Gluconeogenesis

When carbohydrates are not available, the body can create glucose (and subsequently glycogen) from non-carbohydrate sources like protein and fat through a process called gluconeogenesis. This metabolic pathway ensures the body has a steady supply of glucose for essential functions, particularly for tissues like the brain and red blood cells, which rely heavily on glucose for energy.


Steps in Glycogen Creation from Protein or Fat

  1. Gluconeogenesis:
    • The body synthesizes glucose from non-carbohydrate precursors, including:
      • Amino Acids (from protein breakdown).
      • Glycerol (from fat breakdown).
      • Lactate (produced during anaerobic metabolism).
    • This occurs primarily in the liver and, to a lesser extent, in the kidneys.
  2. Conversion to Glycogen:
    • Once glucose is produced via gluconeogenesis, it can be converted into glycogen through glycogenesis, if there is a need to store energy and sufficient energy is available.

Sources for Gluconeogenesis

1. Protein (Amino Acids)

2. Fat (Glycerol)

3. Fatty Acids and Ketones

4. Lactate


When This Process Happens

  1. Fasting or Starvation:
  2. Low-Carbohydrate Diets:
    • When dietary carbohydrates are insufficient, the body shifts to fat and protein metabolism for glucose production.
  3. Intense Exercise:
    • If glycogen stores are depleted during prolonged or high-intensity exercise, gluconeogenesis helps provide glucose.

Efficiency of the Process


Adaptations During Prolonged Carb Restriction

  1. Ketosis:
    • The body reduces its glucose demand by increasing ketone production from fats to fuel the brain and muscles.
    • This spares protein and limits gluconeogenesis.
  2. Protein Conservation:
    • Over time, the body adapts to conserve muscle protein, relying more on fat (ketones) and less on amino acids for energy.

Summary

When carbohydrates are not available: