Evidence & Research Status
This guide maps how GLP-1/GIP/amylin-class compounds relate to growth-hormone-axis, myostatin-pathway, and mitochondrial-support peptides in the published research literature – specifically why muscle retention has become a major research question in GLP-1 studies, and how researchers are studying these categories in combination. This is an overview of published research, not a protocol recommendation.
Nature Medicine – BELIEVE Trial (bimagrumab + semaglutide, phase 2)
MDPI Metabolites – Lean Mass Preservation in GLP-1-Based Obesity Treatment
ACE Fitness – GLP-1s and Lean Mass: What the Research Shows
Evidence Level reflects the general state of published research for each compound category and is not a claim about the safety, efficacy, or approval status of any product sold on this site. All compounds are offered strictly for research use.
A question we hear constantly from researchers working with our GLP-1 compounds: how does Tirzepatide relate to the adjunct peptides in the rest of the catalog – the growth-hormone peptides, the NAD+, the recovery compounds? Is there a reason published research studies GLP-1s alongside these adjunct peptides, or are they unrelated categories that happen to share a website? This guide answers that directly, compound class by compound class, using published trial data rather than marketing language.
The Core Question: What Happens to Lean Mass During GLP-1 Research
Published trials consistently show that lean (fat-free) body mass accounts for roughly 25-39% of total weight lost on semaglutide and tirzepatide, a pattern reported across the STEP and SURMOUNT trial programs and summarized in a 2026 MDPI review of musculoskeletal preservation strategies in GLP-1-based obesity research. That proportion is similar to what’s seen with diet-only weight loss, but because total weight loss is larger with GLP-1 therapy, the absolute amount of lean mass lost is often greater in real terms.
This is precisely the question the phase 2 BELIEVE trial (published in Nature Medicine, 2026) was designed to test. Researchers combined semaglutide with bimagrumab, an antibody that blocks activin type II receptors – the same signaling pathway myostatin uses to limit muscle growth – and compared it against either compound alone. At 72 weeks, the combination arm lost 22.1% of body weight, with 92.8% of that loss coming from fat mass. Semaglutide alone reduced lean mass by 7.4% over the trial; adding the activin-pathway antibody limited that lean mass loss to 2.9%. Bimagrumab itself is a monoclonal antibody, not a peptide, and is not sold on this site – but the trial is the clearest published proof of concept that pairing a GLP-1 with a muscle-preservation-focused compound changes the composition of weight lost, which is exactly why myostatin- and activin-pathway peptides have become an active research area alongside GLP-1 study.
GLP-1, GIP & Amylin-Class Compounds We Carry
These are the incretin-mimetic and amylin-analogue compounds in our catalog – the incretin-class compounds studied in the trials above.
| Compound | Receptor Target | Research Notes |
|---|---|---|
| Semaglutide | GLP-1 (mono-agonist) | Most extensively studied compound in the class; FDA-approved as Ozempic/Wegovy for prescription human use. See our full research guide. |
| Tirzepatide | Dual GIP/GLP-1 agonist | FDA-approved as Mounjaro/Zepbound; SURMOUNT program reports larger average weight loss than single-agonist GLP-1s. See our full research guide. |
| Retatrutide | Triple GIP/GLP-1/glucagon agonist | Investigational triple-agonist; not yet FDA-approved. Early trial data reports the largest average weight loss of the three GLP-1-class compounds studied to date. |
| Cagrilintide | Amylin receptor agonist | Different receptor entirely – studied in combination with semaglutide (as “CagriSema”) for additive appetite-regulation effects. |
| Combined GIP/GLP-1/glucagon + amylin | ||
| Orforglipron | GLP-1 (oral, non-peptide) | An oral small-molecule GLP-1 agonist rather than an injectable peptide – relevant for researchers comparing delivery routes. |
| Tesofensine | Triple monoamine reuptake inhibitor | A structurally unrelated appetite-regulation compound, mechanistically distinct from the incretin class above. |
Growth-Hormone-Axis & Myostatin-Pathway Peptides
This is the category most directly relevant to the lean-mass question above – compounds studied for their role in the GH/IGF-1 axis or in myostatin/activin signaling, the same pathway the BELIEVE trial targeted.
| Compound | Mechanism | Research Notes |
|---|---|---|
| CJC-1295 (with DAC) | GHRH analogue | Stimulates endogenous GH release; often studied alongside a GHRP like ipamorelin. DAC extends half-life via albumin binding (see our CJC-1295 comparison). |
| Ipamorelin | Ghrelin receptor / GHRP | Selective GH secretagogue, frequently paired with CJC-1295 in published studies. |
| Sermorelin | GHRH analogue (shorter fragment) | Earlier-generation GHRH analogue; shorter acting than CJC-1295. |
| Tesamorelin | GHRH analogue | The one compound in this table with an FDA-approved indication (Egrifta, for HIV-associated lipodystrophy) – the most clinically studied GHRH analogue for visceral fat reduction specifically. |
| HGH | Direct GH replacement | Recombinant growth hormone itself, rather than a secretagogue that stimulates the pituitary to release it. |
| IGF-1 LR3 | IGF-1 receptor (long-acting analogue) | Downstream of GH signaling; the LR3 modification extends half-life versus native IGF-1. |
| Follistatin 344 | Myostatin/activin binding protein | Binds and inhibits myostatin and activin – the same signaling family bimagrumab blocks in the BELIEVE trial above, though follistatin and bimagrumab are structurally distinct molecules acting at different points in the pathway. |
One nuance worth flagging for research accuracy: growth hormone signaling and insulin sensitivity have a complicated relationship in the literature – GH can transiently reduce insulin sensitivity even as it supports lean mass, which is itself an active area of study. This is a good example of why “muscle support” and “insulin sensitivity” aren’t always pulling in the same direction mechanistically, even within a single compound class.
Energy & Mitochondrial Support Compounds
Separate from body composition, several compounds in the catalog are studied specifically for cellular energy metabolism – relevant to researchers looking at the fatigue and energy-level side effects sometimes reported during aggressive weight-loss research.
| Compound | Mechanism | Research Notes |
|---|---|---|
| NAD+ | Redox coenzyme / sirtuin & PARP substrate | Central to mitochondrial energy metabolism; see our NAD+ research guide. |
| MOTS-c | Mitochondrial-derived peptide | Studied for its role in metabolic homeostasis and exercise-mimetic effects at the cellular level. |
| SS-31 (Elamipretide) | Mitochondrial membrane stabilizer | Studied for mitochondrial function preservation under metabolic stress. |
Where Insulin Sensitivity Fits
Insulin sensitivity isn’t a separate compound category in our catalog so much as a mechanism built into the GLP-1/GIP class itself. GLP-1 and GIP receptor activation both enhance glucose-dependent insulin secretion, which is why semaglutide, tirzepatide, and retatrutide are studied as much for glycemic outcomes as for weight loss – tirzepatide’s dual GIP/GLP-1 action in particular is reported in the SURPASS trial program to produce larger reductions in HbA1c than single-receptor agonists. This is worth knowing precisely because it means the weight-loss and insulin-sensitivity research questions largely overlap for this compound class, whereas the muscle-preservation question above is a genuinely separate mechanism layered on top.
How Researchers Study These Categories Together
Putting the sections above side by side, the published research pattern looks like this: GLP-1/GIP/amylin compounds are studied for fat loss and glycemic control; myostatin/activin-pathway and GH-axis compounds are studied alongside them specifically to address the lean-mass loss that GLP-1 research consistently reports; and mitochondrial-support compounds are studied separately for the cellular energy question that can accompany rapid weight change. The BELIEVE trial is the clearest published example of two of these categories being combined in a controlled trial and measured together – it is not, however, a study of any specific product sold on this site, and no combination of our catalog compounds has been studied in a trial of that design. Researchers designing their own comparative work should treat each compound class on its own evidence merits rather than assuming results transfer from one compound to a mechanistically related one.
FAQ
Does Portal to Wellness recommend combining these compounds?
No. We don’t publish dosing instructions, stacking protocols, or usage recommendations for human consumption. This article summarizes published research on how these compound classes relate to each other; it is not a protocol.
Is Follistatin 344 the same as the bimagrumab used in the BELIEVE trial?
No. They act on the same myostatin/activin signaling family but are structurally different molecules studied independently. No published trial has tested Follistatin 344 in combination with a GLP-1 compound the way BELIEVE tested bimagrumab with semaglutide.
Why does the article mention FDA-approved drugs like Ozempic and Egrifta?
To describe the published clinical evidence base accurately. Every compound sold on this site is a separate Research Use Only (RUO) product, not the branded pharmaceutical, and is not intended for human or veterinary use.
Research Guides
Portal to Wellness does not publish dosing instructions, treatment schedules, or stacking protocols for human use, and nothing in this article should be read as one. For how the published literature structures related compound categories, see our Incretin & Amylin Receptor Research Compounds and GLP-1 & Metabolic Research Guide.