One of the promising new treatment paradigms for Alzheimer's is to have the patient switch to an extremely high fat, low carb diet, a so-called "ketogenic" diet. The name comes from the fact that the metabolism of dietary fats produces "ketone bodies" as a by-product, which are a very useful resource for metabolism in the brain. It is becoming increasingly clear that defective glucose metabolism in the brain (so-called "type-3 diabetes") is an early characteristic of Alzheimer's. Ketone bodies, whether they enter the astrocyte directly or are produced in the astrocyte itself by breaking down fats, can be delivered to adjacent neurons, as shown in the accompanying figure. These neurons can utilize the ketone bodies both as an energy source (replacing and therefore relieving glucose) and as a precursor to GABA, a critical neurotransmitter that is widespread in the brain.
Evidence that a ketogenic diet might help Alzheimer's was first found through research conducted on mice who had been bred to be prone to Alzheimer's disease . Researchers found that the mice's cognition improved when they were treated with a high-fat low-carb diet, and also that the amount of amyloid-beta in their brain was reduced. The latter effect would be anticipated based on the premise that amyloid-beta promotes full utilization of glucose anaerobically, as I discussed previously. By having ketone bodies as an additional source of fuel, the dependence on glucose is reduced. But another effect that may be more important than this is the availability of high-quality fats to improve the condition of the myelin sheath.
This idea is supported by other experiments done on human Alzheimer's patients  . A placebo-controlled 2004 study  of the effect of dietary fat enrichment on Alzheimer's is especially informative, because it uncovered a significant difference in effectiveness for the fat-enrichment for subjects who did not have the apoE-4 allele as compared with those who did. The experimental test group were given a supplemental drink containing emulsified medium chain triglycerides, found in high concentration in coconut oil. The subjects without the apoE-4 allele showed a significant improvement in score on a standard test for Alzheimer's, whereas those with the apoE-4 allele did not. This is a strong indicator that the benefit may have to do with an increase in uptake by the astrocyte of these high-quality fats, something that the subjects with the apoE-4 allele are unable to accomplish due to the defective IDL and LDL transport mechanisms.