L-BHB vs. D-BHB: Is L-BHB Really "Metabolic Clutter"?

You mix a scoop of a ketone drink, wait an hour, and prick your finger. The meter shows a lower number than you expected. Then you read online that half of your drink is "L-BHB," and that L-BHB is just "metabolic clutter" your body can't use. It is easy to feel like you paid for something that does nothing.

That story has been repeated for years. But when you look at the actual research, it does not hold up well. In this article we walk through where the "clutter" idea came from, what ketone meters can and cannot see, and what newer human and animal studies show about L-BHB in the heart, the liver and the rest of the body.

Why we write about this

Our founder, Dr. Csilla Ari, is a neuroscientist who has studied ketones for many years, and our products use a 50/50 blend of D-BHB and L-BHB. So yes, we have a stake in this question. That is exactly why we want to show you the studies themselves, including their limits, instead of asking you to take our word for it. You can also read our earlier article on D,L-BHB vs. D-BHB for the basics.

A few terms first

• BHB (beta-hydroxybutyrate) is the main ketone body your body makes when you fast or eat very few carbohydrates. It is also sold as a supplement, often bound to minerals as "BHB salts."
• Enantiomers are two versions of the same molecule that are mirror images of each other, like your left and right hands. BHB has two: D-BHB (also written R-BHB or D-3-OHB) and L-BHB (also written S-BHB or L-3-OHB).
• Racemic (D,L-BHB) means a 50/50 mix of both enantiomers.
• Cardiac output is how much blood the heart pumps per minute.
• Afterload is the resistance the heart has to push against when it pumps. Lower afterload means the heart can pump more easily.

Where the "metabolic clutter" idea came from

The idea grew out of two true facts that were stretched too far.

First, when your liver makes ketones during fasting or a ketogenic diet, it makes mostly D-BHB. Because D-BHB is the form your liver produces, it became known as the "natural" or "bioidentical" ketone. However, your body also naturally produces L-BHB, but in smaller quantities, therefore that is bioidentical as well.

Second, most handheld blood ketone meters only detect D-BHB. The test strip uses an enzyme that reacts with D-BHB and not with L-BHB. So if you drink a product that is half L-BHB, the meter simply cannot see that half.

Put those two facts together and it is easy to tell a simple story: "the meter number is lower, so half the product must be useless." The problem is that a lower meter reading tells you what the meter can measure. It does not tell you what is actually in your blood, or what L-BHB is doing there.

What the meter misses: a human study

A 2023 study in the journal Muscles tested this directly. Researchers gave 16 healthy adults either a racemic ketone salt drink (7 grams of sodium D,L-BHB, half D and half L) or a calorie- and flavor-matched placebo, in random order. Data from 14 people were analyzed. Blood BHB was measured two ways: with a common handheld meter and with a lab method called gas chromatography-mass spectrometry (GC-MS), which measured total BHB.

Thirty minutes after the ketone drink, the handheld meter read an average of about 0.47 mmol/L. The lab method read about 3.1 mmol/L in the same blood. The authors concluded that the handheld meter appears to underestimate BHB, and that part of the gap is likely because the meter reads only D-BHB and misses the L-BHB from the racemic drink. They also noted that their lab method measured total BHB rather than each enantiomer separately, which is a limitation.

In plain terms: after a racemic drink, there may be several times more BHB in your blood than your meter shows.

L-BHB stays in the blood longer

One of the clearest differences between the two forms is how long they last. D-BHB is burned for fuel quickly. L-BHB is processed more slowly, so it stays in circulation longer.

• In a rat study published in 2021 in the Journal of Inherited Metabolic Disease, healthy rats were given a single oral dose of racemic D,L-BHB salt. Peak blood levels of L-BHB reached about 1.9 to 2.0 mmol/L, compared with about 0.3 to 0.5 mmol/L for D-BHB. The researchers also reported that L-BHB rose extensively in the brain, heart, liver and muscle.
• In a human study from the University of Oxford published in 2017 in Frontiers in Physiology, blood L-BHB stayed raised for at least 8 hours after a ketone salt drink, while D-BHB returned toward baseline much sooner.

A molecule that lingers in the blood for hours is not behaving like "clutter." It is behaving like a molecule with a longer window of action, which brings us to the heart studies.

What the heart studies show

Study 1: Racemic BHB in people with heart failure

In 2019, a Danish research group published a study in Circulation, one of the leading cardiology journals. Sixteen patients with chronic heart failure with reduced ejection fraction (a weak heart pump) received a 3-hour infusion of BHB or a placebo infusion, in random order. The BHB they used was racemic sodium BHB, a 50/50 mix of D and L.

Compared with placebo, the BHB infusion increased cardiac output by about 2.0 liters per minute (roughly 40%), raised the heart's ejection fraction by about 8 percentage points, and lowered systemic vascular resistance by about 30%. The researchers also saw these blood-flow effects in a smaller group of age-matched volunteers without heart failure.

This was an intravenous infusion in a hospital research setting, not a drink, and it lasted only a few hours. But it shows that a racemic D,L mix had strong, measurable effects on the human heart. Our article on the Na-D/L-BHB heart study covers it in more detail.

Study 2: D vs. L, head to head

The same research community then asked the obvious question: which half of the racemic mix was doing the work? In 2024, researchers published a study in the Journal of the American Heart Association that tested each form separately in pigs, whose hearts are similar in size and function to human hearts.

Three groups of 8 pigs each received a 3-hour infusion of racemic D,L-BHB, pure L-BHB, or pure D-BHB, compared with a control infusion. The results:

• Racemic D,L-BHB and pure L-BHB each increased cardiac output by about 2.7 liters per minute.
• Pure D-BHB raised cardiac output only slightly, and the change was not statistically significant.
• The increase came from lower afterload (the heart had less resistance to pump against), not from the heart squeezing harder.
• Blood BHB levels were higher with L-BHB, which the authors linked to its stronger effect.
• When the researchers tested isolated coronary arteries in the lab, D-BHB and L-BHB relaxed them about equally.

The authors wrote that their findings challenge the idea that D-BHB is the only form with effects on the heart and blood vessels. In other words, in this study the "clutter" half was the half that moved the needle. Read more in our article on the D-BHB vs. L-BHB heart study.

An important caveat: this was an animal study using intravenous infusions. It does not prove that a ketone drink will change cardiac output in healthy people, and nobody should use ketone supplements to treat a heart condition. What it does show is that L-BHB is biologically active.

What about the liver and inflammation?

Two recent animal studies looked at how different ketone supplements affect the liver.

• A 2025 rat study by Dr. Ari and Dr. Dominic D'Agostino, published in Pharmaceuticals, gave rats one of several ketone supplements by mouth daily for 4 weeks (5 rats per group). Rats given D,L-BHB ketone salts kept near-normal liver structure. In contrast, 1,3-butanediol and a ketone ester caused fat buildup in the liver and higher levels of an inflammatory marker called TNF-alpha. The authors noted that both D-BHB and L-BHB have been described as having anti-inflammatory effects, and that L-BHB stays in the bloodstream longer.
• A 2026 mouse study from Brigham Young University, published in Nutrients, compared D-BHB, L-BHB and 1,3-butanediol given by mouth. Both D-BHB and L-BHB raised energy (ATP) levels in the liver after a single dose, and after 8 days both kept inflammatory markers at control levels. 1,3-butanediol, by contrast, lowered liver ATP and raised markers of oxidative stress and inflammation.

These are animal studies, and short ones, so they cannot tell us exactly what happens in people over years. But in both studies L-BHB looked inert to positive, not harmful, which is the opposite of what the "clutter" story would predict.

Disclosure: Dr. Csilla Ari, a co-author of the 2025 Pharmaceuticals study, is the founder of Audacious Nutrition.

"Racemic is just the cheap version." Is it?

Another part of the story is there is a misconception that brands use racemic BHB only because it is cheaper to make. In reality, sourcing raw ingredients, racemic D,L-BHB and pure D-BHB cost about the same per kilogram. So for us, choosing a 50/50 blend is not a cost decision. We use D,L-BHB because of the research above: D-BHB provides fast fuel, and L-BHB stays in circulation longer and has shown its own effects in heart and liver studies.

Dr. Ari's 2025 paper makes the point: the different effects of the D- and L-forms still need to be studied separately in more detail. That is how science should work.

Common questions

Why does my ketone meter show a lower number with a D,L product?

Because most handheld meters only detect D-BHB. In the 2023 human study, the meter read about 0.47 mmol/L while the lab method read about 3.1 mmol/L in the same blood after a racemic drink (D,L-BHB).

Is D-BHB bad, then?

No. D-BHB is the form your body burns quickly for energy, and it is an important part of the blend. The point is simply that L-BHB is not wasted.

The bottom line

The claim that L-BHB is useless "metabolic clutter" comes mostly from the fact that meters can't see it, not from research that tested it. Studies show that L-BHB stays in the blood longer, reaches tissues like the brain, heart and muscle, and in heart studies had effects on blood flow that pure D-BHB did not match. Much of this evidence comes from infusions and animal studies, so more human research is needed, but the current science points toward both halves of a racemic blend having a role.

KETOSTART provides 6 g of D,L-BHB per serving, a 50/50 blend of D- and L-BHB with electrolytes, and is designed to help you reach and maintain ketosis. Just remember that your finger-prick meter will only show you half the picture.

This article is for education only and is not medical advice. These statements have not been evaluated by the FDA. Our products are not intended to diagnose, treat, cure or prevent any disease. Talk to your doctor before changing your diet or supplements, especially if you have a heart condition or take heart medication.

References

1. Holland-Winkler AM, Moore AR, Ansley JK, Fritz NA, Bederman I. Discrepancy of beta-hydroxybutyrate measurements between a blood meter and GC-MS methods in healthy humans. Muscles. 2023;2(4):327–337. View the abstract
2. van Rijt WJ, Van Hove JLK, Vaz FM, et al. Enantiomer-specific pharmacokinetics of D,L-3-hydroxybutyrate: implications for the treatment of multiple acyl-CoA dehydrogenase deficiency. Journal of Inherited Metabolic Disease. 2021;44(4):926–938. View the abstract
3. Stubbs BJ, Cox PJ, Evans RD, et al. On the metabolism of exogenous ketones in humans. Frontiers in Physiology. 2017;8:848. View the abstract
4. Nielsen R, Møller N, Gormsen LC, et al. Cardiovascular effects of treatment with the ketone body 3-hydroxybutyrate in chronic heart failure patients. Circulation. 2019;139(18):2129–2141. View the abstract
5. Gopalasingam N, Moeslund N, Christensen KH, et al. Enantiomer-specific cardiovascular effects of the ketone body 3-hydroxybutyrate. Journal of the American Heart Association. 2024;13(8):e033628. View the abstract
6. Ari C, D'Agostino DP. Divergent hepatic outcomes of chronic ketone supplementation: ketone salts preserve liver health while ketone esters and precursors drive inflammation and steatosis. Pharmaceuticals. 2025;18(10):1436. View the abstract
7. Morris TJ, Morris MD, Parker AJ, et al. Disparate hepatic mitochondrial and inflammatory effects of ketone supplements. Nutrients. 2026;18(4):675. View the abstract