What is Ketosis?

Authored by Justin Liau • 
February 22, 2018

Our bodies’ metabolisms are complicated, fluid systems that have many characteristics. They’re very transient in nature and adapt to the inputs we provide our bodies with. One adaptation state called ketosis, is the state of having elevated ketone levels, typically above 0.5 mM. Whether or not we have ketones in our body is based on the inputs we consume or omit. A state of endogenous Ketosis essentially means the body is in “fat-burning mode” and is a metabolic shift as the body prioritizes ketones and fats over carbohydrates in the hierarchy of energy substrates. 

In order to understand ketosis a little more, we must first understand what fuel sources our body can use for energy. We usually think of carbohydrates, fats, and proteins as being the only available fuel sources for our body. Whilst many parts of the body can use a combination of these fuels, the brain depends heavily on the breakdown of carbohydrates into glucose for fuel. This is due to the fact that fats cannot easily cross the blood-brain barrier to fuel the brain.

Carbs. Many have a love/hate relationship with them. They taste good and they make us feel good. However, these feelings only last so long and soon many of us find ourselves with cravings galore.  If carbohydrates stop coming into the body and carbohydrate stores in the body are depleted, a cascade of hormonal signals causes the body to increase the release of stored fats. In the liver, these fats are converted into ketones which can provide up to 60% of the brain's energy requirements1. Unlike fats, ketones can cross the blood-brain barrier and are readily used as a fuel for the brain. Ketone metabolism ensured that prehistoric man could survive periods of fasting and carbohydrate deprivation2

Achieving Ketosis

So how does one go about achieving this metabolic state that powered our caveman ancestors? Methods to achievie ketosis include fasting, following a structured ketosis diet regimen, or by supplementing with exogenous ketones. You can reap the benefits of ketosis by implementing one of these lifestyle changes today. 


We all go through periods of fasting whether we know it or not — we fast while we’re asleep, for example. Fasting was a common occurrence amongst our hunter-gatherer ancestors and is a prevalent practice in many religions. Three of the most well known fasting protocols include: intermittent fasting, alternate-day fasting, and water fasting. Alternate-day eating and time restricted feeding fall under the intermittent fasting category and are popular fasting regimens. During alternate-day eating, you switch between days of normal eating and days of caloric restriction to 25% of normal caloric intake3. For time restricted feeding you only eat during a short time window each day. This window can range from four to twelve hours. Water fasting means drinking only water, but consuming no calories during the fast. Studies show that fasting can result in fat loss and spared muscle mass4. You can join the conversation about fasting in our WeFast Facebook community.


“Let food be thy medicine and thy medicine be thy food” Hippocrates famously said. Following a well-formulated ketogenic diet is one way to achieve ketosis. This means eating roughly 70-100% of your calories in fats and keeping your carbohydrate intake low. This style of eating will train your body into relying on fats for energy rather than carbohydrates. Fatty acids are then converted into ketones by the liver to fuel your brain and body. Do note that a ketogenic diet  is always a low-carbohydrate diet, BUT low-carbohydrate diets are not necessarily ketogenic (i.e resulting in ketone release). A common pitfall of people attempting the ketogenic diet is overly high protein consumption, which the body converts to glucose via gluconeogensis. A true ketogenic diet must be based on fat for the majority of calories. The ketogenic diet is not the easiest way to get into ketosis, and many have difficulty with adherence. However, the ketogenic diet has been around since the 1920’s and is as well studied as any nutritional protocol, especially for therapeutic purposes. Reduction of appetite, blood sugar control, mood control, and improved energy are among a host of potential benefits of the ketogenic diet. 

Exogenous Ketones

Exogenous ketone bodies are ketones that are consumed through a nutritional supplement. They can result in ketosis (elevated blood ketone levels) without changing the diet. Ketones produced by the liver during a ‘ketogenic’ state (when fasting or following a ketogenic diet) are called endogenous ketones.

Exogenous = ‘Exo’ = external. ‘Genous’ = origin. Originates from a source external from the body.

Endogenous = ‘Endo’ = within. ‘Genous’ = origin. Originates from a source internal to the body.

Taking ketone supplements means the body can be in 'ketosis' without being ‘ketogenic,’ and may deliver some of the benefits of 'ketosis.' Here it is important to note that exogenous ketones don’t trigger natural ketone production; they don’t put you in a ‘ketogenic’ state. They do put you into ‘ketosis’ which simply means that your blood ketone levels are elevated. They also provide their own set of benefits. For example, the administration of ketone of a ketone ester-based drink to athletes during exercise showed unique metabolic benefits of ketone metabolism5. The physiological alterations achieved by acute nutritional ketosis may improve human physical performance in some athletes as indicated by initial endurance test results. Taking exogenous ketones can create a metabolic state that would not normally occur naturally: the state of having full carbohydrate stores as well as elevated ketones. 

Measuring Ketosis

You are in ketosis when you have elevated levels of ketones in your blood, normally counted as above 0.5 mM. The gold standard for measuring ketones is blood ketone measurement with a tool like the Abbott Freestyle or KetoMojo. 

The three types of ketones are:

  • Acetate
  • AcetoAcetate (AcAc)
  • Beta-HydroxyButyrate (BHB)

When the liver releases ketones, they first appear in the blood as BHB and AcAc. Exogenous ketones or ketone supplements can artificially raise the level of BHB and AcAc in the blood. Through natural conversion processes, ketones can appear in the urine or in the breath (as acetone).

In order to obtain the most comparable measures, it is useful to measure blood ketones at the same time each day. Measuring immediately upon waking means that there are fewer potential variables that could alter the measurement, such as exercise, or different food intake. However, it can also be useful to check ketone levels around 60-90 minutes after an intervention such as eating a fat-rich meal or consuming exogenous ketones. 

BHB in blood levels that determine your level of ketosis:

  • No ketosis: under 0.5 mM BHB in blood
  • Low ketosis: 0.5 - 1.5 mM BHB in blood
  • Moderate ketosis: 1.5 - 3 mM BHB in blood
  • High ketosis: over 3 mM BHB in blood

In short, no, the presence of ketones at low levels  is very natural. Ketosis after fasting or following a keto diet is very different from the harmful ketoacidosis seen in Type 1 Diabetes6. In some people the following symptoms can occur temporarily during the transition into ketosis. 

Is ketosis bad? Are there any side effects of being in ketosis? 

Ketosis symptoms:

  • Fruity breath that smells like nail polish. 
  • Shortness of breath.
  • Excessive thirst.
  • Frequent urination.
  • Stomach discomfort.

Ketosis Benefits

  • Improved insulin sensitivity.
  • Improved blood glucose control.
  • Appetite control.
  • Decreased inflammation.
  • Slowdown of muscle protein breakdown.
  • Gene expression.

Depending on your goals and lifestyle you may want to look into achieving ketosis through fasting, diet, or exogenous ketones. Contrary to popular belief, ketosis is a safe, natural state that our bodies have been capable of being in since prehistoric times. Cyclical ketosis is also a viable options which constitutes 5-6 days of ketogenic dieting and 1-2 days of high carb eating. More and more people are discovering the benefits of being in ketosis and they might just align with your health goals.

Scientific Citations

1.Owen, O.E., Morgan, A.P., Kemp, H.G., Sullivan, J.M., Herrera, M.G., and Cahill, G.F. (1967). Brain Metabolism during Fasting. J. Clin. Invest. 46, 1589-&.
2.Cahill, G.F., Jr. (2006). Fuel metabolism in starvation. Annu Rev Nutr 26, 1-22.
3.Varady, K. A., Bhutani, S., Klempel, M. C., Kroeger, C. M., Trepanowski, J. F., Haus, J. M., . . . Calvo, Y. (2013). Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutrition Journal, 12(1). doi:10.1186/1475-2891-12-146
4.Hatori, M., Vollmers, C., Zarrinpar, A., Ditacchio, L., Bushong, E., Gill, S., . . . Panda, S. (2012). Time-Restricted Feeding without Reducing Caloric Intake Prevents Metabolic Diseases in Mice Fed a High-Fat Diet. Cell Metabolism, 15(6), 848-860. doi:10.1016/j.cmet.2012.04.019
5.Cox, P.J., Kirk, T., Ashmore, T., Willerton, K., Evans, R., Smith, A., Murray, Andrew J., Stubbs, B., West, J., McLure, Stewart W., et al. (2016). Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes. Cell Metabolism 24, 1-13.
6.Paoli A, Rubini A, Volek JS, Grimaldi KA. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. European Journal of Clinical Nutrition. 2013;67(8):789-796. doi:10.1038/ejcn.2013.116.
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