The headline is broadly defensible, but the qualifications matter. Effect sizes vary by population, the strongest claims rest on shorter trials, and credible voices push back on how it's typically framed.
And there's actually an IGF-1 and IGF-2. But I think about it in terms of endocrine IGF-1, mostly IGF-1 that's synthesized in the liver and released in the liver versus IGF-1 that's released classically. An example of this would be your IGF-1 levels increase after resistance training or exercise. And that's more of like paracrine or autocrine, and they have more local action.
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Bookmarking — the dossier-vs-overview split is the right call. Most of the time I want overview; sometimes I want receipts.
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So that IGF-1, it's pretty well studied that if you just give people IGF-1, it's not going to, at physiologic levels, it's not going to improve their body composition. However, that IGF-1 that's autocrine and paracrine just working in those local tissues and muscles is likely part of the reason why you get a improved body composition response after exercise.
I think about it in terms of endocrine IGF-1, mostly IGF-1 that's uh synthesized in the liver and released in the liver versus IGF-1 that's released um classically an example of this would be your IGF-1 levels increase after resistance training or exercise. And that's more of like paracrine or autocrine and they have more local action. So that IGF-1 it's pretty well studied that if you just give people IGF-1 it's not going to at uh physiologic levels it's not going to improve their body composition. However that IGF-1 that's autocrine and paracrine just working in those local tissues and muscles is likely part of the reason why you get a improved body composition response after exercise.
the i the one way we explain this to patients is igf-1 is the integral of growth hormone so if you want to get a sense of how much growth hormone is floating around to a first order approximation you get a sense of how much igf somebody has you get a sense of how much igf is being produced by the liver and to your point that's all systemic or what we would really think of as an endogen an endocrine igf
And by the way, administering IGF systemically is a lousy way to get it to the muscle, right? Like it's you want to think of it almost as a paracrine thing, right? Where it has to be delivered into the muscle.