Therapeutic Fasting and Immune Aging

Inclusion Criteria : * Patient affiliated or entitled to a social security scheme * Residing in a Long-Term Care Unit (LTCU) or a Facility for the Elderly Dependent (EHPAD) * A person deemed a priori, by the geriatrician member of the monitoring committee, to be capable of following the dietary recommendations required for the study. * A person deemed a priori, by the clinician in charge, to be able to follow the dietary recommendations required by the study. * Patient who has received informed information about the study and has co-signed a consent to participate in the study with the investigator. Exclusion Criteria : * Inability and/or unwillingness to follow dietary recommendations and/or perform follow-up examinations required for the study * Iso-resource group 1 or 2 according to the AGGIR grid * BMI \< 18.5 kg/m2 or recent weight loss \> 5% in 1 month or recent weight loss \> 10% in 6 months from previous weight * Albuminemia \< 30g/l * All swallowing disorders requiring a specific diet. * Influenza vaccination received prior to inclusion * Episode of influenza or suspected influenza during the 2020-2021 season and prior to inclusion * Any acute medical or surgical event less than 2 weeks prior to inclusion * Presence of systemic inflammatory or autoimmune disease * Presence of an innate or acquired immune deficiency (including taking immunosuppressive treatment) * Presence of a chronic disease which, according to the physician, makes the follow-up of a "fasting diet" and/or the consumption of large amounts of liquids (cf. fasting diet modalities) risky (e.g. insulin-dependent or insulin-requiring diabetes, severe heart failure, severe kidney failure, active cancer, significant undernutrition...) or impossible (e.g. advanced neurodegenerative pathology).