Metabolism myths: 7 things we get wrong about diet and exercise

THE universe of good reasons for putting a live guinea pig in an insulated metal pot is small. I can think of only one: in France, in the winter of 1782, the chemist Antoine Lavoisier and his polymath friend Pierre-Simon Laplace placed their unwitting subject into a double-walled metal chamber, the world’s first calorimeter, and sealed the lid. They had packed snow into the space between the walls, and by comparing the rate at which the guinea pig’s body heat melted the snow to the rate of carbon dioxide it exhaled, they discovered metabolism – the “fire of life” that drives our very existence. At last, science had a physical measure of the life force that enables us to grow, reproduce and move. Physiologists like myself have been counting calories ever since.

Today, a widespread obsession with fitness and body weight has led to a new era of calorie counting. Diet books and magazine workouts promise a kind of shiny metabolic nirvana of calories burned, villainous foods avoided, waistlines melted and health and vitality restored. The reasons they fail – and they almost always do – are as varied as the schemes themselves, but the common theme is a fundamental misunderstanding of metabolism. Yes, diet and exercise are critically important for our health, but they don’t work in the ways we are usually taught. Our bodies aren’t simple calorie-burning engines that we can easily manipulate to keep us looking trim and feeling good. They are complex and dynamic metabolic systems meticulously shaped by evolution for survival and reproduction.