What is Ketosis?

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Many people do not like to read more in depth on the science of keto but I think it is important.  I do not think that you need to become an expert but I do think there is benefit in learning how and why you are eating the way you are.  This will make it easier to stay motivated and allow you to learn how the body works so you can continue to adjust the diet for different goals.

The basic definition of a ketogenic diet that you'll see almost everywhere is that it's a low carb, high fat diet. The purpose of this low carb high fat approach is that you are trying to transition your body's primary fuel source from glucose to ketones.

Why is this Important?

When you are following a traditional standard American diet, one in which you are consuming a lot of carbohydrates, your body's primary fuel source is glucose.  When we consume carbohydrates they are broken down to glucose causing an increase in blood glucose. This increase stimulates our pancreas to secrete insulin. Insulin is a hormone that will help drive this glucose into our cells so that it can be used for energy to help with the processes that need to take place in the body.

Glucose is also our primary fuel source because we are very efficient at using it.  If carbohydrates are available, then we will preferentially use them over any other available energy.  It is worth remembering that as a survival mechanism, the body loves to take the path of least resistance.

The issue with glucose being the bodies primary energy source is that chronic carb consumption and having constant elevated levels of insulin and blood glucose can lead to a lot of health issues, in particular, inflammation and insulin resistance.

Insulin resistance, to put it simply, occurs when our cells lose the ability to communicate with insulin, to allow glucose to enter the cells effectively and produce the energy that is needed. This can lead to your cells essentially starving for energy and your pancreas secreting more insulin, further contributing to the problem.

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Inflammation is the bodies natural response to injury or damage. Consuming a diet high in carbohydrates, especially processed carbohydrates, is a great way to drive up inflammation which not only gets in the way of your cells functioning properly but also induces many impairments in health.

Both Insulin resistance and inflammation are common contributors to conditions like diabetes, Alzheimer's, Parkinson's, cancer, PCOS, and many more.

It is becoming evident that consuming carbohydrates and having glucose as our primary fuel source long term, probably is not the best idea for our health. This is where a ketogenic diet and ketosis can come in.

The purpose of a ketogenic diet is to provide a different fuel source. When carbohydrates are restricted, the body is very smart and is able to find a different source of energy which is where ketosis comes into play.

What is Ketosis?

Ketosis: A metabolic state that is characterized by low levels of glucose and insulin and elevated levels of ketones in the blood.

Ketosis is simply a state where a new fuel source is being produced to make up for a lack of glucose. Ketosis can occur whenever there is a need for fuel such as during carbohydrate restriction, during severe calorie restriction or fasting, and when our body is no longer able to utilize carbohydrates from fuel.

It is important to differentiate between the ways in which ketosis can be induced. When carbs or calories are restricted, nutritional ketosis occurs. When the body is no long able to utilize carbohydrates for fuel, diabetic ketoacidosis or DKA occurs. These are two very different situations.

DKA, which occurs in diabetics, is characterized by an uncontrolled and unsafe rise in blood ketones with subsequent high levels of glucose and insulin. Nutritional ketosis or NK is a controlled and safe rise in blood ketones with subsequent low levels of glucose and insulin. In essence, DKA is dangerous but NK is safe.

Nutritional ketosis is a completely normal metabolic process that we are all able to activate under the defined conditions of low glucose and insulin.  One of the reasons why this process exists is for survival.  Since ketosis kicks in when glucose and insulin is low, and it leads to the production of a different fuel source in ketones, it makes for an incredible survival mechanism to allow us to provide fuel for our brains and bodies during periods of food restriction or fasting.  Since the brain is unable to utilize just fat for fuel, it becomes increasingly important to be able to make another fuel source that the brain can use in ketones.

Ketologist Insight:

The ketogenic diet, which also induces a state of ketosis because of its ability to also create conditions of low glucose and insulin, was founded for its ability to similarly mimic fasting.  This is what make keto important, we can maintain a level of ketosis even after we have ate.

How Does Ketosis Work?

To reiterate, when we consume carbs we have an increase in glucose and insulin.  However, not consuming carb leads to decrease in glucose and insulin.  When we have low levels of glucose and insulin, our pancreas secretes another hormone known as glucagon.  Glucagon can interact with our stored fat, releasing it into the blood where it can be used for energy.

But the body doesn’t stop there.

Interestingly, while most of our body can run on fat for fuel, our brain cannot. Again, this is why we possess this unique metabolic mechanism of ketosis. The liver can break down fat and use it to make ketones. Ketones are little molecules that can serve a big purpose in the body. 

Interestingly, the liver does not possess the necessary enzymes to use ketones, so these energy molecules are instead shuttled out of the liver and into the blood where they can travel to cells to be used for energy, especially by our brain. In fact, whenever ketones are available, the brain will utilize them as a fuel source (1). This is likely because ketones provide more energy and create less oxidative stress when metabolized compared to glucose.

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You can achieve an increase in blood ketones through something as simple as completing a short 16 to 18 hour fast (2).  After just a couple days of ketogenic dieting, you can experience ketone elevation enough to be considered “in ketosis” (3).  Being in ketosis means that you have a higher and more sustained increase in blood ketones, which can be best tested via blood ketone meters.

How Do I Know If I Am in Ketosis?

This is of course one of the most important questions. The most common answer is by testing your ketone levels. Ketones can be tested via urine, blood, and breath with blood testing being the most reliable method (4). The problem with any ketone testing technique is that interpreting the results is difficult.

If testing your ketones is the most recommended approach for determining ketosis, then the most logical next question should be: What range should my ketones be in to be considered in ketosis? The truth is….we don’t know.

There are many studies out there that claim different optimal ketone ranges. There are scientists that suggest that 0.5 mmol is adequate while others saying being between 1.5-3 mmol is recommended. The truth is that the optimal range of ketones is highly bio-individual, depends on the goal, and may vary depending on on how long you have been keto for.

Anecdotally, I have noticed that those who have been following the ketogenic diet for longer, tend to have slightly lower levels of ketones in their blood. My theory is that this could be due to more efficient utilization of the ketones thus leaving less behind in the blood when testing. If this is true, testing you ketones to know if you are in ketosis the longer you follow keto would become increasingly difficult.

Despite this confusion on ketone testing, I am not downplaying its significance. If you are new to keto, testing your ketones to see if you are producing them is a great way to ensure that you are on the right track with your diet. If you are new to keto I recommend aiming to have those blood ketone levels above at least 0.5 mmol. If you have been following keto for a while and you have been testing frequently, then you will have trends to consider to allow you to better interpret your own results.

In addition to testing your blood, there are also tell tale signs of ketosis that can help you out such as:

  • Frequent urination

  • Dry mouth

  • Rapid Weight Loss

At this point it is extremely important to note that being in ketosis only means that you have elevated blood ketones. It does not mean that your body is efficient at utilizing these ketones yet. For this reason, when people ask the question, “How do I know if I am in ketosis?”, they really should be asking, “How do I know if I am keto-adapted?”.

What is Keto-Adapted?

Keto-Adaptation: A state that occurs when your body has become efficient at burning fat and producing and utilizing ketones for fuel.

Just being in ketosis does not mean that you are keto-adapted.  It is important to realize that our body is not accustomed to using fat and ketones for fuel. Most people’s bodies have not done this since they were babies.  For this reason, the cells in our body must up-regulate the processes necessary to take in ketones and use them as fuel.  Typically, this takes a little longer than just the production of ketones. This is why you may see a lag time between when your body is producing ketones and when you actually start to feel some of the benefits of ketosis. This period is what we refer to as the keto-adaptation period.

While there are some tell-tale signs of being keto-adapted, which we will go over in a bit, there is also testing that can still help shed some light. The blood ketone testing mentioned earlier can again at least demonstrate that your body is producing ketones. Additionally, you can test your blood sugar with the same devide for even more insight. Remember, when on a keto diet your glucose should lower so demonstrating low blood glucose WITH elevated blood ketones is a pretty good indication that you are becoming keto-adapted.

From a scientific perspective, having data is important. From a practical stand point, it may not be. For this reason, determining if you are keto-adapted can also be done by answering the following questions:

  • Do I have energy?

  • Am I hungry?

  • How is my sleep?

  • Am I seeing progress?

  • How is my workout performance?

  • Am I able to better focus?

If you are keto-adapted, you are likely experiencing some of these noticeable changes that are great indicators of adaptation. However, becoming keto-adapted is no walk in the park. For many, it means dealing with the dreaded keto-flu to get there.

What is the Keto Flu?

The Keto Flu: Flu-like symptoms that can accompany induction to a ketogenic diet

The keto flu is something that occurs in most new keto dieters.  One of the reasons this occurs is because you are no longer providing your body with its typical fuel source (glucose) but your bodies is not yet primed for using fat and ketones for fuel.  This can lead to things like mental fog, fatigue, and even feelings of depression and anxiety for some.

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It is not just the source of energy that is causing these keto flu symptoms though. In fact, a bigger contributor to your keto-flu symptoms is dehydration and electrolyte deficiency.

Remember, when you stop eating carbs, your blood sugar and insulin levels drop. This causes the kidneys to excrete more water and electrolytes leading to dehydration and electrolyte deficiency which both contribute many symptoms of the keto-flu.

However, there are strategies you can take to prevent this and better manage your keto-flu symptoms or for some, avoid them all together like staying hydrated and replenishing electrolytes.


The truth is, ketosis is a lot more in depth than what I have tried to simply describe here.  It is a complex process that is still being studied everyday to learn more about optimizing it and all of its implications.  However, this general overview should provide you with enough insight to better understand the changes that are occurring in your body!

If you are looking to learn more about keto, check out my article What is Keto? If you are ready to start keto, sign up for my newsletter below and I’ll send you all of the info you need to get started!

Christopher Irvin