Anyone with frailty or mobility problems at its essence is likely to be what could be described as LBM deficient, a (potentially fatal) condition arguably caused by a diet deficient in protein and/or a workout routine deficient in RT components.
On the ZC part of the spectrum, athletes are showing the minimum amount of fiber people can literally thrive on is zero.
As such, fiber deficiency aparently doesn't exist in the absence of carbohydrates, while protein deficiency is a reality independent of other dietary choices. Successfully vegan athletes show that all that is needed to compete against omnivores is the abundant use of plant based high protein foods.
RE: Fiber versus protein