For decades, the mantra “calories in, calories out” has dominated the realm of weight management. At the time of “heroin chic” when I was a teenager, I could have told you how many calories there were in an apple, banana, avocado, packet of Walkers crisps and a Pot Noodle. My packed lunch regularly ended up in the bin as I perceived it to be too calorific to counter balance the horse riding and fitness classes I went to with a friend. I don’t miss those days.