Article

Exogenous Ketones: Understanding Their Role in Ketosis and Performance

Published on Tuesday, February 24, 2026
by Alexander Koch

Nutrition

Wellness

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 you turn fat molecules into ketones, a fuel source that 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 to force 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 translates into allowing one to 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 worsened performance 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 is overwhelmingly against exogenous ketone supplements providing an ergogenic benefit to athletic performances.

For cognition, exogenous ketone supplements have been theorized to help recovery from traumatic brain injury, in a manner similarto 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.

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