Why obese people regain weight after dieting: keeping the kilos off is harder than it looks.
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SYDNEY: Most obese people who lose weight due to dieting regain the majority of it back within a few years, and researchers have pinned the cause on the hormones that regulate body weight.
It's well known that keeping weight off is difficult and many dieters relapse. Now, research has found the hormones that create increased hunger post-weight loss don't subside even after a year has passed. This is because the body has evolved to protect body weight, according to a recent report in the New England Journal of Medicine.
"Our study has provided clues as to why obese people who have lost weight often relapse. The relapse has a strong physiological basis and is not simply the result of the voluntary resumption of old habits," said lead author Joseph Proietto from the University of Melbourne. "Ultimately it would be more effective to focus public health efforts in preventing children from becoming obese."
Not just sloth and gluttony
Historically we haven't had access to food in the way we do now, so had to evolve defence mechanisms to conserve energy, according to Proietto, and in the past our ancestors' bodies stored any fat it could for survival. Now we have a plethora of high fat food at our disposal so those same defence mechanisms are contributing to obesity.
In the study, the researchers focussed on hormones that were located predominately in the gut, but also included one hormone from fat and a few from the pancreas. Volunteers with a BMI of between 27 and 40, and an average weight of 95kg, were put on strict low-energy diets and lost an average of 10 to 13 kg over the initial 10-week programme.
Levels of appetite-regulating hormones were measured at baseline, at the end of the program and one year after initial weight loss. Before being sent home, the volunteers were given dietary and exercise advice.
The results showed that following initial weight loss, the levels of hormones that influence hunger changed in a way which would be expected to increase appetite. Participants regained around 5 kg during the one-year period of study. According to Proietto, this reveals the important roles that hormones play in regulating body weight, making dietary and behavioral change less likely to work in the long-term.
Suppressing the cravings
There are 1.5 billion obese people worldwide, with around 50% of the population in Australia considered overweight or obese.
"Simple messages such as the [Australian government's] 'Swap It' campaign (which suggests that individuals make simple 'swaps' in their daily lives, such as walking to work instead of driving and swapping high-carbohydrate, high-fat sides like hot chips for salads and vegetables) are unlikely to work to change the population to a leaner weight." Proietto said, suggesting that the focus should instead be on keeping the younger generation fit and healthy.
"While we don't need medications to lose weight, what we do need is a way of suppressing hunger post-weight loss," he said. He said developing a drug or supplement that does this and is safe for long-term use would be ideal.
May not be their fault
Head of medicine at the University of Adelaide in South Australia, Gary Wittert, commented that the results of this study were consistent with the typical dieting experiences of being able to lose weight but unable to maintain it for long periods of time. "It is very important to prevent obesity in the first place," he said.
As for the current adult population that are classified as obese, Proietto said it is "not necessarily their fault" and is a biological or genetic state that is difficult to change.
The hunger hormone is difficult to control and further research will need to be conducted in order to change that in the future. He said this would include looking at why the hunger hormones changed, and if they would change differently if the weight loss was slow and involved more exercise.
