The main objective of this clinical trial is to study the metabolic effects of intravenous infusion of the ketone body, 3-hydroxybutyrate (3-OHB), in patients with type 1 diabetes and healthy control subjects. Moreover, the investigators plan to examine regulatory mechanisms of 3-OHB that may be related to diabetic ketoacidosis.

The hypotheses are:

1. 3-OHB related inhibition of lipolysis is impaired in patients with type 1 diabetes.
2. Intravenous infusion of 3-OHB affects signaling pathways involved in the metabolic regulation in patients with type 1 diabetes and healthy controls.
3. 3-OHB infusion improves cardiac function in patients with type 1 diabetes and healthy controls.

The effects of 3-OHB will be investigated by isotopic tracers examinations, fat and muscle biopsies and blood samples. To evaluate effects on cardiac function echocardiography will be performed.

Patients with type 1 diabetes:

Inclusion Criteria:

• Type 1 diabetes diagnosis
• C-peptide negative
• 19 < BMI < 26
• written consent

Exclusion Criteria:

• Severe comorbidity
• Regular medication apart from insulin (except over-the-counter medicines)
• Use of long acting insulin analogues, that work > 24 hours, e.g. Tresiba
• PI finds the patient not fit (e.g. mental illness, too nervous, unacceptable screening blood tests or other).

Healthy control subjects:

Inclusion Criteria:

• 19 < BMI < 26
• written consent

Exclusion Criteria:

• Chronic disease
• Regular medication (except over-the-counter medicines)
• PI finds the patient not fit (e.g. mental illness, too nervous, unacceptable screening blood tests or other).