Saturday, September 12, 2009

Nursing Miscalculations

My son is expected to be (and is, I think), growing at a rate of about an ounce a day (or half a pound a week). Milk from me is his only source of food.
If 90% of his energy inputs go to metabolism, rather than growth, he should need the caloric equivalent of 10 ounces a day.
Because energy is lost at every step, it must take me more than 10 ounces worth of calories to make the milk that is providing him 10 ounces of calories.
If I am eating only the amount of calories needed to maintain my basic non-nursing metabolism, I should be losing more than 10 ounces a day.
In total, I have lost 2 pounds since the original big loss.
Ecological theory, logic problem, life question. . . where are the calculations off?
I can think of several places but would like to hear other hypotheses.


Erin said...

Water retention? What a mystery.

Tucson Trekker said...

How certain are you that you accurately know the amount of calories needed to maintain your non-nursing metabolism? Maybe your body has a weight set-point and will maintain approximately the same weight for a certain range of calorie inputs (I suspect mine does).

Sparkling Squirrel said...

Well, here are my initial speculations:
1) Dianthus is not gaining an ounce of dry mass a day, but rather an ounce of wet mass (?). If 90% of him is water, then he only needs the caloric equivalent of something around an ounce a day (the equivalent of a tenth of an ounce for growth, the rest for metabolism). Meanwhile, the weight I am trying to lose is not water, but rather fat.
2) I am eating far more than I think (I have been super hungry and, because I rarely have time for meals during the day, grab snacky things.
3) I probably overestimate my calories burned. Just because I am exhausted doesn't mean I've actually moved that much.

Other possibilities include that Babies have a more effecient metabolism than the 90% in text books-- they aren't moving that much and are receiving "the perfect food" and the frightening idea that my metabolism has become more effecient in order to feed Dianthus.

Tucson Trekker said...

(Ally wanted to give her opinion)

Tucson Trekker said...

Humans are only about 60% water so I think he needs more calories than you estimated. Still, I guess it's less than in the original figuring. I'd be surprised if metabolism becomes MUCH more efficient during lactation because my prenatal yoga teacher keeps telling us that we won't BELIEVE how much we eat while nursing...

Sparkling Squirrel said...

TT-- You're right; the 90% figure is for carrots, lettuce and cucumbers (I'm always amused that carrots are more water than milk is-- it's just that the non-water parts are considerable more solid).

Irene said...

One of the questions would have to be how many calories does it take to produce milk?

Likely you're eating more calories than required for non-nursing metabolism. I would think that from an evolutionary-benefits perspective, a nursing mother with access to more-than-sufficient food should eat enough to not only feed her baby, but maintain/increase her own body's reserves in case of a food shortage.