Science as in observational studies that observe the effect of fiber in modern diets where food has been stripped off fiber to begin with.

What is low or high fiber depends on the diet as a whole and is not a certain number to target. If you eat a steak with the right amount of fat and protein (basically eat to satiety), you won't have excess protein or bile acids reach the colon, and the meal doesn't contain any starches or sugars in the first place, so there is really no important role for fiber to play.

Fiber typically exists in food items that also have carbs (again, what a coincidence...)