The ketogenic diet (KD) is a metabolic shift, which stimulates the liver oxidation of fatty acids to produce ketone bodies. These ketone bodies represent an alternative fuel source for the brain. The benefits of KD in epilepsia have been demonstrated for decades. This diet may also provide benefits in Alzheimer's disease (AD) where neuronal glucose utilization declines from the early stage. Besides, the KD could decrease neuroinflammation, oxidative stress and enhance mitochondrial biogenesis. In murin models of AD, KD or Medium Chain Triglycerides consumption were associated with lower neuroinflammation but also with a diminution of neuropathologic features of AD (amyloid and tau lesions in the brain). Moreover, behavioural effets and improvements in memory and motor function have been highlighted. In humans, recent studies suggest cognitive benefits (memory, executive function) in AD, including in the Mild Cognitive Impairment (MCI) stage. The feasibility and the adherence to the diet proved to be correct, in small samples, in particular in MCI individuals over a short follow-up period (3 to 6 months). This study aims at examining the feasibility of a KD followed-up for one year in participants with early AD (N=70). Change in brain metabolism will be assessed using PET scan after 12 months, comparing KD with control diet. The effects on cognition, quality of life and daily living functioning will be analysed. The safety, nutritional changes and adhesion to the diet will be monitored throughout the study.