Some people talk of their metabolism like they might talk of the performance of a motor car – slow or fast. Many people carrying excess weight might like to attribute it to their slow metabolism, but there’s no evidence that it works that way. In fact, there is evidence that metabolism is neither slow nor fast, but varies across a gradient both within and between populations. A small number of people are at the upper end of this gradient and are much less likely to gain excess weight than the small number of people who are at the lower end. There are also some people who do have genuinely very slow metabolism, but this is usually down to them having an endocrine or metabolic disorder. But driving on life’s metabolic freeway, most people are neither crawling in the slow lane nor cruising in the fast lane, but changing lanes according to circumstance. Like freeway driving, metabolism is dynamic, flexible, and adaptable.