Child Myths

Straight talk about child development.

Breastfeeding: Speculating Wildly!

Do breastfed babies have different experiences from bottle-fed babies?

Last week, I commented on some of the real problems about researching the effects of breastfeeding on babies' development, and pointed out that many of the claims made about it really cannot be supported by any research that's practical or ethical to do. But this is such an interesting topic that it's hard not to speculate about it, whether we can support the speculations with evidence or not. There's no harm in this as long as no one claims that speculation is the same as evidence-- and who knows, maybe someone can figure out how to investigate further. Anyway, today I am going to let myself speculate freely about some aspects of breastfeeding.

Most work on breastfeeding has concentrated either on the biochemical aspects like the characteristics of human milk, or taken a somewhat mystical view of the power of "eye contact." I propose to try to imagine what experiences a suckling baby may be having, and how those experiences are probably different from those of a bottle-fed baby. Of course I can't know what a baby thinks and feels, but I can observe differences in the two experiences.

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1. Waiting for let-down.

Milk in a bottle flows passively into the baby's mouth, as the baby sucks and the bottle is slanted downward. As soon as the bottle-fed baby begins to suck, the milk appears. Not so for the breast-fed baby, however. The mother's milk does not simply trickle out of her breast, but is expelled by reflex muscular action after the baby's sucking triggers a sensory message to the brain. The beginning of milk ejection is called "let-down", and it takes 45 seconds or more after the baby begins to suck. During that 45 seconds, the baby can get a drop or two of milk that has been at the nipple, but no more than that. He or she has to work for a minute or so without getting rewarded for it. Gratification is delayed. Does this build character? I certainly don't know, but it's true that much of what we call "character" is the ability to persist in our efforts in order to get a future reward.

2. Choosing the right milk.

Bottle-fed babies get formulas that are homogeneous in nature, the same dilution and flavor from the beginning of the bottle to the end. Not so the breast-fed baby. Human milk (like unhomogenized cow's milk) is not consistent in its dilution. Any mother who has pumped milk and held the bottle up to the light can tell you that the first milk to come from the breast in a session (the "foremilk") is thin, watery, and translucent, while the later milk from that breast (the "hindmilk") is thick, creamy, and opaque. This means that a breast-fed baby who is mainly thirsty can take the foremilk from one breast, let go and fuss, be switched to the other breast, and take the foremilk there, without having to imbibe calories along with the fluid as a bottlefed baby does. The hungrier baby can keep on nursing at one breast until the creamy hindmilk, with its higher caloric value, is reached. Does this help the baby link its physical needs with its behavior, and lead to selecting foods as they are needed rather than because they're there? Again, I don't know, but the connection is at least a plausible one.

3. Experiencing flavors.

For the bottle-fed baby, milk is milk is milk. It always tastes the same unless there's something wrong with it. For the breast-fed baby, though, the mother's milk may have very different flavors depending on what the mother has been eating. Strong flavors, like garlic or beer, show up in the taste and the smell of the mother's milk. And according to the work of researchers like Mennella and Beauchamp, babies like these flavored versions of breast milk quite a lot, as they show by nursing longer. It's a myth that babies avoid the breast when the mother has eaten flavorful foods (although they may do so if the mother has a slight breast infection, which gives a saltier taste to the milk on the infected side). Is there any advantage to having different flavors on the menu? Some researchers have speculated that the various tastes of breast milk act as a "flavor bridge" to introduce the baby to the kind of foods the family normally eats, potentially leading to acceptance of a more varied diet, with related health advantages.

These differences between breast-fed and bottlefed babies' experiences are observable and measurable. When I say I'm speculating, I'm referring to the outcomes of these experiences, which are not known. Things could just be different without having different outcomes, and certainly without having a real advantage for one group or the other.


Jean Mercer is a developmental psychologist with a special interest in parent-infant relationships.


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