USC has an ICOI because the university owns the patent of the interventional dietary supplement.

The objective of this study is to test a Fasting-Mimicking Diet (FMD) for its efficacy on improving immune response to flu vaccination in an older adult population (50-75 years of age).

This is a randomized clinical trial to test the safety and efficacy of the fasting-mimicking diet (FMD) in an elderly population (50-75 years of age) receiving their annual influenza vaccination. The study will include two arms: Control (normal diet) and FMD (2 cycles of 5-day fasting-mimicking diet within two months). Participants both arms will receive the standard influenza vaccine.The primary endpoint is anti-influenza antibody titers measured 4 weeks after flu vaccination. Secondary endpoints include: (1) body composition changes, measured as BMI, waist to hip ratio; (2) physiological changes, measured as blood chemistry and motor performance; (3) health outcomes, measured by SF-36 Health survey, dry eye surveys and flu incidents within 12 months of vaccination.

Inclusion Criteria:

• Ability and willingness to provide written informed consent;
• Ability and willingness to undergo 2 cycles of a 5-day dietary regimen;
• Ability and willingness to provide blood samples via venipuncture;
• Seeking to get a seasonal influenza vaccine.

Exclusion Criteria:

Concomitant medications

• Received flu (influenza) shot for the flu season;
• Receiving immunosuppressive therapy (i.e., oral prednisone in doses > 10 mg daily);
• On immunosuppressive drugs for cancer or rheumatologic therapy;
• Receiving insulin or octreotide;
• On hypertension medication. The subject must obtain the treating doctor's approval prior to beginning the study.

Safety-based exclusions:

• Hemoglobin < 9.0 g/dL;
• White blood cell count < 3,500/mm^3;
• Neutrophil count < 2,000/mm^3,
• Platelet count < 125,000/mm^3;
• Medical conditions that are incompatible with the dietary intervention ;
• Medical conditions that are incompatible with the flu vaccination;
• Pregnant or nursing female;
• Alcohol dependency;