While enjoying the dreamy state I entered while nursing my 8 month old son the other day, I pondered: If a lactating woman was stranded without food (but sufficient supplies of water), how long could she survive on her own breast milk? (I’m making the assumption the mother was stranded without her child). Further, could she support another adult?
No; she would die more quickly because energy is lost in the digestion process and in converting the stuff back to milk in her breasts.
No and not really.
Producing milk is very energy expensive. This energy has to come form somewhere. In the absence of food the only place for it to come from is the body’s own fat reserves. And of course milk I matter, and the matter also has t come from somewhere. Again, this is provided by the body, mostly by stripping fat.
The trouble is that it’s not very efficient. Normally when using reserves you are converting fat into food, with a moderate loss of energy. In this scenario you are talking about converting fat into food, with a moderate loss of energy, and then converting that food into milk, with an even greater loss of energy. You’d starve to death far faster than if you simply used the fat reserves directly.
To make matters worse the body doesn’t know why you are trying to produce milk. It assume sit is to feed a child, and it continues to add protein to the mix. Trouble is the body doesn’t add protein, so it starts stripping your muscles to provide it. This is not good.
Milk doesn’t actually produce anything It just takes what’s already available and converts it into another form, losing energy in the process.
Supporting an adult in the short term would be possible. It assumes that the woman has large fat reserves and the other person has none at all. But it would be possible to provide enough food to prolong that person’s life somewhat. She would essentially be feeding them her fat reserves.
Say hello to the fad diet of the future.
You’d need a biochemist. I tried for years to figure out how long a person could go just on their own body fluids & fingernails & stuff & never got an answer. There are too many variables.
In school they taught us that there is only a 10 percent energy transfer from food. Like if you had 10lbs of milk, you could only get 1lb of energy from it. But I dunno if thats the same anymore.
This is a side issue to the OP’s question, but I would further point out that in a desert island scenario, it would be very difficult for the woman to express enough milk to be able to subsist on, even assuming that producing milk wouldn’t strip her fat reserves (which, of course, in reality it would). Absent the presence of an actual baby, your body doesn’t produce the hormones that stimulate the let-down reflex; besides which, hand-expressing is pretty difficult and I’m guessing you don’t have your state of the art electric breastpump on the desert island.
Sure sounds like a perpetual-motion machine to me…
What is a pound of energy? The only relationship I know between energy and mass is E = MC^2. If that’s the pound of energy they mean then a human could live his entire life on a 10 pounds of milk.
I think perhaps you are referring to the efficiency of the body? As in only 10% of the chemical energy in food is recovered, the rest being lost as heat etc.
As a rule of thumb, if you draw a big box round a system, and less energy goes in than comes out, it’s screwed.
I don’t know how long a woman could survive, but it can hardly be better (maybe a bit for some obscure reason) than just sitting there conserving the energy.
Recent previous thread on this question:
http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=177167
Repeat after me, “The Matrix violates the second law of thermodynamics.”
It’s not a matter of Thermodynamics! The woman isn’t a closed system; the OP said she had water, at least. As it turns out, that’s not enough, but not because of freaking conservation of energy.
It is kind of. Food (including milk) is a source of energy. Water is not. If the woman could survive on her own milk then there would need to be, at the very least, no energy lost within the system.
It’s a similar concept, but it’s not the one the Second Law of Thermodynamics addresses. You could also say a man can’t make enough money to live off by giving himself cash gifts, but good luck proving that with dQ <= TdS.
Yeap, Shade’s got it in a nutshell.
- Is the woman producing mass or energy out of thin air?
- Is anything leaving the woman?
- Is there anything entering the woman?
- Does the flow in = flow out?
The woman would be losing water through breathing/urine/feaces, and carbon via exhaled air, as well as a number of vitamins/minerals. Also, energy is lost unless the woman sits in a room at body temperature and does not respirate (ie, dead).