What Are Exogenous Ketones? Fueling Your Body Beyond Carbs
It is likely you know someone who has tried the keto diet. Let’s talk a bit about the theory behind it, which is eating in a way that puts you in the metabolic state of ketosis. Ketosis is a process in which your body converts fat molecules into ketones, a fuel source your brain can use. Your brain cannot directly use fat as an energy source. When consuming a mixed diet, you rely on carbohydrates to fuel your brain. The traditional keto diet is a high-fat diet that cuts out carbohydrates, forcing your body to produce ketones to continue fueling your brain.
What is so great about ketones, and why would you want your body to make them? In theory, ketones are an efficient energy source that supports metabolism in several ways, including sparing carbohydrate stores, increasing muscle protein synthesis, and reducing inflammation and oxidative stress. However, many dietitians have reservations about the keto diet, beyond its well-supported clinical role in treating intractable epilepsy. The main drawbacks to the keto diet are that it is very restrictive and hard to adhere to, and it has been shown to have adverse effects on cholesterol levels in some dieters.
As an alternative, instead of making your own ketones, you can consume exogenous (meaning from outside your body) ketones as dietary supplements. In theory, these supplements would allow one to enjoy some of the beneficial effects of ketones on metabolism without undergoing severe nutritional restriction.
Defining Ketones and Their Natural Production
Normally, ketosis occurs when you virtually stop eating carbohydrates (consuming <50g of carbohydrate/day), which prompts your body to start making ketones from your body fat stores. This process occurs in your liver, producing two main ketone bodies: acetoacetate (AcAc) and β-hydroxybutyrate (BHB). Both ketone types affect metabolism, inflammation, and gene expression in multiple organs, including the brain, heart, and skeletal muscle.
The theory behind the keto diet is that drastically reducing the intake of carbohydrates in your diet will help you lose weight by 1) reducing the total amount of energy you consume and 2) forcing you to turn your body fat stores into ketones to fuel your brain. Proponents of the keto diet also claim that it “virtually eliminates” hunger and increases vigor and energy. Supplementing with exogenous ketones can place one in a state of “acute nutritional ketosis” by elevating blood ketone levels. This may also have some benefits without the restrictive diet.
The Science Behind Exogenous Ketone Supplements
Types of Exogenous Ketones (BHB Salts, Ketone Esters)
Exogenous ketones are either ketone salts or ketone esters. Ketone salts are beta-hydroxybutyrate bound to a mineral, such as sodium, potassium, or magnesium. As supplements, ketone salts are cheaper but have poor bioavailability, requiring higher doses to increase blood ketone levels. Another disadvantage of ketone salts is their potential for unpleasant GI side effects, such as cramping, diarrhea, and gastroesophageal reflux.
Ketone esters are liquid supplements consisting of either AcAc or BHB coupled with a precursor like glycerol or butanediol in an ester bond. Ketone esters offer the advantage of easy absorption, which reduces the dose needed to increase blood ketones. Their disadvantages include a higher cost and a notoriously bad, bitter taste.
Potential Benefits and Applications of Exogenous Ketones
Exploring Effects on Exercise Performance and Cognitive Function
Regarding exercise performance, there is no strong evidence that the traditional keto diet outperforms a conventional mixed diet. Taking exogenous ketones without severely cutting carbohydrates may offer some advantages for skeletal muscle and cognitive performance. Let’s look at the evidence for both.
For skeletal muscle, exogenous ketones could theoretically boost exercise performance by providing a high-efficiency energy source, allowing greater muscle force production with lower oxygen consumption and less lactic acid production. This means one can work at submaximal paces for longer periods without becoming tired. While promising in theory, there is no strong evidence to support this notion.
Clinical trials of exogenous ketone salts found either no effect or worsenedperformance following ingestion of exogenous ketones. Clinical trials of ketone ester ingestion prior to exercise have also mostly shown no positive effects on performance. As a 2022 review paper stated, the evidence overwhelmingly indicates that exogenous ketone supplements do not provide an ergogenic benefit to athletic performance.
Clinical trials of exogenous ketone salts found either no effect or worsenedperformance following ingestion of exogenous ketones. Clinical trials of ketone ester ingestion prior to exercise have also mostly shown no positive effects on performance. As a 2022 review paper stated, the evidence overwhelmingly indicates that exogenous ketone supplements do not provide an ergogenic benefit to athletic performance.
For cognition, exogenous ketone supplements have been theorized to help recovery from traumatic brain injury in a manner similar to creatine monohydrate supplements. Namely, ketones could, in theory, provide an easier-to-access energy source for the brain, which could, in turn, speed healing after injury. Though only one animal study, examining the impact of exogenous ketone supplementation in rats following a traumatic brain injury, has thus far been published, the results of this study were quite promising, as brain-damaged rats receiving exogenous ketone esters saw better improvements in brain structure and function following injury than rats who were not supplemented.
FAQs
What are exogenous ketones?
Exogenous ketones are dietary supplements that provide ketone bodies from an external source rather than requiring your body to produce them through carbohydrate restriction. They are typically available as ketone salts or ketone esters and are designed to temporarily raise blood ketone levels, creating a state known as acute nutritional ketosis.
Can exogenous ketones help with weight loss?
Exogenous ketones are not a magic weight-loss solution. While they can increase blood ketone levels, they do not automatically cause the body to burn more fat. Sustainable weight loss still depends on overall calorie balance, dietary habits, physical activity, and other lifestyle factors. Current research does not support exogenous ketones as a stand-alone weight-loss supplement.
Do exogenous ketones improve athletic performance?
Despite marketing claims, current research does not show consistent improvements in athletic performance from exogenous ketone supplements. Some studies have found no benefit, while others have reported reduced performance or gastrointestinal side effects. More research is needed before these supplements can be recommended as an ergogenic aid.
Are exogenous ketone supplements safe?
Exogenous ketones are generally considered safe for most healthy adults when used as directed, but they may cause side effects such as nausea, stomach cramping, diarrhea, or acid reflux—particularly with ketone salt products. Individuals with diabetes, kidney disease, or other medical conditions should consult their healthcare provider before using ketone supplements.
Do I need to follow a ketogenic diet to use exogenous ketones?
Not necessarily. Exogenous ketones can raise blood ketone levels even when carbohydrates are still being consumed. However, taking ketone supplements while eating a regular diet does not produce the same metabolic adaptations as following a long-term ketogenic diet. Researchers are still studying the potential benefits and limitations of this approach.
References
1Borowicz-Reutt, K., Krawczyk, M., & Czernia, J. (2024). Ketogenic Diet in the Treatment of Epilepsy. Nutrients, 16(9), 1258.https://doi.org/10.3390/nu16091258
2McGaugh, E., & Barthel, B. (2022). A Review of Ketogenic Diet and Lifestyle. Missouri medicine, 119(1), 84–88.https://pmc.ncbi.nlm.nih.gov/articles/PMC9312449/
3Evans, M., McClure, T. S., Koutnik, A. P., & Egan, B. (2022). Exogenous Ketone Supplements in Athletic Contexts: Past, Present, and Future. Sports medicine (Auckland, N.Z.), 52(Suppl 1), 25–67.https://doi.org/10.1007/s40279-022-01756-2
4Fischer, T., Och, U., Klawon, I., Och, T., Grüneberg, M., Fobker, M., ... & Marquardt, T. (2018). Effect of a sodium and calcium DL‐β‐hydroxybutyrate salt in healthy adults. Journal of nutrition and metabolism, 2018(1), 9812806.https://doi.org/10.1155/2018/9812806
5Leaf, A., Rothschild, J. A., Sharpe, T. M., Sims, S. T., Macias, C. J., Futch, G. G., Roberts, M. D., Stout, J. R., Ormsbee, M. J., Aragon, A. A., Campbell, B. I., Arent, S. M., D'Agostino, D. P., Barrack, M. T., Kerksick, C. M., Kreider, R. B., Kalman, D. S., & Antonio, J. (2024). International society of sports nutrition position stand: ketogenic diets. Journal of the International Society of Sports Nutrition, 21(1), 2368167.https://doi.org/10.1080/15502783.2024.2368167
6Vandoorne, T., De Smet, S., Ramaekers, M., Van Thienen, R., De Bock, K., Clarke, K., & Hespel, P. (2017). Intake of a ketone ester drink during recovery from exercise promotes mTORC1 signaling but not glycogen resynthesis in human muscle. Frontiers in physiology, 8, 310.https://doi.org/10.3389/fphys.2017.00310
7O'Malley, T., Myette-Cote, E., Durrer, C., & Little, J. P. Nutritional ketone salts increase fat 727 oxidation but impair high-intensity exercise performance in healthy adult males. In Appl (Vol. 728, pp. 1031-5).https://doi.org/10.1139/apnm-2016-0641
8Whitfield, J., Burke, L. M., McKay, A. K., Heikura, I. A., Hall, R., Fensham, N., & Sharma, A. P. (2020). Acute ketogenic diet and ketone ester supplementation impairs race walk performance. Medicine and science in sports and exercise, 53(4), 776.https://doi.org/10.1249/mss.0000000000002517
9McCarthy, D. G., Bostad, W., Powley, F. J., Little, J. P., Richards, D. L., & Gibala, M. J. (2021). Increased cardiorespiratory stress during submaximal cycling after ketone monoester ingestion in endurance-trained adults. Applied physiology, nutrition, and metabolism, 46(8), 986-993.https://doi.org/10.1139/apnm-2020-0999
10Almeida-Suhett, C., Namboodiri, A. M., Clarke, K., & Deuster, P. A. (2022). The ketone ester, 3-hydroxybutyl-3-hydroxybutyrate, attenuates neurobehavioral deficits and improves neuropathology following controlled cortical impact in male rats. Nutritional Neuroscience, 25(6), 1287-1299.https://doi.org/10.1080/1028415x.2020.1853414
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