Scientists at Washington University School of Medicine in St. Louis have found a surprising new way the body burns calories - even without exercise. Deep within brown fat tissue, they uncovered a hidden“backup heater” that helps the body generate heat and use up energy.

Published in Nature, the study reveals that this alternate heat source could open doors to safer, easier ways to boost metabolism and fight obesity.

Brown Fat: The Body's Built-In Furnace

Unlike white fat, which stores energy, brown fat burns it to keep the body warm. When we're exposed to cold, brown fat becomes active, turning calories into heat through mitochondria - the energy-producing structures inside cells.

Until now, scientists believed that brown fat's ability to generate heat relied entirely on a protein called uncoupling protein 1 (UCP1). But experiments showed that even without this protein, mice could still stay warm - hinting at another system at work.

The Discovery of a“Backup Heater”

The WashU team discovered that peroxisomes, small organelles in cells that process fats, serve as an alternative heat source. When mice were exposed to cold, these peroxisomes multiplied and helped generate heat.

This process was powered by a protein called acyl-CoA oxidase 2 (ACOX2). Mice lacking ACOX2 struggled to maintain body temperature and gained more weight on a high-fat diet. In contrast, those with higher levels of ACOX2 showed better cold tolerance, improved insulin sensitivity, and less weight gain.

Fueling the Body's Natural Furnace

Using advanced imaging tools, researchers confirmed that brown fat cells became hotter when ACOX2 burned certain fatty acids. Interestingly, these fatty acids are not only made by the body but are also found in dairy products, breast milk, and produced by gut microbes.

This finding raises exciting possibilities for diet-based or probiotic therapies that could naturally activate this heat-producing pathway. Researchers are also exploring potential drug compounds that directly boost ACOX2 activity.

Toward Future Metabolism-Boosting Therapies

“By tapping into this alternative energy-burning pathway, we may be able to help the body waste calories in a healthy way,” said Dr. Irfan Lodhi, the study's senior author.“It could make weight management more sustainable than traditional diet and exercise alone.”

While the research was conducted in mice, previous studies suggest similar mechanisms may exist in humans. Individuals with higher levels of these fatty acids tend to have lower body mass indices, offering hope that one day, the body's own“backup heater” could be harnessed to combat obesity and metabolic disorders.

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