Stress can make you fat - and being obese can create stress. A new hypothesis seeks to explain how.
Diet and lack of exercise are not sufficient to explain the worldwide rise in obesity. Stress is one of many other factors which could contribute, according to human biologist Brynjar Foss from the University of Stavanger.
Eating more food high in fat, salt and sugar, combined with reduced physical activity, has been highlighted by the World Health Organisation (WHO) as the key causes of obesity.
Doctors have therefore prescribed slimming and physical exercise. This is followed up by media and commercial industries which promote training, diet and lifestyle advice.
Cause or consequence?
Brynjar Foss and sports scientist Sindre M Dyrstad have focused attention on this issue with the article Stress in obesity: cause or consequence? published in Medical Hypotheses.
The researchers review a number of studies, which show that weight gain and cortisol (the stress hormone) levels are noticeably higher in people who became fatter because of stress.
"If you have high cortisol, you seem to put on weight more easily," says Foss. He and Dyrstad suggest that stress and obesity reinforce each other through positive feedback.
A vicious circle of stress
Getting fatter can potentially trigger the stress response, which in turn encourages additional weight gain.
"When you go up in weight, your body also comes under stress. That probably has a self-reinforcing effect - so you get even fatter," Foss explains.
But dieting can also stimulate cortisol production, which in turn may trigger the stress response and thereby counter the weight loss.
"Should our hypothesis turn out to be correct, it would mean that you'll have to break this stress pattern if you want to halt the weight increase," says Foss.