I doubt the author's conclusion will lead anywhere. It is well established that high levels of triglycerides prevent leptin from crossing the blood brain barrier. My conjecture - and admittedly this is way over my head but a plausible conjecture none the less - is that this is one of the ways that high carb diets negatively impact development of "AD".
First, high carb diets drive high triglyceride levels, and with subsequent development of insulin resistance, high insulin levels. The high trigs mean that less leptin will interact in the brain, perhaps creating the effects described above which drive amyloid-B accumulation at faster rates.
High insulin levels means that the body's scavenger system for amyloid-B, insulin degrading enzyme, is busy with insulin and never has time to attend to amyloid-B.
Third, fasting results in the body finding and using as much protein in the body as possible, and there's some evidence that this "protein scavenging" reduces build of of AGEs (a protein damaged by glycation) and other "junk" proteins that wind up in the plaques associated with AD.
Lastly, high blood sugar levels drives higher levels of advanced glycation end products, which are also accelerants in the plaques that characterize AD.
The example of the diabetics is telling - they get AD at higher rates than everyone else. It would be interesting to know - can AD develop in a person who maintains normal to low blood glucose across their entire lifespan? Or, the same question stated differently: has a person ever been diagnosed with AD who maintained optimal blood sugar levels across a lifetime (or most of a lifetime)?