When it comes to losing weight, it turns out the simple maths of counting calories does not always add up. Fad diets come and go, but the underlying message almost always follows a simple equation: if you consume fewer calories than you burn, the weight will melt away. In principle, it is true. And counting calories can be a useful tool for managing weight. But it only works if you know what numbers you are counting. And what has been billed as basic maths can sometimes look more like Einstein’s...