When you exercise, are you burning just the regular calories, or the calories from fat from what you eat?

You burn the calories from your food first, then muscle mass, then fat, last. That's why it's important that you still maintain a good diet while attempting to lose weight.

Losing muscle mass is self defeating in losing weight. So, eat a balanced diet, high in protein, and keep about 500 calories or so below what you need to lose weight. Then strength train to build muscle (which will burn calories) and do cardio.

The answer is not simple. What most people mostly burn most of the time is blood sugar (glucose). Blood sugar mostly comes from dietary carbohydrates, and to a lesser degree from excess protein in the diet. If need be it also is raided from lean tissue in the body -- internal protein can be converted into blood sugar just as dietary protein can. Note there is a fuel tank of blood sugar called glycogen -- the storage form of blood sugar. You keep a few thousand calories of glycogen stored in muscles and liver that can be shed off as blood sugar when needed. But that glycogen storage is quite limited and can be depleted in a day or two or during prolonged exercise like a marathon.

To some degree we ALSO burn fat (both dietary and body fat). This happens at a low-level in most people, but people who eat low-carb diets will adapt to burning more fat and less blood sugar. One can reach a state where more than 50% of energy expended comes from fat, as opposed to blood sugar (this is called being in ketosis). THAT person is mostly burning fat when they exercise, whereas most people are mostly burning blood sugar.

Sorry, the answer just isn't a simple one. The body is complex.

The calories you burn are based on your basal metabolic rate plus activity plus a small amount with the digestion of your food. You are constantly burning calories. You burn more with the addition of aerobic exercise (intensity plus duration makes a difference).

Excellent free sites: http://www.exrx.net/

http://www.chooseyourplate.gov/

http://www.webmd/com (exercise and diet site)