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Study analysis · Nutrients · 2026

These weight-loss drugs don't work the same for everyone — and the science says you might lose 22 lbs... or just 5.

When people take GLP-1 drugs like semaglutide with diet and exercise, they lose about 10 kg on average, but some lose way more and others lose way less — and we don’t fully know why.

Reading level
Moderate certainty
Level 1a · Systematic review of RCTs

Overview

What the study found

The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.

In simple terms

This study looked at lots of different experiments where people took weight-loss medicines and also changed their diet or exercise. It found that, on average, people lost about 10 pounds more than those who didn’t take the medicine. But because the studies were all different—some had better diets, some had more exercise—it’s not clear if the medicine alone caused all the weight loss.

What’s the bottom line?

This study looked at whether drugs like semaglutide and liraglutide help people lose more weight when combined with diet and exercise, compared to just diet and exercise alone.

How strong is this study?

The researchers did a really good job collecting and checking all the studies, but some of the original experiments weren’t perfectly done—some didn’t track people well or had small groups. So while the big picture looks helpful, we can’t be super sure about every detail, which means we should be careful not to treat this like a perfect answer.

Reporting

40 / 100

  • COI disclosure+40/40
  • Data availabilitydata not shared
  • Code availabilitycode not shared
Methodology

19 / 100

  • Randomizationnot randomized
  • Blindingblinding unclear
  • Control group+15/15
  • Sample sizeno sample size reported
  • Follow-upno follow-up reported
Publication

100 / 100

Statistical

100 / 100

  • P-values+15/15
  • Effect size+20/20
  • Confidence intervals+15/15
  • Pre-registration+15/15

Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.

Where it sits

RCT reviews

Max 100

Randomized Trials

Max 90

Reviews of Cohort Studies

Max 85

Cohort Studies

Max 72

Reviews of Case-Control Studies

Max 63

Case-Control Studies

Max 58

Cross-Sectional & Case Series

Max 50

Expert Opinion

Max 5
StrongerWeaker
Reviews of RCTs (Meta-analyses)
Level 1a
60

60 / 100

Probability of being correct

The highest quality evidence. Systematic reviews and meta-analyses that pool randomized controlled trials, giving the most reliable summary of experimental evidence.

This design can establish causation. This study can establish causation because it synthesizes randomized controlled trials (RCTs), which are the gold standard for determining cause-effect relationships. However, the certainty is limited by high heterogeneity and risk-of-bias concerns in the included trials, meaning the strength of causation is not as strong as it would be in a single high-quality RCT.

No Conflicts

No conflicts of interest identified

No conflicts of interest or funding statements were disclosed in the provided text, and no industry affiliations or funder involvement were mentioned.

The study protocol was registered in PROSPERO and followed PRISMA and Cochrane guidelines, suggesting methodological rigor. However, absence of disclosed funding or COI information limits transparency. No author affiliations or industry ties are mentioned.

Key takeaways

  1. 01

    On average, people lost about 10 kg (22 lbs) or 9.5% of their body weight when using these drugs with lifestyle changes.

  2. 02

    Losing 10 kg is a big improvement for health, but results varied a lot between studies — some people lost much more, others much less.

Surprising findings

  • Heterogeneity was over 95% — meaning the studies were wildly inconsistent.Most people assume meta-analyses give clear, unified answers — but here, the variation between studies was so extreme that the average is almost meaningless.
  • Percentage weight loss and kilogram loss were analyzed separately — and never combined.It’s unusual for a major study to treat two common metrics as completely separate — this signals how unreliable mixing them would be, and how messy the data really is.
  • Some trials used metabolic wards — where people were fed controlled meals — and those skewed results.Most people think these drugs work in real life — but some of the most dramatic results came from highly artificial, controlled environments that don’t reflect real-world use.

Practical takeaways

If you're using GLP-1 drugs, pair them with resistance training 2–3x/week to help preserve muscle mass.

The study didn’t prove exercise prevents muscle loss — it only suggests it might help, based on limited data.

medium confidence

Don’t compare your weight loss to influencers — the average is 10 kg, but your result could be anywhere from 2–18 kg.

Individual results depend on drug type, dose, lifestyle adherence, and biology — none of which are predictable.

low confidence

Ask your doctor for body composition tracking (like DEXA scans) — not just scale weight — to see if you’re losing fat or muscle.

DEXA scans aren’t routinely offered and can be expensive or inaccessible.

medium confidence

Why this study matters

10 kg loss? Not guaranteed.

The study found an average weight loss of 10.08 kg (22.2 lbs) when GLP-1 drugs like semaglutide were combined with lifestyle changes — but the prediction interval ranged from just 2.29 kg to 17.86 kg lost. That means for some people, the effect was barely noticeable, while others lost over 17 kg.

Most ads and headlines make it sound like everyone loses 20+ lbs — but this study shows the average hides massive individual variation, which means your results could be totally different.

The evidence is shaky — and scientists admit it.

The certainty of evidence was rated 'low' by GRADE due to high heterogeneity (I² > 95%) and risk-of-bias concerns across 35 trials. The researchers explicitly warn that the 10 kg average shouldn’t be treated as a universal result.

Even though these drugs are everywhere, the science behind them is far from solid — and the authors themselves are cautioning against overgeneralizing the results.

You might lose muscle — not just fat.

The study found that GLP-1 therapies may reduce absolute lean mass, with muscle loss accounting for up to a quarter of total weight loss in some trials — and there’s no clear evidence these drugs protect muscle.

People think these drugs 'melt fat' — but they might also be shrinking your muscle, which affects metabolism, strength, and long-term health.

Want the whole report?

Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.