Ketones (also called ketone bodies) are substances produced by the body as it breaks down fats for energy, a process called ketosis.

Normally the body obtains the energy it needs from sugars (carbohydrates). A person may begin to break down fats and produce ketones because of:

• Having too little insulin, which prevents the body from using sugar for energy, causing it to break down fat instead.
• Fasting or starvation.
• Prolonged vomiting or diarrhea.
• A diet that is low in sugars and starches (carbohydrates).

Ketone testing can be done anytime using a urine test strip or a blood sugar meter that tests for ketones. If ketone levels are very high or if the person is dehydrated, ketones may begin to build up in the blood. High blood levels of ketones may cause fruity-smelling breath, loss of appetite, nausea or vomiting, and fast, deep breathing. In severe cases, it may lead to coma and death. In a pregnant woman, even a moderate amount of ketones in her blood may harm the fetus.

Ketones may signal diabetic ketoacidosis, a dangerous condition that is caused by very high blood sugar levels.