This study will evaluate the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of single and multiple doses of ARO-ALK7 in adult volunteers with obesity without Type 2 Diabetes Mellitus (T2DM) (Part 1) and the safety, tolerability, and PD of multiple doses of ARO-ALK7 in adult volunteers with obesity with and without (T2DM) receiving tirzepatide (Part 2). In Part 1A eligible participants with obesity will be randomized to receive a single dose of ARO-ALK7 or placebo (PBO) administered on Day 1. In Part 1B, eligible participants with obesity will be randomized to receive two doses of ARO-ALK7 or PBO administered on Day 1 and Day 85. In Part 2, eligible subjects with obesity with and without (T2DM) will be randomized to combined therapy with tirzepatide and ARO-ALK7 (intervention arm) or tirzepatide and PBO (control arm). Tirzepatide will be initiated on Day 15 and administered by subcutaneous (SC) injection weekly. ARO-ALK7 or PBO will be administered by SC injection on Day 1 and Day 85. Subjects in both Part 1 and Part 2 will undergo adipose aspiration pre and post dose.