[chaosist]

The first part is true. It is ultimately a problem of thermodynamics.

The distance runner or cyclist is not obese in your example.

There is simply no way to exercise enough if obese to create the caloric deficit needed.

This is all really part of the problem. Telling obese people to exercise more and don't restrict calories too much just doesn't work. What works if obese is a massive calorie deficit over time because an obese person has a massive amount of calories stored by definition.

It is just a much different situation compared to a distance runner that is already very learn. That person does have to worry about not consuming enough calories exactly because they don't have the stored calories the obese person does.