the 83% fat-mass figure from the SURMOUNT-1 DEXA substudy gets cited constantly in these threads, usually to reassure people that tirz is mostly burning fat, not muscle. fine. but that number says nothing about where the fat comes from, and the regional question is where things get interesting. the body comp data shows visceral adipose tissue (VAT) reducing disproportionately relative to total fat loss. that’s consistent with GIP and GLP-1 receptor distribution - VAT is metabolically active, has high receptor density, responds fast. the face is the opposite: almost entirely subcutaneous fat, superficial SAT, essentially no visceral component. so the mechanism that explains why abdominal girth drops fast on tirz doesn’t explain why the face goes early. two hypotheses I’ve seen floated: (1) superficial facial SAT has different sympathetic innervation and responds to the central appetite suppression signal differently than abdominal SAT, or (2) we just notice the face first because it’s visible at 2 feet, and the proportional loss is actually similar everywhere. I can’t separate those with any data I have. but the next time someone says “tirz targets visceral fat” as a comfort for facial volume loss, that’s not what the mechanism earns. visceral-preferential loss and facial subcutaneous sparing are two different claims.
The second hypothesis is doing more work than this post gives it credit for. The claim that “we just notice the face first” is not purely a perception artifact. There’s a decent body of literature on facial SAT having higher lipolytic sensitivity under caloric restriction generally, not specific to GLP-1 mechanisms, which would make the proportional loss genuinely higher, not just more visible. The VAT/facial SAT distinction you’re drawing is correct, but that doesn’t close the question of whether facial loss is actually disproportionate or just more salient.
the lipolytic sensitivity point is real, and it should have been in my OP. but citing “caloric restriction generally” to settle a question about a dual GIP/GLP-1 agonist is the gap. tirz isn’t just pharmacological caloric restriction; GIP receptor distribution adds a regional signal layered on top of the energy deficit. whether that amplifies or dampens the baseline facial SAT lipolytic response is exactly what stays open, and the CR literature doesn’t get you there.
“exactly what stays open” is fair, but the framing implies GIP receptor distribution is likely adding a regional signal rather than possibly adding one. the case for a GIP-specific effect on facial SAT is real as a hypothesis; what’s missing is any data suggesting facial adipocytes express GIPR at levels that would produce a detectable regional deviation from CR-predicted loss. without that, “dual agonist adds regional layer” and “dual agonist produces deeper deficit faster” are both consistent with what people are observing.