So what would happen if say a guy at 125 lbs had a calorie intake of 6000 calories, 220g proteins, 120g fat and very fiber rich(Shit a lot?), all this each day continuously.
Would he benefit from all these calories and other nutritions? And except gaining some weight, what would the side effects be? Diarrhea?
If you weigh 125lbs, eating those kind of quantities daily IMO would be a really stupid thing to do.
You would feel like absolute shit, be constantly tired, probably feeling sick a lot of the time, I would be unsurprised if you had trouble sleeping and perhaps could suffer other side effects from giving your body such a huge amount of nutrients for such a low body weight - you can overdose on many things which occur naturally in food.
125lbs is a very low weight unless you are very short.
What I would say to someone that weight who is looking at that kind of diet is - don't do it.
If you have just started weight lifting, do you immediately start trying to deadlift 500lbs? Not unless you want to fuck something up.
It's the same with diet. You don't go from a tiny amount of food (to maintain that weight I'm assuming it must be a pretty light diet) to eating a fuckton every day at the snap of your fingers.