Beta-hydroxybutyrate esters or salts depending on the product (esters are more potent and more expensive).
Meta-analysis: exogenous ketones (which raise ketones without restricting carbohydrates) have a measurable effect on cognition; the brain can use them as an alternative fuel. A signal of interest, especially where brain metabolism is compromised; modest magnitude.
View the study (meta-analysis) →⏱ 4 min read
Exogenous ketone bodies are supplements designed to rapidly raise plasma ketone concentrations (especially beta-hydroxybutyrate or BHB, the quantitatively most important ketone body) without needing to follow a strict ketogenic diet or maintain a prolonged fast to produce endogenous ketosis; under normal physiological conditions, ketones rise after 24-72 hours of fasting or after several days of a very low-carbohydrate diet (less than 30-50 g/day), and they constitute an efficient alternative energy fuel for the brain, heart, and other tissues when glucose availability is limited, a metabolic flexibility with potential implications for neuroprotection, cognitive and physical performance, and specific neurodegenerative processes.
The two main commercial forms are BHB salts (beta-hydroxybutyrate bound to sodium, calcium, magnesium, or potassium, the most common in commercial supplements because of their better taste and price) and BHB esters (more sophisticated formulations that release BHB without the mineral load, with more favorable pharmacokinetics but a significantly higher price); both forms raise plasma ketone concentrations for 2-4 hours after ingestion, a "transient ketosis" that partially reproduces some metabolic effects of endogenous nutritional ketosis without requiring strict dietary restriction.
The indication with the most interesting mechanistic basis is the improvement of cognitive function in situations where brain glucose metabolism is compromised: in normal aging, in mild to moderate Alzheimer's disease, and in some neurodegenerative conditions, there is a "brain insulin resistance" or reduced brain glucose utilization that may contribute to cognitive dysfunction; ketones bypass this problem because their brain uptake and utilization do not depend on insulin signaling, which makes them a potentially useful alternative fuel.
Several small studies have documented modest improvements in cognitive function with exogenous ketone supplementation in people with mild Alzheimer's, mild cognitive impairment, and, in some studies, in healthy adults during demanding cognitive tasks; the effects are heterogeneous and the magnitude modest, but the line of research is active with promising results that motivate ongoing clinical trials.
In sports performance, the data are heterogeneous and nuanced: in very prolonged endurance sports (ultraendurance), exogenous ketones could provide an additional fuel that might spare glycogen and prolong performance; in high-intensity, short-to-medium-duration sports, the data suggest that ketones do not improve (and may even reduce) performance because they interfere with the anaerobic glycolytic metabolism that dominates in these efforts; in post-exercise recovery, some studies suggest benefits for glycogen synthesis and reduced protein breakdown.
In pediatric refractory epilepsy, where the classic ketogenic diet is an established treatment, exogenous ketones could be a more convenient and better-tolerated alternative to the strict diet, an active line of research that has not yet reached sufficient clinical validation to replace the established dietary treatment.
In type 2 diabetes and obesity, several small studies have documented improvements in insulin sensitivity and modulation of blood glucose with exogenous ketone supplementation, an indication consistent with the metabolic role of ketones as an alternative to glucose.
The doses studied range from 5 to 25 grams of BHB (varying by product and form); BHB salts are the cheapest option but provide significant amounts of minerals with the dose (especially sodium); BHB esters are more expensive but more efficient at raising plasma ketones; the effect on plasma concentrations is acute (1-3 hours) and chronic supplementation does not produce a metabolic adaptation equivalent to sustained nutritional ketosis.
Generally well tolerated at moderate doses; the most frequent adverse effects are digestive discomfort (nausea, diarrhea, abdominal pain, especially with high doses or cheap products with poor palatability), the characteristic unpleasant taste of the salts and, in some people, headache or transient fatigue; mineral overload with BHB salts can be problematic (therapeutic doses provide significant amounts of sodium that may be unsuitable for people with hypertension or heart failure); people with type 1 diabetes should be cautious because exogenous ketones can interfere with the management of diabetic ketoacidosis and confound monitoring; people with active ketoacidosis (poorly controlled type 1 diabetes, uncontrolled prolonged fasting) should avoid them; in pregnancy and breastfeeding the data are limited and they are not recommended as a precaution; commercial supplements are expensive and the cost-effectiveness should be weighed carefully according to specific goals; the cognitive and metabolic effect is achieved more sustainably and economically with a nutritional ketogenic diet or intermittent fasting, where exogenous ketones are positioned as a complement or a convenience alternative.
Information, not medical advice. Scientific evidence reflects the quality of the studies.