Without carbohydrate in the diet, or in uncontrolled diabetes without an effective way to get glucose into the cell, the body resorts to using to try to make glucose, but ends up with not enough glucose and with too many

With a low carbohydrate diet, or in people with diabetes and no way to get sugar into the cells, the body resorts to using adipose, or fat to make glucose. This is not as effective as using carbohydrates and results in ketones. In healthy people, the production of ketone bodies is fine. Beta oxidation of fatty acids results in acetyl coA, which can be used in the Kreb cycle. In diabetes ketone bodies can increase to levels that result in ketoacidosis, which is a dangerous condition.