What is Ketosis

Ketosis is a natural metabolic state in which the body uses ketone bodies as its primary fuel source, rather than glucose. This occurs when carbohydrate intake is significantly reduced, causing a shift in the body’s primary energy source.

The mechanisms involved in achieving a state of ketosis

Limited carbohydrate intake

When following a ketogenic diet, carbohydrate intake is significantly reduced, typically to around 20-50 net grams per day. This limited glucose supply causes the body to search for an alternative energy source.

Depletion of glycogen stores

Glycogen, the stored form of glucose, is found primarily in the liver and muscles. As carbohydrate intake is reduced, the body depletes its glycogen stores, which leads to a decrease in insulin levels. This is crucial, as lower insulin levels promote the breakdown of fatty acids from stored body fat.

Breakdown of fatty acids

With glycogen stores depleted and insulin levels decreased, the body begins to break down fatty acids from adipose tissue (body fat) into smaller molecules that can be used for energy.

Production of ketone bodies

In the liver, the smaller fatty acid molecules are converted into ketone bodies, primarily acetoacetate, beta-hydroxybutyrate (BHB), and acetone. These ketone bodies serve as an alternative fuel source when glucose is scarce, providing energy to the brain and other organs.

Utilization of ketone bodies

Once the body has produced a sufficient number of ketone bodies, they enter the bloodstream and are transported to cells throughout the body. These cells convert the ketone bodies back into a usable energy source called acetyl-CoA, which then enters the Krebs cycle (also known as the citric acid cycle or TCA cycle) to produce ATP, the primary energy currency of the cell.

Maintenance of Ketosis

To maintain a state of ketosis, it is necessary to continue to limit carbohydrate intake and consume a high amount of fat. This encourages the continued breakdown of fatty acids and production of ketone bodies.

If carbohydrate intake is increased, the body will shift back to using glucose for fuel, and ketone body production will decrease. It will take several days for the body to re-enter a state of ketosis.

Quick Summary

Ketosis is a metabolic state in which the body uses ketones instead of glucose as its primary energy source. This state is achieved through a low-carbohydrate, high-fat diet that depletes glycogen stores, reduces insulin levels, and prompts the breakdown of fatty acids. These fatty acids are converted into ketone bodies in the liver and are then transported to cells to be used for energy. This process can take several days to initiate and requires ongoing adherence to the diet to maintain the state of ketosis.