What are Ketones?

Authored by Justin Liau • 
November 14, 2017

Ketones are an efficient source of energy that the body naturally produces when pushed to its limits. Also called ketone bodies, these molecules are produced by the liver from fatty acids during periods of fasting, carbohydrate restriction, or prolonged exercise. 

Ketones may sound like a new discovery, but the human body has been able to produce them since prehistoric times. During varying seasons of feast or famine, ketones enabled prehistoric man to sustain focus and energy while on the hunt for food. 

Our brains are glucose dependent, but are able to utilize ketones for energy as well, primarily β-hydroxybutyrate (βHB) and acetoacetate (AcAc).

In human biology, there are three different molecules that have a ‘ketone’ group that are found in the body: βHB, AcAc, and acetone. These biological ketones are a fuel source that our bodies can naturally produce from breaking down dietary fat or our body’s fat stores. We can also elevate our blood ketone levels through consuming exogenous ketones, namely ketone ester or salt drinks. It can take many days for ketone production to rise, depending on your individual metabolism. 

The evolutionary function of ketones is to provide a fuel for the brain when blood glucose falls, because fats in their unprocessed form can’t fuel the brain. Fats cannot cross the blood-brain barrier–so ketone production means that the energy stored as fat can be used to sustain the brain. 

Research shows that during starvation, as ketone levels increase, the brain can get up to 60% of its energy from ketones1. Other than keeping our brains going, ketones can help increase insulin sensitivity, control blood glucose levels, lower blood pressure, reduce cravings, improve cholesterol, aid in weight loss, improve energy, and more.

Ketone Metabolism

Ketone body metabolism includes ketone body synthesis (ketogenesis) and breakdown (ketolysis). When the body goes from the fed to the fasted state, the liver switches from an organ of carbohydrate utilization and fatty acid synthesis, to one of fatty acid oxidation and ketone body production. In these states the fat-derived energy (ketone bodies) generated in the liver enter the bloodstream, and are used by other organs, such as the brain, heart, kidney cortex, and skeletal muscle. The precursor for the synthesis of ketones is acetyl coenzyme A (acetyl CoA), which is formed by β-oxidation of free fatty acids in the liver2.

Ketones for Weight Loss

If you are producing ketones naturally, you're going to be burning through fat stores, which could help with weight loss. Simply by following a ketogenic diet, you will be consuming less carbohydrates, and therefore not spiking insulin as much which may also contribute to weight loss. 

But perhaps there is a direct effect of the ketones d-β-hydroxybutyrate (BHB) and acetoacetate (AcAc), which are elevated during prolonged fasting or during a ketogenic diet. Weight loss on a ketogenic diet may be associated with decreased appetite and altered gut hormone levels, and it is possible that these changes are caused by elevated blood ketones3. The study found that consuming ketones via a ketone ester drink lowered human ghrelin (hunger hormone) and appetite. 

Ketones and Diabetes

Diabetic ketoacidosis (DKA) is a serious condition that can lead to diabetic coma (passing out for a long time) or even death. The body produces ketones when it doesn’t have enough insulin to use glucose, the body’s normal source of energy. When ketones build up in the blood, they make it more acidic. They are a warning sign that your diabetes is out of control or that you are getting sick.

Too high levels of ketones (>25 mM) can poison the body and cause DKA. DKA may happen to anyone with diabetes, but it is most common in Type I diabetes. 

Symptoms of ketoacidosis:

  • Constant fatigue
  • Dry skin
  • Nausea, vomiting, or abdominal pain
  • Difficulty breathing
  • Fruity breath
  • Attention issues, confusion

Ketone Supplements and Drinks

There is a multitude of ketone supplements and drinks out on the market right now. There is quite limited research that actually measures what these supplements do for health and performance. The most compelling evidence supports the use of ketone ester (BHB monoester) ketone supplements in athletes doing endurance based exercise. Ketones are metabolized before carbs or fat. The improved performance of ~2% during a cycling time trial suggests ketosis during exercise may be beneficial for some athletes4. This has huge implications for sports as 2% in competition can mean the difference between winning the gold medal and not placing at all. 

Ketones are our body’s emergency fuel units that may have powerful implications and benefits for a plethora of use cases. Whether you practice intermittent fasting, follow a ketogenic diet, or drink ketone esters or salts, ketone bodies can fuel you for the long haul.

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.White H, Venkatesh B. Clinical review: Ketones and brain injury. Critical Care. 2011;15(2):219. doi:10.1186/cc10020.
3.Stubbs, B.Cox, P.; Evans, R.; Santer, P.; Miller, J.; Faull, O.; Magor-Elliott, S.; Hiyama, S.; Stirling, M.; Clarke, K. (2017). On the metabolism of exogenous ketones in humans. Front. Physiol.
4.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.
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