Breast is best, and breast is breast

by Elizabeth O’Sullivan

Compared with feeding at the breast, feeding infant formula is associated with a number of risks for babies; among other things, they suffer from more respiratory infections, more diarrheal disease, and perform worse on tests of cognitive development. For mothers, longer duration of feeding at the breast is associated with a reduced risk of breast cancer, ovarian cancer, and cardiovascular disease. Again, this is a non-exhaustive list.

With all this in mind, the phrase “breast is best!” is used liberally by both the medical community and the media to convey an important public health message. However, its appropriateness in the current U.S. infant feeding climate is unclear. Traditionally, feeding infant formula from a bottle has been the alternative infant feeding option to “breastfeeding.” Now, with the increased participation of mothers in the work force, and the advances made in breast pump technology, most “breastfeeding” women in the U.S. are practicing a hybrid infant feeding behavior by pumping breast milk and feeding it to their babies from a bottle.

“So what?” you say. “We’re told that breast milk is best. As long as the baby gets breast milk, there’s no problem, right?”

Well, maybe not. Think about this:

Figure 1. Figure 1. Image credits: www.mommygearest.com, www.babyfoodchart.com, Getty images

Figure 1. Image credits: http://www.mommygearest.com (left), http://www.babyfoodchart.com (center), Getty images (right)

It’s not clear whether the known benefits of breastfeeding mentioned above result from: a) the composition of breast milk, b) direct at-the-breast feeding or c) a combination of the above (SPOILER ALERT: I think that the answer is c).

Evidence is slowly emerging suggesting that partially or fully substituting at-the-breast feeding with feeding breast milk from a bottle may lead to different infant outcomes. For example, infants fed from a bottle, regardless of whether there is infant formula or breast milk in the bottle, gain more weight per month in the first year of life than infants fed directly at the breast. So, feeding breast milk from a bottle may affect the proposed beneficial effect of breastfeeding on childhood overweight and obesity.

Let’s use some basic facts about breastfeeding and two simple conceptual frameworks to explore other potential differences in infant outcomes that could be caused by feeding breast milk from a bottle.

Breastfeeding fact Why does this matter? Implications for feeding breast milk from a bottle
  1. Babies practice non-nutritive sucking at the beginning of a feed
Babies feeding at the breast have to work hard to get breast milk flowing and may consume less total milk compared with infants feeding from a bottle. Babies fed from bottles, whether it’s breast milk or infant formula, receive a constant flow of milk from the beginning to the end of a feed. The volume of milk consumed may partially explain the different growth patterns of breastfed and bottle-fed babies.
  1. Breast milk composition changes over the course of a single feeding
The increasing fat content, decreasing ghrelin (a hormone that stimulates hunger) content, and increasing leptin (a hormone that tells the body when it’s full) content might be a signal to babies that their “meal” is coming to an end. Breast milk that has been expressed and put in a bottle is constant in composition and babies do not receive dynamic messages during their meal. This may affect their ability to self-regulate their intake.
  1. Breast milk composition evolves over the course of infancy
Babies feeding at the breast receive the appropriate nutrients and volume of liquid for their age. Infants may be fed pumped breast milk that has been stored in the fridge or freezer for weeks or even months, resulting in a mismatch between infant age when the milk was produced and age when it was consumed.
  1. Breast milk contains antioxidants, immunoglobulins, and anti-infective factors
These components help babies prevent and fight infections. Immune components can be affected by freezing and re-heating pumped breast milk.
  1. When feeding at the breast, the baby decides when he/she is finished
This may help babies learn how to self-regulate their calorie intake. Babies fed breast milk from a bottle can be coaxed into consuming more than they want/need. This is termed caregiver-led feeding.
  1. Mother and baby have a shared immune system through breast milk
A mother can provide her infant with immune protection specific to the disease-causing elements (pathogens) in their environment. A mother entirely relying on a pump to feed breast milk receives no feedback from her baby about specific pathogens to which it has been exposed; this may reduce capacity to provide specific immune protection.

The following simplified conceptual frameworks help us to understand how feeding breast milk from a bottle is a different behavior to feeding at the breast, with an example of the potential consequences. For the sake of simplicity, I’m displaying only the examples of growth and infection; other outcomes that may differ by mode of breast milk feeding include: duration of any breast milk feeding, timing of the introduction of solid foods, and infant cognitive outcomes. We have good evidence for the boxes in red; the blue boxes highlight hypotheses.

Figure 2: Feeding at the breast.

Figure 2: Feeding at the breast.

Figure 3: Feeding breast milk from a bottle.

Figure 3: Feeding breast milk from a bottle.

Despite all I’ve just said, feeding breast milk from a bottle isn’t necessarily always a bad thing; I suspect that the risks to infants are greatest when fed infant formula, lower when fed pumped breast milk, and lowest when fed directly at the breast. Many mothers who pump and feed breast milk from a bottle do so because they have to return to work. In these situations, babies who might otherwise be given infant formula continue to receive breast milk.

Unfortunately, this problem is not uncommon. Many women in the U.S. must return to paid employment shortly after giving birth due to lack of mandated paid maternity leave. Provisions in the Affordable Care Act do specify requirements for adequate break times to pump breast milk and the most recent amendments require health insurance plans to provide breastfeeding equipment (i.e. breast pumps) for nursing women. However, the encouragement and promotion of pumping as a way to increase “breastfeeding” sends the message that these two behaviors are equivalent, and I hope I’ve convinced you that they’re not.

The differences between feeding at the breast and feeding breast milk from a bottle are of public health importance. As such, we need to understand more about how women are feeding their babies so that we can learn about the consequences of these behaviors, and consequently create a supportive environment for breastfeeding mothers. Unfortunately, current national surveillance surveys, and many research studies, measure only the infant’s breast milk intake, with no distinction between modes of breast milk delivery. Women are asked: “Was [child] ever breastfed or fed breast milk” and “How old was [child’s name] when [child’s name] completely stopped breastfeeding or being fed breast milk?” These questions don’t distinguish between feeding infants their own mother’s breast milk from the breast, from a bottle, or another mother’s breast milk.

Given that it is biologically plausible that feeding breast milk from a bottle could have a significant impact on many maternal and infant outcomes, we should be asking women about specific breast milk feeding modes on national surveys and in research settings. In fact, to establish whether they do have an impact on health outcomes, we must ask about them. If we don’t ask, we’ll never know.

Elizabeth O’Sullivan is a 2011 fellow of the Fulbright Science & Technology Award program, from Ireland, and a PhD Candidate in Human Nutrition at Cornell University. 

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2 thoughts on “Breast is best, and breast is breast

  1. Breast feeding is best for babies and provides many benefits. It is important that, in preparation for and during breast feeding, you eat a healthy, balanced diet. Great article!

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