Inclusion Criteria:  BMI<28 Age - 20-35 Are used to exercise in aerobic sports (running, swimming, Zumba, ball games, functional training, surfing, tennis, wrestling ext.). Exercise at least twice a week, for a minimum duration of the last 6 months.  Exclusion Criteria:  Consumption of antibiotics (PO) or probiotics 3 months prior to the first day of the experiment. Diagnosis of type 1 or type 2 diabetes. Pregnancy, fertility treatments, breastfeeding women six months prior to enrollment and during the study. Chronic disease (e.g. AIDS, Cushing syndrome, CKD, acromegaly, hyperthyroidism etc.) Cancer and recent anticancer treatment Psychiatric disorders Coagulation disorders Gastrointestinal disorders Bariatric surgery Alcohol or substance abuse BMI>28 Any physical condition precluding the completion of a routine effort test