The calorie, as it appears today on every food label, was defined in 1824 by French chemist Nicolas Clément – as a unit of heat, not food. Its link to nutrition only appeared decades later, through the experiments of Wilbur Atwater, an American chemist who literally burned food samples in a calorimeter to measure their energy.
The Atwater method, refined in the late 1800s, still underlies nearly every nutrition label used today – over 120 years later. It’s remarkably long-lived for a system devised before anyone had a concept of the microbiome, hormones, or individual metabolism.
That doesn’t make the number useless – quite the opposite, it remains the most practical way we have to compare foods. But it’s worth knowing that behind that “kcal” on the label sits, in fact, a century-old lab experiment.
A small historical detail, for a number we look at daily without ever questioning it.
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