1- 3,500 calories = 1 pound of body fat. MYTH. While it is true that burning a pound of body fat will yield 3,500 calories over a laboratory bunsen burner, the body simply does not work that way. If it did, you would lose a pound every two days if you starved yourself. But nearly everyone has gained two or three pounds in a single day without eating 10,000 calories. And folks on VLC diets routinely lose two pounds a day without using 7,000 calories or starving themselves. How? The body is not a bunsen burner. It does not "burn" calories. It utilizes them, and can be persuaded to utilize them either very efficiently (bad for weight loss) or wastefully (ideal for weight loss)
2- Weight loss is accomplished by eating less and exercising. MYTH. A 13 year study has definitively killed this theory, which never made sense anyway. Sure the "math" seems to make sense, but totally disregards the primary job of your metabolism: keeping you alive. If you both eat less and exercise more, your body will read your situation as a crisis. What would you do if you were a submarine captain and your boat sunk? More would be demanded of you while at the same time your resources just became a limited commodity. You would conserve in every way you could, right? Your body does the same thing. Demand more energy output while providing less energy input, your metabolism will conserve everything it can. Extreme examples of this are known as "starvation mode", wherein the body can actually gain weight while eating less than a quarter of it's normal caloric requirement. The body does this by reducing the demands of the Basal Metabolic Rate (BMR), which is another discussion for a different day.
https://www.quora.com/Why-am-I-not-...ccurately-calculated-500-calorie-deficit-diet