Exogenous Ketones for Women: Is There Anything Different?
Exogenous ketones, sold as ketone esters or ketone salts, promise a fourth fuel for exercise alongside carbohydrate, fat and protein. They have attracted attention from cyclists, runners and triathletes, including many women. Yet when you read the studies closely, almost all participants were men. Our editors look at what this means for female athletes.
What exogenous ketones are
Ketone bodies, chiefly beta-hydroxybutyrate (βHB) and acetoacetate, are produced by the liver during fasting, prolonged exercise or a very low-carbohydrate diet. They can be used as fuel by muscle, heart and brain. "Exogenous" simply means taken from outside rather than produced by the body.
Two main product types exist. Ketone salts bind βHB to sodium, potassium, calcium or magnesium. Ketone esters link βHB to an alcohol, such as butanediol, and raise blood ketone levels considerably more. Esters tend to taste unpleasant and cost more, while salts deliver a large mineral load at the doses needed.
Stubbs and colleagues described how these products behave in humans: blood βHB rises within 30–60 minutes and returns towards baseline over several hours. Esters can produce levels similar to several days of fasting, while salts typically produce a smaller rise.
In the UK, ingredients without a significant history of consumption before 1997 fall under novel food rules, now administered by the Food Standards Agency. The authorisation status of particular ketone ingredients can change, so checking the label and the FSA register is worthwhile.
Evidence on performance and recovery
Interest was sparked by Cox and colleagues in 2016, who reported that a ketone ester drink improved time-trial distance in trained cyclists. The ester shifted fuel use towards fat and ketones, sparing muscle glycogen. Many subsequent studies, however, failed to reproduce a performance benefit, and a few found impaired performance.
A meta-analysis by Valenzuela and colleagues in 2020 concluded that acute ketone supplementation does not, on average, improve endurance performance. Gastrointestinal discomfort and dose-dependent acid-base disturbances may offset any metabolic advantage.
The recovery picture is more interesting. Poffé and colleagues found that ketone ester taken after training and before sleep during a period of heavy overload reduced markers of overreaching, including a smaller drop in energy intake and better maintained performance. This suggests a possible role in recovery rather than racing.
| Outcome | Overall evidence | Women included? |
|---|---|---|
| Endurance time-trial performance | Inconsistent; meta-analysis shows no average benefit | Rarely; mostly male cyclists |
| Glycogen sparing | Some support with esters | Very limited |
| Recovery during overload | Promising single studies | Mostly men |
| Cognitive function under fatigue | Early, mixed data | Some mixed-sex samples |
Evans, Cogan and Egan's physiological review emphasised that the context, dose and form of ketone matter a great deal, which partly explains the inconsistent findings.
Female physiology and the research gap
Women tend to rely more on fat and less on carbohydrate at a given relative exercise intensity, partly because of oestrogen. Since ketones also shift substrate use, it is plausible that the response could differ between the sexes. Plausible, however, is not the same as demonstrated.
Across the menstrual cycle, oestrogen and progesterone fluctuate, influencing insulin sensitivity, fat oxidation and fluid balance. No published trial has tested whether ketone supplements perform differently in the follicular versus luteal phase, or in women using hormonal contraception.
Elliott-Sale and colleagues have published methodological guidelines urging researchers to define and verify menstrual status in female participants. Very few ketone studies meet these standards, so their results cannot be confidently applied to women.
Body size is another practical issue. Doses are often given per kilogram in studies but as fixed servings in commercial products. A smaller athlete taking a full serving designed for an average male cyclist will receive a higher relative dose and may be more likely to experience gut symptoms.
Side effects and safety
The most common complaint is gastrointestinal: nausea, cramping, bloating and diarrhoea, particularly with salts and during intense exercise. Esters can also cause a burning taste and mild headache.
Ketone salts deliver substantial amounts of sodium and other minerals. For an athlete with high blood pressure, kidney issues, or on a low-sodium diet, this load matters. Ketone esters can lower blood pH slightly, which is relevant during maximal efforts.
Groups who should avoid exogenous ketones or only use them under medical supervision include:
- pregnant or breastfeeding women, owing to absent safety data;
- people with type 1 diabetes or on SGLT2 inhibitors, because of the risk of confusing or masking ketoacidosis;
- people with kidney or liver disease;
- anyone with a history of disordered eating, as ketone products are sometimes marketed for appetite suppression.
Ketones are not prohibited by the World Anti-Doping Agency. As with any supplement, choosing products tested under a recognised anti-doping scheme reduces the risk of contamination.
Should a female athlete try them?
For most recreational athletes, ketone supplements are expensive and unlikely to change race results. Carbohydrate intake, pacing, training consistency and sleep have a far greater effect.
Elite female endurance athletes who wish to experiment should do so in training, not on race day, starting with a small serving to assess tolerance. Recording cycle phase alongside responses may reveal individual patterns.
Ketones should never replace adequate energy intake. Low energy availability is common among female athletes and leads to hormonal disruption and bone loss. A supplement that suppresses appetite could make this worse.
Working with a sports dietitian helps to place ketones in context, decide whether there is any rationale for them, and avoid unnecessary spending.
Conclusions of the editorial team
Exogenous ketones are a genuinely interesting area of sports science, but the performance evidence is inconsistent and comes overwhelmingly from men.
There are good theoretical reasons to expect sex differences in response, yet no trials have tested them properly. Women should be cautious about extrapolating headline findings.
Gastrointestinal effects, mineral load and absent data in pregnancy are the main practical concerns. If you would like to read more, we suggest our articles on carbohydrate periodisation for endurance athletes, on GABA for women, and on relative energy deficiency in sport.
References
- Cox PJ, Kirk T, Ashmore T, et al. Nutritional ketosis alters fuel preference and thereby endurance performance in athletes. Cell Metab. 2016;24(2):256–268.
- Evans M, Cogan KE, Egan B. Metabolism of ketone bodies during exercise and training: physiological basis for exogenous supplementation. J Physiol. 2017;595(9):2857–2871.
- Stubbs BJ, Cox PJ, Evans RD, et al. On the metabolism of exogenous ketones in humans. Front Physiol. 2017;8:848.
- Poffé C, Ramaekers M, Van Thienen R, Hespel P. Ketone ester supplementation blunts overreaching symptoms during endurance training overload. J Physiol. 2019;597(12):3009–3027.
- Valenzuela PL, Morales JS, Castillo-García A, Lucia A. Acute ketone supplementation and exercise performance: a systematic review and meta-analysis of randomized controlled trials. Int J Sports Physiol Perform. 2020;15(3):298–308.
- Elliott-Sale KJ, Minahan CL, de Jonge XAKJ, et al. Methodological considerations for studies in sport and exercise science with women as participants: a working guide for standards of practice for research on women. Sports Med. 2021;51(5):843–861.
