The connection between calories and weight loss has been proven through scientific experiments dating back more than a century. A calorie is a measure of energy with two distinct definitions in scientific contexts. When discussing calories and weight loss, however, a calorie is the amount of energy it takes to raise the temperature of a gram of water by 1° Celsius. Food calories are measured in this way.
Even lying in bed, a person burns calories through the most basic of bodily functions. This is called a resting metabolic rate. While the resting metabolic rate varies from person to person, the average is between 1000-1400 calories per day. When one adds daily activity to routine, like walking or riding a bike, one should compensate for that extra energy burned through the intake of additional food calories. Eating food is like fueling a car; the body simply will not run without calories.
Many people in today's society take in more calories than they burn in an average day. This is when weight gain occurs. The excess food calories are stored as fat in the body, available to be used when needed. When surplus food calories build up as fat, a person becomes obese.
When discussing calories and weight loss, it is important to remember that all people are different. A large man will require many more calories than a petite female. This is because the larger a person is, the more energy is required to perform those basic functions like pumping the heart and breathing. A larger person requires more energy to do everything beyond those basic functions as well.
The key to calories and weight loss is to burn more calories than are consumed. This is done two ways: through dieting and exercise. Both increase weight loss, but an ideal weight loss plan is a combination of the two. There are many so-called “fad” diets that people try as a miracle fix to curb weight gain, but the basic concept behind calories and weight loss remains the same. In order to lose weight, a person must consume fewer calories or burn those calories off somehow. Fad diets focus on other things like carbohydrate intake, and while they may be effective for some people, they are not considered to be the optimal solution to weight loss.
The person credited with introducing concepts that connect calories and weight loss is the German physician Julius Mayer in a paper published in 1848. Before that time, people made no connection between what they ate and how much weight they gained or lost. Mayer introduced the idea that the source of energy was found in food, and thus increasing or decreasing food amounts impacts weight gain or loss.