When it comes to dieting, the calorie has always been king. Not only does every packet in the supermarket have calories listed on the side, but since last year every café and restaurant has had to print them on their menus. The tyranny of the calorie counters is upon us. And it’s all thanks to the first law of thermodynamics. Calories in, in the form of food and drink, minus calories out, in the form of exercise, equals energy stored, in the form of fat.
“A calorie is a calorie,” says Naveed Sattar, professor of metabolic medicine at the University of Glasgow. “If you take on more calories, you’re going to put on more weight if you don’t run them off.”
The calorie, though, is under attack. Every week another expert joins a growing group of those who say that, for most people, calorie counting simply does not work as a weight-loss strategy. “The whole calorie counting industry is, in my opinion, a bit of a fraud,” says Tim Spector, professor of genetic epidemiology at King’s College London. “It doesn’t tell people that while anyone can lose weight in the short term — whether you’re on a low-fat diet, a keto diet, a carnivore diet or a fresh-air diet — keeping that weight off in the long term is hard.”
That is backed up by the data. A review of weight-loss strategies led by the National Institute of Diabetes and Digestive and Kidney Diseases in the US found that even if dieters are initially successful, half of the lost weight is regained within two years, and within five years more than 80 per cent is put back on.
Andrew Jenkinson, a consultant in weight-loss surgery at University College London Hospital (UCLH), says our obsession with calories ignores a central part of the way the body works. “The body tries to maintain a particular weight setting,” he says. It does this by adjusting the “basal metabolic rate” — the energy used to carry out unconscious body functions such as breathing, pumping the heart and maintaining temperature.
The energy used to run these functions is adjusted by the body as a way to conserve or expel reserves. “It can be changed by 600 to 700 kilocalories a day, depending on whether we’re on a really low-calorie diet or whether we’re overeating,” Jenkinson says. “If we overeat, our metabolism will increase and if we starve ourselves it will slow down.”
A calorie may be a calorie but the way the body responds to that calorie can differ markedly, depending on the performance of our metabolism.
The microbiome also plays an underestimated role. Different individuals share just 25 per cent, on average, of the bacteria in their gut. And this bacteria has a big impact on the way food is metabolised. Spector’s research has shown that even identical twins often have completely different reactions to the same food.
Hormones also make life difficult. “When you are dieting your body ramps up hunger and does everything just to get you started eating again,” Spector says. “Your appetite levels are going through the roof.”
Dr Chris van Tulleken, an infectious diseases doctor at UCLH, says modern diets make this harder. The additives and manufacturing methods used in ultra-processed food confuse the brain’s hunger-reward system, meaning we end up consuming more and more calories to make ourselves feel full. Self-control and willpower don’t come into it, he says, because modern food makes it almost impossible to regulate our eating habits.
“Wild animals don’t have any nutritional information available but there is no obesity at all among them,” he says. “Even when animals have abundant food, they don’t need to count calories to regulate their energy balance. The only reason we have to count calories is because of the weird food we eat that has subverted our evolved mechanisms.”
Van Tulleken says avoiding ultra-processed food helps the body regulate itself — but acknowledges this is very difficult because convenience products are cheaper, easy to consume and heavily marketed. “If you just eat real food, it all more or less takes care of itself,” he says. “But that is an impossibility for most people.”
Calorie counting is also difficult because dieters often fail to work out how much they have eaten. “It’s very hard to know what 30g of Coco Pops is and then how much milk to add,” van Tulleken says. “Our ability to count calories is diminishing. It may be subconscious bias because we feel ashamed and so we will try to give ourselves a better mark. It may be because we’re eating out more.”