The logic behind the study begins with the ketogenic diet, a high-fat, very low-carbohydrate regimen that forces the body to burn fat and produce ketone bodies, chiefly beta-hydroxybutyrate and acetoacetate. These molecules serve as alternative fuel for the brain when glucose is scarce, but beta-hydroxybutyrate is more than an energy source. It is also a signaling molecule: it inhibits histone deacetylases, enzymes that silence genes, thereby boosting expression of protective factors such as brain-derived neurotrophic factor; it binds the HCAR2 receptor to dampen inflammation; and it can block assembly of the NLRP3 inflammasome, a molecular machine that drives inflammatory responses. Rodent studies have linked ketogenic diets to preserved memory, muscle mass, and physical function, and short-term ketogenic diets have improved memory in middle-aged female mice and older male rats. Human evidence, however, remains mixed, with small trials in mild cognitive impairment and Alzheimer’s disease showing modest or null effects.

Sticking to a strict ketogenic diet is difficult, particularly for older adults who may be vulnerable to nutritional shortfalls. The California team therefore turned to a supplement strategy: the ketone monoester (R)-3-hydroxybutyl (R)-3-hydroxybutyrate, known commercially as deltaG. When eaten, carboxylesterase enzymes in the small intestine split the compound into beta-hydroxybutyrate and 1,3-butanediol; the liver then converts the butanediol into additional beta-hydroxybutyrate and releases it into circulation. This raises blood ketones for several hours without severe carbohydrate restriction, allowing researchers to ask whether selected effects of a ketogenic metabolic state can be reproduced simply by elevating beta-hydroxybutyrate availability.

The experiment involved 24-month-old C57BL/6 mice, roughly equivalent in age to an elderly human, obtained from the National Institute on Aging’s aged rodent colony. At the start of the intervention, animals were randomized to a control diet or a ketone ester diet in which 21.5 percent of carbohydrate-derived calories were replaced with the ester, with vitamins, minerals, and fiber matched between groups. Each mouse received a fixed isocaloric daily ration of 12.2 kilocalories for eight weeks. Over the intervention, the researchers tracked body weight and composition by nuclear magnetic resonance relaxometry, tested spatial memory in the Barnes maze and recognition memory in the novel object recognition task, measured anxiety-like behavior in an open field, assessed motor coordination on a rotarod and grip endurance on a wire hang, and finally profiled metabolites in liver, hippocampus, muscle, serum, and urine using proton nuclear magnetic resonance spectroscopy. They also quantified 76 oxylipins, lipid messengers derived from polyunsaturated fatty acids that regulate inflammation and vascular tone, in the hippocampus.

The proximal metabolic effects were unambiguous. After seven weeks, postprandial beta-hydroxybutyrate was dramatically higher in ketone ester-fed animals of both sexes, with a very large diet effect, and postprandial glucose was significantly lower. Notably, ester-fed females reached higher blood ketone levels than ester-fed males, a sex difference consistent with prior reports that females achieve higher circulating beta-hydroxybutyrate under ketogenic feeding. The divergence began downstream. Male mice on the ester diet ended the study weighing less than at baseline, with significantly lower body fat percentage and higher lean mass adjusted for body weight, although absolute lean mass was unchanged. Females showed no comparable body composition shift, but they did display lower absolute lean mass and, intriguingly, a higher gastrocnemius muscle mass relative to body weight.

Metabolomic profiling revealed that the two sexes were essentially running different metabolic programs in response to the same supplement. In males, serum and urine metabolomes did not separate cleanly by diet in multivariate models, but individual markers pointed toward altered handling of branched-chain amino acid catabolites and nicotinamide-related metabolites, alongside higher hepatic glycine and sarcosine, intermediates of one-carbon metabolism. In females, the diet produced broad, statistically significant shifts in the serum, urine, and liver metabolomes, touching amino acids, glycolytic products, and tricarboxylic acid cycle intermediates such as fumarate, aspartate, glutamine, and glutamate, which fell in ester-fed females. The authors caution that because the ester diet also reduced starch and removed maltodextrin, and because food intake and energy expenditure were not directly measured, these changes cannot be attributed exclusively to beta-hydroxybutyrate signaling.

The cognitive results were the study’s most striking sex-specific finding. On the Barnes maze probe trial, in which mice must locate a target hole on a circular platform from memory, ester-fed females made significantly fewer primary errors than control females, an incidence rate ratio of 0.57, meaning they explored roughly 43 percent fewer wrong holes before finding the target. Males showed no such benefit. The effect was specific: recognition memory, open-field anxiety measures, and motor tests were unchanged in both sexes, and the wire hang test in females was limited by a ceiling effect, with most animals reaching the maximum 180 seconds. The authors emphasize that the Barnes maze result should be read as a task-specific change in spatial search performance rather than broad cognitive enhancement.

In the hippocampus, the molecular picture in females was suggestive but complex. Ester-fed females expressed significantly lower levels of interleukin-1 beta messenger RNA, a cytokine downstream of inflammasome activation that has been implicated in hippocampal dysfunction, while IL-18, interferon-gamma, and BDNF transcripts were unchanged. Hippocampal oxylipin profiles shifted in a mixed direction: pro-inflammatory species such as prostaglandin F2 alpha and thromboxane B2 rose alongside species often classified as anti-inflammatory or pro-resolving, including 15-oxo-ETE, prostaglandin E1, and two epoxy fatty acids. Exploratory correlation analyses showed that hippocampal beta-hydroxybutyrate was inversely associated with IL-1 beta expression, but Barnes maze errors did not correlate significantly with any of these molecular measures, so the study does not establish a causal chain from ketones to reduced neuroinflammation to better memory.

The authors are candid about limitations. The aged cohort suffered substantial attrition before and during the intervention, raising possible survivorship bias; biochemical profiling was performed only after a 12-hour fast, which likely blunted between-group ketone differences; and the ester diet differed from the control diet in carbohydrate amount and composition, not merely in ketone content. Neuroimmune endpoints were measured at the transcript level only, without protein or inflammasome activity assays. The team also notes recent work associating continuous ketogenic diet exposure with p53-dependent cellular senescence in mice, even as other studies suggest beta-hydroxybutyrate itself can mitigate senescence in several models, underscoring that diet composition, duration, and delivery method may determine whether ketone elevation helps or harms.

For now, the study stands as rigorous preclinical evidence that a ketone ester supplement can produce robust metabolic changes in aged animals while its behavioral and body-composition effects split along sex lines. The researchers call for follow-up work that disentangles ketone-specific effects from carbohydrate reduction, measures food intake and energy expenditure directly, validates inflammatory findings at the protein level, and ultimately tests whether similar sex-specific responses appear in older humans. Until then, the message for the booming ketone-supplement market is one of caution: the same molecule may mean very different things to an aging male body and an aging female brain.

Subject of Research: Sex-specific effects of ketone ester supplementation on cognition and metabolism in aged mice

Article Title: Ketone ester supplementation in aged mice produces sex-specific cognitive and metabolic effects

Article References: Roslund, K. J., Coates, L. C., Sattar Sultani, S., Hayes, D., Diaz, S., Rutkowsky, J. M., Zhou, Z., Ramsey, J. J., Taha, A. Y., & Slupsky, C. M. (2026). Ketone ester supplementation in aged mice produces sex-specific cognitive and metabolic effects. GeroScience. https://doi.org/10.1007/s11357-026-02546-8

Image Credits: AI Generated

DOI: 10.1007/s11357-026-02546-8

Keywords: ketone ester, beta-hydroxybutyrate, aging, cognition, spatial memory, hippocampus, neuroinflammation, metabolomics, oxylipins, body composition, sex differences, GeroScience