In a new study, researchers found that the brain mechanism that enables us to maintain a constant body temperature may also be the key to rapid weight loss.
In experiments involving mice that were given a calorie-restricted diet, they discovered that blocking a brain receptor that normally regulates body heat resulted in significant weight reductions.
The research was done by scientists at Scripps Research.
The findings will be further explored as a potential treatment approach for obesity, which the World Health Organization has called a global epidemic.
Obesity affects virtually all age and socioeconomic groups—increasing risk for heart disease, stroke, diabetes, cancer, and many other serious health conditions.
The team says up to 50% of what people eat every day is used as energy to maintain body temperature.
But when food is scarce, mammals adapt by lowering their temperature, limiting energy expenditure and the loss of body weight.
Some species can go into complete hibernation. Of course, humans don’t hibernate when they’re on a calorie-restricted diet, but they do naturally experience a lower body temperature just like other mammals.
And that makes it harder to lose weight when on a diet.
The team examined the cellular mechanisms that regulate the body’s cooling response to calorie restriction.
They found that the possibility that opioid compounds that naturally occur within the body could be mediating these effects.
Next, the team tested whether blocking the activity of opioid receptors would affect body temperature during calorie restriction. It did.
They also determined that this mechanism was uniquely regulated by one of the three known opioid receptor types: the kappa opioid receptor.
The finding made sense, as the kappa receptor is the most abundant opioid receptor in the part of the brain already known to play a role in regulating both body temperature and feeding.
The team then wondered if by blocking the kappa receptor, the body would continue to burn up calories to regulate heat even when food was restricted.
In one set of experiments, the scientists observed two groups of lean mice that had already been on calorie-restricted diets for six weeks.
One group was then treated with a drug to block the kappa receptor. This group showed greater energy expenditure and lost an additional 6% of body weight.
The team says blocking the kappa opioid receptor during calorie restriction nearly doubled the bodyweight loss that the obese animals would normally undergo if their receptor was functional.
However, when animals were allowed to eat freely, blocking the kappa opioid receptor had no effects on body temperature and did not alter the normal rate of body weight loss.
This means that the medicine is able to affect body weight only in animals that are dieting.
The findings suggest a possibility that by translating these findings into humans, a drug may be able to help those who are struggling to lose weight, despite their adherence to a calorie-restricted diet.
As a next step, the team would like to explore whether existing medicines that are known to block the kappa receptor could be repurposed and refined to safely treat obesity.
One author of the study is Professor Bruno Conti, Ph.D.
The study is published in Current Biology.
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