You say carbs are bad for the brain. This is utter nonsense, the only nutrient the brain uses is glucose, which, last time I looked, is a carbohydrate. Fats can’t pass through the blood brain barrier.
If you have a look at wiki (I know) the ketogenic diet we have this:
"Normally, the carbohydrates contained in food are converted into glucose, which is then transported around the body and is particularly important in fueling brain-function. However, if there is very little carbohydrate in the diet, the liver converts fat into fatty acids and ketone bodies. The ketone bodies pass into the brain and replace glucose as an energy source"
I have seen at least one person on youtube who has experience much improvement in their parkinson's symptoms using a ketogenic diet. However I admit that going Keto is extremely difficult for most.
You say: Blood magnesium levels have nothing to do with glucose control.
From this site I read:
“Results from three very large studies indicate that people who consume a diet rich in magnesium have a lower risk of getting Type 2 diabetes.”
People with diabetes are more likely than those without to be low in magnesium. According to an article on About.com, “Elevated blood glucose levels increase the loss of magnesium in the urine, which in turn lowers blood levels of magnesium.” So getting enough magnesium is especially important in diabetes.
So I would say there is at least a chance that Magnesium has some impact on blood glucose.
And your improvement in symptoms can’t possibly be due to Mannitol - virtually none is absorbed by the intestine.
That is your opinion
This from the clinicrowd website on Mannitol and Parkinson's - dated October 2017:
We can however already hint that we already see some statistics, such as :
88% regained sense of smell
70% improved and maintained quality of life
64% improve their energy and vitality level
This correlates to my experience. The important thing to note is that Clinicrowd gain no benefit from this stance - they are just reporting facts - as Mannitol is a cheap sugar there is no financial gain to be had.
I have also come across several people on healthunlocked who have benefitted from Mannitol.
Also Gary Sharp on http://www.outthinkingparkinsons.com/articles/mannitol
Since there appear to be more and more evidence that Parkinson's starts in the gut it is not unreasonable to think that it can also be stopped there.