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Calorie counting doesn’t add up

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Calories are “chronically misunderstood”, says Emily Thomas in the BBC podcast The Food Chain. We’ve been using the same “blunt measuring tool” for more than 100 years. It all started with the American chemist Wilbur Olin Atwater in the 19th century. He would stick people in a sealed copper chamber for days, monitoring their food intake, excretory output and heat emissions to calculate how many calories they were getting from food. His experiments form “the basis of every single calorie count we see today”.

The trouble is, Atwater “never took into account” the energy we use to digest and metabolise food. It’s much harder for our bodies to extract the calories from protein and fibre than from fatty or highly processed food. For every 100 calories of protein we eat, we absorb only 70 calories, which means the figures on food packaging will be “30% off”. But we absorb nearly all the calories from the fat we consume. Our absorption also depends on our age, gut bacteria, hormones, the amount we sleep and even how we chew and whether we cook our food. A stick of raw celery contains six calories; cooked, it’s more like 30. It’s time to update Atwater’s system to take all these factors into account.

Listen to the podcast here.