Metabolic flexibility refers to the ability of the body to switch from one fuel to another depending on fuel availability  and the demands of energy throughout the day.  A healthy, flexible metabolism can switch between carbohydrates to proteins to fats easily as needed. The body seems to lose this ability as we get sicker and sicker. Impaired metabolic flexibility is associated with metabolic syndrome, cardiovascular disease, diabetes, liver disease, brain disorders and cancer. Some recommendations for improving and restoring metabolic flexibility are daily exercise, fasting, time restricted eating and ketosis.