessed for obesity and related chronic diseases, and vice versa.

A multidisciplinary approach that focuses on promoting a healthy lifestyle is important. Further research on how best to deliver lifestyle interventions is needed, along with government action on taxes, tariffs, and trade laws to encourage the supply and consumption of healthy food and physical activity choices, he says.