It's a lot more complicated than that. The human body is not a simple engine with a fixed metabolism. Even if we switch to a more variable metabolism model, simply scaling your eating to your activity will not necessarily cause you to lose weight. The body first looks for equilibrium, and then when equilibrium is a problem it will start looking into stored energy. It's not just a question of "activity x burns y calories." Some of those calories are burnt in healing - our muscles strengthen by tearing, and then healing larger. You don't eat, your body may delay that maintenance, waiting until energy is available. So you haven't actually lost any weight - you've just prevented yourself from gaining weight, which is actually a bad thing, because that muscle would make you healthier.
Wait, so if I burn 2000 calories in a day but only consume 1500 calories, I won't lose weight?
I am not arguing that it's not as simple as the 500 calorie deficit going 100% towards fat reduction, but I don't see how it is possible to not lose weight like this. Weather or not the exercise builds muscle, it will reduce mass.
Naturally, if you consume 25% fewer calories than you burn, you will lose weight. However, you will be less healthy as a result. There's a very narrow band where you can actually lose weight in a healthy manner. It varies from person to person, and furthermore, you are making yourself weaker and more vulnerable to disease if you are eating less than your caloric requirements.
So you're saying "you're fat, that's your problem, you should just eat less." The issue is that eating less causes its own problems, and for some people those can seriously outweigh the benefits of being thinner. For some people, their ability to metabolize fat is so retarded that what you suggest really isn't feasible. They will likely starve to death before they get rid of their fat.
These people are, of course, rare, but the same issue exists in lesser values for other segments of the population.
We aren't talking about the "rare" individuals. The obesity problem seen in the United States is almost exclusively due to people eating crap food (sugar sugar sugar) and not exercising, period.
I am not a doctor, but I'd still be willing to wager that the health benefits of going on a diet/exercise regimen, thus losing weight, FAR outweigh any potential downsides to dieting. Seriously, how can you say "oh, overweight people might be harmed by diet restrictions and exercise" when for 99% of the cases out there this simply isn't the case?
There is no way to lose weight besides caloric intake being less than caloric expenditure. By saying "you are making yourself weaker and more vulnerable to disease" you are effectively saying (though probably not meaning) "you should not slim down". Trying to drop 25 pounds in a week is pretty insane, but a well balanced 1-2 year plan, approved by a doctor, will go a long ways towards health and not against it.
The linked article specifically talked about a case where the woman's doctor told her there are genetic reasons for her obesity.
Also, there is a limit to where losing weight is an unquestionably good idea. I certainly have enough excess body fat that no one wants to see my bare chest. That said, I'm not clinically speaking overweight, and I have very low blood pressure, and I'm fairly active. I certainly would benefit from cardio (as would most people) but focusing on fat rather misses the point, which is primarily keeping arteries clean and your heart strong. This is actually quite possible for an obese person.
You can gain or lose 25 pounds next month easily and without any ill effects of any kind. Try it.
I would like to see any sort of evidence that it is possible for some people to have very little ability to metabolize fat. I think the body type argument is a rounding error when it comes to obesity.
Visit Asia. There are incredibly few obese people, and most people are probably too thin. Why? Caloric intake and expenditure.
I don't have any supporting evidence, but I have read over and over that you cannot exceed more than 2 pounds of loss per week without doing some damage. 25 pounds in a single month is HUGE.
Anecdote: Myself, plus 3 guys I work with decided to lose weight. We all succeeded (I lost about 50 pounds over 9 months), but the guy who lost 3.5 pounds per week started having serious medical issues.
The difficult part is the burning the 2000 calories. You do not have complete control over how many calories you burn. In the example DrSprout gives, if your body senses that you are burning too many calories it may adjust what is it does to conserve energy. In this case by delaying the process of healing the muscles.
In short, the way to lose weight is by burning more calories then you consume. But the difficult part is finding out how to do so in a healthy and sustainable weight. The means for doing so will vary from individual to individual.
