Ketogenic Diet for Adults with Type 1 Diabetes

Inclusion Criteria: * Age ≥18 and ≤65 years * T1D diagnosed \>1 year prior to screening * HbA1c 7.0%-9.0% * Stable insulin delivery method for the past 30 days * Ability to read all device instructions and insulin pump settings * eGFR ≥60 mL/min/1.73 m2 * Use of an insulin pump or insulin delivery by multiple daily injections * Use of personal CGM for at least 12 weeks and willing to change to Dexcom CGM for the duration of the study, if using a different sensor, to reduce variability in glucose values associated with different CGM products * Use of cellular phone with data capability for wireless connectivity to the CGM system. Exclusion Criteria: * Body mass index \<20.0 or \>34.9 kg/m2 * Severe gastroparesis or history of bariatric surgery * Diabetes-related hospitalization (including for diabetic ketoacidosis or severe hypoglycemia) within 12 months of screening * Poorly controlled hypertension (SBP ≥160 mmHg or DBP ≥100 mmHg) * Taking diabetes medications, other than insulin (particularly SGLT2 inhibitors, which are associated with an increased risk of euglycemic DKA) * Structured exercise \>210 minutes per week * Pregnant, lactating, not using effective birth control if premenopausal, or planning to become pregnant within the 6-month study period * Unstable weight (\>4% change in the last 2 months) * Significant organ system dysfunction (e.g., severe pulmonary, renal, hepatic, or cardiovascular disease) * Anemia (Hgb \<10 g/dL) * Major psychiatric illness * Active tobacco use (\>8 cigarettes/day) or illegal drug use * Regular alcohol consumption (\>10 standard drinks per week) * Use of medications known to affect the study outcome measures or increase the risk of study procedures that cannot be temporarily discontinued for this study * Familial hypercholesterolemia * Active eating disorder * Dietary restrictions incompatible with a very-low-carbohydrate KD, vegan diet, vegetarian diet, severe lactose intolerance, severe aversion/sensitivity to eggs, fish, nuts, wheat, or soy, and any anaphylactic food allergy * Already consuming a low-carbohydrate (\<130 g/day) diet * Persons who are not able to grant voluntary informed consent * Persons who are unable or unwilling to follow the study protocol or who, for any reason, the research team considers an inappropriate candidate for the study.