Zepbound and Mounjaro may turn on the body’s calorie-burning brown fat
Tirzepatide, better known as Mounjaro or Zepbound, may fight obesity in more ways than previously understood.
Date:
September 26, 2026ro and Zepbound, activated calorie-burning brown fat in obese mice, revealing a potential metabolic effect beyond appetite suppression. If confirmed in humans, the finding could help explain the drug’s powerful benefits and inspire more comprehensive treatments for obesity and diabetes.
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Tirzepatide has become an important treatment for obesity and related conditions such as diabetes, but scientists are still working to understand exactly how it affects the body. A study in mice now suggests that the drug may improve metabolism directly by activating brown adipose tissue, a form of fat that specializes in using energy.
According to the researchers, the findings provide new clues about how tirzepatide works and could help guide the development of broader treatments for obesity and other metabolic disorders.
The research was led by Marion Peyrou, Ramón y Cajal researcher at the Faculty of Biology and the Institute of Biomedicine of the University of Barcelona (IBUB), the Sant Joan de Déu Research Institute (IRSJD) and the CIBER in Physiopathology of Obesity and Nutrition (CIBEROBN).
Tirzepatide Targets Two Hormone Receptors
Tirzepatide (generic name of the drug Mounjaro) is approved for weight management in adults with obesity or overweight with comorbidities, as well as for treating poorly controlled type 2 diabetes mellitus.
Unlike some other obesity medications, tirzepatide targets the receptors for two hormonal factors at the same time: GIP and GLP-1. This dual mechanism can produce substantial weight loss, largely because the drug reduces food intake.
Researchers wanted to determine whether tirzepatide also produces metabolic changes that cannot be explained simply by eating less.
To investigate, the team examined how the drug affected different fat deposits in an experimental mouse model, since this kind of detailed tissue analysis cannot readily be performed in humans. Obese mice — fed a high-fat diet — were treated with tirzepatide.
The researchers then compared those animals with mice that did not receive the drug but were given the same amount of food. By controlling food intake this way, the scientists could distinguish changes caused directly by tirzepatide from those resulting from reduced calorie consumption.
Mounjaro Activates Calorie-Burning Brown Fat
The analysis showed that tirzepatide activated brown adipose tissue. Unlike white adipose tissue, which primarily stores fat and tends to accumulate in obesity, brown fat specializes in using energy and ‘burning’ calories from food.
“This activation is associated with an increased capacity to burn metabolic energy and with the production of batokines by brown adipose tissue, molecules that are beneficial for metabolism,” says Marion Peyrou.
The finding suggests that tirzepatide may influence metabolism in ways that extend beyond the weight loss caused by appetite suppression and reduced food intake.
“This drug not only reduces body weight, but also has beneficial effects on metabolism. Active brown adipose tissue ‘burns’ glucose and fat within the body, which would contribute to its positive effect not only in reducing body weight, but also in lowering blood glucose and fat levels, and improving metabolism,” the researcher points out.
A Broader Strategy for Treating Obesity
Scientists have long viewed brown fat activation as a potentially useful strategy for treating obesity and other metabolic diseases. However, previous efforts to activate brown adipose tissue with drugs have often been unsuccessful because of unwanted side effects, particularly those affecting the heart.
“Tirzepatide, although it activates brown adipose tissue, does not have these negative effects; on the contrary, it shows cardiovascular benefits. If our findings are confirmed in humans, it would reinforce the importance of developing therapeutic strategies that not only reduce food intake but also increase energy expenditure and brown fat activation,” explains the researcher.
The results support the idea that obesity therapies may be more effective when they target several physiological processes at once instead of focusing only on appetite.
“This could help improve weight control and reduce associated disorders, such as type 2 diabetes and other metabolic disorders,” she adds.
Toward More Personalized Obesity Treatment
A clearer picture of how tirzepatide works could also influence how drugs in this class are prescribed in the future.
“Identifying which patient profiles could benefit most, for example those with more compromised energy expenditure, would open the door to more personalized medicine, based not only on appetite or weight control, but also on overall metabolic status,” she emphasizes.
The researchers caution, however, that the findings come from mice and cannot yet be assumed to apply in the same way to people. Human and mouse metabolism can differ substantially, as can the distribution of fat tissue and responses to medications.
“As this is a study conducted on mice, we must be cautious, as there may be significant differences between species in terms of metabolism regulation, adipose tissue distribution and response to drugs. Therefore, we need more clinical evidence on the action of these drugs on fat in humans,” concludes Peyrou.
Materials provided by University of Barcelona. Note: Content may be edited for style and length.
- Alberto Mestres-Arenas, Tania Quesada-López, Albert Blasco-Roset, Marta Giralt, Francesc Villarroya, Anna Planavila, Marion Peyrou. Differential effects of the anti-obesity drug tirzepatide on adipose tissues: Brown fat as a key target. Biomedicine, 2026; 195: 119057 DOI: 10.1016/j.biopha.2026.119057
University of Barcelona. “Zepbound and Mounjaro may turn on the body’s calorie-burning brown fat.” ScienceDaily. ScienceDaily, 26 September 2026. <www.sciencedaily.com/releases/2026/09/260925093210.htm>.
University of Barcelona. (2026, September 26). Zepbound and Mounjaro may turn on the body’s calorie-burning brown fat. ScienceDaily. Retrieved September 26, 2026 from www.sciencedaily.com/releases/2026/09/260925093210.htm
University of Barcelona. “Zepbound and Mounjaro may turn on the body’s calorie-burning brown fat.” ScienceDaily. www.sciencedaily.com/releases/2026/09/260925093210.htm (accessed September 26, 2026).
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