The study compared a ketogenic diet (KD), periodic water fasting (WF), and a control diet, over three months. The control diet called for ad libitum food intake, while the WF arm called for subjects to do a 3-day water fast on 3 consecutive days within the first 14 days of each month of the trial (with all other days allowing for ad libitum food intake). The KD called for a maximum of 30 grams of carbohydrate per day and a moderate to low protein intake (0.8 g/kg body weight), with encouragement to limit meat intake, but this was not required.
Subjects on the KD had blood beta-hydroxybutyrate (BHB) and breath acetone measurements to confirm adherence. Only 9 of 23 subjects (39%) met the pre-determined threshold of 0.8 mmol/L for BHB concentration at three study visits, but 18 of 23 (78%) had levels ≥ 0.6 mmol/L at two of three visits, and the same number showed higher BHB levels at all on-diet visits compared with their baseline, suggesting at least some level of adherence.
Compared to the control and WF, subjects following the KD exhibited greater decreases in body fat mass and total liver volume. Subjects on the KD also showed greater decreases in total kidney volume but this did not reach significance. Compared to the control and WE groups – and contrary to the typical progressive decline in kidney function in patients with ADPKD – subjects on the KD actually showed improved kidney function, as measured by creatinine-based eGFR and cystatin C-based eGFR.
While more research is needed, the authors of this study noted, “…considering the usually relentless progressive loss of kidney function in ADPKD and the fact that the only available treatment slows eGFR decline by 26%–30% only, the findings of our study would be of very high clinical relevance if a disease-modifying effect can be confirmed in the future.”
See this previous article for more on the effects of carbohydrate restriction on chronic kidney disease and general renal function.