In this article

What is IGF-1?

IGF-1 (Insulin-like Growth Factor 1) is a hormone produced mainly by the liver in response to growth hormone signaling from the pituitary gland. Once released into the bloodstream, it acts on nearly every tissue in the body, driving cell growth, tissue repair, and metabolic regulation. It’s especially important for muscle protein synthesis, bone density, and the general maintenance of lean tissue as we age.

Levels of IGF-1 rise through childhood and adolescence, peak in early adulthood, and then decline steadily from there. That decline is a normal part of aging, but the rate and degree vary a lot from person to person, shaped by nutrition, sleep, exercise, and body composition. Abnormally low levels can point to growth hormone deficiency, malnutrition, or liver dysfunction, since the liver is where most of the production happens. Abnormally high levels can be associated with growth hormone excess or, in some research contexts, have been studied in relation to other long-term health considerations. A single number rarely tells the full story on its own, which is why we treat IGF-1 as one input among many rather than a standalone verdict.

Why it’s especially relevant right now

IGF-1 has become a more interesting marker to watch as GLP adoption has climbed. Rapid weight loss changes the hormonal environment in ways that don’t show up on a scale. Appetite suppression can mean lower overall caloric and protein intake, and lower protein intake is one of the biggest levers affecting both IGF-1 production and muscle retention. That connection matters because muscle isn’t just about strength. Lean mass plays a direct role in metabolic rate, glucose regulation, and how well the body holds onto its progress.

This ties directly into one of the most consistent findings from recent industry research on GLP users: most people losing weight on these medications are losing some amount of muscle along with fat, and most aren’t tracking it. Cardio activity tends to increase, but strength training, the single best lever for preserving lean mass, is often the most neglected part of the routine. IGF-1 sits right at the intersection of that story. It’s a hormonal signal that reflects whether the body is in a state that supports muscle maintenance or one that’s working against it.

What this means in practice

Tracking IGF-1 alongside body composition gives a more complete picture than either one alone. Body composition scanning shows what’s changing (the ratio of fat loss to muscle loss). IGF-1 offers a window into part of why that’s happening on a hormonal level, and whether protein intake and resistance training are keeping pace with the rate of weight loss. Watched over time, a downward trend paired with disproportionate muscle loss is a signal worth acting on, whether that means adjusting protein intake, adding resistance training, or flagging it for a conversation with a prescriber.

That’s the same logic behind pairing IGF-1 with metabolic, thyroid, and nutritional markers in a single panel rather than testing it in isolation. Hormones don’t operate independently, and neither does weight loss. A marker like IGF-1 is far more useful in context than as a standalone data point.

Getting the full picture

We offer IGF-1 as an optional upgrade alongside our core panels, collected through our EasyDraw arm-based draw and processed at a CLIA-certified, CAP-accredited lab, so it’s easy to add to your existing testing routine without a separate blood draw or lab visit.

Want to see where your IGF-1 stands? Add it to your next panel and track it alongside your other biomarkers over time.

References

  1. MedlinePlus. “IGF-1 (Insulin-like Growth Factor 1) Test.” National Library of Medicine. https://medlineplus.gov/lab-tests/igf-1-insulin-like-growth-factor-1-test/
  2. Kouvari M, et al. “About 31% of weight lost by adults during GLP-1 therapy comes from lean mass.” Healio, reporting on a systematic review and meta-analysis of 9 RCTs. https://www.healio.com/news/endocrinology/20250313/about-31-of-weight-lost-by-adults-during-glp1-therapy-comes-from-lean-mass
  3. “Greater lean-body-mass decline with tirzepatide than semaglutide in routine care, revealed by body-composition digital phenotyping.” medRxiv preprint, nference, 2026. https://www.medrxiv.org/content/10.64898/2026.04.11.26350687.full.pdf