For years doctors have been telling their patients to cut out 3500 calories and they will lose 1 pound of fat. By cutting 500 calories daily, one should lose a pound each week. The calculation came from simple thermodynamics: If one burns a pound of fat in a bomb calorimeter, it releases 3500 Kcals. So, it would stand to reason that our bodies are just a simple physics equation. When their patients did not lose weight, they surmised the patient was overeating. Studies have since proven the 3500 calorie per pound theory wrong, as challenged by the following article in NEJM.
So, the new math shows that one must create a calorie deficit of between 4500 and 7000 calories for each pound of fat. The reasons behind this include:
- Reduction of calories and weight loss leads to lower levels of the fat burning hormone leptin, resulting in a lower metabolism.
- Reducing calories often leads to decreased levels of physical activity.
- Creating a calorie deficit from increased activity often leads to compensatory increases in intake.