You can use 1 gr. or 70 gr. Your body will use what it needs in other words.
There are some "numbers" thrown around like for instance 40 gr. Ok, say for instance your diet consisted of 100% protein(extreme, but using this for a point). So, if you take in 200 gr. of protein in a meal, and nothing else, the body would use only 40 gr. and discard the rest?
In that case you would soon starve to death!