“Best for body composition” depends on what “best” means — speed, magnitude, fat-mass specificity, lean-mass preservation. The published research literature gives concrete numbers for each. This article maps the compound ranking across body-composition endpoints actually measured in trials.
The ranking by published trial endpoint
| Rank | Compound | Body weight reduction | Trial duration | Class |
|---|---|---|---|---|
| 1 | Retatrutide | 24.2% | 48 weeks | Triple agonist (GLP-1/GIP/glucagon) |
| 2 | Tirzepatide | 22.5% | 72 weeks | Dual agonist (GLP-1/GIP) |
| 3 | Semaglutide | 14.9% | 68 weeks | Single GLP-1 agonist |
| 4 | Liraglutide | ~8% | 56 weeks | Single GLP-1, daily |
All published in peer-reviewed clinical research (NEJM). Detailed trial breakdowns in our three-way comparison.
The body composition split
Weight loss is not pure fat loss. DEXA scan data from STEP and SURMOUNT trials shows approximately:
- 65-75% of weight loss is fat mass
- 25-35% is lean mass
This ratio is similar to traditional caloric restriction research — the GLP-1 class doesn’t preferentially spare lean tissue. Resistance training during the protocol shifts the ratio toward better lean preservation.
Fat-mass specific endpoint
For pure fat-mass reduction (the metric most relevant to body composition research):
- Retatrutide 12mg: ~18-19% fat mass reduction
- Tirzepatide 15mg: ~16-18% fat mass reduction
- Semaglutide 2.4mg: ~10-11% fat mass reduction
The triple-agonist glucagon arm produces additional energy expenditure on top of intake reduction. This shifts the fat-mass-to-lean-mass loss ratio favourably.
Speed of effect — week 12 milestones
For research protocols measuring early response (week 12 of dosing):
- Retatrutide 12mg: ~10% body weight loss at week 24 (extrapolated from 48-week trajectory)
- Tirzepatide 15mg: ~7% at week 12
- Semaglutide 2.4mg: ~5% at week 16
See our phase 3 weekly trajectory article for the full week-by-week timing data.
Tissue-repair peptides — different category
BPC-157 and TB-500 do not feature in body-composition research because their mechanism targets tissue repair, not energy regulation. These are reference compounds for injury / recovery research, not weight loss.
GHRH/GHRP combinations — historical context
Pre-GLP-1 era, GHRH analogues (CJC-1295, Sermorelin) + GHRPs (Ipamorelin, GHRP-2) were the leading peptide research stack for body composition. Endpoints were modest (~3-5% reduction over 12-16 weeks) and the literature primarily measured IGF-1 elevation and visceral fat reduction rather than full body weight. The GLP-1 class has supplanted this stack as the reference compound for body composition research.
Mots-c and mitochondrial peptides
MOTS-c shows metabolic improvements in research models but the body composition magnitude is small compared with GLP-1 class. Research interest is mechanistic (mitochondrial-nuclear signalling) rather than primary weight loss.
5-Amino-1MQ — adjacent angle
NNMT inhibitor research shows adipose-specific energy effects without primary weight loss endpoints. Useful as combination research adjacent to GLP-1 protocols, not as standalone fat-loss compound.
Choosing for the research question
- Maximum body composition magnitude → Retatrutide (newest, highest endpoint)
- Most-validated long-term data → Semaglutide (longest published track record)
- Best-tolerated for research workflow → Tirzepatide (lower nausea profile in some research)
- Mechanism research on GIP → Tirzepatide
- Energy expenditure pathway research → Retatrutide (glucagon arm)
Chempeptides supplies all three with batch-specific CoA — see the research catalogue.
For laboratory research use only. Trial data summarised from peer-reviewed research.