Ketosis and ketogenic diet

What are ketones or ketone bodies?

Ketones, also known as ketone bodies, are small, water-soluble molecules that (predominantly) result from the breakdown of fatty acids via ß-oxidation in the mitochondria of hepatocytes. The terms ketones or ketone bodies refer to the following three compounds:  Acetone, acetoacetate und beta-hydroxybutyrate.

The smallest ketone, acetone, is largely exhaled through the lungs. Little is presently known about its effects in metabolism. Acetoacetate and beta-hydroxybutyrate can be converted into each other, whereby the respective ratio depends on the redox state of the cell. Both ketones are efficient substrates for mitochondrial energy production, while they also exert a number of signaling functions.

Measurement of ketone bodies is possible in three different ways – in the breath, urine or blood. Measurement in the urine detects acetoacetate excreted by the body; it is considered less reliable than blood measurements, however, although it is suitable as an inexpensive introduction and control at the onset of a ketogenic diet. Measurements in the blood with the aid of a finger prick records beta-hydroxybutyrate levels in the capillary pool. The concentration of acetone can be measured in exhaled air. It provides information about the formation of ketones from fatty acids and thus the extent of fat oxidation. . Measurement in the blood is considered the most reliable method, but at present is the most expensive.

How are ketone bodies formed?

Ketone bodies are formed in the cells of the liver and transported via the bloodstream to all tissues in the body. With few exceptions, ALL cells in the body can use ketone bodies and fatty acids for energy. The exceptions are the red blood cells (erythrocytes), the cells of the retina, and to a lesser extent, the brain. The residual glucose requirement can be met by synthesizing glucose from triglycerides and certain amino acids in a process termed gluconeogenesis.

Ketone bodies can be formed from fatty acids and from some amino acids. Ketogenesis, i.e. the formation of ketone bodies, is primarily regulated by insulin and glucagon.

When are Ketones formed?

If glycogen stores in the liver decrease, either through fasting or carbohydrate restriction, the body begins to produce ketone bodies. At the same time, we see physiologically low insulin and blood glucose levels. Medium chain fatty acids (MCTs) also show a stimulatory effect on ketogenesis [i].

Ketosis is a natural metabolic state

Ketosis is a natural metabolic state and completely harmless. In fact, ketones play an important role especially in the first weeks of our life.  Ketones have a great importance for the brain of the newborn. For example, newborns that are breastfed are naturally high in ketosis; breast milk contains many MCTs. Ketones are not only essential for the energy supply of the young brain, but also provide important building blocks [ii].

[i] Bach, Andre, et al. “Ketogenic response to medium-chain triglyceride load in the rat.” The Journal of nutrition 107.10 (1977): 1863-1870.

[ii] Patel, M. S., et al. “The metabolism of ketone bodies in the developing human brain: development of ketone‐body‐utilizing enzymes and ketone bodies as precursors for lipid synthesis.” Journal of neurochemistry 25.6 (1975): 905-908.