There was a neuropharmacologist at MIT, named Richard Wurtman, [now retired]who did a lot of animal studies on dietary protein and its' direct effect on neurotransmitter levels in the brain. He was somewhat controversial about 30 years ago when I first heard of him. He is married to a nutritionist, Judith Wurtman. Richard was supposed to have come up with a diet for Parkinsons, based on a protein/carb ratio of 1:5 if I recall correctly. He didn't recommend low protein diets, or restricting protein to just the evening meal. I see references to a book published by him on the topic, but I cant locate it anywhere. The nutritionist for the National Parkinson Foundation site, Kathrynne Holden, recommends a ratio of protein/carb of 1:7, which seems high in carbs to me. What and when to eat is a major problem for some of us using frequent doses of sinemet. Also, unexplained weight loss is major problem for some PD patients, mostly women, as I recall.
It would be nice is someone (?) would coordinate studies on this mundane issue and come up with some real information that helps people.