Inclusion Criteria:  A person who has given oral consent. For patients with early stage Alzheimer's disease, both the primary caregiver and the patient will need to give oral consent. ADULT Body Mass Index (BMI) < 30 kg/m². Patients meeting the diagnostic criteria for early-stage Alzheimer's disease: imaging (cerebral MRI), neuropsychobiological criteria (consultation with neuropsychological assessment, CSF biomarkers) and CDR (Clinical Dementia Rating Scale) rated at 1 or 1.5 - for the "subjects with early-stage Alzheimer's disease" group Patients meeting the diagnostic criteria for minor cognitive impairment: imaging (brain MRI) and neuropsychological assessment with a CDR scale of 0.5 - for the group "subjects with minor cognitive impairment". Absence of cognitive problems and normal neurological assessment - for the healthy group. Fasting at least 2 hours before PEG measurement  Exclusion Criteria:  - A person who is not affiliated to or not a beneficiary of a social security system. Person subject to a measure of legal protection (curatorship, guardianship) Person subject to a judicial safeguard measure Pregnant, parturient or breastfeeding woman Adult unable to express consent or perform cognitive testing. Minor No Caregiver for Mild Alzheimer's Disease Patients Active smoker Diabetes (type 1 or type 2) Taking a treatment that interferes with taste Body Mass Index (BMI) ≥ 30 kg/m2 MMS Score <20 Cerebral MRI finding another cause of neurocognitive disorder (except for Fazekas 1 vascular lesions accepted). Known COVID-19 infection