Industrial food processing, which subjects foods to extremely high temperatures and pressures, might be freeing up even more calories. The food industry, says Wrangham, has been “increasingly turning our food to mush, to the maximum calories you can get out of it. Which, of course, is all very ironic, because in the West there’s tremendous pressure to reduce the number of calories you’re getting out of your food.” He expects to find examples of structural differences that affect caloric availability in many more foods. “I think there is work here for hundreds and probably thousands of nutritionists for years,” he says.

There’s also the problem that no two people are identical. Differences in height, body fat, liver size, levels of the stress hormone cortisol, and even gut microbes can influence the energy required to maintain the body’s basic functions. Between two people of the same sex, weight and age, this number may differ by up to 600 calories a day – over a quarter of the recommended intake for a moderately active woman. Even something as seemingly insignificant as the time at which we eat may affect how we process energy. In one recent study, researchers found that mice fed a high-fat diet between 9am and 5pm gained 28 per cent less weight than mice fed the exact same food across a 24-hour period. The researchers suggested that irregular feedings affect the circadian cycle of the liver and the way it metabolises food, thus influencing overall energy balance.

All of these factors introduce a disturbingly large margin of error for an individual who is trying, like Nash, Haelle and millions of others, to count calories. The discrepancies between the number on the label and the calories that are actually available in our food, combined with individual variations in how we metabolise that food, can add up to much more than the 200 calories a day that nutritionists often advise cutting in order to lose weight. Nash and Haelle can do everything right and still not lose weight.

None of this means that the calorie is a useless concept. Inaccurate as they are, calorie counts remain a helpful guide to relative energy values: standing burns more calories than sitting; cookies contain more calories than spinach. But the calorie is broken in many ways, and there’s a strong case to be made for moving our food accounting system away from that one particular number. It’s time to take a more holistic look at what we eat.