Ketogenesis: A Deeper Look at the Fat Burning Process

The whole point of the ketogenic diet is to get into “ketosis.” In this state your body’s predominant fuel source is fat (ketones) and not glucose, which is made from carbs and sometimes protein. If you’ve spent any time on the diet or maybe read some literature on the subject, you likely already know this. What you may not know, is what exactly goes on in the human body when it’s in ketosis?

I’m going to try to keep this explanation as simple as possible. I’m not trying to wow you with a bunch of scientific jargon, although there is going to be some in this post. What I am trying to do is help you have a deeper understanding of ketosis and the process that makes it work, Ketogenesis.

Normally when carbs are eaten, they are broken down into glucose and put into the bloodstream. From there, three things will happen; the glucose will be used immediately by the cells in your body, stored as glycogen in the liver and muscles, or stored as fat. Normally your body wants to break carbs down into glucose but, because you’ve stopped eating them, it has to turn to gluconeogenesis. Gluconeogenesis is a process in which glucose is made from material other than carbohydrates. An example of that is amino acids undergoing gluconeogenesis to create glucose. Gluconeogenesis occurs while you are in ketosis because there are some parts of your body that need glucose and cannot be fueled by ketones.

The processes and pathways our bodies use to perform biochemical reactions are very complex. With that being said, I will break this down into small chunks and easily understandable steps the best I can.

Ketogenesis – From Stored Fat to Usable Energy

Ketogenesis is the process in which fatty acids are taken and manufactured into ketone bodies, that are then used for energy or excreted by other means . Basically, the fat itself can’t be used as energy and must be broken down and changed into a usable energy source. Ketogenesis begins when the body runs out of usable glucose.

Step 1

Fatty acids are broken down, by a process called beta-oxidation, into acetyl-CoA.

Acetyl-CoA is created when acetic acid is bound to coenzyme A.  Because fat molecules are pretty long, a lot of acetyl-CoA is made. The glucose molecules aren’t as long as the fat molecules, and consequently, create less acetyl-CoA. When following a low fat diet, acetyl-CoA is made from pyruvate, which is made from glucose in a process called glycolysis. After that the Krebs cycle happens.

Step 2

The acetyl-CoA manufactured from the fatty acids enters the Krebs cycle.

Keep in mind that when eating a high fat low carb diet, the body is forced to use the much longer fatty acids to make acetyl-CoA instead of the short glucose molecules. As a result, too much acetyl-C0A is made. When this happens, the Krebs cycle cannot keep up with the amount of acetyl-CoA being produced. Because of the overload, not all of the acetyl-CoA enters the Krebs cycle (to undergo gluconeogenesis). As a result, the excess acetyl-CoA is diverted and used to synthesize ketone bodies.

Step 3

The acetyl-CoA that doesn’t undergo gluconeogenesis is synthesized into ketone bodies.

Two acetyl-CoA molecules are synthesized to form acetoacetyl-CoA. Now, when a third acetyl-CoA molecule is bound to the acetoacetyl-CoA molecule , 3-hydroxy-3-methylglutaryl CoA (HMG CoA) is formed. Afterwards, that HMG CoA molecule is split apart. Once that happens acetoacetate (a ketone body) is formed, and one more acetyl-CoA molecule is produced. The acetoacetate molecule can be broken down further into beta-hydroxybutyrate, which is another type of ketone body. Acetone (another type of ketone) is formed in small quantities as well when ketones are broken down.

Wrap Up

Here’s a summary of what we just went over

  • Ketogenesis is the process in which fatty acids are taken and manufactured into ketone bodies, that are then used for energy or excreted by other means .
  • Fatty acids are broken down, by a process called beta-oxidation, into acetyl-CoA.
  • The acetyl-CoA manufactured from the fatty acids enters the Krebs cycle.
  • When eating a high fat low carb diet, the body is forced to use the much longer fatty acids to make acetyl-CoA instead of the short glucose molecules resulting in the Krebs cycle being overloaded.
  • Most of the acetyl-CoA cannot go through the Krebs cycle and is diverted and used to synthesize ketone bodies.
  • Two acetyl-CoA molecules are synthesized to form acetoacetyl-CoA which is then joined with one more molecule of acetyl-CoA to make 3-hydroxy-3-methylglutaryl CoA (HMG CoA).
  • The HMG CoA molecule is split apart forming acetoacetate.
  • The acetoacetate molecule is broken down further into beta-hydroxybutyrate.

So that’s a simplified, or rather over simplified, explanation of what happens during ketogenesis. When I first started the Ketogenic Diet back in 2012, I didn’t know how any of these processes worked. Once I did figure out the inner workings of it all, it didn’t enhance weight loss or fat burning, but it did help me better explain the diet to people that would ask me about it. Learning is a never ending process and the more you know about your individual body, the more successful you’ll be in reaching your goals.

ketogenesis
Ketogenesis Flow Chart

Thanks for reading. Please share and subscribe to keep up to date with new info. I’ll see you on the next one.