How does the body use, store, and burn energy?

How does the body use, store, and burn energy?

In a fed state, energy production looks something like this:

  1. Food is absorbed and turned into glucose.
  2. Rise in glucose (blood sugar)
  3. Pancreas makes insulin
  4. Insulin levels rise
  5. Insulin ushers blood sugar (Glucose) into cells for energy 
    • 5a. Blood sugar first gets stored as glycogen in the liver and muscles
    • 5b. Extra blood sugar is stored as fat

In a fasted state (not eating), energy production looks something like this:

  1. Insulin levels drop
  2. Body burns stored energy (liver and muscle glycogen)
  3. The glycogen releases glucose (up to around 24-36 hour mark)
  4. The liver manufactures glucose from amino acids, which is called gluconeogenesis (from the 24-48 hour mark)

    • The body makes the “right” amounts of necessary sugar on demand!
  5. Lipolysis begins to take place around the 48-hour mark, which is the breakdown of fat for energy. Specifically, triglycerides.
  6. The triglyceride breaks down into a glycerol molecule and fatty acids
  7. The glycerol molecule is used as a form of gluconeogenesis so amino acids can be reserved for protein synthesis.
  8. The fatty acids make ketones for energy (mainly Beta-HBA and acetoacetate).

How our body uses energy? Energy as Money Analogy

  1. Glucose (Cash) – There is instant access. It is available from food and/or produced by the liver.
  2. Glycogen (Checking Account) – When out of cash, we pull energy from glycogen which is produced in the liver and muscles.
  3. Fat (Long Term Savings) – When out of glucose and glycogen, you can hit this hard to get to energy reserve.


The switch to being a fat burner: In the absence of insulin, hormone-sensitive lipase (HSL) allows for the breakdown of triglycerides and the formation of free fatty acids to be used as an energy source. The more you restrict sugar and starch and protein intake, the more glucagon output can be amplified. Glucagon then begins to stimulate HSL as an indirect means of increasing the release of free fatty acids from triglycerides. Glucagon then stimulates the uptake of these free fatty acids by the liver and its mitochondria so they can begin to be burned for energy. Insulin inhibits HSL. Glucagon stimulates HSL. HSL allows the breakdown of triglycerides for energy.

Fasted vs Overfed State


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