The mantra in obesity treatment is 'eat less and move more'. But a leading group of obesity experts writing in The Lancet Diabetes & Endocrinology question the belief that this is sufficient to treat obesity. They argue that obesity is a chronic disease with largely biological causes that cannot be cured with just diet and exercise.
Many people with obesity can lose weight for a few months, but 80%-95% regain their lost weight eventually. One explanation for this limited long-term success is that reducing caloric intake triggers several biological systems that drive us to eat high-calorie foods and gain weight. These biological systems evolved when humans needed to survive times of food scarcity. But in modern humans who have had obesity for some time, these biological adaptations encourage calorie consumption and the storage of fat to protect an individual's highest sustained weight. Overriding this fat-loss defence does not appear possible for most individuals through just lifestyle changes, say the authors, particularly in a 21st century environment that promotes the consumption of calorically dense, high-fat foods along with low energy expenditure.
"Although lifestyle modifications may result in lasting weight loss in individuals who are overweight, in those with chronic obesity, bodyweight seems to become biologically 'stamped in' and defended", explains Dr Christopher Ochner, lead author and Assistant Professor of Pediatrics and Psychiatry at the Icahn School of Medicine at Mount Sinai in New York, USA.
"Therefore, the current advice to eat less and exercise more may be no more effective for most individuals with obesity than a recommendation to avoid sharp objects for someone bleeding profusely."
Moreover, he point outs, recent evidence suggests that these biological adaptations could persist indefinitely, even in formerly obese individuals who achieve a healthy bodyweight through dieting. "Few individuals ever truly recover from obesity; rather they suffer from 'obesity in remission'. They are biologically very different from individuals of the same age, sex, and bodyweight who never had obesity."
The authors argue that if weight loss is to be sustained in the long-term, at least some of these biological factors need to be addressed. However, current biologically based interventions are limited to antiobesity drugs, weight-loss surgery, and intra-abdominal vagal nerve blockage, which do not permanently correct the biological factors that undermine weight-loss effort. To date, only Roux-en-Y gastric bypass, a common surgical procedure for extreme obesity, has been shown to reverse obesity-induced changes in appetite hormones and the brain's response to food. This, say the authors, might explain why bariatric surgery is the only treatment showing long-term effectiveness in individuals with sustained obesity.
According to Dr Ochner, "Many clinicians are not aware of the reasons individuals with obesity struggle to achieve and maintain weight loss. Obesity should be recognised as a chronic and often treatment-resistant disease with both biological and behavioural causes that require a range of medical interventions including biologically based interventions such as pharmacotherapy or surgery as well as lifestyle modification." He adds, "Ignoring these biological factors and continuing to rely on behavioural modification will surely result in the continued inability to treat obesity effectively and the premature death of millions of individuals each year."