The main finding
In one sentence: A 2025 review of 13 randomized trials of GLP-1 medicines in adults with obesity found that dietitian involvement was described in only 6 of them, so the review could not say how much of the weight loss came from nutrition support rather than the medicine.
A pooled result summarizes several studies that differed in who was enrolled, how long they ran and what they compared. It is not a prediction for one person.
On this page
Why this study matters
Most trials of GLP-1 medicines, a class that includes semaglutide (Wegovy, Ozempic) and liraglutide (Saxenda, Victoza), gave participants some form of diet and activity advice alongside the medicine. Readers often want to know how much that advice mattered. This review set out to map what dietitians actually did in those trials, and to pool the weight-loss results. It is useful mainly for what it could not find.
Who was in the study
The review included 13 randomized clinical trials of GLP-1 medicines in adults with obesity who did not have diabetes. Dietitian procedures were evaluated in the 6 trials that described them. The published summary does not give the total number of participants, the specific medicines, the doses, or the trial lengths.
What the researchers did
This was a systematic review and meta-analysis. A systematic review searches for all relevant studies using a set method. A meta-analysis combines their results into one estimate. The researchers searched two databases, PubMed and Scopus, for eligible trials. They extracted data and assessed study quality.
For the trials that described dietitian involvement, the researchers checked which steps of medical nutrition therapy were included. Medical nutrition therapy is a structured process a dietitian follows: screening, assessment, intervention and monitoring.
The weight-loss results were pooled across trials. Nutrition support was not randomized on its own in these trials, so the pooled numbers reflect the medicine plus whatever support each trial gave.
What they found
The review's main finding about dietitians is that their role was incompletely described (R32-C142). Only 6 of 13 trials reported dietitian procedures in enough detail to evaluate. Because of this, the authors could not isolate how much benefit came from nutrition therapy.
The pooled results for the GLP-1 medicines were:
| Measure | Pooled mean difference | 95% confidence interval |
|---|---|---|
| Body weight | -5.4 kg | -5.8 to -5.0 kg |
| Waist circumference | -5.5 cm | -7.7 to -3.25 cm |
| Weight loss as a percentage of starting weight | -7.75% | -11.1% to -4.3% |
A mean difference is the average gap between the medicine group and the comparison group. The confidence interval is the range within which the true value would likely fall. The minus signs mean the medicine groups lost more.
These pooled figures mix different medicines, doses, trial lengths and comparison groups. They describe the class of medicines across the trials reviewed, not any one medicine. They should not be used to compare one medicine with another, or to compare this review with a single trial.
The authors concluded that GLP-1 medicines reduce weight and waist size, and that trials need to include and describe dietitian care more fully to understand the separate effect of nutrition therapy.
Side effects and people who stopped
The published summary we reviewed does not report side effects or dropout rates.
What this study does not tell you
- It cannot separate the dietitian's contribution from the medicine's. That is its central limitation and its main point.
- The 13 trials differed in medicine, dose, length and comparison group. The pooled number is an average across all of that variation.
- The pooled percentage of -7.75% is not comparable with the percentage from any single trial or medicine.
- Only two databases were searched, which may have missed some trials.
- People with diabetes were excluded, so the findings do not apply to them.
- The summary we reviewed does not state who funded the review.
What it means in Canada
For Canadian readers, this review is a reminder that the weight loss reported in GLP-1 trials happened alongside diet and activity support of varying quality, not from the medicine alone. It does not measure what a dietitian adds. For medicine information, see semaglutide in Canada and tirzepatide in Canada. For coverage, see public drug coverage by province. To find dietitian and lifestyle services, see compare services.
Common questions
Did GLP-1 trials include dietitian support?
Of 13 trials reviewed, only 6 described dietitian procedures well enough to evaluate. The review could not separate the dietitian's effect from the medicine's.
What was the pooled weight loss with GLP-1 medicines in this review?
The pooled mean difference was -5.4 kg (95% confidence interval -5.8 to -5.0) and -7.75% of starting weight (-11.1 to -4.3), across trials with different medicines and designs.
Can this review tell me how much a dietitian adds to a GLP-1 medicine?
No. Nutrition support was not randomized separately in these trials, so the review could not measure its added effect.
Related reading
Other studies in this library that bear on the same question.
Does seeing a dietitian help with weight? A review of 62 trials
STEP 3: semaglutide with intensive behavioural therapy
Cochrane review: semaglutide for adults with obesity
What a large evidence review found about weight-loss programs
Source
Original paper: Israa Moetaz, Dietitian role in GLP-1 obesity-trial systematic review, Clinical obesity, 2025. PubMed: https://pubmed.ncbi.nlm.nih.gov/40530685/. DOI: https://doi.org/10.1111/cob.70030. Funding: The summary we reviewed does not state the funding source. How we summarized it: abstract and extracted data.
This page explains a published study. It is not medical advice and does not describe whether a medicine is right for you. Talk to your doctor, nurse practitioner or pharmacist about your own situation. Reviewed and signed by two pharmacists registered in British Columbia, 2026-09-18.
Evidence records behind this page
Each record is a row in the clinical evidence file, taken from the published paper named above. The caution column is the limit the researcher recorded for that number.
This table scrolls sideways.
| Record | What the paper reports | Type | Population | Caution | Source |
|---|---|---|---|---|---|
| R32-C142 | A review of GLP-1 weight-management trials found that dietitian support was incompletely characterized, so it could not isolate how much additional benefit came from nutrition therapy. | cross-trial context | adults with obesity without diabetes in GLP-1 randomized trials | Pooled medicine effect cannot isolate the dietitian's added effect; cross-trial heterogeneity and no direct comparison of nutrition intensity. | PubMed 40530685 |