Researchers at the Pennington Biomedical Research Center have found new clues about how the drug tirzepatide, also known by the brand name Zepbound, helps people with obesity lose weight.
In a first-of-its-kind study, published in Cell Metabolism, the scientists looked at how tirzepatide affects the way the body uses energy, burns fat, and controls appetite.
Tirzepatide is a new type of medication that acts on two important hormones in the body: GIP and GLP-1. These hormones help control blood sugar levels and appetite.
In earlier studies, tirzepatide has already shown that it can lead to major weight loss and improvements in overall health.
But until now, researchers didn’t fully understand exactly how it worked inside the body during weight loss.
In this study, 55 people with obesity took part. They were randomly assigned to either receive tirzepatide or a placebo for 18 weeks. Both groups were also put on a diet that reduced their daily calorie intake.
The study was designed so that neither the participants nor the researchers knew who was getting the real drug until the end of the study—a method known as a blinded clinical trial.
The results showed that people taking tirzepatide lost much more weight than those taking the placebo. One of the key findings was that tirzepatide helped people eat fewer calories, especially at lunch and dinner, by making them feel less hungry. At the same time, it made their bodies burn more fat for energy instead of relying mostly on carbohydrates or proteins.
However, one important thing did not change. Normally, when people lose a lot of weight, their bodies start using less energy—a survival response that can make it harder to keep the weight off. This is called metabolic adaptation. In studies with animals, drugs like tirzepatide had helped stop this energy slowdown.
But in this human study, even though tirzepatide increased fat burning and helped participants lose weight, it did not prevent the usual drop in the body’s metabolic rate that comes with weight loss.
The researchers measured how participants’ bodies used energy while sleeping and throughout the day. They found that even though tirzepatide improved fat burning, the overall decrease in energy use was similar between those who took the drug and those who took the placebo, once body weight and body composition changes were taken into account.
Dr. Eric Ravussin, a lead scientist on the study, said that while tirzepatide is clearly very effective at helping people lose weight and burn more fat, it does not stop the body’s natural tendency to slow down its metabolism after weight loss. Still, he emphasized that tirzepatide remains a powerful new option for treating obesity.
Other researchers who worked on the study included Dr. Corby Martin, Dr. Robbie Beyl, Dr. Frank Greenway, and Dr. Guillermo Sanchez-Delgado. The research was funded by Eli Lilly and Company, the manufacturer of tirzepatide. Some of the early results were shared at the American Diabetes Association’s 83rd Scientific Sessions in 2023.
Dr. John Kirwan, Executive Director at Pennington Biomedical, said that their research is helping pave the way for smarter and more effective treatments. He noted that drugs like tirzepatide, which belong to a class called GLP-1 receptor agonists, not only offer a new path to weight loss but also help people manage their overall health better.
While more studies are needed to fully understand how tirzepatide affects long-term metabolism, this study adds to the growing evidence that it is one of the most promising treatments for obesity available today.
If you care about weight loss, please read studies that hop extract could reduce belly fat in overweight people, and early time-restricted eating could help lose weight .
For more health information, please see recent studies that Mediterranean diet can reduce belly fat much better, and Keto diet could help control body weight and blood sugar in diabetes.
The research findings can be found in Cell Metabolism.
Copyright © 2025 Knowridge Science Report. All rights reserved.
