Lactose pulls water into the milk by osmotic pressure along the concentration gradient. To put that into English, the lactose pulls water in in the body's attempt to equalize the electrochemical properties of the fluid inside and outside of the milk ducts. We can use the flow of water between the blood and interstitial fluids as an example to understand this process: One molecule of salt in the blood stream will pull in one molecule of water from the surrounding tissues. One molecule of albumin (the major blood protein) will pull in something like 18 molecules of water. This is why people who have protein energy malnutrition get swollen - they are not taking in enough protein to make albumin, so nothing is making water come back into the bloodstream from the body tissues, and water gets "stuck" there. This is not the only cause of edema, but it is the cogent one in toxemia/eclampsia. Lactose has a high "osmotic pressure", like albumin does. This means it attracts lots of water per molecule, though I'm not sure how much exactly. Therefore, lactose has the primary responsibility for milk volume....the more lactose the breast makes, the more water is pulled into the milk, and the more volume the mom has. There is also an inverse relationship between lactose and sodium in the milk. When lactose production falls rapidly, pores between milk gland cells open up (we think to protect the breast during involution), and more sodium can enter the milk. This happens during mastitis too, as the metabolism of the breast falls during the inflammation. The above is a simplification, but I hope it still retains sufficient validity to be useful. If not, I'm sure someone will say so! Nicely, of course! ;-} -- Catherine Watson Genna, IBCLC New York City mailto:[log in to unmask] *********************************************** The LACTNET mailing list is powered by L-Soft's renowned LISTSERV(R) list management software together with L-Soft's LSMTP(TM) mailer for lightning fast mail delivery. For more information, go to: http://www.lsoft.com/LISTSERV-powered.html