Weight loss and body composition explored
Tirzepatide is a novel glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist that works to activate the GIP and GLP-1 receptors, respectively, found in areas of the brain important for appetite regulation, decreasing food intake, and modulating fat utilization.
The phase 3, double-blind, randomized, controlled trial included data from 2,539 adults with a BMI greater than or equal to 30 kg/m2 (class I, II, III obesity) or greater than or equal to 27 kg/m2 (overweight) with one or more weight-related complications, excluding diabetes. At baseline, mean body weight was 104.8 kg, mean BMI was 38.0 kg/m2, and 94.5% of participants had BMI greater than or equal to 30 kg/m2.
Patients were randomized to once-weekly subcutaneous tirzepatide (5 mg, 10 mg, or 15 mg) or placebo for 72 weeks. The primary objective was to show that tirzepatide was superior to placebo in terms of percentage change in body weight and proportion of participants with body-weight reduction of greater than or equal to 5%. The percentage change from baseline body weight and proportion of participants with body weight reduction greater than or equal to 5% were also assessed across BMI categories of greater than or equal to 27 to less than 30 kg/m2, greater than or equal to 30 to less than 35 kg/m2 (class 1 obesity), greater than or equal to 35 to less than 40 kg/m2 (class 2 obesity), and greater than or equal to 40 kg/m2 (class 3 obesity).
In addition, in a retrospective subanalysis, body composition was evaluated in a subpopulation that underwent dual-energy x-ray absorptiometry, assessing change from baseline body composition within age subgroups less than 50 years (n = 99), 50-64.9 years (n = 41), and greater than or equal to 65 years (n = 20).
The average weight reduction over the 72 weeks of follow-up was –16.0%, –21.4%, and –22.5% with tirzepatide 5 mg, 10 mg, and 15 mg, compared with –2.4% for participants taking placebo (all P < .001 vs. placebo).
The percentages of participants reaching target weight reductions of greater than or equal to 5%, greater than or equal to 10%, greater than or equal to 15%, greater than or equal to 20%, and greater than or equal to 25% were recorded. Over 90% achieved greater than or equal to 5% weight loss, irrespective of BMI and tirzepatide dose, while 55.5% and 62.9% in the 10-mg and 15-mg groups achieved greater than or equal to 20% weight loss, and 35.0% and 39.7% in the 10-mg and 15-mg groups achieved greater than or equal to 25% weight loss, respectively.
By increasing BMI category, in the 10-mg group, weight loss was –18.2 kg, –21.9 kg, –22.0, and –20.7 kg; and in the 15-mg group, weight loss was –18.1kg, –21.2 kg, –24.5 kg, and –22.8 kg. Weight loss in the 5-mg group ranged from –16.6 kg to –15.9 kg from lowest to highest BMI category.
“In the lower-weight categories, there is less weight to lose, so we see a flattening of the curve [with a] maximum of around 18%, so it may be that as we learn more about a drug that is so potent, we recognize that we don’t need to use such a high dose in people with BMI 27-30 kg/m2,” he explained. “It’s the higher BMI categories where we need the higher dose.”
As with lifestyle and surgical treatments, participants taking tirzepatide had around a three times greater percentage reduction in fat mass than lean mass, resulting in an overall improvement in body composition, reported Dr. Aronne.
“We want loss of fat, not lean mass, and we know that we lose around one part lean to three parts fat mass when on a diet and exercise regimen,” he went on to explain. “We see exactly this [balance of lean-to-fat-mass loss] here with 33.9% total fat mass reduction in the treatment group, compared with 8.2% in the placebo group.”
Visceral fat mass reduction was 40% in the treatment group, compared with 7.3% with placebo. “It’s good to see there’s more loss of visceral fat,” said Dr. Aronne. Lean mass loss was 10.9%. “So around three times greater reduction in fat over lean mass loss, resulting in overall improvement of body composition,” he reported.
Also, in older people (≥ 65 years) there was approximately no difference in fat versus lean mass loss, compared with younger people, despite older people being more likely to lose more lean mass.
With respect to patient-reported outcomes based on the 36-item Short-Form Health Survey (SF-36), Dr. Aronne said that physical functioning scores significantly improved at 72 weeks, compared with placebo, particularly in participants with physical function limitations at baseline.
“In an interesting subanalysis, those with physical limitations at baseline showed a significant improvement versus placebo of over 5% difference [considered significant],” he added.
Safety and tolerability were previously reported in the NEJM article. The most common adverse events with tirzepatide were gastrointestinal, and adverse events causing treatment discontinuation occurred in 4.3%, 7.1%, 6.2%, and 2.6% of participants receiving 5-mg, 10-mg, and 15-mg doses or placebo, respectively.
“A revolution is coming in the treatment of obesity and cardiometabolic disease, and most physicians cannot grasp this. We’re finally getting the efficacy we’ve been looking for that will produce benefits in every realm,” concluded Dr. Aronne. “These data show that we are now hitting all the secondary endpoints and making our patients better.”
“I think this bodes well. I always envisioned a time when the treatment of obesity would come first before the treatment of cardiometabolic complications of obesity, and I think we’re on the verge of that era with semaglutide, tirzepatide, and the very exciting treatments to come.”
The SURMOUNT-1 trial was sponsored by Lilly. Dr. Aronne is cofounder, chief scientific advisor, and a member of the board of directors for Intellihealth. He is also a paid scientific advisory board member for Eli Lilly.
A version of this article first appeared on Medscape.com.