Science - Death of the calorie
"“I was always tired and hungry and I would get really moody and distracted,” he says. “I was thinking about food all the time.” He was constantly told that if he got the maths right – consuming fewer calories than he burned each day – the results would soon show. “I really did everything you are supposed to do,” he insists with the tone of a schoolboy who completed his homework yet still failed a big test. He bought a battery of exercise monitoring devices to measure how many calories he was expending on his runs. “I was told to exercise for at least 45 minutes at least four or five times a week. I actually ran for more than an hour every day.” He kept to low-fat, low-calorie food for three years. It simply didn’t work. At one point he lost about 10kg but his weight rebounded, though he still restricted his calories.
Dieters the world over will be familiar with Camacho’s frustrations. Most studies show that more than 80% of people regain any lost weight in the long term. And like him, when we fail, most of us assume that we are too lazy or greedy – that we are at fault.
As a general rule it is true that if you eat vastly fewer calories than you burn, you’ll get slimmer (and if you consume far more, you’ll get fatter). But the myriad faddy diets flogged to us each year belie the simplicity of the formula that Camacho was given. The calorie as a scientific measurement is not in dispute. But calculating the exact calorific content of food is far harder than the confidently precise numbers displayed on food packets suggest. Two items of food with identical calorific values may be digested in very different ways. Each body processes calories differently. Even for a single individual, the time of day that you eat matters. The more we probe, the more we realise that tallying calories will do little to help us control our weight or even maintain a healthy diet: the beguiling simplicity of counting calories in and calories out is dangerously flawed...
The calorie – which comes from “calor”, the Latin for “heat” – was originally used to measure the efficiency of steam engines...
Atwater transformed the way the public thought about food, with his simple belief that “a calorie is a calorie”. He counselled the poor against eating too many leafy green vegetables because they weren’t sufficiently dense in energy. By his account, it made no difference whether calories came from chocolate or spinach: if the body absorbed more energy than it used, then it would store the excess as body fat, causing you to put on weight.
That idea captured the public imagination...
Because counting calories was seen as an objective arbiter of the health qualities of a foodstuff, it seemed logical that the most calorie-laden part of any food item – fat – must be bad for you. By this measure, dishes low in calories, but rich in sugar and carbohydrates, seemed healthier...
A US Senate committee report in 1977 recommended a low-fat, low-cholesterol diet for all, and other governments followed suit. The food industry responded with enthusiasm, removing fat, the most calorie-dense of macronutrients, from food items and replacing it with sugar, starch and salt. As a bonus, the thousands of new cheap and tasty “low-cal” and “low-fat” products which Camacho used to diet tended to have longer shelf lives and higher profit margins.
But this didn’t lead to the expected improvements in public health. Instead, it coincided almost exactly with the most dramatic rise in obesity in human history...
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”...
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...
Our fixation with counting calories assumes both that all calories are equal and that all bodies respond to calories in identical ways... Yet a growing body of research shows that when different people consume the same meal, the impact on each person’s blood sugar and fat formation will vary according to their genes, lifestyles and unique mix of gut bacteria.
Research published this year showed that a certain set of genes is found more often in overweight people than in skinny ones, suggesting that some people have to work harder than others to stay thin (a fact that many of us already felt intuitively to be true). Differences in gut microbiomes can alter how people process food. A study of 800 Israelis in 2015 found that the rise in their blood-sugar levels varied by a factor of four in response to identical food.
Some people’s intestines are 50% longer than others: those with shorter ones absorb fewer calories, which means that they excrete more of the energy in food, putting on less weight.
The response of your own body may also change depending on when you eat. Lose weight and your body will try to regain it, slowing down your metabolism and even reducing the energy you spend on fidgeting and twitching your muscles. Even your eating and sleeping schedules can be important. Going without a full night’s sleep may spur your body to create more fatty tissue... You may put on more weight eating small amounts over 12-15 hours than eating the same food in three distinct meals over a shorter period.
There’s a further weakness in the calorie-counting system: the amount of energy we absorb from food depends on how we prepare it. Chopping and grinding food essentially does part of the work of digestion, making more calories available to your body by ripping apart cell walls before you eat it. That effect is magnified when you add heat: cooking increases the proportion of food digested in the stomach and small intestine, from 50% to 95%. The digestible calories in beef rises by 15% on cooking, and in sweet potato some 40% (the exact change depends on whether it is boiled, roasted or microwaved)...
The difficulty in counting accurately doesn’t stop there. The calorie load of carbohydrate-heavy items such as rice, pasta, bread and potatoes can be slashed simply by cooking, chilling and reheating them. As starch molecules cool they form new structures that are harder to digest. You absorb fewer calories eating toast that has been left to go cold, or leftover spaghetti, than if they were freshly made. Scientists in Sri Lanka discovered in 2015 that they could more than halve the calories potentially absorbed from rice by adding coconut oil during cooking and then cooling the rice...
The message from many public authorities and food producers, especially fast-food companies that sponsor sports events, is that even the unhealthiest foods will not make you fat if you do your part by taking plenty of exercise. Exercise does, of course, have clear health benefits. But unless you’re a professional athlete, it plays a smaller part in weight control than most people believe. As much as 75% of the average person’s daily energy expenditure comes not through exercise but from ordinary daily activities and from keeping your body functioning by digesting food, powering organs and maintaining a regular body temperature. Even drinking iced water – which delivers no energy – forces the body to burn calories to maintain its preferred temperature, making it the only known case of consuming something with “negative” calories. A popular expression in English tells us not to “compare apples and oranges” and assume them to be the same: yet calories put pizzas and oranges, or apples and ice cream, on the same scale, and deems them equal...
Counting calories has disrupted our ability to eat the right amount of food, he says, and has steered us towards poor choices...
The simplicity of calorie-counting explains its appeal. Metrics that tell consumers the extent to which foods have been processed, or whether they will suppress hunger, are harder to understand. Faced with the calorie juggernaut, none has gained wide acceptance.
The scientific and health establishment knows that the current system is flawed... a label in Australia can give a different count from one in America for the same product.
Officials at the WHO also acknowledge the problems of the current system, but say it is so entrenched in consumer behaviour, public policy and industry standards that it would be too expensive and disruptive to make big changes. The experiments that Atwater conducted a century ago, without calculators or computers, have never been repeated even though our understanding of how our bodies work is vastly improved. There is little funding or enthusiasm for such work. As Susan Roberts at Tufts University says, collecting and analysing faeces “is the worst research job in the world”...
Many of us know instinctively that not all calories are the same. A lollipop and an apple may contain similar numbers of calories but the apple is clearly better for us."
