In starvation adipose tissue utilizes ketone body or fatty acid
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Here is a clear answer based on authoritative biochemistry textbooks:
Adipose Tissue in Starvation: Uses Fatty Acids, NOT Ketone Bodies
In starvation, adipose tissue utilizes fatty acids (specifically, its own stored fatty acids via lipolysis) as its primary fuel — not ketone bodies.
Why Not Ketone Bodies?
Ketone bodies (acetoacetate, β-hydroxybutyrate, acetone) are produced by the liver from fatty acids and exported to peripheral tissues. However, adipose tissue does not significantly utilize ketone bodies for energy. The key reason:
- Thiophorase (succinyl-CoA:3-ketoacid CoA transferase) is the enzyme required for ketone body utilization (ketolysis). Adipose tissue lacks sufficient activity of this enzyme to use ketone bodies as fuel.
- Ketone bodies are preferentially consumed by brain, skeletal muscle, heart, and kidney — tissues that either cannot use fatty acids directly (brain) or have high energy demands.
What Adipose Tissue Does in Starvation
- Lipolysis is activated — low insulin and high glucagon/catecholamines stimulate hormone-sensitive lipase (HSL) in adipose tissue.
- Triacylglycerols are broken down into free fatty acids (FFAs) and glycerol.
- FFAs are released into the blood as non-esterified fatty acids (NEFAs/FFAs).
- The adipocytes themselves use these fatty acids for their own energy needs via β-oxidation.
- Glycerol is exported to the liver for gluconeogenesis (adipose lacks glycerol kinase and cannot reuse glycerol locally).
The Big Picture
| Tissue | Fuel in Starvation |
|---|---|
| Adipose tissue | Fatty acids (own stored fat via lipolysis) |
| Brain (early) | Glucose |
| Brain (prolonged starvation) | Ketone bodies |
| Skeletal muscle | Fatty acids → ketone bodies |
| Liver | Fatty acids (produces ketone bodies for export) |
| RBCs | Glucose only (no mitochondria) |
"Adipose tissue releases nonesterified fatty acids in the fasting state. In prolonged fasting and starvation, these are used by the liver for synthesis of ketone bodies, which along with the fatty acids provide the major fuel for muscle." — Harper's Illustrated Biochemistry, 32nd Ed.
In summary: Adipose tissue uses fatty acids in starvation. It releases FFAs into the circulation (fueling the rest of the body and enabling hepatic ketogenesis), and oxidizes fatty acids locally for its own energy. Ketone bodies are the fuel of the brain in prolonged starvation, not adipose tissue.
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