The duration of the study is 2 years. Participants will have 8 follow-up appointments in the first year and 4 visits in the second year. Most of these visits will last 1- 2 hours. A review of interval health, a physical exam, an assessment of diabetes control including recent 5 day insulin use and blood sugar (e.g., glucose) testing, and blood collection for laboratory testing will occur at each visit. Four of the visits will last about 5 hours, during which participants will undergo mixed-meal tolerance testing (MMTT). This involves drinking a special drink, similar to a milkshake, and having blood specimens taken over a 4-hour period.