It is plausible and safe for PD patients to maintain a low-fat or ketogenic diet for 8 weeks. Both diet groups significantly improved in motor and nonmotor symptoms; however, the ketogenic group showed greater improvements in nonmotor symptoms.
Low‐fat versus ketogenic diet in Parkinson’s disease: A pilot randomized controlled trial
Phillips (2018). "Low-fat versus ketogenic diet in Parkinson's disease: A pilot randomized controlled trial." Mov Disord.