If you carry extra weight around your middle, you may have heard that where fat sits matters as much as how much you weigh. A new analysis of a major trial suggests that tirzepatide, a once-weekly injection already used for weight loss and diabetes, can help shift that belly fat into a healthier range.
The study looked at a measure called waist-to-height ratio (WHtR). It is a simple calculation: your waist size divided by your height. A ratio of 0.5 or higher means you have excess belly fat, which raises your risk for heart disease, diabetes, and other problems. The goal is to get below 0.5.
Researchers reanalyzed data from a phase 3 trial that included 2,538 adults with obesity or overweight plus at least one weight-related complication (but not diabetes). Participants were randomly assigned to receive either tirzepatide (at doses of 5, 10, or 15 mg once weekly) or a placebo, along with a reduced-calorie diet and increased physical activity. The main trial lasted 72 weeks (about 16.6 months), and people with prediabetes were followed for up to 176 weeks (about 3.4 years).
At 72 weeks, about 16.7% of people taking the higher doses of tirzepatide (10 or 15 mg) achieved a WHtR of 0.49 or lower, meaning they moved into a healthier range. More strikingly, 54.7% of those on tirzepatide improved their WHtR category (for example, from high to moderate risk), compared with only 9.6% on placebo. Among participants with prediabetes who were followed longer, 12.2% on tirzepatide reached the healthy WHtR target at 176 weeks, versus 9.3% on placebo. And 46.4% on tirzepatide improved their category, compared with 9.3% on placebo.
Safety information was not reported in this analysis, so we cannot comment on side effects or tolerability. The original trial did report common side effects like nausea and diarrhea, but those details are not part of this post-hoc analysis.
It is important to understand the limitations. This is a post-hoc analysis, meaning the researchers looked at the data after the trial was over to ask a new question. It was not the main goal of the study. Post-hoc analyses are useful for generating ideas, but they are not as reliable as a study designed from the start to test a specific question. Also, the long-term results only apply to people with prediabetes, because only they were followed beyond 72 weeks. The WHtR is a surrogate measure, not a direct outcome like heart attacks or diabetes. So we cannot say for sure that improving WHtR leads to fewer health problems.
For now, this analysis adds to the evidence that tirzepatide can help reduce belly fat, but it does not prove that the drug prevents disease. If you are considering tirzepatide, talk to your doctor about whether it is right for you, and remember that diet and exercise remain key parts of any weight management plan.
