REMAIN-1

1. Participant-provided, written informed consent to participate in the study in accordance with local regulations

2. Adult participants aged 21-70 years, inclusive

3. Prior to tirzepatide therapy, have a BMI of ≥ 30 kg/m2 (obesity) and ≤ 45 kg/m2.

4. Have achieved at least 15% weight loss on tirzepatide therapy at Visit 7 (Participants in Stage 1, who enter the study on tirzepatide, must have a documented pre-tirzepatide weight confirming they have lost at least 15% body weight on tirzepatide)

5. Have a history of at least 1 self-reported, unsuccessful, dietary effort to lose body weight

6. All female participants of childbearing potential must have a negative urine pregnancy test at screening and a negative urine pregnancy test at study visit 7 prior to study intervention. Postmenopausal females with amenorrhea for at least 2 years will be eligible if they are > 50 years of age. Postmenopausal females with amenorrhea for at least 2 years, who are ≤ 50 years, must also have documented serum follicle stimulating hormone levels > 35 mUI/mL

7. Able to walk at least 400 yards (roughly the distance of a track) and climb a flight of stairs without difficulty due to either musculoskeletal injuries/diseases or cardiopulmonary diseases

8. If sexually active, WOCBP must use one of the following birth control methods during the entire course of the study as specified:

1. Medical conditions that contraindicate the use of tirzepatide for weight management, as detailed in the tirzepatide prescribing information

2. BMI ≥ 40 kg/m2 at Visit 7

3. Females who are or intend to be pregnant or breastfeeding during the study

4. Known serious hypersensitivity to tirzepatide or any of the excipients in tirzepatide

5. History of infectious liver disease excluding recovered Hepatitis A infection

6. History of pancreatitis within 6 months of screening or any prior history of recurrent pancreatitis (i.e., two or more episodes of pancreatitis)

7. Potentially unreliable participants or those judged by the investigator to be unsuitable for the study

8. Unable or unwilling to follow the dietary restrictions specified by the clinical protocol

9. Known history of or active binge eating disorder or suspected binge eating disorder based on binge eating disorder assessment questionnaire

10. Known history of or active substance abuse including alcohol within the past 2 years that, in the opinion of the investigator, may preclude the participant from following the protocol and completing the study

11. Have history of use of marijuana or tetrahydrocannabinol (THC)-containing products within 3 months of screening or unwillingness to abstain from marijuana or THC-containing products use during the study

Diabetes-related conditions:

12. History of type 1 or type 2 diabetes (T2D) or screening values consistent with T2D, or history of any genetic form of diabetes

13. HbA1c > 6.5% or fasting glucose > 125 mg/dL consistent with T2D diagnosis according to the American Diabetes Association Standards of Care 2024 (Participants with isolated impaired fasting glucose [100 to 125 mg/dL, inclusive] may enroll in the study)

Laboratory values or clinical abnormalities:

14. Estimated glomerular filtration rate (eGFR) < 50 mL/min/1.73m2 at screening, as assessed by serum creatinine using the revised 2021 CKD-EPI equation

15. Serum calcitonin level ≥ 20 ng/L at screening if eGFR ≥ 60 mL/min/1.73m2 or serum calcitonin level ≥ 35 ng/L if eGFR < 60 mL/min/1.73m2

16. Fasting triglycerides > 500 mg/dL (> 5.6 mmol/L)

17. Abnormal liver function at screening, defined as any of the following: aspartate aminotransferase (AST) > 3X upper limit of the normal reference range (ULN), ALT > 3X ULN, or serum total bilirubin (TB) > 3X ULN

18. Values of systolic blood pressure (SBP) > 180 mmHg and/or diastolic blood pressure (DBP) > 110 mmHg

19. Any ECG or clinical laboratory abnormality which precludes safe involvement in the study in the opinion of the investigator Gastrointestinal

20. Known structural or functional disorder of the esophagus including any swallowing disorder, esophageal chest pain disorders, drug-refractory esophageal reflux symptoms, or active and uncontrolled GERD defined as Los Angeles Grade C or D esophagitis

21. Known structural or functional disorder of the stomach including active gastric ulcer, chronic gastritis, gastric varices, hiatal hernia (a large hiatal hernia or type II and higher paraoesophageal hernia), cancer, or any other disorder of the stomach

22. Clinically significant gastric-emptying abnormality (i.e., severe gastroparesis or gastric outlet obstruction) including a drug-induced abnormality or an abnormality experienced in a person who chronically takes drugs that directly affect GI motility such as metoclopromide or erythromycin

23. Previous GI surgery to treat the duodenum such as participants who have had a Billroth 2, Roux-en-Y gastric bypass, gastric sleeve, or other similar procedures or conditions

24. Known intestinal autoimmune disease including celiac disease, ulcerative colitis, Crohn's disease, lupus erythematosus, scleroderma, or other autoimmune or connective tissue disorder that affects the small intestine

25. Any history of or current other gastrointestinal condition which would preclude an upper GI endoscopy in the opinion of the investigator Cardiovascular

26. New York Heart Association Class III or IV heart failure within 3 months prior to screening

27. History of myocardial infarction or stroke within 6 months of screening

28. Unstable symptomatic or life-threatening arrhythmia or heart block. Note: Asymptomatic atrial fibrillation is not considered to be life-threatening, and patients with asymptomatic atrial fibrillation will be permitted to enter the study

Related to other concomitant conditions or medical history:

29. Any concurrent medical condition/disorder or clinically symptomatic cardiovascular, gastrointestinal (including pancreatitis), hematological, pulmonary, psychiatric, acute or chronic infectious disease, active retinal disease or other disorder which, in the investigator's opinion, would interfere with the participant's ability to complete the trial, require administration of treatment that could affect the interpretation of the efficacy or safety variables, or preclude safe involvement in the study

30. Self-reported weight gain > 5 kg within 3 months prior to screening

31. Family history or personal history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia (MEN) syndrome 2

32. History of an active or untreated malignancy or in remission from a clinically significant malignancy within the last 5 years (except for treated basal cell or squamous small cell carcinoma of the skin with no evidence of recurrence)

33. Secondary hypothyroidism or inadequately controlled primary hypothyroidism (thyroid-stimulating hormone [TSH] value outside the range of 0.4 to 6.0 mIU/L at screening)

34. Known thyroid cancer

35. Any uncontrolled endocrine condition such as multiple endocrine neoplasia

36. History of hemoglobinopathies (sickle cell anemia, thalassemia major, sideroblastic anemia) or other blood disorder

37. Any uncontrolled psychiatric disorder as assessed by the investigator

38. Any history of known genetic cause of obesity such as Prader-Willi Syndrome

39. History of COVID infection with prolonged symptoms for >4 weeks

Related to past or current medication use:

40. Administration of any investigational drug or participation in an interventional clinical research study within 30 days or 5 half-lives (whichever is longer) of screening visit

41. Use of any oral or injectable hypoglycemic agents or any other prescription or over-the-counter diabetes or weight loss medications within 12 months prior to screening visit, (except in the case of tirzepatide use in the stage 1 training arm of the study only)

42. Use of any other medications known to cause weight gain or weight loss in the opinion of the investigator

43. Receiving or have received, within 3 months prior to screening, chronic (>14 days) systemic (excluding inhaled, intraocular, intra-articular or topical) corticosteroid treatment or likely to require (in the opinion of the investigator) concurrent treatment with corticosteroids (excluding inhaled, intraocular, intra-articular or topical) during the course of the study

44. Treatment with antihypertensive or lipid-modifying medications which are not on a stable dose for at least 8 weeks prior to screening or anticipated changes or dose adjustments within 30 days following randomization into the study

45. Treatment with thyroid hormones which are not on a stable dose for at least 8 weeks prior to screening

46. Use of anticoagulation therapy (e.g., warfarin, coumadin, or novel oral anticoagulants [NOACs]) or anti-platelet agents (e.g., thienopyridine) which cannot be discontinued for 5-7 days or 2 drug half-lives before the procedure Other Exclusions

47. Investigator site personnel directly affiliated with this study and/or their immediate families. Immediate family is defined as a spouse, parent, child, or sibling, whether biological or legally adopted

48. Fractyl Health employees