The nail has been hit on the head. And I guess difficulty is relative, but in my experiences, “very difficult” would certainly apply.
There is also the fact that many people tend to gain a percentage of fat and water weight, while relying on a greater quantity of carbs. For most anyone I’ve spoken to, trying to adhere to a plan like that requires consistent work and a diet which can typically reach in excess of 4k calories, daily. Also, while some higher level people do it, it generally wasn’t something you’d want to do quickly, because your body also needs time to rest or acclimate to the additional weight (age matters, too). Personally, I’d have to especially focus on my knees and such, just to ensure my own health. YMMV.