Two people start tirzepatide on the same day, at the same dose, with the same starting weight. Six months later, one has lost twice as much as the other. That gap gets waved away as “individual variation” more often than it gets explained. A Mayo Clinic study published this summer traced part of it to something measurable in the gut itself — and, just as usefully, showed why that measurement isn’t something you can walk into a clinic and order yet.
What the researchers did
The team, led by gastroenterologist Michael Camilleri, studied 483 adults with obesity. After a standardized breakfast, each participant had their stomach’s emptying rate tracked by scintigraphy — a scan that follows a small amount of radioactive tracer mixed into the meal — while rating their own hunger on a standard scale. Blood was drawn before eating and again at 15, 45, and 90 minutes after, measuring three hormones the gut releases in response to food: GLP-1, peptide YY, and cholecystokinin. All three normally rise after a meal and signal fullness back to the brain.
That combination of results sorted people into three physiologic groups. The one that stood out — about 27% of participants (130 of 483) — had a mismatch: their stomachs emptied quickly, but their post-meal GLP-1 and peptide YY levels stayed low instead of rising the way they should have. Tissue samples backed up the blood work, showing reduced expression of the genes that produce those hormones in the gut lining. Researchers labeled this the “discordant” or hungry-gut subtype — food moves through fast, and the hormonal brake that’s supposed to follow doesn’t engage the way it does in most people.
Of the study’s 483 participants, 61 had gone on to start tirzepatide after being phenotyped, which let the researchers look back at how each group actually responded. At six months, people in the discordant group had lost an average of 21.5% of their body weight, compared with 11.7% in the other groups — nearly double.
What this does not establish
The physiology is a genuinely interesting finding. The path from “genuinely interesting finding” to “something a clinic can use on you tomorrow” is longer than the headlines suggest.
The outcome data comes from a small, retrospective slice of the study. The 21.5%-versus-11.7% comparison is built on 61 people, not 483, and it wasn’t a randomized comparison — it’s a look back at whoever happened to start tirzepatide after being phenotyped for an unrelated reason. That’s a real signal worth following up on, not proof that phenotypes cause the size of the response. The study’s own authors were explicit that prospective studies — trials designed in advance to test this — are needed before it moves into routine practice.
The test itself isn’t available outside a research setting. Identifying the hungry-gut subtype required a nuclear medicine scan plus four timed blood draws measuring hormones that aren’t part of any standard metabolic panel. There is no version of this you can ask your provider to order this week. Until someone builds and validates a simpler proxy — a single blood marker, a questionnaire, a genetic test — the finding describes a mechanism, not a tool.
A subtype is not a guarantee, in either direction. Even inside the discordant group, 21.5% is an average, not a floor. Some people in that group presumably lost less than that, and some people outside it lost more. A physiologic explanation for why averages differ between groups still leaves plenty of individual variation unexplained within each group.
The part that applies to compounded medications
The tirzepatide used in this study was the manufactured branded product, taken as part of routine clinical care that the researchers then reviewed retrospectively. Compounded tirzepatide — the kind NoBsRx provides provider-guided access to — is prepared by state-licensed pharmacies for an individual patient. It is not an FDA-approved product, and it was not the subject of this study. Whether the same active compound behaves identically in a compounded preparation is a reasonable assumption to make about the drug’s pharmacology, but it is not something this study, or any study of the branded product, actually tested.
Why “I’m not losing as fast as my friend” has an answer worth chasing
The useful takeaway isn’t a home test you can’t get yet. It’s permission to stop treating a slower response as a personal failure or a sign the medication isn’t working. Some of that gap appears to be gut physiology that was set before you ever took a dose — not effort, not compliance, not a flaw in the plan.
What you can act on today is the review that happens before and during treatment. A licensed provider looking at your labs, your history, and how you’re actually responding a few months in is the mechanism that exists right now for catching a mismatch between expected and actual results — long before a bedside test for gut phenotypes ever reaches a clinic. If six months in you’re well outside what you expected, that’s a conversation about your case, specifically, not a number from someone else’s chart.
That kind of ongoing review is part of what each program’s published price covers, not an add-on you have to ask for. It’s also why we’re direct, in our FAQ and everywhere else, that treatment is never guaranteed — a study average, even a well-designed one, was never going to be a promise about your specific result.
This post is general information, not medical advice. It does not describe a guaranteed benefit or outcome of any NoBsRx program. Compounded medications are not FDA-approved. Treatment is never guaranteed — eligibility, diagnosis, and every treatment decision are made by independent licensed providers based on an individual clinical assessment, and availability varies by state. Do not start, stop, or change any medication based on an article. Talk to a licensed provider about what fits your own health history.