Ketosis: Your Body as a Fat Burning Machine!

Ketosis: Your Body as a Fat Burning Machine!


One of the biggest questions I receive about the Paleo diet, or any diet that preaches restricted carbohydrate intake is, where will we get out energy from? Everyone knows carbohydrates and its end product (glucose) is the only way we can fuel our body, right? False, this is a common misconception; in fact our body has physiological mechanisms in place such that we can run on any of the three main energy substrates: protein, fats, and carbohydrates.

Let’s start with a brief look at the goal of our metabolic system. The whole goal of our metabolic system is to provide our body the fuel it needs to function.  The fuel we humans rely on is chemical energy, the energy present in the chemical bonds of the food we eat.  While carbohydrates are the quickest source of energy for your body to turn into fuel, it is not the only source; in fact it is not even the most efficient. Research has shown that there is no clear “requirement” for dietary carbohydrates in human adults1 (citation 13).  Our body has two mechanisms in place in which we can provide the substrates needed to fuel our body without dietary carbohydrate: gluconeogenesis (the production of glucose from proteins/amino acids) and ketosis (the production of ketone bodies from fatty acids).  As the majority of Americans are concerned with fat-loss and it is ketosis is a hot topic we are going to focus on the latter. I will try and keep the nerdy side of me at bay and limit the biochemistry and specific metabolic pathways to a minimum.

In a state of carbohydrate restriction (i.e. a low carbohydrate diet) our metabolic system must figure out a way to provide enough glucose to the brain and other tissues (red blood cells, and specific kidney cells) that function only on glucose. If you aren’t ingesting carbohydrates where the heck do we get it? I mean our blood and our brain are pretty important for functioning right?  At this point our body can begin to catabolize (essentially consume) must tissue for its amino acids and turn that into glucose, but do we really want our hard earned muscle to wither away?

This is where ketosis steps in; your body decides to start utilizing fat as your primary fuel source, using your “spare tire” to feed the brain and a handful of other systems in your body.

Yes, that is right, your body starts turning fat into fuel. Plus, you don’t even have to be in the “fat burning zone” that your wonderful elliptical machine tells you that you have to stay in for what seems in eternity just to get your body to burn those love handles. So how exactly does this work? And is it bad for you?

The process of ketosis begins with a process called lipolysis.  Fat (triaglycerol) is cleave to provide 3 fatty acid chains along with a single glycerol molecule.  While most of the body is able to utilize the fatty acids as an alternative energy source through a process known as beta-oxidation, the glucose obligatory tissue are not.  This is where the liver takes charge. The liver takes the byproducts of beta oxidation (Acetyl CoA) does a complicated song and dance and pops out ketone bodies (Acetoacetate and 3-hydroxybutarate).The liver cannot utilize these ketone bodies so it packages them and ships them to extra-hepatic tissue ( the brain, heart, etc.)2 . In fact, in many tissues ketone bodies is a superior fuel source in terms of efficiency.  While there are a whole host of other processes that go on during this process that are extremely interesting I will digress and continue on with the next question. If you are a visual person like me, I found a wonderful little picture that is quick and dirty to go along with all this wordy nonsense.


Is ketosis bad for you? Ketone bodies are indeed acidic; they can and do effect the acid base balance in the body so can create an acidic state in my blood?  Before we begin this discussion I need to clear the air.  We are talking about Ketosis, not Ketoacidosis. Ketosis is a normal physiological response in which the production of ketone bodies is controlled and regulated. In ketosis, the blood pH remains buffered within normal limits 3.  It is believed that because ketone bodies directly affect lipolysis in adipose tissue and affect insulin and glucagon (hormones that regulate blood glucose levels) which can potentially control the rate of their own production. This regulated and controlled state of dietary ketosis is harmless2. In conjunction with accelerated fat loss, ketosis is believed to help ameliorate insulin resistance, diseases resulting from free radical damage, along with disease resulting from hypoxia4.  Ketoacidosis on the other hand is a very serious situation. Ketoacidosis occurs the production of ketone bodies is uncontrolled are produced in enormous quantities, resulting in the acidification of the blood. The inability of the body to regulate ketone production is linked to a malfunction in the bodies signaling system (the hormones insulin and glucagon).  Ketoacidosis is generally a complication of diabetes mellitus, so if you are diabetic (type I or type II) ketosis is something you probably shouldn’t dive right into.

What does all this mean? Your body does not need pasta, pop-tarts, bagels, or orange juice to function. You can fuel your body with adequate protein and fat intake and use your stored adipose tissue (those pesky love hands) to provide yourself with plenty of energy to tackle the day. In fact, why don’t you scarf down some eggs and bacon for breakfast and turn your body into a fat burning machine!

  1. Westman, E. (2002). Is dietary carbohydrate essential for human nutrition. American Journal of Clinical Nutrition, 75, 951-954.
  2. Manninen, A. H. (2004). Metabolic effects of the very-low-carbohydrate diets: Misunderstood “villans” of human metabolism. Journal of the International Society of Sports Nutrition, 1(2), 7-11.
  3. Salway, J. G. (1999). Metabolism at a glance. Oxford: Blackwell Science.
  4. Veech, R. L. (2004). The therapeutic implications of ketone bodies: the effects of ketone bodies in pathological conditions: ketosis, ketogenic diets, redox states, insulin resistance, and mitochondrial metabolism. Prostaglandins, Leukotrienes and Essential Fatty Acids(70), 309-319.

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