Calories dictate weight gain or loss. Exercise produces stronger muscle which increases metabolic burn rate.
If you do not have a particular problem which prevents you from burning calories (thyroid) you can eat anything you want and maintain your weight as long as you do not over eat calories.
They measure the calories in food by burning it and measuring the heat given off. People are not furnaces. There are empty calories in all foods. . . And there are non-digestible calories in much of it. . . And human fat is not dietary fat. We make our own. . . And it is NOT made out of calories.
Before anyone can lose weight, they have to put themselves into ketosis, and start burning fat, not readiy available carbohydrates. Feed the body carbs, and the body never needs to go to the fat stored for energy.
So, no, Sirchtruth, it is NOT simple math. All calories are not equally digestible. Try eating 5000 calories of sawdust and see how much weight you gain. Human beings make their own fat not from fat they in jest or from calories the take in, but from carbohydrates they injest by use of insulin in the Krebs cycle. Learn a little about it before you spout pseudo science about diet.
A recent study in which dieters were fed equal caloric dietary intakes of low fat, low protein, or low carb diets. At the end of the test, they found the group on the low carb diet had lost weight twice as fast and had lost far more weight than either of the other two groups. . . And the low carb group had lower blood pressures and better regulated blood sugar and blood lipids levels than before the diets started. The other groups did not show any improvements in BP or Lipids.
I know what i'm talking about. 120 pound weight loss in two years without being hungry, due to knowledgible use of the Krebs cycle. Went from a 54" waist to a 40" waist without exercising —I have a very bad back. My girlfriend (243 lbs weight loss and kept it off for eight years, Registered Nurse, CCM, Dietary Expert) and I are workiing on a soon to be publishing cookbook with of low carb recipes including bread with just 5 grams of carbs per slice that looks, tastes, and feels like normal bread, cheesecake with 125 calories per full 1/8 cake slice, 15 grams carbs per slice including whipped cream topping and chocolate ganache topping or other fruit topping(!) that our friends cannot tell is not a Cheesecake Factory 900 calorie load of poison. . . and other similar delights to keep the low carb lifestyle interesting.
So your statement that you can eat anything you want and maintain your weight is wrong... Totally.