when you're eating 1500kcal, 300kcal is 20%.
when you're eating 3000kcal, 300kcal is 10%
just doing an easy BMR calculation, a 25yr old kid who's 6ft tall, weighs 250lbs and is 'very' active would need 4085 kcal per day to maintain bodyweight.
so, in terms of percentages, adding 300kcals to a 1500kcal diet is the equivilant to adding nearly 1000kcal to a 4000kcal diet.
so, who's 'grossly overeating'? the 1500kcal guy eating an extra slice of pizza per day? or the 250lb 4000kcal guy eating an extra 3.5 slices of pizza per day?
the answer is they're the fucking same.
#1 it takes a certain amout of food (kcals... kcal's = energy for those of you who skipped 3rd period bio to smoke weed and giggle in h.s.)
#2 it takes a certain amount of food OVER AND BEYOND BMR to GROW (grow= storing/repairing tissue)
there's no way you're going to continue to grow if you're not eating enough kcals, not even if your diet consists of 90% protein and 10% fats and carbs.