Do you still need diet and exercise on Wegovy or Zepbound? What the trials actually tested
The short answer: the headline weight-loss numbers you've seen for these medications did not come from people taking the medication alone. In both of the trials those figures come from, every participant was also given a structured diet and activity plan. The drug was tested as an addition to that support — not as a replacement for it.
The numbers everyone quotes
Two trials produced the figures you see repeated online.
STEP-1 tested semaglutide 2.4 mg — the dose sold as Wegovy — in 1,961 adults over 68 weeks. Average weight loss: 14.9%.
SURMOUNT-1 tested tirzepatide — sold as Zepbound — in 2,539 adults over 72 weeks. At the 15 mg dose, average weight loss: 20.9%.
These are large, well-conducted trials. Nearly everything written about these medications traces back to them.
What else every participant received
This is the part that rarely makes it into a headline. In both trials, every participant — including everyone in the placebo group — was also:
placed on a reduced-calorie diet targeting a 500 kcal/day deficit.
given a goal of at least 150 minutes of physical activity per week.
seen regularly for counseling. In STEP-1, individually every four weeks. In SURMOUNT-1, with a dietitian or other qualified health professional.
So what those trials established was what happens when the medication is added on top of structured nutrition and activity support. Nobody in either study was simply taking the drug.
That isn't a criticism of the trials — it's good trial design. But it does mean the numbers describe a package, and most people are handed only one part of it.
And if you have type 2 diabetes, those numbers were never yours
Neither trial included a single person with type 2 diabetes. It was an explicit exclusion — STEP-1 ruled out anyone with a diagnosis or an HbA1c at or above 6.5%.
When the same medications were studied in people who do have type 2 diabetes, average weight loss was meaningfully smaller:
Without diabetes | With type 2 diabetes | |
Semaglutide 2.4 mg | 14.9% (STEP-1) | 9.6% (STEP-2) |
Tirzepatide 15 mg | 20.9% (SURMOUNT-1) | 14.7% (SURMOUNT-2) |
If you have diabetes and your own results have never looked like the numbers you see online, that is not a personal failure. You were not in those studies. You were being compared against a group you were never part of.
(A note on how these are counted: all four figures include everyone who started each trial, including people who stopped the medication partway through, so they can be compared directly. You will sometimes see 22.5% and 15.7% quoted for the tirzepatide trials — those count only people who stayed on treatment, which is why they're higher.)
What this means if you're taking one of these
The medication is doing real work. So was everything else those participants were given, and that part is usually missing in real life.
If your prescription came with no nutrition plan, no activity target and nobody checking in, you have been handed one part of a three-part intervention and measured against results produced by all three.
That is worth knowing — not because you're doing anything wrong, but because the missing parts are the ones you can actually do something about.
Where this came from, and what I'd flag about it
I found this synthesis in a commentary in Obesity Pillars by Noronha and colleagues. That paper was supported by an unrestricted educational grant from Nestlé Health Science, and several of its authors disclose financial relationships with Novo Nordisk, Eli Lilly and others. The paper also states that the sponsor had no involvement in its conception, analysis, approval or the decision to publish.
Both of those things are true and you should have both. It's also a summary rather than a trial — which is why the numbers above are taken from the original studies rather than from the commentary.
References
* Noronha JC, Van Gaal LF, Neeland IJ, et al. Optimizing GLP-1 therapies for obesity and diabetes management. Obesity Pillars. 2025;16:100222.
* Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP-1). N Engl J Med. 2021;384:989–1002.
* Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205–216.
* Davies M, et al. Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP-2). Lancet. 2021;397(10278):971–984.
* Garvey WT, Frias JP, Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2). Lancet. 2023;402(10402):613–626.
* Mozaffarian D, et al. Nutritional priorities to support GLP-1 therapy for obesity — joint advisory, ACLM / ASN / OMA / TOS. Obesity Pillars. 2025;15:100181.
This is general information, not medical advice. Your plan is yours and your care team's.
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