The theory behind food combining is that different types of food are digested best in different chemical environments within our digestive systems. By keeping carbohydrates and proteins separate, the digestive system can be kept in balance and control of appetite becomes easier. Dr Nick Finer, head of the obesity clinic at Luton and Dunstable Hospital, explains, "The principles of the diet are mysterious and unscientific. If it works, and it may work, it is by restricting food intake. You could have a similar diet in which you were not allowed to combine red and green food. That would clearly restrict your food intake."
One issue unexplained by proponents of the diet is how normal eating, in which carbohydrates and proteins are routinely combined in the same meal, leads to weight gain. If the combination results in poor digestion, as the theory claims, that would mean fewer calories are absorbed, which should result in weight loss. Tom Sanders, professor of human nutrition at Kings College, London, says, "Food combining is a game people play to make eating difficult and unpleasant. It's a bit like saying you have got to stand on your head when you eat."
Eating only one type of food at a meal is a way of inducing "sensory specific satiety", which results in fewer calories being consumed. The principle is familiar to every child: there is always room for pudding.
Professor Sanders, who is the author with Peter Bazalgette of the anti- diet book, You Don't Have To Diet, believes, "The diet industry is a racket. The more money we spend on it, the fatter we get. Diet books are full of half truths and bogus science." For those who eat a high-fat diet - lots of chips, cakes and chocolate - the easiest way to cut the calories is to eat less fat. But for those already eating a low-fat diet there is only one option: eat less.
Jeremy Laurance is the Independent's Health Correspondent