Effects of Ketosis on Brain Function in Patients With T1DM

Inclusion Criteria: * Males and females with T1D for at least 1 year * Age 18 to 40 years * Tanner stage ≥ IV * BMI 18.5-35 kg/m2 * Stable glycemic control (HbA1c 6.5-9%) * Use of a continuous glucose monitor (CGM) * Use of an insulin pump * Attendance of at least 1 diabetes care visit over the past 12 months (including virtual) Exclusion Criteria: * Ketoacidosis or severe hypoglycemia with seizure or coma in the past 6 months * Dietary restrictions or intolerances that are incompatible with the planned food deliveries, e.g. celiac disease, gastroparesis, certain food allergies * Following a weight-loss or otherwise restrictive diet * Vigorous exercise \>2 hours on \>3 days a week * History of an eating disorder or at risk for eating disorder, assessed by the Eating Disorders Diagnostic Scale (EDDS) * Major medical illness or use of medications other than insulin and metformin that could interfere with metabolic or glycemic variables * Significant psychiatric illness * Smoking, use of recreational drugs, or excessive alcohol consumption * Pregnancy or breastfeeding * Anemia * For participants who undergo MRI: 1. Standard MRI exclusion criteria 2. Irregular menses 3. Use of psychotropic medication other than SSRIs or other mild antidepressant or anxiety medications (unless these medications are safe to be held for several days to allow for the acquisition of MRI data).