Liraglutide Causes Weight Loss Primarily From Fat While Shifting the Body to Burn More Fat for Fuel
Six months of liraglutide treatment produced 10.5 kg weight loss primarily from fat mass (-8.7 kg) while largely preserving lean tissue, and shifted metabolism toward increased fat burning (+352 kcal/day) without reducing overall energy expenditure.
Quick Facts
What This Study Found
After 6 months of liraglutide treatment in 11 obese adults:
Body composition changes:
- Total weight loss: -10.5 kg (P < 0.001)
- Fat mass loss: -8.7 kg (P < 0.001), predominantly from trunk: -5.1 kg (P < 0.001)
- Lean tissue loss: only -1.7 kg (P = 0.02) — largely preserved
Metabolic changes (24-hour whole-room calorimetry):
- 24h energy expenditure: no significant change (metabolic rate maintained)
- 24h sleeping metabolic rate: no significant change
- Fat oxidation: +352 kcal/day (P = 0.03)
- Carbohydrate oxidation: -422 kcal/day (P = 0.003)
- Protein oxidation: stable
The preservation of energy expenditure despite weight loss is notable because metabolic slowing typically accompanies weight loss and drives regain.
Key Numbers
How They Did This
Prospective single-arm study at the Obesity and Lipodystrophy Center, University Hospital of Pisa. 11 patients with obesity (8 female, mean age 49, mean weight 103 kg) were treated with liraglutide at clinically titrated doses for 6 months. 24-hour energy expenditure and substrate oxidation were measured via whole-room indirect calorimetry (metabolic chamber) at baseline and 6 months. Body composition was assessed by DXA (dual-energy X-ray absorptiometry) at both timepoints.
Why This Research Matters
One of the biggest concerns about weight loss drugs is that they might cause 'bad' weight loss — losing muscle along with fat, or slowing metabolism so weight regain is inevitable. This study provides reassuring metabolic data: liraglutide's weight loss was 83% fat (especially dangerous trunk fat), muscle was largely preserved, and total energy expenditure didn't drop. The shift toward fat burning suggests the body is efficiently using fat stores rather than just reducing metabolism. These findings help explain the quality of weight loss with GLP-1 drugs.
The Bigger Picture
Understanding the metabolic quality of GLP-1RA-induced weight loss is crucial as millions of people use these drugs. This study provides some of the most detailed metabolic data available, using gold-standard whole-room calorimetry. The finding that energy expenditure is maintained (avoiding the metabolic adaptation that sabotages traditional dieting) helps explain why GLP-1RA weight loss may be more sustainable. The shift toward fat oxidation aligns with the favorable cardiometabolic outcomes seen in GLP-1RA trials.
What This Study Doesn't Tell Us
Very small sample size (n=11) significantly limits generalizability and statistical power. No control group — all changes attributed to liraglutide could partially reflect diet/lifestyle changes. Only liraglutide was tested; results may not apply to other GLP-1RAs like semaglutide. The 6-month duration captures early weight loss but not long-term metabolic adaptation. The 1.7 kg lean tissue loss, while modest, warrants monitoring in longer-term treatment. The study population was predominantly female (8/11).
Questions This Raises
- ?Does semaglutide show the same favorable fat oxidation shift and metabolic rate preservation as liraglutide?
- ?Would resistance exercise combined with liraglutide prevent the modest lean tissue loss entirely?
- ?Does the fat oxidation shift persist long-term or eventually normalize as the body reaches a new weight equilibrium?
Trust & Context
- Key Stat:
- 83% of weight loss came from fat -8.7 kg fat vs -1.7 kg lean tissue over 6 months, with trunk fat accounting for -5.1 kg of the fat loss
- Evidence Grade:
- This is a prospective single-arm study using gold-standard metabolic measurements (whole-room calorimetry and DXA). The measurement quality is exceptional, but the very small sample (n=11) and lack of a control group limit the strength of causal conclusions.
- Study Age:
- Published in 2025, this is a very recent study providing detailed metabolic insights into GLP-1RA therapy using state-of-the-art measurement technology.
- Original Title:
- Effects of 6-month treatment with the GLP-1 receptor agonist liraglutide on 24-hour energy metabolism and body composition in adults with obesity.
- Published In:
- Journal of endocrinological investigation, 48(11), 2735-2745 (2025)
- Authors:
- Basolo, Alessio, Paolucci, Giordano, Piaggi, Paolo, Angeli, Valentina, Bechi Genzano, Susanna, Fierabracci, Paola, Vignali, Edda, Bologna, Chiara, Salvetti, Guido, Chiovato, Luca, Natali, Andrea, Krakoff, Jonathan, Landi, Alberto, Santini, Ferruccio
- Database ID:
- RPEP-10109
Evidence Hierarchy
Frequently Asked Questions
Does liraglutide cause muscle loss along with fat loss?
This study found that 83% of the weight lost on liraglutide came from fat and only 16% from lean tissue (-1.7 kg out of -10.5 kg total). This is a favorable ratio compared to diet-only weight loss, which typically loses 25-35% from lean tissue. The trunk fat loss (-5.1 kg) is particularly beneficial since visceral (belly) fat is the most metabolically dangerous type.
Does liraglutide slow down your metabolism?
Surprisingly, no. Normally when you lose weight, your body reduces its energy expenditure (metabolic adaptation) to fight the weight loss. This study found that 24-hour energy expenditure was maintained after 10.5 kg of weight loss with liraglutide. Instead, the body shifted to burning more fat for fuel (+352 kcal/day from fat) while burning less carbohydrate, suggesting a metabolically favorable adaptation rather than a metabolic slowdown.
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Cite This Study
https://rethinkpeptides.com/research/RPEP-10109APA
Basolo, Alessio; Paolucci, Giordano; Piaggi, Paolo; Angeli, Valentina; Bechi Genzano, Susanna; Fierabracci, Paola; Vignali, Edda; Bologna, Chiara; Salvetti, Guido; Chiovato, Luca; Natali, Andrea; Krakoff, Jonathan; Landi, Alberto; Santini, Ferruccio. (2025). Effects of 6-month treatment with the GLP-1 receptor agonist liraglutide on 24-hour energy metabolism and body composition in adults with obesity.. Journal of endocrinological investigation, 48(11), 2735-2745. https://doi.org/10.1007/s40618-025-02717-y
MLA
Basolo, Alessio, et al. "Effects of 6-month treatment with the GLP-1 receptor agonist liraglutide on 24-hour energy metabolism and body composition in adults with obesity.." Journal of endocrinological investigation, 2025. https://doi.org/10.1007/s40618-025-02717-y
RethinkPeptides
RethinkPeptides Research Database. "Effects of 6-month treatment with the GLP-1 receptor agonist..." RPEP-10109. Retrieved from https://rethinkpeptides.com/research/basolo-2025-effects-of-6month-treatment
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkPeptides research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.