Body CompositionSupplement GuideAug 2026

Best Peptides for Muscle Growth and Fat Loss in 2026

Q: Why do these trials report lean body mass rather than muscle mass?

Because lean body mass is what the scanner measures. Dual-energy X-ray absorptiometry sorts tissue into fat, bone mineral and a lean soft tissue compartment, and that compartment holds body water, organs and connective tissue as well as muscle, so fluid shifts land in the same column as muscle. The systematic review at PMID 17227934 found people treated with growth hormone significantly more likely to experience soft tissue edema, which is why the design column matters when reading a lean mass figure from that drug class.

Q: Do results in patients treated for HIV-associated fat accumulation apply to a healthy trained adult?

They describe the group that was enrolled. The trials at PMID 18057338 and PMID 15249570, and the pooled analysis at PMID 41545261, all enrolled adults with antiretroviral-associated changes in fat distribution, and they were enrolled because of that condition. Baseline visceral fat, hormone status and the reason for treating all differ in a healthy trained adult, so the size of any effect in that group is not settled by those papers. A diagnosed condition affecting body composition is managed with a doctor, not from a table.

Q: Why do two studies of the same drug report different numbers?

Method, duration and population each move the figure. The review at PMID 41996180 reported a median muscle-related share of weight loss of about 29% among studies using bioimpedance or DXA and about 25.3% among studies using CT or MRI, from the same drug class. The bimagrumab figures at PMID 33439265 cover 48 weeks while the trial at PMID 15249570 ran 12. And the tirzepatide substudy at PMID 39996356 was 73% female with a mean weight of 102.5 kg, a different starting point again.

Q: What does a rodent study establish, and what does it leave open?

It establishes that an effect occurred in that species, by that route, at that dose, on that endpoint. The Zucker rat study at PMID 11146367 measured body weight gain over 19 days of oral dosing and found 15.8 g against 35.6 g in controls, which is a finding about rats. It leaves open whether the route reaches the same tissue in a person and whether the dose scales. The rat work at PMID 14554208 measured tendon load to failure, not fat or muscle.

Q: What is worth asking a doctor before considering anything in this category?

What will be measured and how often, what the baseline looks like on a scan rather than a scale, whether glucose handling should be checked given that the trial at PMID 18981485 recorded fasting glucose rising and insulin sensitivity falling, and whether an existing condition or medication changes the picture. Anyone already losing weight on an incretin drug has a further conversation to have, since PMID 41877354 and PMID 41996180 both measured lean tissue coming off alongside fat.

Q: How does vial quality change the way these figures should be read?

A trial result describes a defined compound at a known purity, made to a specification. A vial bought outside a pharmacy supply chain is a different object until a batch certificate ties it to an identity and a purity figure, with a testing lab and batch number that can be traced. Reconstituted peptide also degrades faster in Vietnamese ambient heat than in the climates most storage guidance assumes, and degradation is not visible in the vial.

Searches for this phrase return trial findings and product copy side by side, and the two are hard to separate once a number is quoted away from its study. Each entry below is one study, with who was enrolled, what was measured, what the paper reported, how it was designed and its PubMed ID, so any figure can be checked against its source. A result recorded in patients treated for a medical condition is reported here as exactly that.

The trial record

Each row is one study. Read the population column before the result column, because it decides how far a number travels.

Compound	Population (n)	What was measured	Result	Design	PMID
Tesamorelin	412 adults with HIV and abdominal fat accumulation	Visceral adipose tissue on CT at 26 weeks (primary)	Fell 15.2% and rose 5.0% on placebo; triglycerides -50 mg/dL against +9 mg/dL (P<0.001)	Randomised, placebo-controlled, multicentre	18057338
Tesamorelin	Five randomised trials pooled, adults with HIV-associated lipodystrophy	Lean body mass, visceral adipose tissue, trunk fat, limb fat	Lean body mass +1.42 kg (95% CI 1.13 to 1.71); visceral adipose tissue -27.71 cm2; trunk fat -1.18 kg	Meta-analysis of randomised trials	41545261
Growth hormone-releasing hormone	31 HIV-infected men aged 18 to 60 with lipodystrophy	Lean body mass and trunk fat by DXA at 12 weeks	Lean body mass +0.9 kg against -0.3 kg on placebo (P=.04); trunk fat -0.4 kg against +0.2 kg (P=.03)	Randomised, double-blind, placebo-controlled	15249570
MK-677 (ibutamoren)	65 healthy adults aged 60 to 81	Fat-free mass and abdominal visceral fat at 12 months (co-primary)	Fat-free mass +1.1 kg against -0.5 kg on placebo (P<0.001); no significant change in visceral or total fat; limb fat +1.1 kg against +0.24 kg	Two-year randomised, double-blind, placebo-controlled	18981485
Growth hormone	18 study populations of community-dwelling adults, mean age 69	Fat mass, lean body mass and weight against no growth hormone	Fat mass -2.1 kg (95% CI -2.8 to -1.35); lean body mass +2.1 kg (1.3 to 2.9); weight +0.1 kg (P=0.87)	Systematic review of randomised trials	17227934
Bimagrumab (anti-activin receptor antibody)	75 adults with type 2 diabetes and BMI 28 to 40; 58 completed	Total body fat mass at week 48 (primary); lean mass and waist	Fat mass -7.5 kg against -0.18 kg on placebo; lean mass +1.70 kg against -0.4 kg; waist -9.0 cm (all P<.001)	Phase 2 randomised, double-masked, intravenous	33439265
Tirzepatide	160 SURMOUNT-1 participants with obesity or overweight, 73% female	DXA fat mass and lean mass to week 72	Weight -21.3%, fat -33.9%, lean -10.9% against -5.3%, -8.2% and -2.6% on placebo; about 75% of loss was fat in both arms	DXA substudy of a randomised phase 3 trial	39996356
Semaglutide, tirzepatide, liraglutide	20 randomised trials, 15,782 adults with overweight or obesity	Share of total weight lost that was lean mass, by DXA or MRI	Semaglutide 35.2% (95% CI 31.5 to 38.9), tirzepatide 25.4%, liraglutide 26.8%, lifestyle 26.2% (p=0.42), lifestyle plus resistance training 17.5% (14.2 to 20.8)	Meta-analysis of randomised trials	41877354
Liraglutide, semaglutide, tirzepatide, dulaglutide	35 primary studies, median 78 participants, median 26 weeks	Share of weight loss in muscle-related indices, by BIA, DXA, CT or MRI	Median 28.3% (IQR 15.9 to 39.9); about 29% in BIA or DXA studies and about 25.3% in CT or MRI studies	Systematic review	41996180
Dietary protein with resistance and interval training	40 young men in a roughly 40% energy deficit, 4 weeks	Lean body mass and fat mass by a four-compartment model	Higher-protein arm +1.2 kg lean and -4.8 kg fat; lower-protein arm +0.1 kg lean and -3.5 kg fat (P<0.05)	Single-blind randomised parallel-group	26817506
Protein supplementation with resistance training	49 studies, 1,863 healthy adults	Fat-free mass, one-repetition maximum, fibre cross-sectional area	Fat-free mass +0.30 kg (95% CI 0.09 to 0.52); no further gain above about 1.62 g per kg per day of total intake	Meta-analysis and meta-regression	28698222
Follistatin gene therapy	6 people with sporadic inclusion body myositis against 8 matched untreated	Six-minute walk distance, annualised	+56.0 m per year treated against -25.8 m per year untreated (p=0.01)	Open-label AAV gene therapy with a matched comparator	28279643
MOTS-c	Mice, high-fat-diet and ageing models	Insulin sensitivity, diet-induced obesity, AMPK signalling	Prevented age-dependent and diet-induced insulin resistance and diet-induced obesity	Animal and in vitro	25738459
BPC-157	Rats with a surgically transected Achilles tendon	Load to failure, Achilles functional index, histology	Faster tendon recovery than saline on biomechanical, functional and histological assessment over 14 days	Animal, controlled	14554208
AOD-9604 (hGH 176-191)	Obese Zucker rats, 19 days of daily oral dosing	Body weight gain and adipose lipolytic activity	Weight gain of 15.8 g against 35.6 g in controls, with raised adipose lipolytic activity	Animal, controlled	11146367

Growth hormone axis studies

Tesamorelin and the growth hormone-releasing hormone used in PMID 15249570 act upstream of growth hormone rather than replacing it, and both were trialled in adults being treated for antiretroviral-associated fat accumulation. One measurement caveat travels with those rows: lean body mass by absorptiometry counts body water as lean tissue, and soft tissue edema occurred significantly more often on growth hormone in the review at PMID 17227934.

The dose administered in the 2007 New England Journal of Medicine trial of tesamorelin (PMID 18057338) was:

2 mg by subcutaneous injection, once daily, for 26 weeks.

Disclaimer: a published trial parameter, given to patients with HIV-associated abdominal fat accumulation under medical supervision, quoted so that row can be read in context. It is not a recommendation, a starting point or a protocol for anyone.

MK-677 reaches the same axis through a different receptor, mimicking ghrelin to raise pulsatile growth hormone secretion by mouth. Its trial named fat-free mass and abdominal visceral fat as co-primary end points at 12 months and recorded no change in isokinetic strength or function, with the authors stating that the study lacked power to evaluate functional end points (PMID 18981485). A 2026 review in Frontiers in Endocrinology sets the published clinical evidence for growth hormone axis performance peptides against the protocols people follow when self-administering them (PMID 42395176).

The dose administered in the 2008 Annals of Internal Medicine trial of MK-677 (PMID 18981485) was:

25 mg orally, once daily, with body composition end points assessed after 12 months.

Disclaimer: a trial parameter from a supervised study in adults aged 60 to 81, quoted so the fat-free mass and glucose figures have context. It is not advice and not a protocol.

Compound detail sits on the MK-677 guide and the tesamorelin profile, with the secretagogue mechanism in HGH peptides explained.

Weight loss drugs and lean tissue

The incretin rows come from trials designed around weight, with body composition read out afterwards. PMID 41877354 and PMID 41996180 each reported comparator arms as well as drug arms. In PMID 41877354 the lifestyle-only arm and the drug arms were statistically comparable on the share of weight lost as lean mass (p = 0.42), and the arm that added resistance training reported a lower share than either. In PMID 41996180 muscle-related losses exceeded the prespecified benchmarks in about two thirds of incretin arms and in nearly half of the non-drug arms that produced weight loss.

Compound detail sits on the semaglutide and tirzepatide profiles, with the head-to-head reading in tirzepatide versus semaglutide.

Activin and myostatin pathway

Bimagrumab is a monoclonal antibody given by intravenous infusion, not a peptide, and its phase 2 trial measured fat mass and lean mass over the same 48 weeks in the same participants (PMID 33439265). Follistatin enters through a gene therapy trial that put an AAV-carried isoform directly into quadriceps muscle and measured walking distance rather than body composition (PMID 28279643). Neither describes an injected peptide bought as a vial.

Animal studies

The BPC-157 entry is a rat Achilles tendon transection model in which healing was assessed biomechanically, functionally, microscopically and macroscopically (PMID 14554208), so its endpoint is tendon repair rather than fat or muscle. AOD-9604 enters through obese Zucker rats given a daily oral dose for 19 days (PMID 11146367). MOTS-c enters through the paper that identified it, a 16 amino acid mitochondrially encoded peptide acting largely on skeletal muscle through AMPK (PMID 25738459). Species, route and dose scaling sit between those findings and a human conclusion.

Compound profiles are on the BPC-157 and MOTS-c pages, and the route question is covered in oral versus injectable peptides.

Training and protein

The 4-week trial at PMID 26817506 used no drug and a four-compartment model rather than a single scan, which measures body water separately from lean tissue. The meta-analysis at PMID 28698222 places a ceiling on the protein side: across 49 studies, supplementation stopped adding to fat-free mass beyond a total intake of about 1.62 g per kg per day, with the effect smaller as age rose and larger in participants who already trained.

The intakes assigned in the 2016 American Journal of Clinical Nutrition trial (PMID 26817506) were:

2.4 g of protein per kg of body weight per day against 1.2 g per kg per day, for 4 weeks, on a diet roughly 40% below requirements.

Disclaimer: intakes assigned in a supervised trial of young men training six days a week, quoted so that row has context. Protein needs vary with kidney function, age, training load and total intake, so this is not a target for any individual.

Practical detail on intake sits in the protein guide, and the fat side is covered in how to lose belly fat.

Quality, heat and legality

Trial figures describe a compound made to a specification. Applying one to a vial bought outside a pharmacy supply chain assumes an identity and purity that only a traceable batch certificate can support, and the method for reading one is in how to verify a COA. Heat is the second local variable, since powder and reconstituted vials both degrade faster in Vietnamese ambient conditions than in the climates most storage guidance was written for, covered in the heat and storage guide.

Legal status is a separate question, set out in peptide legality in Vietnam, and the neighbouring category is compared in SARMs versus peptides.

How the searches were run

Each entry records a query as submitted, the index and the date. A result here is a fact about that query: a paper indexed only under a MeSH entry term will not surface in a plain name search, which is why synonyms and MeSH terms are included.

("BPC 157"[tiab] OR "BPC-157"[tiab] OR "pentadecapeptide BPC"[tiab]) AND ("body composition"[tiab] OR "lean mass"[tiab] OR "muscle growth"[tiab] OR "fat loss"[tiab] OR hypertrophy[tiab])PubMed, 9 August 2026: 1 record, a rat model of pulmonary hypertension (PMID 34356886).
("thymosin beta-4"[tiab] OR "TB-500"[tiab] OR TB500[tiab] OR "Thymosin beta 4"[MeSH Terms]) AND ("body composition"[tiab] OR "lean mass"[tiab] OR "fat mass"[tiab] OR hypertrophy[tiab])PubMed, 9 August 2026: 6 records.
AOD9604[tiab] OR "AOD-9604"[tiab] OR "hGH 176-191"[tiab] OR "growth hormone fragment 176-191"[tiab]PubMed, 9 August 2026: 22 records, one of which is the Zucker rat study in the table.
(sermorelin[tiab] OR "GHRH(1-29)"[tiab] OR "Sermorelin"[MeSH Terms] OR "growth hormone-releasing hormone"[tiab]) AND ("lean body mass"[tiab] OR "fat mass"[tiab] OR "body composition"[tiab]) AND randomized controlled trial[pt]PubMed, 9 August 2026: 6 records, one of which is PMID 15249570 in the table.
("MOTS-c"[tiab] OR "MOTSc"[tiab]) AND ("body composition"[tiab] OR "lean mass"[tiab] OR "fat mass"[tiab]) AND humans[mh]PubMed, 9 August 2026: 4 records, three measuring circulating MOTS-c in people and one a rodent study of adipose homeostasis.
("CJC-1295"[tiab] OR CJC1295[tiab] OR ipamorelin[tiab] OR "Ipamorelin"[Supplementary Concept]) AND ("body composition"[tiab] OR "lean mass"[tiab] OR "fat mass"[tiab] OR hypertrophy[tiab])PubMed, 9 August 2026: 3 records, a clinical review of secretagogues in hypogonadal men, a CJC-1295 study in knockout mice, and a laboratory study of secretagogues and adiposity.

Frequently Asked Questions

Why do these trials report lean body mass rather than muscle mass?

Because lean body mass is what the scanner measures. Dual-energy X-ray absorptiometry sorts tissue into fat, bone mineral and a lean soft tissue compartment, and that compartment holds body water, organs and connective tissue as well as muscle, so fluid shifts land in the same column as muscle. The systematic review at PMID 17227934 found people treated with growth hormone significantly more likely to experience soft tissue edema, which is why the design column matters when reading a lean mass figure from that drug class.

Do results in patients treated for HIV-associated fat accumulation apply to a healthy trained adult?

They describe the group that was enrolled. The trials at PMID 18057338 and PMID 15249570, and the pooled analysis at PMID 41545261, all enrolled adults with antiretroviral-associated changes in fat distribution, and they were enrolled because of that condition. Baseline visceral fat, hormone status and the reason for treating all differ in a healthy trained adult, so the size of any effect in that group is not settled by those papers. A diagnosed condition affecting body composition is managed with a doctor, not from a table.

Why do two studies of the same drug report different numbers?