Health Benefits of Exogenous Ketones - What the current evidence does — and does not — support for cognitive, cardiovascular, metabolic, and post-viral health

CLINICIAN-AUTHORED REVIEW

Yoon Hang Kim, MD, MPH

Board-Certified in Preventive Medicine | Integrative & Functional Medicine MD •

Exogenous ketones — supplements that raise circulating β-hydroxybutyrate (BHB) without requiring strict carbohydrate restriction — have moved from a niche athletic supplement to a metabolic therapy being tested in Alzheimer's disease, heart failure, type 2 diabetes, and post-viral fatigue. This review synthesizes the most current systematic reviews, randomized trials, and mechanistic discoveries (through late 2025) to help clinicians distinguish where the evidence is mature, where it is mechanistically promising but clinically immature, and where caution is warranted.

1. Background and Forms

Exogenous ketones are a class of supplements that deliver — or rapidly generate — β-hydroxybutyrate (BHB), the dominant circulating ketone body. They bypass the dietary carbohydrate restriction or prolonged fasting that would otherwise be required to reach nutritional ketosis (blood BHB ≥ 0.5 mmol/L). The commercially and clinically relevant formulations differ meaningfully in their pharmacokinetics, palatability, tolerability, and mineral load.

Principal formulations

Ketone salts (KS) bind BHB to sodium, potassium, calcium, or magnesium. They are inexpensive and widely available, but they deliver a significant mineral load and typically raise BHB only to approximately 1–3 mmol/L.

Ketone monoesters (KME) — most commonly (R)-3-hydroxybutyl (R)-3-hydroxybutyrate — are more potent, raising BHB to 2–6 mmol/L within roughly one hour and sustaining ketosis for three to four hours. They have a famously unpleasant taste but avoid the mineral load of salts.

1,3-butanediol is a non-toxic alcohol that the liver converts to BHB. It provides more sustained ketosis than ester boluses and is the formulation chosen for the ongoing KETO-AHF acute heart failure trial. Reported side effects include mild euphoria and dizziness resembling alcohol intoxication.

Free D-BHB is a newer, bioidentical, salt-free preparation. A 2024 safety study in 24 healthy adults across 720 drink administrations found secondary symptoms after only 6.2% of doses, none severe, and no acid-base or electrolyte abnormalities.

Medium-chain triglycerides (MCT) are technically a precursor rather than a ketone; the liver converts them to BHB, typically raising levels to 0.3–1.0 mmol/L. MCTs alone will not produce sustained therapeutic ketosis.

Beyond fuel: BHB as a signaling metabolite

The therapeutic case for exogenous ketones no longer rests on substrate provision alone. BHB is now understood as a bona fide signaling metabolite that inhibits class I HDACs, suppresses the NLRP3 inflammasome, directly interacts with misfolded proteins to support proteostasis, and modulates endothelial function, mitochondrial efficiency, and appetite-regulating hormones. Many of the clinically observed benefits — even at low BHB concentrations near 0.3 mmol/L — cannot be explained by energy provision alone.

2. Cognitive and Neurodegenerative Disease

The cognitive evidence base is the most mature of any application. A 2025 systematic review and meta-analysis of 29 randomized trials (1,347 participants; 18 studies, 875 participants in the pooled analysis) reported a modest but statistically significant positive effect of exogenous ketones on cognitive performance, with a standardized mean difference of 0.26 (95% CI: 0.11–0.40; p = 0.0007). The effect was consistent across study durations, ketone form (monoester vs. MCT), population (healthy vs. Alzheimer's disease), and the presence of acute cognitive stressors.

The biological rationale is well-grounded. Positron emission tomography studies have shown for two decades that cerebral glucose uptake falls early in Alzheimer's disease, while cerebral ketone metabolism remains intact. Exogenous ketones can therefore partially rescue the brain's energy deficit without needing to restore glucose uptake — a particularly useful property given that brain insulin resistance is itself part of Alzheimer's pathophysiology.

In Parkinson's disease, narrative reviews and small trials report improvements in both motor and non-motor symptoms with ketogenic interventions, though sample sizes are small and trial designs heterogeneous. Mechanistic work also supports a role in amyotrophic lateral sclerosis and related proteinopathies.

A particularly important 2025 finding from the Buck Institute (published in Cell Chemical Biology) identified a previously unappreciated mechanism: BHB directly interacts with damaged and misfolded proteins, rendering them insoluble so that cellular degradation pathways can clear them. This proteostasis effect — distinct from the traditional energy-rescue and anti-inflammatory explanations — opens a new therapeutic rationale for ketones in both aging and Alzheimer's disease, and suggests that the effect may extend beyond the brain to other tissues where protein aggregation drives dysfunction.

3. Cardiovascular Disease

Heart failure with reduced ejection fraction (HFrEF)

Acute infusion of 3-hydroxybutyrate in HFrEF patients produces dose-dependent increases in cardiac output, an effect that does not differ significantly from age-matched controls — suggesting the cardiovascular response to ketones is a universal, evolutionarily preserved metabolic adaptation rather than a rescue unique to failing hearts. Chronic ketone ester supplementation in preclinical models of established heart failure blunts the decline in ejection fraction, reduces cardiomyocyte hypertrophy, lowers periostin expression (a marker of activated fibroblasts), and diminishes cardiac fibrosis.

The multicenter, randomized, double-blind KETO-AHF trial is now testing 1,3-butanediol 33 g three times daily versus placebo in patients hospitalized for acute heart failure with LVEF ≤ 35%. The regimen is designed to maintain 3-OHB between 1 and 2 mmol/L for at least 20 hours per day — a range previously shown to be safe and associated with improved cardiac function in short-term trials.

Heart failure with preserved ejection fraction (HFpEF)

Clinicians should note an important phenotype-specific limitation. The KETO-HFpEF crossover trial, published in JACC: Heart Failure in 2025, found that despite robust ketosis and decreased estimated left ventricular filling pressures, acute ketone ester did not improve peak VO2 or constant-intensity exercise tolerance in symptomatic HFpEF patients. The implication is that exercise intolerance in HFpEF is multifactorial and cannot be fully corrected by substrate shifting alone. This is a useful corrective to overgeneralization of the HFrEF data.

Pleiotropic vascular effects

Beyond energetics, exogenous ketones acutely lower triglycerides without adverse effects on other lipid fractions; improve endothelial function; reduce oxidative stress and mitochondrial inefficiency; and attenuate cardiac remodeling. Small trials have reported reductions in mean arterial pressure and systolic blood pressure with chronic supplementation.

4. Metabolic Health, Glycemic Control, and Body Composition

Acute and short-term effects on blood glucose

A Cochrane-methodology systematic review and meta-analysis published in Advances in Nutrition (Falkenhain et al., 2022) pooled data from 43 trials and provided the clearest quantitative picture to date. Acute ingestion of exogenous ketones produced a mean increase in blood BHB of 1.73 mmol/L (95% CI: 1.26–2.21) and a mean decrease in blood glucose of 0.54 mmol/L (95% CI: −0.40 to −0.68; p < 0.001) compared with baseline. The glucose-lowering effect was observed in both fasted and fed states, with higher doses producing larger reductions, and the attenuation of postprandial glucose lasted at least four hours.

The authors proposed that the mechanisms may differ by metabolic context: in the fasted state the glucose-lowering effect likely reflects reduced hepatic glucose output, while in the fed state the effect may be mediated by improved insulin sensitivity. A separate mechanistic study showed that exogenous D-BHB lowers blood glucose in part by decreasing the availability of L-alanine for gluconeogenesis. BHB also appears to have direct insulinogenic effects on pancreatic islets, though the magnitude depends on the concurrent glucose concentration and duration of exposure.

Glycemic control in type 2 diabetes

Two complementary studies define the current evidence — and its important caveats — in type 2 diabetes. A 28-day open-label interventional study by Soto-Mota and colleagues (Endocrinology, Diabetes & Metabolism, 2021) gave 25 mL of ketone monoester three times daily to 21 insulin-independent T2D patients on stable glucose-lowering therapy. Over 1,588 drinks consumed, adverse reactions occurred after fewer than 0.5% of doses, and electrolytes, acid-base status, and renal function remained normal. Compared with baseline, all four glycemic control markers improved significantly:

▸  HbA1c: 7.7% → 7.2% (p < 0.01)

▸  Fructosamine: 335 → 290 µmol/L (p < 0.01)

▸  Mean daily glucose: 140 → 133 mg/dL (p < 0.01)

▸  Time in range: 67% → 69% (p < 0.01)

However, a subsequent higher-quality trial tempers this optimism. Falkenhain and colleagues (American Journal of Physiology-Endocrinology and Metabolism, 2024) conducted two randomized, double-blind, placebo-controlled crossover trials in T2D patients: one testing an acute monoester dose (0.3 g/kg body mass, n = 18), and one testing thrice-daily premeal monoester (15 g, n = 15) for 14 days. Although BHB rose to approximately 2 mmol/L, there were no significant differences versus placebo in either acute plasma glucose or serum fructosamine at 14 days. The authors concluded that longer-duration and larger trials are needed before exogenous ketones can be recommended as a glucose-lowering intervention in T2D.

Clinically, this pattern is familiar: acute glucose-lowering is robust and reproducible across populations, but translating that physiological effect into durable glycemic improvement requires sustained ketosis, careful timing relative to meals, and likely longer intervention periods than have been formally tested. The Soto-Mota open-label signal and the Falkenhain null RCT are not contradictory so much as complementary — they bracket the range of realistic expectations for the practitioner considering this approach.

Body composition

A 2025 randomized, double-blind, placebo-controlled trial in Nutrients (n = 51) tested 8 weeks of racemic BHB mineral salts twice daily alongside modest caloric restriction in overweight and obese adults. Within the BHB group, participants showed significant reductions in fat mass (approximately −2 kg), improved body fat percentage, and an increased lean-to-fat mass ratio. LDL cholesterol decreased, HOMA-IR and uric acid remained stable, and ALT showed a small but significant within-group decrease. Lean mass was largely preserved, with no declines in resting metabolic rate.

This is clinically relevant in the current era of GLP-1 receptor agonist weight loss, where disproportionate lean mass loss is an emerging concern. The authors specifically raised the possibility that exogenous ketones could be evaluated as an adjunct to pharmacologic weight-loss therapies to better preserve lean tissue, though this remains a hypothesis pending dedicated trials.

Hepatic considerations

Formulation matters for hepatic safety. Preclinical data published in 2025 showed that chronic BHB salt supplementation preserved hepatic architecture, reduced TNF-α, and minimized steatosis, whereas certain other precursors raised hepatic concerns. For patients with nonalcoholic fatty liver disease, BHB itself — not upstream alcoholic precursors — should be prioritized.

5. Inflammation and Immunometabolism

The anti-inflammatory case for BHB has a clearly defined mechanistic anchor. In work published in Nature Medicine, Youm, Nguyen, and colleagues demonstrated that BHB — but not acetoacetate, butyrate, or acetate — suppresses NLRP3 inflammasome activation in response to urate crystals, ATP, and lipotoxic fatty acids. The mechanism involves blockade of K⁺ efflux and inhibition of ASC oligomerization and speck formation, independent of chirality, AMPK, reactive oxygen species, autophagy, GPR109A, or UCP2.

Critically, this inhibition does not require BHB oxidation in the TCA cycle, meaning BHB can dampen innate immune signaling without consuming ATP and without competing for receptor occupancy. BHB suppresses NLRP3-mediated IL-1β and IL-18 production in human monocytes, and in vivo reduces caspase-1 activation.

Given the role of NLRP3 in gout, atherosclerosis, multiple sclerosis, metabolic syndrome, and the "inflammaging" phenotype, this mechanism connects many of the disparate indications where exogenous ketones have shown clinical promise. It also provides a plausible biological explanation for why BHB would benefit conditions — such as Alzheimer's disease and heart failure — that share sterile inflammation as a driver of progression.

6. Long COVID, ME/CFS, and Post-Viral Fatigue

This is the clinical area where mechanistic rationale is strongest but randomized trial data remains thinnest — a pattern familiar to integrative practitioners. Mitochondrial dysfunction is now causally linked to the dominant long COVID symptoms, including cognitive disturbance, fatigue, muscle weakness, breathlessness, and cardiac symptoms, through a combination of energy production deficits, oxidative stress, immune dysregulation, and endothelial dysfunction.

A 2025 PNAS study demonstrated that lymphocytes from both ME/CFS and long COVID patients exhibit elevated oxidative stress, with damaged mitochondria consuming excess host energy — a direct metabolic correlate of the post-exertional malaise that defines both illnesses. A 7T magnetic resonance spectroscopy study in Molecular Psychiatry in 2025 found that patients with ME/CFS and long COVID appear to have less efficient oxidative respiration in the brain and muscle while retaining preserved ability to use lipids as fuel. The authors explicitly raised the question of whether alternative substrates such as ketone bodies — which bypass glycolysis and enter the TCA cycle directly — could restore energy provision, citing prior reports of reduced fatigue in ME/CFS patients on ketogenic interventions.

To date, no large randomized controlled trial of exogenous ketones has been completed in long COVID or ME/CFS populations. The parallel REGAIN trial is evaluating oxaloacetate, a related metabolic intervention. Clinicians considering a trial of exogenous ketones in post-viral fatigue should do so as a deliberate, monitored therapeutic experiment with clear outcome measures, not as a generalized recommendation.

7. Safety, Tolerability, and Clinical Cautions

Across the published literature, the safety profile of exogenous ketones is reassuring but non-trivial. In a systematic review of 33 comparisons, approximately half reported no adverse events or no difference from placebo; the remainder reported predominantly gastrointestinal symptoms (bloating, diarrhea, nausea, cramps, heartburn) and occasional headache, light-headedness, or dizziness. Only three participants across all studies withdrew due to adverse effects.

Formulation is the single most important tolerability variable. Ketone salts produced adverse effects in approximately 85% of comparisons, compared with roughly 40% for ketone monoesters — a meaningful clinical signal when selecting a product. The free D-BHB study reported that only 6.2% of 720 drink administrations produced any secondary symptom, none severe, with no dose-response relationship.

No exogenous ketone preparation has been shown to induce detrimental changes in liver or kidney function at the doses studied. Notably, in migraine patients with baseline metabolic risk markers, inflammatory and hormonal markers (CRP, cortisol, insulin, thyroid) tended to improve rather than worsen on ketone supplementation.

Clinically relevant cautions

▸  Mineral load: ketone salts deliver significant sodium, potassium, or calcium; avoid or use cautiously in poorly controlled hypertension, chronic kidney disease, and heart failure on loop diuretics.

▸  1,3-butanediol: can produce euphoria and dizziness resembling mild alcohol intoxication; counsel patients on driving and machinery operation.

▸  Type 1 diabetes: exogenous ketones raise circulating BHB; while they do not cause ketoacidosis in healthy individuals, insulin-dependent patients require close monitoring.

▸  Weight loss claims: exogenous ketones may acutely suppress appetite and ghrelin, but they do not mimic the fat-oxidation effects of endogenous ketosis; they are not a substitute for a ketogenic diet when dietary ketosis is the goal.

▸  Supplement quality: the FDA does not independently test ketone supplements for purity or composition; third-party tested products are strongly preferred.

8. Evidence Gaps and Clinical Perspective

The most rigorous recent systematic review — PROSPERO-registered, PRISMA-compliant, with a literature search updated through February 2025 — analyzed 51 studies across neurological (22), metabolic (22), cardiovascular (5), psychiatric (1), and inflammatory (1) disorders. The authors concluded that heterogeneity in study designs, patient populations, ketone formulations, and outcome measures — combined with short durations and variable risk of bias — limits firm conclusions on long-term safety and clinically meaningful endpoints.

In plain terms: the short-term mechanistic and physiologic data are compelling, and the acute clinical effects in specific populations (HFrEF, MCI, metabolic syndrome) are reproducible. The long-term outcome data — mortality, hospitalization, cognitive decline trajectories, quality of life — are still being generated, and most trials remain under three months in duration.

References

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23. Mitochondrial dysfunction in long COVID: mechanisms, consequences, and potential therapeutic approaches. PMC11336094. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11336094/

24. Oxidative stress is a shared characteristic of ME/CFS and Long COVID. PNAS. 2025. https://www.pnas.org/doi/10.1073/pnas.2426564122

25. Brain and muscle chemistry in myalgic encephalitis/chronic fatigue syndrome (ME/CFS) and long COVID: a 7T magnetic resonance spectroscopy study. Mol Psychiatry. 2025. https://www.nature.com/articles/s41380-025-03108-8

26. Mitochondrial function is impaired in long COVID patients. PMC12344680. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12344680/

About the Author

Yoon Hang (John) Kim, MD, MPH is board-certified in Preventive Medicine and Integrative/Holistic Medicine and founder of Direct Integrative Care, a membership-based telemedicine practice. He completed his integrative medicine fellowship at the Andrew Weil Center for Integrative Medicine (University of Arizona) as an Osher Fellow, is UCLA-trained in Medical Acupuncture, and is an IFM Scholar. Dr. Kim practices across six states (IA, IL, MO, GA, FL, and TX) via telemedicine and at Hill Country Integrative Medicine in Fredericksburg, Texas.