Congrats on the children and on your nursing relationship with them.
One NIH definition of the "recommended daily intake" is to
calculate your daily baseline protein needs (non-pregnant,
non-nursing) as 0.36 grams per pound of body weight,
which they always write as 0.8 g/kg.
Then allow 20g more protein per day if you are nursing 1 child.
They don't have any recommendation how to compute lactational
needs for more than one child. Some people use 20g/day for
nursing twins, but the same people seem to assume twins are
supplemented with formula.
The US recommended daily intake values are inflated so that they
are sufficient for 90% of adults rather than being sufficient for the
average person. So they include sedentary people and athletes,
male and female, elderly and young, but not extreme situations
like professional body-builders or people with digestive disabilities.
Obviously a pound of fat doesn't require as much daily protein as a
pound of muscle or skin, so I personally subtract 10% of my
recommended daily allowance because my bodyfat percentage (34%)
is at least 10% beyond a healthy level.
Another official recommendation is not to exceed 20% of daily calories
from protein because supposedly it might stress the kidneys. After
some reading and research, I've decided not to follow that
recommendation while I'm dieting, but some nutritionists are
pretty adamant about it.
Weight watchers has a pretty simple formula for daily protein needs,
including if you're nursing one child, but they make you get
a doctor's advice if you're nursing more than one.
There are lots of studies and charts for the daily protein needs of
infants, so you might be able to look up the daily protein needs of each
child, according to their weights and age, and then calculate backwards
that 100% of their protein must be coming from you, and therefore from
your diet. But it sounds like you already have your target level for what
nursing should add to your diet.
As a lactating mother, I'd say from experience that dieting can
decrease my milk supply even if my protein intake is sufficient
and even if I'm drinking plenty of skim milk / calcium, but that's
because I'm cutting calories enough that I "feel" like I'm on a
diet and I have less energy. I don't worry about it because
mine are older. Besides, mine respond by increasing the amount
of time spent nursing, and I welcome the chance to spend
more time sitting on my butt.
Best wishes,
Lisa