Exogenous ketones have gained popularity in the keto community for their ability to quickly raise blood ketone levels. While they aren’t a replacement for a well-formulated ketogenic diet, they may have potential benefits in certain situations, ranging from easing the transition into ketosis to supporting therapeutic interventions.
In this article, we’ll break down what exogenous ketones are, how they work, when they might be helpful, and what to consider when choosing and using them.
What are Exogenous Ketones?
When you follow a very low-carb diet, your body naturally produces endogenous ketones – primarily beta-hydroxybutyrate (BHB) – from fat in the liver. This shift from using glucose to fat as the primary fuel source is known as nutritional ketosis.
Exogenous ketones, by contrast, are ketones made outside the body and taken as a supplement, typically in the form of ketone salts, ketone esters, or MCT oil. These can raise blood ketone levels within minutes, even without carbohydrate restriction.
Types of Exogenous Ketones
1. Ketone Salts
Ketone salts combine BHB with minerals like sodium, potassium, magnesium, or calcium. They’re affordable and widely available, but may only raise ketone levels modestly (about 1.0 to 2.0 mmol/L) within 30 to 60 minutes. They may cause mild gastrointestinal discomfort, although this is relatively uncommon.
2. Ketone Esters
Ketone esters are more potent and fast acting. The most common form is the BHB monoester. Studies show that the BHB monoester rapidly raises blood ketone levels, peaking at about one hour and maintaining ketosis for three to four hours, depending on the dose. Ketone esters are typically used in research and clinical settings, but their unpleasant taste, higher cost, and digestive side effects may limit regular use.
Understanding the Two Forms of BHB: D and L
BHB, the primary ketone body found in most exogenous ketone supplements, exists in two mirror-image forms, or enantiomers: D-BHB and L-BHB.
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- D-BHB (also written as R-BHB) is the form naturally produced by the body during nutritional ketosis. It is readily metabolized and used by cells (especially in the brain and muscles) for energy.
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- L-BHB (also written as S-BHB) is not produced endogenously in humans and is metabolized more slowly. Together with D-BHB, it may help lower inflammation by blocking a key inflammatory pathway (the NLRP3 inflammasome) and potentially provide other benefits.
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Racemic vs. Pure D-BHB Supplements
Many commercial ketone products contain a racemic mixture known as D/L-BHB, which is a 50/50 blend of D-BHB and L-BHB. However, some formulations use pure D-BHB, which mimics the form the body naturally produces and utilizes most efficiently.
Expert Positions on D-BHB vs. D/L-BHB
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- Dr. Elena Gross, a neuroscientist and migraine researcher, favors pure D-BHB, citing its superior bioavailability and relevance for therapeutic use, especially in neurological conditions.
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- Dr. Dominic D’Agostino and Dr. Csilla Ari acknowledge that while D-BHB is the body’s preferred energy source, L-BHB may still offer benefits. They report that studies comparing the two forms demonstrate that L-BHB remains in the bloodstream longer and may offer unique anti-inflammatory and cardioprotective effects not seen with D-BHB alone. And experts in polycystic kidney disease research, including Dr. Thomas Weimbs, report that L-BHB appears to share many of D-BHB’s signaling benefits, such as reducing inflammation and disease progression.
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Overall, there is no definitive consensus on the distinct roles of D- and L-BHB, and more research is needed to determine their individual and combined effects. For now, racemic D/L-BHB blends remain common in research and commercial products as scientists continue to explore how each form contributes to metabolic and therapeutic outcomes.
Common Brands of Exogenous Ketones
Exogenous ketone products vary by formulation, purpose, and the form of BHB used. Some are intended for general use, while others are designed for specific therapeutic applications. Below are examples, grouped by category:
Ketone Salts (typically D/L-BHB unless otherwise noted):
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- Keto Start – D/L-BHB
- Perfect Keto – D/L-BHB
- KetoCitra – D/L-BHB; developed for polycystic kidney disease (PKD)
- MigraKet – Pure D-BHB; developed for migraine management
- KetoLogic – D/L-BHB
- TruMacro – D/L-BHB
- Kenetik – D/L-BHB
- Ketond – D/L-BHB
Ketone Esters:
Note: Keto-Mojo has not evaluated these products and does not endorse any specific brand.
MCT Oil
Medium-chain triglycerides (MCTs) are fats typically made up of C8 (caprylic acid) and C10 (capric acid) fatty acids. They’re rapidly digested, easily absorbed, and quickly converted by the liver into ketones, making them a helpful tool for supporting endogenous ketone production.
Although MCT oil isn’t classified as an exogenous ketone, it can raise ketone levels naturally and is commonly used to enhance energy, support ketosis, or ease the transition into a ketogenic state. MCT oil is tasteless and odorless, but it’s best to start with small amounts, as high doses may cause digestive issues in some individuals.
Learn more about MCT oil here or purchase it using the links provided here.
Are Exogenous Ketones Safe?
Exogenous ketones are not regulated by the FDA, so their ingredients, quality, and effectiveness can vary widely between brands, and marketing claims may not always be supported by evidence. Some products may omit ingredients on the label or include additives such as caffeine, so it’s important to read labels carefully.
Both ketone salts and esters have been shown to raise blood ketone levels quickly and appear safe for occasional or long-term use, although research on their effectiveness is still emerging. The depth and duration of ketosis achieved are highly individual, so it’s best to consider your goals before using them.
BHB salts are typically bound to minerals like sodium, potassium, magnesium, or calcium, which can help replenish electrolytes during keto adaptation. However, the high sodium content (up to 1,000 mg or more per serving) may be unsuitable for people with certain health conditions, such as uncontrolled hypertension. Some users also experience stomach upset, so starting with a small dose and increasing gradually can help assess tolerance.
It’s best to discuss with your healthcare provider if you’re considering exogenous ketones, especially if you have a medical condition or are taking medications.
What About Alcohol?
Alcohol and ketones are both processed by the liver, and drinking alcohol may temporarily reduce the body’s ability to produce its own ketones by slowing fat oxidation. However, exogenous ketones bypass this process, so blood ketone levels could still rise when taking them together with alcohol.
In a randomized, single-blind, cross-over study, 10 healthy adults consumed a ketone salt supplement or placebo before receiving a controlled dose of alcohol. The supplement raised blood BHB levels by approximately 2 mmol/L, and they remained elevated for about 90 minutes. Compared to placebo, ketone supplementation lowered blood and breath alcohol levels, reduced desire, and increased disliking, which suggests it may blunt alcohol’s physical and psychological effects. A rodent study using BHB salts showed similar effects on ketone levels, alcohol intake, and response. However, more research is needed to better understand the effects of exogenous ketones on alcohol metabolism and response. In the meantime, it’s best to use caution when combining ketone supplements and alcohol, particularly in large doses.
Potential Benefits and Use Cases
1. Weight Loss
Exogenous ketones are not a substitute for a low-carb or ketogenic diet. Taking them without restricting carbohydrates may reduce fat burning (lipolysis) since the body prioritizes ketones for energy.
However, some users find that elevated ketone levels reduce appetite, which may help lower calorie intake and support weight loss. They may also be helpful during the early stages of keto to ease symptoms of the “keto flu.”
2. Athletic Performance
Some research suggests that ketone esters may enhance endurance and support recovery by improving mitochondrial efficiency and sparing glycogen. Others report that exogenous ketones may enhance endurance performance and help reduce symptoms of overreaching, including fatigue, performance decline, and delayed recovery. However, results are mixed, and in some cases, ketones may hinder high-intensity performance.
More studies are needed before exogenous ketones can be widely recommended for sports performance.
3. Therapeutic Applications
Ongoing research is exploring exogenous ketones for a range of clinical uses:
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- Alzheimer’s disease: A 2025 systematic review and meta-analysis of 29 studies (1,347 participants) found that exogenous ketones have a modest but statistically significant positive effect on cognitive function, regardless of ketone type, population, or study duration.
- Parkinson’s disease: In a randomized, placebo-controlled crossover study, ketone ester supplementation significantly improved endurance exercise performance in people with early-stage Parkinson’s disease, suggesting it may be a helpful adjunct to exercise therapy.
- Epilepsy: The ketogenic diet is well established as an effective therapy for seizure control in children with epilepsy by promoting high levels of endogenous ketosis. Emerging preclinical data suggests that exogenous ketones may help enhance or sustain these ketone levels, potentially serving as a useful supplement to dietary therapy.
- Cancer: Some studies suggest that ketones may help preserve muscle mass and support metabolic management in cancer patients. Achieving a Glucose Ketone Index (GKI) below 1, which may slow tumor growth, is often difficult with diet alone. Exogenous ketones might help bridge the gap.
- Mental health: Emerging research suggests that exogenous ketone supplements—alone or alongside a ketogenic diet—may help alleviate psychiatric symptoms by modulating metabolic and signaling pathways, though further studies are needed to confirm their safety, mechanisms, and therapeutic efficacy.
- Metabolic health: Early research suggests potential benefits for improving glucose regulation and insulin sensitivity, particularly in people with type 2 diabetes, with the strongest effects observed from ketone esters.
- Cardiovascular health: In a placebo-controlled study, a ketone diester beverage (BH-BD) significantly raised blood ketone levels to 2.1 mmol/L and produced acute improvements in cardiac output, myocardial blood flow, and heart function in healthy adults.
- Aging: A pilot study is currently underway to evaluate whether ketone esters can help prevent frailty and maintain function in older adults.
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Summary
While peer-reviewed research on ketone supplements is still limited, early findings are promising. Although they shouldn’t replace a well-formulated ketogenic diet in clinical settings, exogenous ketones may offer supportive benefits in several therapeutic areas. If you decide to use exogenous ketones, choose high-quality products carefully, and test your ketone levels at 30 minutes, 1-hour, and 2-hour increments after ingesting the supplement in order to monitor your response.
