Fasted State Metabolism Diagram – Fuel Between the Organs

All 14 boxes on the diagram

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Fasted state 9

Glucagon The hormone of the fasted state. It makes the liver release glucose into the blood.
Glucose The liver releases it into the blood. The brain depends on a steady supply.
Glycogenolysis The breakdown of glycogen into glucose. Glucagon switches it on in the liver.
Gluconeogenesis Making new glucose from non-carbohydrate molecules. Glycerol and some amino acids are its raw materials.
Lipolysis The breakdown of stored triglycerides. It releases fatty acids and glycerol into the blood.
Fatty acids Set free when fat tissue splits its triglycerides. The liver turns some of them into ketone bodies.
Glycerol The backbone of a triglyceride. The liver can build new glucose from it.
Ketone bodies Made in the liver from fatty acids. The brain can use them as fuel in a long fast.
Amino acids Set free when muscle protein is broken down. The liver builds new glucose from some of them, mainly in a longer fast.

Fed state 5

Insulin The hormone of the fed state. It makes cells take up fuel and store it.
Glucose (fed state) Absorbed from the small intestine into the blood. Liver, muscle and fat tissue take it up.
Glycogen The storage form of glucose. Liver and muscle both make it after a meal.
Triglycerides The storage form of fat. Fat tissue builds them from fatty acids and glycerol.
Protein Built from amino acids that cells take up. Insulin favors building it over breaking it down.

How this list was compiled: Every name and every arrow read on 2026-10-03 and kept only where two independent sources give it. (1) Wikipedia, text only: Glycogenolysis, Gluconeogenesis, Lipolysis, Ketone bodies, Starvation response and Insulin (its list of actions), https://en.wikipedia.org/wiki/Gluconeogenesis and https://en.wikipedia.org/wiki/Ketone_bodies . (2) Colorado State University, VIVO Pathophysiology, Physiologic Effects of Insulin and Glucagon, https://vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/insulin_phys.html and https://vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/glucagon.html : glucose uptake by muscle and fat, glycogen in the liver, fatty acids and triglyceride in fat tissue, amino acid uptake; glycogen breakdown and new glucose in the liver under glucagon. (3) Karimi and others, Adaptive Effects of Endocrine Hormones on Metabolism of Macronutrients during Fasting and Starvation, Metabolites 14:336 (2024), open access, https://europepmc.org/article/PMC/PMC11205672 : fat split into fatty acids and glycerol, glycerol and amino acids from muscle protein as raw materials for new glucose, ketone bodies from fatty acids as fuel for the brain, glycogen and triglyceride made under insulin. (4) For the two captions on the arrows out of fat tissue (a fat molecule is a glycerol backbone that carries fatty acids, and fatty acids are long chains): Wikipedia, Glycerol, Fatty acid and Triglyceride; Colorado State University, VIVO Pathophysiology, Absorption of Lipids, https://vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/absorb_lipids.html ; and a printed text read by full-text search on archive.org, Elements of Biochemistry (1984), https://archive.org/details/elementsofbioche0000sche . The layout and the words in the boxes are our own. Licence: own work

The drawing: Drawn for this site on 2026-10-03 from plain geometry; the blank tags are placed from the answer table. Own original chart; nothing traced or copied. Licence: own work

How it works

Each chart shows four organs and the fuel that moves between them. The boxes say what happens in plain words, each under its name; the quiz blanks the names. The first chart is the fasted state, the second the fed state.

Read the full guide

The fasted state

Start at the top left: blood sugar falls and the pancreas releases glucagon. The liver responds in two ways, glycogenolysis and gluconeogenesis, and sends glucose to the brain. Fat tissue splits stored fat by lipolysis into fatty acids and glycerol. In a long fast muscle gives up amino acids and the liver turns some fatty acids into ketone bodies.

The fed state

After a meal insulin rises and the arrows turn around. Glucose from the small intestine is stored as glycogen, fatty acids as triglycerides, and amino acids are built into protein.

On the fasted chart, follow each arrow from fat tissue or muscle back to its box: it says what was broken down there.

Questions and answers

What happens in the fasted state?

Insulin falls and glucagon rises. The liver releases glucose, by breaking down glycogen and by building new glucose. Fat tissue releases fatty acids and glycerol, and in a long fast the liver turns some of the fatty acids into ketone bodies.

What is the difference between the fed state and the fasted state?

In the fed state insulin is high and fuel is stored: glucose as glycogen, fatty acids as triglycerides, amino acids as protein. In the fasted state glucagon is high and those stores are broken down, which keeps glucose in the blood.

What fuel does the brain use in the fasted state?

Glucose, which the liver keeps releasing into the blood. In a long fast the liver also makes ketone bodies from fatty acids, and the brain can use them as a second fuel.

What is the difference between glycogenolysis and gluconeogenesis?

Glycogenolysis breaks down glycogen that is already stored and releases its glucose. Gluconeogenesis builds new glucose from molecules that are not carbohydrates, such as glycerol and some amino acids. Both happen in the liver, and glucagon switches both on.

How do I drag the labels onto the diagram to identify specific aspects of fasted-state metabolism?

Start at the liver, where glycogenolysis and gluconeogenesis happen. Fat tissue sends it fatty acids and glycerol, muscle sends amino acids, and glucose and ketone bodies leave for the brain. The chart here is the site's own drawing.