Calories are everywhere: on food labels, menus, fitness trackers and smartphones. They have become one of the most recognisable and influential concepts in modern nutrition. This article explores the origins of calorie counting, the evidence behind current policies, such as menu labelling and the growing recognition of its limitations in both practice and public health.

Calorie-counting apps, first appearing in the mid-2000s, are now among the most downloaded weight-loss tools worldwide, and calorie labelling is embedded in public health policy across many countries. But how did a unit of heat measurement become such a dominant feature of dietary advice? More importantly, does our current fixation on calories actually improve health outcomes, or does it risk oversimplifying nutrition in ways that may do more harm than good?