Intermittent Calorie Restriction, Insulin Resistance, and Biomarkers of Brain Function

Background: \- Insulin removes sugar from the blood to use for energy. Insulin resistance means that cells may not respond to insulin normally. It can lead to serious diseases. Researchers want to see how diet affects insulin resistance, weight, and brain chemicals related to Alzheimer s disease. Objectives: \- To compare two forms of diet and their effects on insulin resistance and the brain. Eligibility: \- Women ages 55 70 with insulin resistance. Design: * This study requires 6 clinic visits over 9 12 weeks. Participants must fast before visits. * Visit 1, screening: * Medical history, physical exam, and blood and urine tests. * Participants will get a wrist device to wear for 4 days. * Visit 2: * Weight and waist measurement. * Blood drawn. * Questionnaires and thinking tests. * Lumbar puncture. Skin will be numbed and a needle inserted between bones in the back will remove \<TAB\>fluid. * Participants will drink a nutrition shake. Blood will be taken 12 times over 4 \<TAB\>hours through a thin tube in \<TAB\>the arm. * Brain MRI. Participants will lie on a table that slides in and out of a cylinder in a strong magnetic field. \<TAB\>They will have a coil on their head and may do tasks. * Participants will get advice about healthy eating and be randomly put in one of 2 groups. One group will get \<TAB\>nutrition shakes to drink. * Visits 3 5: * Weight and waist measurements, vital signs, blood draw, and questionnaires. * Between visits, participants will get a call or email to check how they are doing. * Visit 6: Repeat of visit 1. * Participants will wear the wrist device for 4 more days, have a follow-up contact, then the study is finished.