Ketogenesis

When the fat metabolism is accelerated a large quantity of acetyl-CoA will become available. That is because acetyl-CoA is produced from the beta-oxidation of fatty acids (see also the page on fat metabolism).

At this moment the body will start the fourth way to produce energy: ketogenesis.

In this process ketone bodies or ketones are produced from acetyl-CoA.
The liver will transport these ketones via the blood to the tissues where they can be burnt for energy.
Also the brain is capable of using ketones for energy.

Because this process needs acetyl-CoA, also this process will not properly work in patients with MCAD deficiency.
That is why many (but not all) patients with MCAD deficiency who are going through a metabolic crisis, will have an inappropriately low amount of ketones in their blood and urine.

In a person who doesn't have MCAD deficiency the amount of ketones will strongly increase if the fasting continues. Ketones are acid and can disturb the body's acid-base balance, causing a serious condition called ketosis. On the other hand the liver's ability to deliver ketones to the tissues such as brain and muscle, is an important mechanism for providing energy in periods of starvation. In short, it's the lesser of two evils.

Only when also the supply of body fat gets depleted, the body will start to break down essential proteins for energy, such as antibodies, enzymes and hemoglobine. Shortly after this will lead to loss of liver and muscle function and, ultimately, death.

Read further about genetics and how MCAD deficiency is inherited >