Samantha Lee / Business Insider A little-known Los Angeles physician named Lulu Hunt Peters played a major role in popularizing the use of calorie counting for weight loss Her 1918 book, "Diet and Health with a Key to the Calories," was the world's first best-selling diet book Despite the ubiquity of calories today, recent studies reveal that they are an imperfect measure of nutrition In recent years, there's been a positive trend away from focusing only on calories.