Beta-hydroxybutyrate, usually shortened to BHB, is a small molecule the liver makes from fatty acids when glucose runs low. It is the most abundant of the three ketone bodies and serves as a critical backup fuel for the brain, heart, and muscles during fasting, prolonged exercise, or very low carbohydrate intake. But over the past decade, research has revealed that BHB does far more than just deliver calories to energy-hungry tissues. It acts as a signaling molecule that can dial down inflammation, change which genes get turned on or off, suppress appetite, and even influence how the body ages. That dual identity as both fuel and chemical messenger is what makes BHB one of the more interesting molecules in metabolic science right now.
Where BHB Comes From
Your liver produces BHB whenever it starts burning large amounts of fat and glucose is scarce. The classic triggers are fasting, starvation, and very low carbohydrate diets, but extended endurance exercise can also ramp up production. Fatty acids released from stored body fat travel to the liver, where they are broken down and converted into ketone bodies, with BHB being the dominant product. From there, BHB enters the bloodstream and is carried to tissues that need energy.1PubMed Central. β-Hydroxybutyrate: A Signaling Metabolite In a person eating a typical mixed diet, blood BHB levels sit well below half a millimole per liter. After an overnight fast they creep up slightly, and after two or three days without food they can reach several millimoles per liter.
A key enzyme in the liver called HMGCS2 controls the pace of ketone production. When researchers knock out this enzyme in mice, the animals cannot raise BHB levels during fasting, and their livers show a distinctly abnormal metabolic response, confirming that BHB production is not just a passive byproduct of fat burning but an actively regulated process with downstream consequences.2PubMed Central. Role of ketone signaling in the hepatic response to fasting
How Tissues Use BHB for Energy
Once BHB reaches peripheral tissues, cells convert it back into acetyl-CoA, the universal currency that feeds the energy-producing machinery inside mitochondria. The brain is the organ that benefits most dramatically. Unlike fatty acids, which cannot efficiently cross the blood-brain barrier, BHB crosses it on a dedicated carrier-mediated transport system.3PubMed. Starvation-induced changes in transport of ketone bodies across the blood-brain barrier During prolonged fasting, BHB can supply a substantial share of the brain’s energy, which is one reason humans can survive weeks without eating as long as they have body fat to draw from.
The heart is another eager consumer. Even under normal conditions the heart oxidizes small amounts of ketones, but in heart failure that reliance increases. Failing hearts in mouse models showed a significant jump in ketone oxidation when BHB was available at higher concentrations, with ketone-derived fuel contributing up to about a quarter of the energy going into the cell’s main metabolic cycle.4Cardiovascular Research. Increased ketone body oxidation provides additional energy for the failing heart without improving cardiac efficiency Researchers have described BHB as a “metabolic stress defense” for the struggling heart, suggesting the shift toward ketone use is an adaptive response rather than a sign of further dysfunction.5PubMed Central. The failing heart utilizes 3-hydroxybutyrate as a metabolic stress defense
BHB as a Signaling Molecule
The finding that shifted BHB from “simple fuel” to “molecule with a second career” came when researchers discovered it acts as an inhibitor of a class of enzymes called histone deacetylases, specifically class I HDACs. Histones are the spool-like proteins that DNA wraps around, and how tightly or loosely they hold the DNA determines whether nearby genes can be read. By blocking HDACs, BHB increases histone acetylation, effectively loosening the grip and switching on genes that protect against oxidative stress. In one landmark study, BHB treatment boosted the activity of genes encoding FOXO3A and MT2, both of which help cells defend against damage from reactive oxygen species.6PubMed Central. Suppression of oxidative stress by β-hydroxybutyrate, an endogenous histone deacetylase inhibitor
BHB also talks to cells through a receptor on their surface called GPR109A. This receptor sits on fat cells, immune cells, and the cells lining blood vessels, among others. When BHB activates GPR109A on fat cells, it slows the release of more fatty acids, creating a negative feedback loop that keeps ketone production from spiraling out of control. On immune cells and endothelial cells, the same receptor activation dampens inflammatory signaling and may protect against atherosclerosis.7Heliyon. Metabolic regulation and epigenetic role of beta-hydroxybutyrate in health and disease 8PubMed Central. β-Hydroxybutyrate Suppresses Lipid Accumulation in Aged Liver through GPR109A-mediated Signaling
Beyond HDAC inhibition and receptor activation, BHB can also be directly attached to histone proteins in a modification called beta-hydroxybutyrylation, distinct from acetylation. In fasted mice, this modification was enriched across thousands of DNA sites in the brain, and the genes it turned on were tied to circadian rhythm regulation, hinting that BHB connects the body’s metabolic state to its internal clock.9PubMed Central. Brain histone beta-hydroxybutyrylation couples metabolism with gene expression
Turning Down Inflammation
One of the most studied signaling effects of BHB is its ability to block a specific arm of the immune system called the NLRP3 inflammasome. This protein complex acts like an alarm system inside immune cells, triggering the release of powerful inflammatory signals when it detects danger. In many chronic diseases, the inflammasome fires too often or too aggressively. BHB suppresses its activation in response to urate crystals, ATP, and harmful fatty acids, reducing the production of the inflammatory cytokines IL-1β and IL-18 in human immune cells. In animal models, BHB or a ketogenic diet reduced inflammasome-driven disease in conditions resembling gout and certain inherited inflammatory syndromes.10PubMed Central. The ketone metabolite β-hydroxybutyrate blocks NLRP3 inflammasome-mediated inflammatory disease
The gout connection is especially interesting because gout flares are directly triggered by urate crystal deposits activating the NLRP3 inflammasome in joint tissues. In experiments looking specifically at gout, BHB inhibited inflammasome activation in both macrophages and neutrophils, the two cell types most responsible for the painful swelling of a gout attack. Rats fed a ketogenic diet showed reduced gout flares, and the protective effect held across immune cells from both young and older animals.11Cell Reports. β-Hydroxybutyrate Deactivates Neutrophil NLRP3 Inflammasome to Relieve Gout Flares
Brain Health and Cognitive Function
The brain’s ability to use BHB as fuel has drawn attention in Alzheimer’s research. In Alzheimer’s disease, brain cells appear to lose their ability to use glucose efficiently, creating an energy crisis that worsens neuronal damage. BHB offers an alternative fuel source that can bypass some of this glucose-handling deficit. In a small clinical study of 20 people with Alzheimer’s disease or mild cognitive impairment, a single drink containing medium-chain triglycerides (which the liver quickly converts to BHB) raised blood BHB levels and improved performance on a paragraph recall test compared to a placebo drink. Participants with higher resulting BHB levels showed the greatest improvement.12PubMed. Effects of beta-hydroxybutyrate on cognition in memory-impaired adults
This is still early-stage evidence, but the interest is driven by BHB’s multiple mechanisms of action in the brain: it provides energy, reduces oxidative stress through HDAC inhibition, modulates inflammation, and may influence the metabolism of the amyloid and tau proteins that accumulate in Alzheimer’s.13PubMed. The potential pharmacological mechanisms of β-hydroxybutyrate for improving cognitive functions
Epilepsy is another neurological condition where BHB shows promise. Ketogenic diets have been used to treat drug-resistant epilepsy for over a century, but the reason they work has been poorly understood. A recent study identified BHB as the key antiepileptic component: it inhibits HDAC1 and HDAC2, which leads to increased production of GABA, the brain’s main inhibitory neurotransmitter. BHB also preserved glutamate (the raw material for making GABA) by deactivating an enzyme that would otherwise divert it. Mice given BHB directly showed resistance to chemically induced seizures, and the protective effect depended on maintaining a high ratio of GABA to glutamate.14Cell Discovery. Ketogenic diet-produced β-hydroxybutyric acid accumulates brain GABA and increases GABA/glutamate ratio to inhibit epilepsy If this holds up, BHB-based treatments could eventually offer the seizure-reducing benefits of a ketogenic diet without requiring the diet itself.
Appetite and Body Weight
People on ketogenic diets frequently report reduced hunger, and BHB appears to be a major reason why. A study in healthy volunteers found that a ketone ester drink that raised blood BHB to about 3.3 millimoles per liter suppressed hunger and the desire to eat by roughly half over a period of several hours compared to a calorie-matched carbohydrate drink. The ketone drink also kept ghrelin, the so-called “hunger hormone,” suppressed for significantly longer.15PubMed Central. A Ketone Ester Drink Lowers Human Ghrelin and Appetite
A separate study in healthy young men confirmed the ghrelin connection. Ketone ester ingestion that pushed BHB levels to about 5.5 millimoles per liter lowered acyl ghrelin (the active form) by about 25 percent, and the suppression lasted longer than what was seen with a glucose drink of equal calories. The researchers concluded that the appetite-suppressing effects of elevated BHB are likely driven primarily by reduced ghrelin rather than by changes in other gut hormones.16PubMed. Acute ketosis inhibits appetite and decreases plasma concentrations of acyl ghrelin in healthy young men This is worth noting for anyone interested in weight management, though it remains unclear whether sustained BHB supplementation produces meaningful long-term weight loss.
Exogenous BHB Supplements
You do not have to fast or eat a ketogenic diet to raise BHB levels. Exogenous ketone supplements, sold as either ketone esters or ketone salts, can push blood BHB into the low millimolar range within minutes. In a recent tolerability study, a ketone monoester drink raised blood BHB to about 2.4 millimoles per liter within 15 minutes at a full dose, while a combined ester-salt formula peaked at about 2.1 millimoles per liter at 30 minutes. Half-dose versions of both reached roughly 1.1 to 1.2 millimoles per liter.17PubMed Central. Tolerability and Acceptability of an Exogenous Ketone Monoester and Ketone Monoester/Salt Formulation in Humans
An important distinction between the two formats: ketone esters deliver the D-isoform of BHB, which is the form your body naturally produces and uses. Ketone salts typically deliver a racemic mixture, meaning over half of the BHB is the L-isoform, which clears from the blood much more slowly and is not efficiently metabolized. So while total BHB levels after a salt drink can look similar to an ester drink on a blood test, the biologically active portion is lower.18Oxford University Research Archive. Metabolism of exogenous ketones Ketone esters also tend to taste quite bitter and can cause gastrointestinal discomfort at higher doses, which is a practical consideration for anyone experimenting with them.
Exercise Performance
Athletes have been the most enthusiastic early adopters of exogenous BHB, drawn by the idea of providing muscles with an extra fuel source alongside carbohydrates. The theory is appealing: BHB could spare muscle glycogen stores during endurance events, extending the time before fatigue sets in. Some research supports the idea that ketone bodies can shift metabolic fuel use and contribute to mitochondrial energy production during exercise.19PubMed Central. The science of ketogenic supplements for athletes: boosting endurance, efficiency, and energy metabolism
The actual performance data, however, are mixed at best. In a well-controlled cycling study, athletes drank a ketone ester or placebo during a simulated race that included 180 minutes of steady riding followed by a time trial and a sprint. The ketone ester did not spare muscle glycogen, did not improve power output in the time trial, and did not extend time-to-exhaustion in the sprint. Power output and sprint duration were virtually identical between the two conditions.20PubMed Central. Exogenous ketosis impacts neither performance nor muscle glycogen breakdown in prolonged endurance exercise Other studies have shown small benefits or no effect, and gastrointestinal distress and electrolyte imbalances remain practical concerns with higher doses during physical activity. For now, the evidence does not strongly support BHB supplementation as a reliable ergogenic aid.
Muscle Preservation
Separate from athletic performance, BHB may help protect muscle mass during periods when it would normally break down, such as during fasting, illness, or aging-related wasting. In cell and animal studies, BHB maintained the balance between muscle protein building and breakdown by influencing key regulatory pathways that control whether muscle cells grow or shrink. It also appeared to support protein quality control by influencing the cellular cleanup systems that remove damaged or misfolded proteins.21PubMed Central. Mechanism of reduced muscle atrophy via ketone body (D)-3-hydroxybutyrate This is still largely preclinical research, but it adds to the picture of BHB as something more than a passive fuel molecule.
Aging and Longevity
The collection of BHB’s signaling effects, reduced oxidative stress, lower chronic inflammation, improved mitochondrial function, and epigenetic changes, reads like a checklist of mechanisms relevant to aging. This has led researchers to investigate BHB specifically as an anti-aging metabolite. Its ability to inhibit HDACs and thereby activate stress-resistance genes, combined with its anti-inflammatory action through the NLRP3 inflammasome and GPR109A receptor, suggests it could slow several of the molecular processes that drive age-related decline. Researchers have also identified beta-hydroxybutyrylation of histones as a distinct epigenetic modification that may play roles in metabolic homeostasis and neuroprotection as the body ages.22PubMed Central. β-hydroxybutyrate as an Anti-Aging Metabolite
Animal studies with caloric restriction and ketogenic diets, both of which raise BHB, have shown lifespan extension in various model organisms. Whether the same applies to humans is unknown, and separating BHB’s effects from all the other metabolic changes caused by fasting or dietary restriction remains a challenge. But the mechanistic case is strong enough that BHB is being explored both through dietary strategies and direct supplementation as a potential intervention for age-related diseases.
Kidney Disease and Other Emerging Applications
BHB’s anti-inflammatory and metabolic properties have sparked interest in kidney disease, especially diabetic kidney disease, where chronic inflammation and metabolic dysfunction drive progressive organ damage. Early research suggests that BHB may slow disease progression by improving how kidneys handle glucose and fat, regulating cellular recycling processes, and reducing fibrosis and oxidative stress.23BMC Nephrology. Ketogenic diets and β-hydroxybutyrate in the prevention and treatment of diabetic kidney disease: current progress and future perspectives Most of this work is in animal models, and it is too soon to say whether BHB supplementation or ketogenic diets will become part of standard kidney disease management.
An Evolutionary Backstory
The reason BHB does so many things may be rooted in human evolutionary history. Our ancestors faced unpredictable food supplies, and the ability to fuel a large, energy-hungry brain during famine was a survival advantage. BHB’s role as a brain fuel was likely critical: it allowed humans to maintain cognitive function during extended periods without food, something that would have mattered enormously for a species that depends on intelligence to find its next meal.24PubMed Central. Brain Ketone Bodies in Health, Evolution and Disease
Humans are also unusual among mammals in being born with a substantial layer of body fat. This fat develops during the third trimester of pregnancy and serves as a reservoir for fatty acids that can be converted to ketones to fuel the infant brain, which consumes a disproportionate share of the newborn’s total energy budget. The evolution of this fat layer in early hominins is thought to have been a key adaptation enabling brain expansion over evolutionary time.25PubMed. Energetic and nutritional constraints on infant brain development: implications for brain expansion during human evolution In this view, BHB is not just a fasting fuel but a molecule that helped make large human brains possible in the first place. Its signaling roles, regulating stress defenses, inflammation, and gene expression, may have been layered on over millions of years as additional benefits of a metabolite that was already abundant during the periods of metabolic stress that shaped human physiology.