Fed state vs Fasting state
How to tell Fed state and Fasting state apart when a board question makes them look alike.
Fed state stores fuel through insulin; fasting state mobilizes fuel through glucagon, epinephrine, gluconeogenesis, lipolysis, and ketones.
Side by side
Fed state favors insulin signaling, glucose uptake, glycogen synthesis, glycolysis, fatty acid synthesis, and protein synthesis after a carbohydrate-containing meal.
Fasting state favors glucagon and epinephrine signaling, glycogenolysis early, gluconeogenesis later, lipolysis, beta-oxidation, and ketogenesis with prolonged fasting.
Insulin activates dephosphorylated storage pathways and increases GLUT4 insertion in muscle and adipose tissue.
Glucagon/epinephrine raise cAMP and phosphorylation, mobilizing stored fuel and preserving plasma glucose for brain and red cells.
High insulin, low glucagon, active glycogen synthase, PFK-2 activity, and lipogenesis support fed state.
High glucagon, active glycogen phosphorylase, hepatic gluconeogenesis, ketones, and adipose hormone-sensitive lipase support fasting state.
The trap
Both use liver metabolism, but insulin stores while glucagon mobilizes; do not call every hepatic pathway fasting.
The repair move
For fuel-state questions, identify insulin versus glucagon first, then name the pathway direction.
Try a free question
CoreA 24-year-old woman eats a large bowl of pasta. Two hours later, serum insulin is high, glucagon is suppressed, and her liver shows increased glycogen synthase activity and active fatty acid synthesis from acetyl-CoA. Which metabolic state is she in?
Show answer and explanation
Answer: A. Fed state. Insulin signaling after a carbohydrate-rich meal dephosphorylates and activates glycogen synthase and acetyl-CoA carboxylase, driving glucose storage as glycogen and conversion of excess carbon to fatty acids.
Why the other choices are tempting
- B. Early fasting features glycogenolysis driven by glucagon and rising cAMP, not active glycogen synthesis.
- C. Prolonged fasting (1-3 days) features hepatic gluconeogenesis and rising ketones, with insulin near baseline.
- D. Starvation (>3 days) features dominant ketogenesis and protein sparing, not active lipogenesis.
- E. Refeeding occurs after starvation and risks hypophosphatemia from sudden insulin surge; this patient was not previously starved.
Flashcards
Tap a card to flip it.
What clue supports Fed state?
Choose Fed state when the stem gives this pattern: Fed state favors insulin signaling, glucose uptake, glycogen synthesis, glycolysis, fatty acid synthesis, and protein synthesis after a carbohydrate-containing meal.
What clue supports Fasting state?
Choose Fasting state when the stem gives this contrasting pattern: Fasting state favors glucagon and epinephrine signaling, glycogenolysis early, gluconeogenesis later, lipolysis, beta-oxidation, and ketogenesis with prolonged fasting.
Quick answers
What is the fastest way to tell Fed state from Fasting state?
Fed state stores fuel through insulin; fasting state mobilizes fuel through glucagon, epinephrine, gluconeogenesis, lipolysis, and ketones.
What is the key clue for Fed state?
Fed state favors insulin signaling, glucose uptake, glycogen synthesis, glycolysis, fatty acid synthesis, and protein synthesis after a carbohydrate-containing meal.
What is the key clue for Fasting state?
Fasting state favors glucagon and epinephrine signaling, glycogenolysis early, gluconeogenesis later, lipolysis, beta-oxidation, and ketogenesis with prolonged fasting.
What is the common trap with Fed state vs Fasting state?
Both use liver metabolism, but insulin stores while glucagon mobilizes; do not call every hepatic pathway fasting.