After 2 weeks of fasting where does most energy come from?

• A. Protein from muscle
• B. Adipose tissue
• C. Liver glycogen
• D. Blood glucose

Answer: (B)

In prolonged fasting, the body shifts to using fat stores as the main energy source. After about a day, liver glycogen is depleted, so glucose comes from gluconeogenesis rather than stored glycogen. Lipolysis in adipose tissue releases fatty acids that are oxidized by most tissues to supply energy, making adipose tissue the primary source. The liver also produces ketone bodies from fatty acids to power the brain and other tissues, which helps spare glucose. Muscle protein breakdown does occur but becomes a less prominent energy source over time. So, after two weeks of fasting, most energy comes from adipose tissue.