Ketones. When fat is broken down for energy, the body produces by-products called ketones (or ketone bodies) and releases them into the urine. Large amounts of ketones in the urine may signal a dangerous condition known as diabetic ketoacidosis. A diet low in sugars and starches (carbohydrates), starvation, or prolonged vomiting may also cause ketones in the urine. http://www.webmd.com/hw/lab_tests/hw6580.asp