Bridget Jones's Diary features the motif of Bridget recording the daily number of calories she consumes. Her numbers elicit either shame when she eats what she considers too much or self-congratulation when she eats very little. The practice satirized in the book is known as counting calories, a common component of many diets that has also become associated with disordered eating.
The concept of calories can be traced back to the 19th century, when scientists began to study the relationship between food and energy. In 1824, a French chemist named Nicolas Clément discovered that the heat produced by burning food was proportional to its energy content. In the early 20th century, scientists discovered that not all calories are equal and that the body metabolizes different types of food in different ways. Today, calories are still used as a common way to measure the energy content of food and many consider calorie counting to be a helpful tool for managing one's diet and weight. However, the practice is not without its critics.
The phrase "calories in versus calories out" is meant to describe the supposedly simple rule that a person will lose weight as long as they eat (in) fewer calories than they burn (out) through exercise, digestion, and the body's basal metabolic functions. Many weight- and fat-loss diets prescribe a calorie-deficit eating plan that restricts daily intake to as low as 1,200 calories—about half of the recommended 2,000–2,500.
However, research has shown that while these "crash" diets may help people lose weight quickly, as many as 96 percent of people tend to put the weight back on as soon as they return to eating normally. This phenomenon is called "metabolic adaptation," and results from the hypothalamus trying to keep a person's body weight at a "set point," just as the hypothalamus tries to keep body temperature constant. New research has shown that not all bodies respond to calories in the same way, and an individual's gut microbiome also has a significant influence on their weight, as different organisms have different abilities to break down and use calories.
As a more effective alternative to calorie counting for weight management, some experts recommend focusing on the quality of food, exercising, reducing stress, checking whether medications are encouraging weight fluctuation, and consulting a specialist.
