The data showed that during a clinical trial of tirzepatide, the active substance of Mounjaro, participants experienced a reduction of 33 to 36 percent in fat mass and 10 to 11 percent in lean mass, varying based on age group. These findings indicate that lean mass was only a quarter of the weight lost.
Why Lean Mass Matters
Lean mass is the total body weight minus body fat weight, incorporating the weight of organs, skin, bones, body water, and muscle mass. During weight loss, body water and muscle mass are the two key components of lean mass to focus on since the weight of organs, skin, and bones remains relatively stable.Lean body mass is closely associated with basal metabolic rate, determining the calories burned at rest. Consequently, losing lean mass can decrease metabolism, resulting in the body burning fewer calories.
Muscle Matters Even More as People Age
Loss of muscle mass is especially problematic for older adults. “As old people lose muscle, they become less capable of maintaining balance, among other things, and are at risk for falls, hip fractures, and head injuries, all with catastrophic consequences,” Dr. Mert Erogul, board-certified in emergency and obesity medicine, told The Epoch Times.How to Build and Maintain Muscle Mass
Muscle serves as a metabolically active tissue responsible for absorbing and storing energy, underscoring the significance of maintaining muscle for metabolic health, Erogul added. “Maintaining muscle is simply a matter of using it and feeding [it] with protein.” Protein is an essential component of the immune system, implying that an improved lean body mass can enhance the body’s ability to combat illness, infections, and stress more effectively.How Mounjaro Works
Mounjaro’s active substance, tirzepatide, is a single molecule known to suppress appetite by activating the body’s receptors for glucose-dependent insulinotropic polypeptide (GIP) and GLP-1, natural incretin hormones.Concerns About Mounjaro and Its Side Effects
Despite the remarkable weight-reducing effects of these drugs, some doctors express concerns about their side effects and the underlying mechanism of action.“They essentially operate on the same mechanism as an eating disorder,” Lauren Muhlheim, a certified eating disorder specialist and clinical psychologist, told The Epoch Times, adding that people tend to lose weight because they eat less, not because the drugs magically burn fat.
Muhlheim cautioned that individuals who do not consume sufficient food may be at risk of binge eating later and developing anorexia.
In the 2022 study involving 2,539 participants, the most commonly reported side effects were gastrointestinal disorders, including nausea, diarrhea, and constipation. Approximately 80 percent of participants receiving tirzepatide experienced at least one adverse event, compared to 72 percent in the placebo group.
Serious adverse events were reported by 6.3 percent of participants, totaling 160 individuals, with similar occurrences in both the tirzepatide and placebo groups. However, researchers believe approximately one-fifth of these events were associated with COVID-19. Additionally, the study recorded 11 deaths, with seven occurring in the tirzepatide group and four in the placebo group.
How Other Diabetes Medications Impact Weight Loss
On the other hand, a 2021 double-blind study pointed out that semaglutide led to a more significant reduction in fat mass than lean body mass. However, it didn’t specify how much more significant the drop was. A 2020 study showed that after 52 weeks with semaglutide, total fat mass (baseline 33.2 kilograms) was reduced by 3.4 kilograms, and total lean mass (baseline 51.3 kilograms) was reduced by 2.3 kilograms.Semaglutide is the active substance of Ozempic and Wegovy, hugely popular among people who want to lose weight. Wegovy has been approved to treat chronic weight management, while Ozempic is only for Type 2 diabetes patients.
“It is relevant to understand the effect of weight loss on fat mass and lean mass, particularly in the elderly. This new analysis shows that around three-quarters of the weight loss was fat mass, which is consistent across different ages,” said Louis Aronne, a professor at the Comprehensive Weight Control Center at Weill Cornell Medicine College in New York.
Aronne and colleagues presented the new analysis at the 30th European Congress on Obesity held in Dublin, Ireland, on May 17–20. The abstract has been peer-reviewed by the Congress selection committee.
Aronne, who has received funding from Eli Lilly, was among the authors of the 2022 study that received support from the same company.