Fasting, the fat burning saga

Fasting, the fat burning saga

Part one: Ketosis

As we have seen in previous articles, fasting long enough gives us the chance to switch from using glucose and glycogen as main source of energy to using fats as the main source of energy. But what does it really mean to burn fats?


What are they?

To start we have to understand what fats are made of (this explanation will go a little bit into detail but bear with me for a little) .

The fat in our bodies is stored mainly in the form of triglycerides. Triglycerides are molecules made up from 3 fatty acids, and a molecule of glycerol that acts as a backbone for them. The process of burning fats implies breaking up this triglycerides in a way such that, the fatty acids, can go to different kinds of cells and be used directly, while the glycerol, can be turned into glucose by gluconeogenesis in order to supply energy to those cells that can’t use fats.

Now you may be asking yourself ” Sure, now I know what are the fats, but how are ketones related?”

The thing is that there is a small  problem, which is, that not all the cells in our body can obtain energy using fatty acids. The brain for example is in constant need of  glucose being the major consumer of this energy source. In normal situations this wouldn’t be a problem due to the high supply of glucose, but during a fast the supply of glucose is limited.

This means that we have to find another way to supply the brain with energy in a way such that, part of the glucose produced from glycerol, can reach those cells that can’t use fatty acids. And here is where ketones come into play.

Don’t be a picky eater

Why ketones are important

You may be curious about my choice of titles, and I will explain why I chose it, it wasn’t random mind you, but before that lets understand what are ketones.

When we speak of ketones we are referring mainly to 3 different compounds, which are acetoacetate (AcAc), 3-hydroxibutyrate (3HB) and acetone. The importance of this ketones for us comes from the fact that they can be used as a source of energy for our brain and as such can leave glucose for those tissues that can’t use fatty acids. The advantage in the use of ketones comes from the fact that these molecules are obtained from fatty acids. The importance of ketones and the fact that the brain can use them will be made apparent with the analogy.

ketones are obtained from fatty acids

Tactician’s choices

Photo by Henry Hustava on Unsplash

Now you may ask, ”Why should I care if ketones come from fatty acids or from any other thigh?”. To exemplify their importance lets use an analogy.

Let’s say you are a tactician in charge of an army in olden times, and your army is currently facing in a battle of attrition that has been going on for a few days. Due to the long battle your army is running low on supplies.

Your army is formed by an incredibly strong cavalry and a few units of infantry and the food has to be divided among them. Although you feel torn about it you give more preference to the cavalry since you know that they are your main card for victory, but you can’t stop giving supplies to your infantry since they form the bulk of your army and your cavalry would be overrun the moment you lose them.

In this situation when your back is against the ropes and you don’t know what to do, you see a miracle happening, a unit with an ally flag is coming your way and the have supplies!! You feel saved and distribute the new supplies to feed the cavalry while using the ones you already had to feed the infantry. And this is how ketones are important when fating.

When fasting as we said there comes a moment when we are using our fat stores and from this part goes to those organs that can use fatty acids while the glycerol is turned into glucose for the brain and other organs that can’t use fatty acids.

The supplies in this analogy are the glycerol stores, and the cavalry is the brain while the infantry are the rest of the organs that have to use glucose. While the new supplies are the ketones that help save the day, due to the fact that ketones come from transforming fatty acids and as such help feed the brain while giving more room for the usage of glucose for the rest of the organs.

Remember that there are tissues that cant use fatty acids and see themselves forced to fight with the brain for a limited supply of glucose, and you really don’t want to fight with the brain for resources.

In this situation where this tissues see themselves at risk of having less energy that required, is where the ketones are important, since the fact that they come from fatty acids and can feed the brain, they can ease the strain the brain has in the glucose supply.

To summarize, you can think of ketones as an alternative source of supply that gives the foot soldiers a food when it would otherwise go mostly to the brain.

For more articles about health and nutrition follow the link. If you liked this post and want more subscribe to our newsletter.


Jason Fung, Jimmy Moore ”The  Complete Guide To Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting”.2016. Victory Belt Pub.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.