Lactate as a Fuel: What the science shows

Lactate gels are the story of this year's Tour de France, and the science underneath them is real. Lactate is not a waste product, and it is not what makes your legs burn. It is one of the body's central fuels. Whether taking in more of it improves performance, and for whom, is a separate question. A real mechanism is not the same as a proven benefit, and the benefit shown so far may apply only to the very top of the sport.

For most of a century, lactate was blamed for fatigue and written off as the by-product of hard efforts. The burn in your legs on a steep climb is real, but it comes from hydrogen ions released when carbohydrate is broken down quickly for energy — not from lactate. Lactate is produced alongside those ions and actually mops some of them up, which delays fatigue rather than causing it. It was simply present at the scene, and got the blame.

Modern physiology corrected the record. Through what George Brooks named the lactate shuttle, the body continuously moves lactate from where it is produced, in hard-working muscle, to where it is used — the heart, the brain, other working muscle — and oxidizes it for energy (Brooks, 2018). It is a fast fuel the body takes up readily, often in preference to glucose. It is a raw material the liver can turn back into glucose. And it is a signalling molecule that helps trigger training adaptations. As blood lactate rises, even the brain draws a growing share of its energy from it (van Hall et al., 2009).

Glucose leaves the gut through one transporter, SGLT1, and fructose through another, GLUT5, and each can only move so much per hour. Picture the gut as a stadium emptying after a show: the fuel you take in is the crowd, and those transporters are the exits. Send through more than the exits can clear and people pile up at the doors — the fuel that can't get out sits in the gut, draws in water, and ferments, which is what the cramping and bloating of over-fuelling actually are. Glucose's exit is full near 60g per hour; opening fructose's separate exit lifts the usable total toward 90, and with a trained gut up toward 120g per hour. That is the current limit of carbohydrate delivery, and the front of the sport now fuels right at it to cover the roughly 25,000 to 33,000 kJ burned in a single Grand Tour stage.

Once both exits are full, the only way to move more fuel is to find another way out. Lactate has one: it leaves through a different transporter again, MCT1 — a side exit the carbohydrate crowd never uses. That is the whole appeal. At a sold-out stadium, a third exit clears people the main two no longer can. It is also the catch, and it is the part the marketing skips: a stadium is only sold out at the very top of the sport. Fuel at an everyday pace and the crowd is a fraction of the size — the two main exits are never close to full, and the side exit opens onto an empty concourse, with no queue for it to clear.

This is where care matters most, because the loudest claims come from the companies selling lactate. Set the mechanism beside the evidence, question by question, and the line between the two is clear.

That "fat and glycogen" row is where the maker's most interesting claim sits. From Lab to Field describes lactate as wearing two hats depending on how hard you are going. At low intensity, with oxygen plentiful, they propose it signals the body to spare glycogen and lean more on fat. At high intensity, when oxygen is scarce, it flips — acting as a buffer and helping the muscle keep burning carbohydrate to hold a power output that would otherwise fade. It is an elegant idea. It is also the maker's proposed mechanism rather than a demonstrated outcome, and the wider evidence is more cautious: raising blood lactate tends to suppress fat breakdown in the moment rather than promote it, so even the direction of the low-intensity effect is unsettled.

The independent trials are thinner and more mixed than the marketing suggests. Two small 2024 randomized trials pulled in different directions: one found no time-trial benefit at all, despite measurably raising bicarbonate and lowering perceived effort (Bordoli et al., 2024); the other found only a modest work-rate change over a 20-minute test, in a study where blood lactate did not actually rise (Ewell et al., 2024). Reviewing the field, Asker Jeukendrup places lactate below carbohydrate, sodium, and nitrate on the evidence hierarchy, and his conclusion is plain: when the claims get big, it is marketing rather than science (Jeukendrup, 2026).

The mechanism has never been the obstacle. Delivery has. To move performance, the doses in question are on the order of 10 to 25g of lactate per hour, and getting that in by mouth has failed for forty years for the same reasons. Lactate salts carry a heavy load of sodium, potassium, calcium or magnesium; in the amounts required, they draw water into the gut, unbalance electrolytes, and taste aggressively sour.

The most telling study is recent. McCarthy and colleagues tried oral sodium lactate fifteen separate times, across different doses, volumes, and formulations. Blood lactate barely moved, and gastrointestinal distress was severe enough to cause repeated vomiting (McCarthy et al., 2024). Where lactate has raised blood levels cleanly, it has been by intravenous infusion at controlled pH and volume — not something usable mid-race (Pedersen et al., 2022). Formulation decides everything, and no one has yet solved it in something an everyday athlete would drink from a bottle. It is worth being plain about the shortcut the mechanism implies: if the goal is more circulating lactate, the fructose already in a normal carbohydrate mix raises it measurably, and lactate supplements do not (Jeukendrup, 2026).

Everything above describes a problem that lives at 120g per hour. Almost no one lives there. In our 2024 study of 110 Canadian endurance athletes, 94.7% fuelled at 90g per hour or less. Measured in real races, everyday cyclists average around 49g per hour, barely 40% of the ceiling (Lanpir et al., 2025). The gap is not discipline. An everyday ride burns a fraction of a Grand Tour stage, and the body only draws carbohydrate as fast as the effort demands it — so at everyday intensities there is neither the demand for 120g per hour nor the room for a fuel that only earns its place beyond it.

There is a quieter catch, too. Lactate's uptake depends on MCT1 capacity, which is built over months the same way carbohydrate tolerance is — it is not plug-and-play. For an athlete fuelling below the ceiling, the levers that actually move performance are the proven ones: carbohydrate at a ratio the gut can absorb, hydration, and sodium, done consistently. It is the same pattern the category has always run on — built for the one percent, then sold to the rest.

Lactate may turn out to be a genuine breakthrough. For now it is a breakthrough for the top one percent — the athletes already fuelling at the ceiling it is designed to lift. We took it seriously enough to study it ourselves, and that is where we landed: a real fuel with unproven delivery, aimed at a problem our athlete does not have.

The specific evidence we would need to see is that exogenous lactate adds a measurable benefit at everyday intakes — below the carbohydrate ceiling, not only above it. If that is shown, the work becomes how to bring it to everyday athletes in a form that fits how they actually fuel: a powder, or a booster added to a bottle, priced to use every session rather than saved for race day. Until then, the proven levers come first. Our Performance Drink Mix is built on the same carbohydrate science the category runs on, in a 2:1 glucose-to-fructose ratio with 200mg of sodium, made for every-session use, and the rest of our fuelling research sits in the Performance Lab. Don't break a ceiling you haven't reached.