Ketones and Endurance Performance – The Short Scoop

The Hype

Ketones burst onto the scene as a potential "magic fuel" for endurance, promising to spare carbs, reduce lactate, and boost efficiency. Sounds amazing, right?

The Theory

• Glycogen Sparing: Burn ketones, save your precious carb stores for later.
• Less Lactate: Shift away from carb-heavy burning, less lactic acid pain.
• More Efficient Fuel: Get more energy for the same amount of oxygen.
• Brain Boost & Recovery: Sharper mind during exercise, faster muscle repair afterward.

The Reality (from the Lab)

• Mixed Results: One early study showed a ~2% performance gain in cyclists.
• More Often: Other rigorous studies, especially at higher intensities, showed no benefit or even a ~2% worse performance.
• Side Effects: Nausea, stomach issues, and a weird taste are common.
• No Carb Replacement: Ketones are always added with carbs, not instead of them.

Overall Verdict: Current science is skeptical. A 2022 meta-analysis of 9 studies found no clear performance enhancement on average. Any small gains are usually within the margin of error or could be placebo.

Ketones and Endurance: Are We Fueling the Future or Just Blowing Smoke?

For years, the endurance world has had one true north: carbohydrates. We've carb-loaded, gelled up, and chugged sports drinks like our lives depended on it. And they pretty much did. Carbs were the undisputed heavyweight champs of athletic fuel. But then, a new contender stepped into the ring, draped in an air of scientific mystique: ketones.

Suddenly, these molecules, usually associated withfasting or hardcore keto diets, became the latest buzz in performance enhancement. Imagine a fuel that could spare your precious energy stores, banish the dreaded "lactate burn," and even make your body a more efficient machine. Sounds like a dream, right? The promise of unlocking superhuman endurance has sent researchers scrambling to unlock the secrets of ketone ester supplementation.

But is this just a lot of hype, or are ketones the real deal? Let's peel back the layers of scientific jargon and dig into what's actually happening in the lab.

The Ketone Playbook: How Were They Supposed to Work Their Magic?

The initial excitement around ketones wasn't just pulled out of thin air. There were some pretty compelling theories about how these little guys could boost your game:

The Glycogen Guardian & Alternative Fuel

Think of your muscle glycogen as your race-day bank account. You want to guard that like it's your last dollar. The big idea with ketones is that when you chug a ketone ester, your blood gets flooded with these new fuel molecules (primarily β-hydroxybutyrate, or β-HB). Your muscles, being the adaptable things they are, can then tap into this alternative fuel.

The theoretical payoff? If your muscles are burning ketones, they're not burning as much of your precious carbohydrate stores. This could mean you save that vital muscle glycogen for when you really need it – say, the last few miles of a marathon or that brutal final sprint. One early study even hinted at this, showing less glycogen breakdown when ketones were added to a carb drink during a two-hour cycling session. If you could keep more in the tank for the long haul, that's a serious competitive edge.

The Lactate Levels: Keeping the Burn at Bay

Do you know that searing burn in your legs when you're pushing hard? That's often associated with lactate accumulation and the resulting acidity in your muscles. The theory here is that by shifting your fuel preference away from rapid carb burning (glycolysis), ketones could lead to less lactate buildup.

And guess what? Some studies did show around 50% lower plasma lactate levels in ketone-fed athletes during steady-state exercise. By potentially blunting that lactic acid rush, ketones help keep your muscle pH more stable, delaying that all-too-familiar fatigue. Basically, if your muscles are happily munching on ketones and fats, they're less likely to go into full-on anaerobic panic mode, which means less lactate and less of that unpleasant "burn."

The Efficiency Edge: More Bang for Your Breath?

This one's more subtle but intriguing nonetheless. The idea is that ketones might be a more "oxygen-efficient" fuel. Imagine getting more energy (ATP) for the same amount of oxygen you're sucking in. If that holds true in a real-life athlete, it could mean you're cranking out more power without working any harder.

Some early whispers from elite cyclists suggested that a combo of ketones and carbs could improve gross efficiency. But here's the kicker: most studies haven't seen a significant change in VO₂ or overall efficiency with ketone drinks. A few isolated reports have shown tiny gains, but it's been more of a whisper than a shout. It's tough to measure these subtle metabolic shifts, and so far, the "super-efficient fuel" claim hasn't truly ignited.

Beyond the Legs: Brains and Bounce-Back

Ketones aren't just muscle fuel; they're also brain food. So, could a ketone-fueled brain keep you sharper and more focused and help you nail your pacing during a grueling event? It's a fun thought, but human studies haven't really hammered this home yet.

Where ketones might truly shine, however, is in recovery. Scientists are exploring if chugging ketones after exercise could help your muscles rebuild glycogen stores faster and even kickstart muscle protein synthesis. Think of it as giving your recovery a turbo boost. But it's important to note: these recovery perks usually require you to combine ketones with plenty of carbs and protein, and they haven't consistently translated into better performance on the next day. So, great for bouncing back, maybe not so much for mid-race heroics.

The Lab Reports: A Mixed Bag of Results

Alright, enough with the theories. What happens when we actually test ketones in real athletes? Prepare for some whiplash because the results have been, well, let's say, "inconsistent."

The Spark that Lit the Fire: Cox et al. (2016)

This was the study that got everyone buzzing. Back in 2016, researchers had trained cyclists knock back a ketone monoester drink (with carbs) before a 90-minute cycling session. They saw blood ketone levels shoot up, and the cyclists' muscles started burning more fat and ketones, less carbs. The cherry on top? A ~2% improvement in a 30-minute time trial! Cyclists covered about 400 meters more. This was it—the first real hint that ketones could be a performance enhancer. Game on, right?

The Cold Shower: Leckey et al. (2017)

Hold your horses. Just a year later, a follow-up study with professional cyclists poured cold water on the party. These athletes did a 50-minute time trial after taking a ketone diester plus carbs. Blood ketones were high, but performance actually got ~2% worse! Plus, they reported more stomach issues and higher perceived effort. The takeaway? Ketones don't play nice with high-intensity efforts when your body desperately needs quick carbs. And those tummy troubles? Definitely not a recipe for success.

When Carbs Are King: Poffé/Peters et al. (2021)

Let's talk marathon-length efforts. Researchers had cyclists do a three-hour ride with plenty of carbs, followed by a hard finish, then gave them a ketone monoester or placebo. Verdict? No significant difference in performance. No difference in muscle glycogen, either. If you're already nailing carb intake, throwing ketones into the mix might not add any oomph. With a full carb tank, ketones may just be extra baggage.

The Latest Blow: McCarthy et al. (2023)

Just last year, another rigorous study delivered a dose of reality. Trained cyclists did a 20-minute time trial after taking a ketone monoester optimized for blood levels without gut issues. Result? Performance was still ~2% worse compared to placebo. Even with minimal stomach upset, power output was lower. It seems that even when you manage side effects, ketones can make high-intensity efforts feel harder, fighting against your body's need for fast carbs.

The Big Picture: Don't Hold Your Breath

Most other acute trials have followed suit—no clear performance benefit. A 2022 meta-analysis of nine studies concluded that acute ketone ingestion doesn't enhance endurance performance on average. Any small gains (1–2%) are often within the margin of error or could be placebo. Plus, it's hard to "blind" athletes to a ketone drink—that taste is a dead giveaway!

The current scientific vibe leans toward skepticism. While ketones are a tantalizing idea, they haven't consistently delivered as an ergogenic aid for endurance.

The Nitty-Gritty: Timing, Dosing, and Playing Nice with Carbs

If you're still curious, here's what the research says about usage and why it's complex:

When to Chug: Before, During, or After?

Most performance studies gave ketones before or at exercise start. Dosing during long events to maintain levels has been tried, but sipping a strange liquid mid-race often backfires. Post-exercise ketones focus on recovery, not immediate performance.

How Much to Take: The Goldilocks Zone

Doses typically range from 0.25–0.5 g/kg body weight (25–50 g for a 70 kg athlete). This yields blood β-HB levels of 1–5 mM. Too high (>4 mM) → nausea, no extra benefit; too low (<1 mM) → no effect. The "sweet spot" seems around 2–3 mM β-HB, but even hitting that doesn't guarantee a win.

Sharing the Spotlight: Ketones + Carbs

In almost every study, ketones were added to—not replacing—carbs. Your body still needs carbs, especially for high-intensity efforts. Ketones can impair carb usage at higher intensities, potentially harming performance. Researchers have tried extra carbs or buffers; none have reliably boosted performance. So while ketones + carbs is standard, it's no silver bullet.

The Upshot: Why the Mixed Messages?

• The Intensity Conundrum: Ketones may help long, low-intensity efforts (glycogen sparing), but hurt short, intense bursts where carbs are critical.
• The "Ugh" Factor: Exogenous ketones often cause nausea, cramps, weird taste, and mild acidosis—increasing perceived effort and fatigue.
• Placebo or Real? A 1–3% change is tiny, often within test variability or placebo. Blinding is tough given the taste.