Based on a PET/MRI protocol, the aim of this study is to evaluate and compare the response to the dietary supplementation of two different MCT oils (60% C10 + 40% C8 or 100 % C8) in two groups, patients with Alzheimer's disease and healthy elderly people (N=10/group). After a baseline evaluation, participant will test one of the supplements during two successive periods of one month; each period of time ending with 18F-FDG and 11C-acetoacetate PET scans.