PeptidesInfo

Research area

Body composition

Body-composition claims span the entire evidence spectrum. GLP-1/GIP drugs have large trials showing weight loss (with some lean-mass loss); tesamorelin has trials showing visceral-fat reduction in one population; growth-hormone secretagogues have hormone-level data only; and most 'fat-burning' fragments have no human trials at all.

Abstract illustration of a peptide chain used as the body composition research hub image

Evidence map: peptides studied in this area

How grades work →
PeptideEvidence for this areaRegulatory statusWhat has been studied
SemaglutideEstablished evidenceFDA-approved for this useSTEP trials show mean placebo-subtracted weight loss of roughly 12% over 68 weeks; a proportion of lost weight is lean mass.
TirzepatideEstablished evidenceFDA-approved for this useSURMOUNT-1 showed dose-dependent weight loss up to about 21% at 72 weeks; DEXA substudy data show both fat and lean mass reduction.
TesamorelinEstablished evidenceFDA-approved for this useReduces visceral fat by roughly 15–18% in HIV-associated lipodystrophy in phase 3 trials; effect reverses when stopped. Off-label body-composition use in other populations lacks comparable trials.
Collagen peptidesPreliminary evidenceNot FDA-approvedA few small trials in older men and premenopausal women report modest lean-mass gains when combined with resistance training; effect sizes small, mechanism unclear.
CJC-1295Preclinical evidenceNot FDA-approvedIncreases GH/IGF-1 in small human studies; no body-composition outcome trials. Graded preclinical for this specific claim.
IpamorelinPreclinical evidenceNot FDA-approvedAnimal data on GH release and appetite; no human body-composition trials.

Grades reflect the strength of evidence for this research area specifically. Definitions: Established, Promising, Preliminary, Preclinical, Unsupported, Conflicting.

Read the endpoint, not the headline

"Weight loss" and "fat loss" are not the same measurement. Most trials report total body weight; fewer report body composition by DEXA or MRI; fewer still report visceral versus subcutaneous fat. When a claim says a peptide "burns fat", check whether the study measured fat at all.

Where the strong evidence is

Semaglutide and tirzepatide are the only peptides with large randomised trials showing clinically meaningful, sustained weight loss. Both trials programmes also show that a meaningful fraction of the weight lost is lean tissue — a finding that has driven interest in combining these drugs with resistance training and adequate protein, and in newer agents designed to preserve muscle. Tesamorelin has phase 3 evidence for visceral-fat reduction, but only in HIV-associated lipodystrophy, and the effect reverses on discontinuation.

Where the evidence is thin

Growth-hormone secretagogues such as CJC-1295 and ipamorelin are widely marketed for "lean muscle" and "fat loss". The human studies that exist measure hormone levels over hours to weeks, not body composition over months. Growth hormone itself, in older adults, produces small changes in lean and fat mass with a notable side-effect burden (fluid retention, joint pain, glucose intolerance) in trials — which is a reason for caution, not a reason to assume secretagogues will do better.

What we watch for

  • New DEXA-based trials of incretin drugs and muscle-preserving co-therapies.
  • Any registered human trial of a GH secretagogue with a body-composition endpoint.
  • Long-term safety of chronic GH/IGF-1 elevation, including cancer signals in observational data.

Analyses in body composition

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Peptides for Muscle Growth: What the Evidence Supports

Growth-hormone peptides are sold almost entirely on muscle claims. No controlled trial has measured muscle with them. The one peptide with positive lean-mass data is the one nobody markets for it.

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Are Peptides Worth It? A Framework for Deciding

Whether a peptide is worth it depends on four things: what benefit is proven, in whom, for how long, and whether the effect lasts after you stop. Here is that framework applied to every peptide we cover.

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Peptide Benefits: What the Evidence Actually Supports

Peptides are credited with dozens of benefits. Some are proven in large trials, some are modest and real, and some have never been tested in a person. This is every major benefit claim, sorted by how strong the human evidence is.

Benefits5 min read

GLP-1 Benefits Beyond Weight Loss: Heart, Kidney, Liver, and Sleep

Semaglutide and tirzepatide have now shown benefits in cardiovascular events, kidney disease, liver disease, heart failure and sleep apnoea — each in its own trial, in its own population. Here is what each one actually demonstrated.

Benefits4 min read

Collagen Peptide Benefits: What to Expect, and When

Collagen peptides have more randomised human trials than any other supplement peptide. The benefits are real, small, and take 8–24 weeks to appear. Here is what each one is worth in measurable terms.

Research analysis5 min read

GLP-1 Peptides: Established Uses Versus Emerging Research

Semaglutide and tirzepatide are the best-evidenced peptides in medicine — for specific uses. We separate the approved indications with large trials from the emerging research (kidney, liver, heart failure, sleep apnoea, Alzheimer's) and the open questions about regain, muscle loss and compounded products.

Research analysis5 min read

CJC-1295 and Ipamorelin: Growth Hormone Research and Unanswered Risks

The 'CJC/ipa' stack is sold for muscle, fat loss, sleep and anti-aging. The human evidence is a handful of short hormone-level studies, two abandoned development programmes, and no outcome trials — plus a set of risks that have never been studied because the trials were never run.

Research analysis4 min read

Tesamorelin: Approved Use, Off-Label Interest, and Clinical Evidence

Tesamorelin is the one GHRH analogue that finished phase 3 and won FDA approval — for excess abdominal fat in HIV-associated lipodystrophy. We separate that established evidence from the off-label uses it is now marketed for: general visceral fat, liver fat, and cognition.

Research analysis4 min read

Collagen Peptides: Joint, Skin, and Recovery Evidence

Oral collagen peptides are the rare non-drug peptide product with multiple randomised trials. The effects on skin hydration, activity-related joint pain and (with training) lean mass are real but small, and most trials are industry-funded. Here is what the studies show and where the gaps are.