Lactate Is a Fuel and Signal, Not Just a Waste Product

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Lactate — long dismissed as a waste product of exercise — is now understood to be an important fuel and metabolic signal in its own right. When cells have excess pyruvate or lack sufficient oxygen, they convert it to lactate rather than burning it in the mitochondria. Rutter explains that the heart is particularly adept at burning lactate as fuel. Research by Josh Rabinowitz at Princeton has demonstrated that lactate circulates as a meaningful energy carrier throughout the body. During intense exercise, lactate produced by muscles also signals the brain to produce BDNF (brain-derived neurotrophic factor), a protein that promotes formation of new neural connections — which reframes high-intensity exercise as beneficial for brain health partly through this lactate pathway.