I sure hope you eat more than 800 calories per day…
The difference between 800 calories of fruits and veggies and 800 calories of meat and bread is that you’ll be eating all day long to get in the veggies but you’ll only eat a meal or two of meat and bread, because those foods are more calorie dense. Then there’s a concern with how much sodium, fat, and carbs you’re consuming. However, if you burn 800 calories (which is an excessive amount to burn in one workout), it’s 800 calories – period.
Not all calories are created equal. 500 calories of nutritious food is healthier than 500 calories of chocolate because of the different things these foods do to your body. A calorie burned is a calorie burned, though.
I think you may need some education on eating well, because it sounds like you’re under the impression that you should burn the same amount of calories as you eat, all during your workouts. Wrong, horrible idea.