When we eat a meal, our body detects that we've consumed calories and responds by burning fat in order to make room for them. The catch for the weight-conscious is that if we don't burn off those newly-arrived calories, they just end up being stored as more fat. For people with metabolic disorders or other conditions, exercise just isn't enough to keep that from happening. Soon, however, a newly-developed drug could help. It triggers the body's "burning fat to make space for calories" response, even when the patient hasn't eaten anything.

Known as fexaramine, the drug was developed by a team at California's Salk Institute for Biological Studies, led by Prof. Ronald Evans. It activates a protein called the farensoid X receptor (FXR) that is ordinarily "turned on" at the beginning of a meal, and which causes the body to burn fat in preparation for the incoming calories.

While other drugs have previously been developed to artificially trigger FXR, they end up entering the patient's bloodstream. From there, they affect multiple parts of the body, causing side effects such as heart disease, high blood pressure and insomnia.

By contrast, when administered orally, fexaramine is absorbed only into the gut. This should not only drastically decrease side effects, but it reportedly also allows the drug to work better than others at causing fat to be burned. This is because it mimics the natural process by beginning the reaction from within the intestines, instead of from multiple locations in the body.

"The body’s response to a meal is like a relay race, and if you tell all the runners to go at the same time, you’ll never pass the baton," said Evans. "We’ve learned how to trigger the first runner so that the rest of the events happen in a natural order."

In lab tests, one group of obese mice were given fexaramine pills every day, while a control group received none. After five weeks of taking the pills, the treated mice ceased gaining weight and lost body fat, plus their blood sugar and cholesterol levels were lower than those of the control group. Additionally, some of their remaining white fat deposits changed into easier-to-burn beige fat.

The scientists are now looking towards human clinical trials. It is hoped that fexaramine could ultimately be used to treat not only obesity, but also diseases such as diabetes – although patients would still be advised to also make diet and lifestyle changes.

Along somewhat similar lines, a food additive being developed in the UK is designed to stimulate the gut to produce appetite-regulating hormones, thus causing the patient to "feel full" after eating less food.

A paper on the Salk research was recently published in the journal Nature Medicine.

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