Periodic Fasting for Treatment of Long Covid in Adults: a Pilot Study

Inclusion Criteria: * Age 18-64 * Diagnosis Long Covid Syndrome (post-acute COVID-19 symptoms persisting ≥12 weeks) * Normal body Mass Index (18.5 to 25 kg/m2) * Marginal Iron status ( PF\< 25 ng/ml) * Able to communicate in and comprehend English and/or German and/or French language * Present written / signed declaration of consent * Ability to understand the patient information and willingness to sign the consent form * Consent to specimen collection and specimen use Exclusion Criteria: * Current underweight condition (body mass index less than 18.5 kg/m2) or weight loss exceeding 3 kg within the last month or 5 kg within the last three months. * Existing / current eating disorder within the past five years (e.g., anorexia, bulimia). * Psychiatric condition that limits understanding of the examination protocol (unable to consent) * Severe internal disease (e.g. kidney deficiency with creatinine \> 2mg/dl), chronic inflammatory illness other than LCS * Participation in another intervention study. * Existing vegan diet or fasting during the last six months * Pregnancy or breastfeeding status. * Presence or suspicion of pre-existing ME/CFS or early autonomous dysfunction * Diagnosis of chronic inflammatory bowel diseases, celiac disease or colorectal cancer according to the guidelines of the German Society of Gastroenterology * Use of anti-psychotic drugs * Antibiotic use during the previous 12 months * Start of novel drug therapy * Contraindication for additional blood draws (e.g. hemoglobin \<10)