Death of the calorie | 1843
illions of dieters give up when their calorie-counting is unsuccessful. Camacho was more stubborn than most. He took photos of his meals to record his intake more accurately, and would log into his calorie spreadsheets from his phone. He thought about every morsel he ate. And he bought a proliferation of gadgets to track his calorie output. But he still didn’t lose much weight.
One problem was that his sums were based on the idea that calorie counts are accurate. Food producers give impressively specific readings: a slice of Camacho’s favourite Domino’s double pepperoni pizza is supposedly 248 calories (not 247 nor 249). Yet the number of calories listed on food packets and menus are routinely wrong.
Susan Roberts, a nutritionist at Tufts University in Boston, has found that labels on American packaged foods miss their true calorie counts by an average of 8%. American government regulations allow such labels to understate calories by up to 20% (to ensure that consumers are not short-changed in terms of how much nutrition they receive). The information on some processed frozen foods misstates their calorific content by as much as 70%.
That isn’t the only problem. Calorie counts are based on how much heat a foodstuff gives off when it burns in an oven. But the human body is far more complex than an oven. When food is burned in a laboratory it surrenders its calories within seconds. By contrast, the real-life journey from dinner plate to toilet bowl takes on average about a day, but can range from eight to 80 hours depending on the person. A calorie of carbohydrate and a calorie of protein both have the same amount of stored energy, so they perform identically in an oven. But put those calories into real bodies and they behave quite differently. And we are still learning new insights: American researchers discovered last year that, for more than a century, we’ve been exaggerating by about 20% the number of calories we absorb from almonds.
The process of storing fat – the “weight” many people seek to lose – is influenced by dozens of other factors. Apart from calories, our genes, the trillions of bacteria that live in our gut, food preparation and sleep affect how we process food. Academic discussions of food and nutrition are littered with references to huge bodies of research that still need to be conducted. “No other field of science or medicine sees such a lack of rigorous studies,” says Tim Spector, a professor of genetic epidemiology at Kings College in London. “We can create synthetic DNA and clone animals but we still know incredibly little about the stuff that keeps us alive.”
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All carbohydrates break down into sugars, which are the body’s main fuel source. But the speed at which your body gets its fuel from food can be as important as the amount of fuel. Simple carbohydrates are swiftly absorbed into the bloodstream, providing a fast shot of energy: the body absorbs the sugar from a can of fizzy drink at a rate of 30 calories a minute, compared with two calories a minute from complex carbohydrates such as potatoes or rice. That matters, because a sudden hit of sugar prompts the rapid release of insulin, a hormone that carries the sugar out of the bloodstream and into the body’s cells. Problems arise when there is too much sugar in the blood. The liver can store some of the excess, but any that remains is stashed as fat. So consuming large quantities of sugar is the fastest way to create body fat. And, once the insulin has done its work, blood-sugar levels slump, which tends to leave you hungry, as well as plumper.
Getting fat is a consequence of civilisation. Our ancestors would have enjoyed a heavy hit of sugar perhaps four times a year, when a new season produced fresh fruit. Many now enjoy that kind of sugar kick every day. The average person in the developed world consumes 20 times as much sugar as people did even during Atwater’s time.
But it is a different story when you eat complex carbohydrates such as cereals. These are strung together from simple carbohydrates, so they also break down into sugar, but because they do so more slowly, your blood-sugar levels remain steadier. The fruit juices that Camacho was encouraged to drink contained fewer calories than one of his wholegrain buns but the bread delivered less of a sugar hit and left him feeling satiated for longer.
Other macronutrients have different functions. Protein, the dominant component of meat, fish and dairy products, acts as the main building block for bone, skin, hair and other body tissues. In the absence of sufficient quantities of carbohydrates it can also serve as fuel for the body. But since it is broken down more slowly than carbohydrates, protein is less likely to be converted to body fat.
Fat is a different matter again. It should leave you feeling fuller for longer, because your body splits it into tiny fatty acids more slowly than it processes carbohydrates or protein. We all need fat to make hormones and to protect our nerves (a bit like plastic coating protects an electric wire). Over millennia, fat has also been a crucial way for humans to store energy, allowing us to survive periods of famine. Nowadays, even without the risk of starvation, our bodies are programmed to store excess fuel in case we run out of food. No wonder a single measure – the energy content – can’t capture such complexity.
Our fixation with counting calories assumes both that all calories are equal and that all bodies respond to calories in identical ways
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