This "exercise mimicry" could potentially treat obesity, diabetes, and muscle loss by activating certain metabolic pathways. Further refinement and human trials are planned for the future.

A brand-new drug tested in mice has shown promising results, potentially paving the way for a new class of weight-loss medications that mimic the effects of exercise.

The new compound fools obese mice into believing their muscles are working harder than they actually are, thereby boosting the animals' metabolism and reducing body weight.

It also enhances the mice's endurance, enabling them to run nearly 50% more than before.

The drug belongs to a class of "exercise mimetics" that can provide some of the benefits of exercise without the need for increased physical activity.

While the new therapy is still in the early stages of development, it may one day be tested in humans to treat diseases such as obesity, diabetes, and age-related muscle loss.

The study comes at a time when many drugs have made breakthroughs in reducing appetite to help treat these metabolic diseases.

However, the new drug, named SLU-PP-332, does not affect appetite or food intake. Nor does it cause the mice to exercise more. Instead, it promotes natural metabolic pathways that usually respond to exercise.

Essentially, the drug makes the body behave as if it is training for a marathon, leading to increased energy expenditure and faster metabolism of body fat.

"This compound is basically telling the skeletal muscle to make the same changes you see during endurance training," said the researcher. "When you treat mice with this drug, you can see their whole-body metabolism shift to using fatty acids, much like when people are fasting or exercising. The animals start losing weight."

The new drug targets a group of proteins in the body called ERRs (Estrogen Related Receptors), which are responsible for activating some of the most important metabolic pathways in energy-consuming tissues such as muscle, heart, and brain.

When people exercise, ERRs become more active, but they have proven difficult to activate with drugs—until now.

In another paper published in March, the researchers reported that they had successfully engineered SLU-PP-332 to enhance ERR activity.

They observed that the compound enabled normal-weight mice to run 70% longer and 45% farther compared to mice not receiving the drug.

In their latest study, the team tested the drug on obese mice. Treating obese mice twice a day for a month resulted in 10 times less fat gain and a 12% reduction in body weight compared to untreated mice.

Yet, the mice still ate the same amount of food and did not exercise any more than usual.

"They are simply expending more energy to live," said Burris.

Researchers found evidence that the compound may also treat heart failure in mice by strengthening the heart muscle.

So far, the drug has not produced any serious side effects.

The next step in developing SLU-PP-332 as a drug candidate will be to refine its structure, ideally to make it into a pill rather than an injection.

The drug will then be tested for side effects in more animal models before moving on to human trials.

Other exercise-mimicking drugs have been tested but have not yet reached the market, partly because developing new drugs takes years. Treating obesity with medication has historically been difficult due to the complexity of the condition.

The greatest promise of this new drug may be in preserving muscle mass during weight loss (which often threatens lean muscle) or during aging, when the body's natural response to exercise weakens.

But more research is needed to understand the full potential of the drug.