Say a person consumes 2000 calories in a day. During the course of that same day works out and burns 1000 calories. Is the total number of calories taken in for the day 2000 (calories eaten) 1000 (calories burned from exercise) = 1000 for the day?
Actually, no. Thats why dieticians and nutritionists go to school to learn this stuff. There are too many factors that go into this for me to explain. Thats why I recruited my friend Lisa Andrews, MEd, RD, LD. All the letters after her name means shes better qualified to answer this question than I am.
So heres her answer:
Whew! When do you have time to eat when you're burning up 1000 calories in one day?
The incoming calories versus outgoing calories equation is not quite that simple. Calorie requirements will vary depending on age, sex, metabolism, activity level, stress, heredity, etc. Most individuals require at minimum, 1200 calories per day just to function (maintain heart rate, blood pressure, body temperature, etc).
When you dip below your body's baseline needs, by either not eating enough or by exercising too much, your body will burn lean tissue (from muscle) as well as fat to provide enough calories to function. Don't lose the muscle you've built by under eating.
Id even suggest visiting a local dietician to figure out how many calories you need and then work from there figuring out how many you want to burn.
There it is from the horses mouth.