Lactate as fuel
In plain language
A triathlete builds up over months towards an Ironman. During the long cycling stages his lactate rises high, and while running he gets heavy legs, stomach complaints and loss of concentration. Why can one athlete keep going endlessly while another collapses? The old story went: lactate is waste that acidifies your muscles. That is not correct.
Lactate is in fact fuel. Your body returns it to muscles, heart and brain to extract energy from it. And remarkably: certain gut bacteria can convert lactate into propionate, a short-chain fatty acid that gives muscles extra energy. Waste for one becomes fuel for another — and comes back as energy. Those who use this system efficiently acidify less and last longer. How well that succeeds varies from person to person and depends on your microbiome and your mitochondrial resilience.
The science behind
The classic idea that lactate is a tiring waste product has been revised: the lactate shuttle describes how lactate is transported between and within cells and serves as an energy source for muscles, heart and brain. A widely discussed finding in Cell Metabolism (2019, Scheiman et al.) showed that endurance athletes had more Veillonella bacteria after exertion, which convert lactate into propionate — an SCFA that can once again serve as fuel. In animal models this improved endurance capacity, a striking example of host-microbiome crosstalk.
More diversity in the microbiome goes together with better performance and fewer gastrointestinal complaints in endurance athletes (Frontiers in Nutrition), while mitochondrial resilience determines how efficiently lactate and fatty acids are used in extreme exertion (Sports Medicine). In this way three systems become interwoven: the muscle that produces lactate, the mitochondria that burn it, and the microbiome that recycles it. Acidification is then less a sign of ‘too much waste’ and more of a system that does not pump the fuel around fast enough.
The common thread is co-metabolism: whether someone smoothly reuses lactate or gets stuck in it arises from the interplay of DNA, microbiome (presence of lactate-utilising bacteria), metabolites and lifestyle (training, nutrition, recovery) together. It explains why identical training work results in smooth continuation for one athlete and collapse for another. This reading is supportive and observational — not a medical diagnosis.
Illustration & CosmoTalks
How your microbiome moves along with training, recovery and performance — five episodes.
- S4·E1 — Your gut trains along
- S4·E2 — Nutrition as fuel én as signal
- S4·E3 — Why one athlete recovers faster
- S4·E4 — Inflammation: ally and saboteur
- S4·E5 — Injuries often begin in the gut
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The common thread of this science, from insight to daily application, by Petra Van Gucht.
See the books →Scientific references
• Brooks GA. (2018) — The science and translation of lactate shuttle theory. Cell Metabolism.
• Clauss M., et al. (2021) — Exercise, gut microbiome and performance. Front Nutr.
• Van Gucht P. — EDGE (COSMO trilogy): energy, endurance and crosstalk.
Frequently asked questions
- Is lactate really not a waste product?
- No. Lactate is a fuel that your body returns to muscles, heart and brain. Some gut bacteria even convert it into extra energy.
- What do Veillonella bacteria do?
- They can convert lactate into propionate, a short-chain fatty acid that once again serves as fuel — an example of host-microbiome crosstalk.
- Why do I acidify faster than someone else?
- Acidification depends on how quickly your body pumps lactate around and reuses it, partly determined by mitochondrial resilience and microbiome.
- Can I improve my lactate utilisation?
- Training and a diverse microbiome usually help. The precise approach is personal; this remains supportive, not medical advice.
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