While in ketosis, the body utilizes fatty acids as an alternative source of energy due to the glucose deficit. To accomplish this, acetyl CoA, which is normally oxidized into H2O and CO2 as part of the citric acid cycle, is converted by the liver into acetoacetate and 3-hydroxybutyrate, also known as ketone bodies. These ketone bodies are now free to flow where needed and be used as fuel for metabolic processes. It is worthwhile to note that ketone bodies are very effective respiratory fuels; whereas 100 g of glucose generates 8.7 kg of ATP, 100 g of 3-hydroxybutyrate can yield 10.5 kg of ATP, and 100 g of acetoacetate 9.4 kg of ATP. Most areas of the body, such as the brain, will use ketones whenever provided to them (in fact the blood-brain barrier has a very effective transporter for ketone bodies). However, there are still some processes that are partial to glucose for energy metabolism. In these cases, glucose is supplied by hepatic gluconegenesis, where the liver converts non-carbohydrate sources (such as fatty acids and amino acids) into glucose.