I don't follow. The body spends much more time digesting food than is normally spent exercising.
I've read that constant digesting gets in the way of the body doing nightly internal cleanup processes that detox your system, as energy is diverted to process food instead. That might be another source of problems.
The more exercise you do the more you have to eat to maintain your body. If you are following a healthy diet you will need to increase even more your total amount of food due the fact that generally healthy food has less calories. Also, there is nothing more stressful for the body than exercise.
> there is nothing more stressful for the body than exercise
I think you are postulating. There was an article here a week or two ago that showed how bodies frequently in motion tend to live longer and be healthiest. There are different types of effects on the body from activities, and I'd be willing to bet that a body that's constantly in a state of digestion is stressed more than one in natural motion. However, I say this with a disclaimer that I'm guessing based on recent articles posted here. But if you really think otherwise, you should just provide a source.
Also, unless you are training for the Olympics, you do not need to linearly scale your food intake in proportion to your exercise. The average diet for many people does not need to change much after introducing exercise because the average diet already is usually too many calories.
If everything else is kept the same (never true), that would be correct. Like everything else in this area of research (which depends upon NHST), you will find conflicting studies if you search. Here are some layperson sources (I didn't bother looking deeper):
I've read that constant digesting gets in the way of the body doing nightly internal cleanup processes that detox your system, as energy is diverted to process food instead. That might be another source of problems.