If you are not absorbing all the nutrients from the food you eat, then
you are wasting all those extra calories.
A condition called negative nutrition affects your ability to absorb
nutrients from food.
If you are not absorbing to the max then you won't get maximum benefit from the food you eat
or the drinks you buy.
Even the most powerful weight
gain drinks will have absolutely no effect if your body is just
letting all the benefits go in one end and out the other.
Otherwise you can eat
and eat but if your body isn't absorbing nutrients you won't gain
weight.