Final answer:
C) Fat is the normal metabolic by-product of ketones since ketones are produced during fat metabolism when the body uses fats as an alternative energy source due to a lack of carbohydrates.
Step-by-step explanation:
The normal metabolic by-product of ketones is fat. Ketones themselves are byproducts of fat metabolism. When the body has an insufficient supply of carbohydrates, such as during fasting, low carbohydrate diets, or in cases of diabetes mellitus, it turns to fats as an alternative energy source.
During this process, fatty acids are oxidized, leading to an accumulation of acetyl-CoA, which, if in excess, converts to ketone bodies such as acetoacetate and ß-hydroxybutyrate. These ketone bodies can then be used by other tissues as an energy source when glucose is limited, ultimately showing up in the urine as a sign of fat catabolism.
Moreover, ketone body oxidation is essential during prolonged starvation, where the brain, traditionally thought to rely solely on glucose, starts utilizing ketones for energy. The primary ketone body in the blood is ß-hydroxybutyrate, produced in the liver and utilized by organs such as the heart and kidney.
Furthermore, excess ketones can lead to conditions like diabetic ketoacidosis if not regulated in individuals with diabetes.