Zepbound and Mounjaro Show Brown-Fat Effect in Mice

Tirzepatide, marketed as Mounjaro and Zepbound, affected energy use in obese mice beyond the changes associated with eating less. The animals had received a high-fat diet. Researchers treated some with the medicine, then compared them with untreated mice consuming an equal quantity of food. This design helped separate the drug’s direct effects from those caused by lower calorie intake.

The medicine stimulated brown adipose tissue, which expends energy rather than primarily storing fat as white adipose tissue does. Activated brown fat uses glucose and fat and produces batokines, molecules described as metabolically beneficial. The result indicates that tirzepatide may influence metabolism as well as appetite. Tirzepatide acts on both GIP and GLP-1 receptors, and its reduction of food intake is considered a major contributor to weight loss.

For people, tirzepatide may be used to manage poorly controlled type 2 diabetes mellitus. It also has approval for managing weight among adults with obesity, or those who are overweight and have comorbidities. However, this brown-fat response has been demonstrated only in mice. Differences between species include metabolic regulation, fat-tissue distribution and reactions to medicines. More clinical evidence is needed to determine whether tirzepatide affects human fat similarly. Confirmation could encourage treatments addressing appetite, energy expenditure and brown-fat activity together, while helping identify patients whose impaired energy expenditure may make them especially likely to benefit.