> What if people took the same tack when it comes to mental processes? "Math is challenging, so I refuse to do any". "Reading books is too hard because I have to look up some of the words". Surely we can agree that challenging your mind is a good thing.
Don't try to generalize my argument into absurdity. Simply not doing math because it is difficult doesn't solve the underlying problem, which is probably to become proficient at math. Now if there were easier ways to become proficient at math than what you were already doing, that would be more in line with my argument.
The key thing is solving problems. Simply giving up on learning math, or reading, solves no problem.
> Is it impossible to find any enjoyment in challenging your body as well as mind?
Challenging your body and maintaining good health are distinct goals, though they may be satisfied through the same processes. If you want good health, and a certain diet makes that easier, then I will say that it is no sense in maintaining whatever old diet you had simply because that would make it harder. If you want to challenge your body, and simply maintaining good health is not challenging enough, there are endless possibilities. Recreational sports, for example. Gymnastics. Parkour. But personally I would not choose to do things that were clearly suboptimal for my body solely because it would be more challenging. I might do it because I gain other things, such as eating tasty but unhealthy food, but I wouldn't choose to do it if the goal was only to make things harder for myself.