This can happen to Type 1 or 2 diabetics: ketosis can trigger a dangerous condition called ketoacidosis. This occurs when the body stores up too many ketones — acids produced as a byproduct of burning fat — and the blood becomes too acidic, which can damage the liver, kidneys, and brain. Left untreated, it can be fatal.

It’s more rare in others, but the jury is still out on long-term affects.