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How exactly does a mother's food get turned into breast milk?

The creation of breast milk isn't actually part of the digestive process. During digestion, a pregnant woman breaks down her dinner and converts it into fatty acids, proteins and sugars, says Mary McLaughlin, a pediatric nutritionist at the Frances Stern Nutrition Center at New England Medical Center.But those nutritional building blocks are not instantly turned into milk; instead, they enter the mother's plasma, a colorless component of blood.

Milk production occurs in the mammary cells. Mammary cells collect fatty acids, proteins and sugars from the plasma to produce milk, which is a combination of water, fat, lactose and minerals and vitamins. An infant's suckling plays a major role in stimulating the hormones that cause milk release. The amount a baby feeds affects the amount of milk the breasts produce, but it does not generally change the speed, says McLaughlin. When a baby feeds more, more milk is produced.

Milk is produced even when a woman skips a meal or is undernourished, says McLaughlin. A woman generally builds up between 4 to 9 pounds of fat during pregnancy, and these fat stores can be used during lactation if her diet is inadequate. Producing milk generally requires eating an extra 750 calories per day, McLaughlin says.