Brown fat burns energy to generate heat and is therefore considered a promising target for new treatments against obesity. Researchers at the University of Basel and University Hospital Basel have now tested whether a drug can activate brown fat in humans. Their results show that a pharmaceutical approach may be more difficult than expected.
Unlike white fat, which mainly stores energy, brown adipose tissue consumes energy to produce heat. People with active brown fat also tend to be leaner and have a more favorable metabolic profile.
Cold is the natural stimulus for brown fat. Researchers have therefore been looking for ways to reproduce this effect with medication. A team led by Professor Matthias Betz from the University of Basel and University Hospital Basel has now investigated whether stimulating the beta2 adrenergic receptor can activate brown fat in humans. They have published their results in Cell Metabolism.
Drug and cold compared
The researchers compared the effects of mild cold with those of fenoterol, a drug that stimulates beta2 adrenergic receptors. Eleven healthy volunteers completed both experiments. The team measured energy expenditure and used PET/CT scans to assess the activity of brown fat.
Both cold and fenoterol increased energy expenditure. But only cold clearly activated brown fat. After cold exposure, the tissue took up substantially more glucose than after treatment with fenoterol.
“We were surprised that energy expenditure increased strongly with fenoterol even though we could not detect a comparable activation of brown fat,” says Betz. “Our study shows that an increase in energy expenditure does not automatically mean that brown fat has been activated.”
The researchers do not yet know which tissues or processes account for the additional energy consumption caused by fenoterol. Their results suggest that other tissues, such as skeletal muscle or white adipose tissue, may be involved.
More than one receptor may be needed
The study also points to a more complex regulation of brown fat in humans. Analyses of human tissue suggest that several receptors or biological signals may have to work together to fully activate brown fat. This could matter for future obesity treatments. Current weight loss drugs reduce appetite, but as people lose weight, the body often adapts by lowering its energy expenditure. “Ideally, we could combine a reduction in appetite with an increase in energy expenditure,” says Betz. “But first we need a better understanding of how brown adipose tissue is regulated.”
Cell Metabolism
Beta2-adrenergic stimulation by fenoterol increases energy expenditure without activating human brown adipose tissue
12-Aug-2026