Ketogenic Dietary Interventions in Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Inclusion Criteria: 1. Male and female ADPKD patients (based on genetics or imaging) ≥ 18 and ≤ 60 years 2. Indicators of rapid progression, either of the following: * Mayo class 1C-E (measured on screening) * Truncating PKD1 mutation, * onset of arterial hypertension/urological symptoms \< 35 years (patient history) * first- or second degree family members reaching ESRD at \< 60 years of age (patient history), * eGFR loss \> 2.5 ml/min/yr (as determined by at least 4 serum creatinine values within the last 4 years, with at least 6 months between each measurement ), * PROPKD score \> 6 (patient history) 3. CKD-stages G1-3 as determined by eGFR (CKD-EPI) 4. Written informed consent Exclusion Criteria: 1. Underweight or obese individuals ( as defined by BMI ≤ 18.5 kg/m2 or ≥ 35 kg/m2) 2. Exposure to a ketogenic diet (classical ketogenic diet or modified Atkins)for more than 2 weeks within the last 6 months 3. Participation in a weight-loss program within the last 6 months based on patient history 4. Vegetarian / vegan lifestyle based on patient history 5. Current treatment (or within the last 6 months) with tolvaptan or a somatostatin analogue based on patient history 6. Inability to give informed consent 7. Conditions prohibiting the use of a ketogenic diet (Liver damage, pancreatic failure, pyruvate-carboxylase deficiency, defects in fatty acid oxidation/gluconeogenesis/ketolysis/-neogenesis, hyperinsulinism) based on patient history 8. Diagnosis with any disorder of fatty acid metabolism including Carnitine deficiency (primary), Carnitine palmitoyltransferase (CPT) I or II deficiency, Carnitine translocase deficiency, Beta-oxidation defects, Medium-chain acyl dehydrogenase deficiency (MCAD), Long-chain acyl dehydrogenase deficiency (LCAD), Short-chain acyl dehydrogenase deficiency (SCAD), Long-chain 3-hydroxyacyl-CoA deficiency, Medium-chain 3-hydroxyacyl-CoA deficiency, Pyruvate carboxylase deficiency based on patient history 9. Eating disorder based on patient history (as defined by the assessment of the study physician) 10. Alcohol abuse based on patient history (as defined by the assessment of the study physician) 11. Type 1 diabetes mellitus based on patient history 12. Insulin-dependent type 2 diabetes mellitus based on patient history 13. Contraindication regarding the MRI exam e.g. non-MRI suitable implants ( including cardiac pacemakers, cochlear implants, aneurysm clip), claustrophobia, large tatoos with metal-containing ink 14. Patients, who may be at risk from the blood loss due to scheduled blood draws at the discretion of the physician 15. Pregnancy or breastfeeding 16. Absence of safe contraceptive measures or non-occurrence of menopause (in women) 17. Participation in other interventional trials 18. Persons who are in a dependency/employment relationship with the investigators 19. Accommodation in an institution by judicial or administrative order.