Final answer:
Glucose is the preferred fuel source for the human body, obtained from dietary sugars and carbohydrates or from the breakdown of glycogen stores. Fatty acids and ketone bodies can serve as alternative energy sources when glucose is scarce.
Step-by-step explanation:
The fuel source that the human body prefers to run off of is glucose. This simple sugar is the primary energy source for both anaerobic and aerobic metabolism. Our bodies obtain glucose directly from dietary sugars and by the breakdown of other carbohydrates, such as those found in fruits, vegetables, and grains.
When glucose is not immediately available from dietary sources, the body can derive it from glycogen, which is stored in the liver and skeletal muscles. In the absence of glucose, the body may utilize fatty acids from triglycerides found in adipose tissue or, during extended periods of starvation, produce ketone bodies for energy.
The brain, which is a particularly energy-hungry organ, relies almost exclusively on glucose. However, during periods of extreme glucose depletion, such as fasting or a low-carbohydrate diet, the brain can adapt to use ketone bodies as an alternative energy source.