 The investigators are conducting a research study on nutrition in mitochondrial disease. The investigators are interested in the kind of carbohydrates that people eat. Carbohydrates are an important source of energy. Certain kinds of carbohydrates tend to raise blood sugar more in healthy people, and others tend to raise blood sugar less in healthy people. The investigators would like to know if by eating the right type of carbohydrate, people with mitochondrial disease can avoid high lactate levels, high blood sugar levels, and, later, low blood sugars. 