High-fat, low-carbohydrate ketogenic diet beginning 72 h before the study.Nothing by mouth, except water and oral pills, for 3 overnight fasts before the exam.First 2 nights from 08:00 PM until at least 08:00 AM the next morning. The night before the test from 08:00 PM until the time of the test.For diabetics, consider avoiding prolonged fasting, preferably complete the examination during afternoon hours after ketogenic breakfast and morning insulin, followed by 6-h fasting. This evidence concerns the gene INS and diabetes mellitus.