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.
