Mounjaro May Switch On the Body’s Calorie-Burning Brown Fat, Mouse Study Suggests
Key Takeaways:
- A study in mice found that tirzepatide (Mounjaro) activates brown adipose tissue, a type of fat that specialises in using energy, and that this effect cannot be explained by reduced food intake alone.
- Unlike earlier drug-based attempts to activate brown fat, which were often hampered by side effects affecting the heart, tirzepatide shows cardiovascular benefits.
- The researchers stress that the findings come from mice and need to be confirmed in humans, but suggest they could pave the way for more personalised obesity treatment based on a person’s overall metabolic status.
Looking beyond appetite suppression
Tirzepatide has become an important treatment for obesity and related conditions such as type 2 diabetes, yet scientists are still working to understand exactly how it acts on the body. New research in mice now suggests that the drug may improve metabolism directly by activating brown adipose tissue, a form of fat that specialises in using energy rather than storing it.
According to the research team, the findings offer fresh insight into how tirzepatide works and could help shape the development of broader treatments for obesity and other metabolic disorders.
The study was led by Marion Peyrou, a 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).
A drug that targets two hormone receptors
Tirzepatide, the active ingredient in Mounjaro (also marketed as Zepbound), is approved for weight management in adults living with obesity, or with overweight alongside related health conditions. It is also approved for treating type 2 diabetes mellitus that is poorly controlled.
What sets tirzepatide apart from some other obesity medications is that it acts on the receptors for two hormonal factors at once: glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). This dual mechanism can lead to substantial weight loss, largely because the drug reduces how much a person eats.
For healthcare professionals supporting people who are prescribed tirzepatide and similar medicines, understanding these mechanisms is becoming increasingly relevant to everyday practice – an area explored in The College of Contemporary Health’s GLP-1RAs in Focus CPD course.
The researchers set out to establish whether tirzepatide also brings about metabolic changes that cannot simply be attributed to eating less.
How the study was designed
To answer this question, the team examined how the drug affected different fat deposits in an experimental mouse model, as this kind of detailed tissue analysis cannot readily be carried out in humans. Mice with obesity, which had been fed a high-fat diet, were treated with tirzepatide.
The researchers then compared these animals with a second group of mice that did not receive the drug but were given exactly the same amount of food. By matching food intake in this way, the scientists were able to separate the changes caused directly by tirzepatide from those that resulted from consuming fewer calories.
Tirzepatide activates brown fat
The analysis showed that tirzepatide activated brown adipose tissue. White adipose tissue mainly stores fat and tends to build up in people living with obesity, whereas brown fat specialises in using energy and “burning” the calories obtained 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 go beyond the weight loss brought about 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.
Avoiding the pitfalls of earlier approaches
Scientists have long regarded brown fat activation as a potentially valuable strategy for treating obesity and other metabolic diseases. However, previous attempts to activate brown adipose tissue using drugs have frequently 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 view that obesity treatments may be more effective when they act on several physiological processes at once, rather than focusing on appetite alone.
“This could help improve weight control and reduce associated disorders, such as type 2 diabetes and other metabolic disorders,” she adds.
Towards more personalised obesity treatment
A clearer understanding of how tirzepatide works could also influence how medicines in this class are prescribed in future.
“Identifying which patient profiles could benefit most, for example those with more compromised energy expenditure, would open the door to more personalised medicine, based not only on appetite or weight control, but also on overall metabolic status,” she emphasises.
Caution needed before applying the findings to people
The researchers are clear that because the findings come from mice, it cannot yet be assumed that tirzepatide acts in the same way in humans. Metabolism can differ considerably between the two species, as can the distribution of fat tissue and the way each responds 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.
CCH insight
As research continues to reveal how dual GIP/GLP-1 receptor agonists such as tirzepatide act on the body – from appetite regulation to potential effects on energy expenditure – healthcare professionals need a confident, up-to-date understanding of these medicines to support the people in their care. The College of Contemporary Health’s GLP-1RAs in Focus CPD course offers a practical grounding in how these therapies work and how they fit into modern obesity and diabetes care.
Source: Biomedicine & Pharmacotherapy
