In the Dixon cycle, what happens to triglycerides in adipocytes when energy is needed?

• A. They diffuse into blood, bind to albumin, and are carried to tissues where the liver re-synthesizes TAGs.
• B. They are stored permanently in adipose tissue as glycerol.
• C. They are converted to glucose within adipose tissue.
• D. They are excreted in the urine.

Answer: (A)

When energy is needed, triglycerides in adipose tissue are broken down by lipolysis into free fatty acids and glycerol. The fatty acids then diffuse into the bloodstream and bind to albumin, allowing them to travel to tissues that will use them for energy. In the liver, these fatty acids are re-esterified to form triglycerides again and are packaged into VLDL for transport to other tissues. Meanwhile, glycerol is carried to the liver, where it can be used for gluconeogenesis or contribute back to triglyceride synthesis as needed. This movement of fatty acids from fat stores to the liver for reassembly of triglycerides is the essence of the Dixon cycle. The other ideas—that triglycerides stay permanently in fat, are converted to glucose in adipose tissue, or are excreted in urine—do not reflect how energy mobilization and transport work.