Dan John has often said "The body is one piece". Less eloquently, your body is a single unit and you have to treat it as such when you train.
Your diet is one piece, too.
You can't just change one part of your diet without affecting the others.
"I'll just eat more (fill in: protein/fiber/carbs/fat)" Sure, and this will raise your total calories, so you're not just changing one part of your diet. The ratios of macronutrients will change, too, which means whatever you eat more of will be a larger proportion of your diet.
. . . and less (fill in usually one of carbs or fat." This will skew your ratios of protein:fat:carbs even more, as one goes up and another goes down. Unless you're counting calories and counting grams of protein:fat:carbs, you're not necessarily going to eat the same amount of calories.
"I'll just do this crash diet, lose some weight, and then go back to eating the way I do now and maintain the new weight." That has a terrible success record - because your "diet" and your "eating the way I do now" are both parts of the same cumulative process of body transformation. They aren't really diet A and diet B, they're all Your Diet, with just varying periods of intake levels. You haven't really changed anything, you've just changed one small part.
If the body is one piece, so is the total food supply you provide it.