(and other techy stuff)

Although ketones have been known about for over a century, they have only only recently enjoyed public attention, and only some of that positive. Many people, including medical professionals, associate ketosis (the process of burning fat for energy) with a dangerous condition called ketoacidosis, where both sugar and ketone levels are elevated. Understanding how the body uses energy is key to understanding the benefits and dispelling the myths.

Let's start with the basics, what are ketones?


Ketones are part of fat metabolism in the body, created in the liver under certain circumstances. Most organs in the body can use ketones as a source of energy, in addition to glucose (sugar in the blood). There are three ketone bodies:

  • Acetoacetate, the precursor of the other two
  • β-hydroxybutyrate, a compound that is further broken down for energy (not technically a ketone)
  • Acetone, either used for energy or exhaled as waste

Ketones are fatty acids, which will be important to remember later.


Ketosis is a state where there are more ketone bodies in the bloodstream than the body needs for its immediate use. Levels can be detected by directly testing the blood or indirectly by measuring the amount of one type of ketone body (acetoacetate) excreted through urine.

Nutritional Ketosis

Ketosis which has been brought about by changes in diet, either through fasting or carbohydrate restricted meal plan, such as Atkins, Paleo, or Keto weight loss diets.


A dangerous medical condition where insufficient insulin results in glucose and ketones levels getting too high. Too much glucose can result in dehydration, while too many ketones can result in the blood becoming too acidic. Nutritional ketosis can not result in ketoacidosis as long as the body is able to produce insulin.

Exogenous Ketones

Consumption of ketone esters or salts which results in a state of ketosis independent of diet.


The human body is an amazing machine! As fascinating as it can be to read about, much of the material seems to be either simplified to the point of boring or chock full of organic chemistry aimed at graduate students. I aim to make this section give a clear overall picture, with more fun details linked to particularly complex aspects. Keep me honest, though, and let me know if I got anything wrong. I'm more at home with physics than chemistry...


Metabolism is the various chemical processes that occur within the body in order to sustain life. Some processes build or create components and some processes break down components. We will focus on how the body uses different energy sources to fuel cellular activity.


Digestion is the break down of consumed nutrients. It's the first step in the process, essentially, because we can't use sunlight like plants. Digestion is helped along by substances known as enzymes. Various enzymes help break up different types of food into smaller compounds, as the cells can't use them in their original form.


Macronutrients are three primary classifications of food, Protein, Carbohydrates, and Fats. When percentages are given for a type of diet, it's usually for the ratios of these three macronutrients.

  • Proteins are broken down into amino acids
  • Fats are broken down into lipids
  • Carbohydrates are broken down into sugars

Cellular Energy

Most sources drill down through all of the chemical reactions to get to how cells actually get energy from our food. It makes more sense to me to work from the cellular level up to the macronutrients. Part of this is due to the amazing flexibility of the body to accomplish the same goal through different means. Since we want to understand the difference between using carbohydrates for energy and using consumed or stored fat for energy, we can focus on where those two diverge.

Adenosine triphosphate (ATP)

ATP is the main energy source for cells. It also does other stuff. Once a cell uses it for energy, it's recycled into its precursors. It comes from the citric acid cycle, also known as the Krebs cycle or the tricarboxylic acid (TCA) cycle. When reading other material that mentions ATP, know that it's the final form all the other stuff takes in the journey from food to something the cells can actually use.

Watch a video explanation here:
ATP: Adenosine triphosphate: Learn more about ATP: how it stores energy, and how that energy is released

Citric Acid Cycle

A complex process that takes the bigger building blocks and, among other things, creates the ATP that provides the actual energy for cells. It's mentioned quite a bit in more technical articles on ketosis, but for our purposes, we just need to know it's what's between ATP and Acetyl-CoA (up next).

Krebs / citric acid cycle: Overview of the Krebs or Citric Acid Cycle

Acetyl coenzyme A (acetyl-CoA)

Acetyl-CoA feeds the citric acid cycle. It also plays a part in balancing carbohydrate and fat metabolism, and this is where things get kinda confusing. Protein, carbs, fats, and ketone bodies get converted into Acetyl-CoA through enzyme reactions or β-oxidation, the splitting of long carbon chains of fatty acids into Acetyl-CoA. Acetyl-CoA is first used for energy via the citric acid cycle, then excess is stored to capacity as glycogen, then the rest as ketone bodies, which eventually becomes stored as body fat, or adipose tissue.

So, carbs and protein take somewhat of a direct path from ingestion to energy, while fats can loop through Acetyl-CoA via ketones. The diagram below shows a simplified version of the process (minus the ketone loop).

Diagram of Metabolic Pathways