Flavors in breast milk? From the food that mothers ingest?
Yes, it really happens, and babies can taste the difference.
It might even affect their food preferences later in life.
A mother eats a spicy meal, then nurses her baby an hour later. Will the flavors make their way into the breast milk? Will her baby detect undercurrents of garlic? Top notes of ginger and coconut?
The baby probably isn't mulling it over with the vocabulary of a foodie. But the basic notion isn't far-fetched. A mother's diet really can affect the taste of her milk, and babies don't just notice these flavors. They also respond to them. Here's how we know.
What happens if you ask a bunch of breastfeeding mothers to swallow some garlic pills?
Researchers tried it, and confirmed through lab analyses that the garlic made its way into the women's milk. The flavor peaked between 1.5 to 3 hours after ingestion, at which point the women were asked to feed their 3-month-old babies.
Compared with babies whose mothers had swallowed placebo pills, the "garlic babies" spent more time feeding. They apparently liked the garlic (Mennella and Beauchamp 1991).
A similar experiment suggests that babies enjoy vanilla, too (Mennella and Beauchamp 1996). And when researchers asked lactating women to ingest flavor capsules, they found that all four flavors -- banana, caraway, anise, and menthol -- could be detected in breast milk later on. Banana peaked after just one hour, but the others lasted longer (Hausner et al 2008).
So it seems likely that many food flavors make their way into breast milk. Does this have any lasting effects?
Julie Mennella and colleagues wanted to find out, so they recruited a group breastfeeding women, and then randomly assigned some of the mothers to drink carrot juice each day for the first 2 months postpartum.
Months later, when the babies were 5-6 months old, the researchers brought the babies into the lab for a taste test. On different days, the babies were offered plain cereal and carrot-flavored cereal. What happened next?
All the babies made screwy, disapproving faces when they encountered the carrot-flavored cereal. But compared with babies in a control group, the babies who had been exposed to "carroty" breast milk reacted less negatively (Mennella et al 2001). They seemed to recognize the taste of carrots -- more than three months after their mothers had stopped drinking carrot juice.
Does it make any difference when babies first encounter new foods in their milk? Do flavors in breast milk have more impact depending on the timing of exposure?
Menella and her colleagues pursued this question in a second experiment. Once again, researchers randomly assigned lactating volunteers to drink juice each day -- this time, expanding the regimen to include 4 different juices (vegetable, beet, celery, and carrot).
But the researchers also tested infants of different ages. Some mothers were instructed to begin drinking the veggie-flavored juices when their babies were only 2 weeks old. Other mothers were told to start at 6 weeks, and still others waited until 12 weeks.
When the babies were 8 months old, they took the taste test. What now?
All babies exposed to carrot flavors in breast milk were more accepting of the carrot-flavored cereal, and ate more of it. But the effect was strongest among the infants who had started at 2 weeks (Menella et al 2017).
And interestingly, these babies had been exposed for only 4 weeks. So their enhanced liking for carrot juice was linked with experiences they'd had as newborns approximately 7 months earlier -- a month-long phase when their mothers had drunk several different veggie drinks, just one of which which was carrot juice (Menella et al 2017).
Does this mean that any amount of exposure to flavors in breast milk will make babies like a given food?
No. In fact, in the first study, the carrot-exposed babies didn't eat more carrot-flavored cereal. They just showed fewer negative reactions to the taste.
Moreover, when a team from the University of Coperhagen tested the effects of caraway exposure on 5-8 month old breastfeeding babies, they found that 10 days of exposure to carroway flavors in breast milk had no impact on the babies' acceptance of a carroway-flavored purée (Hausner et al 2010).
So the research doesn't tell us that exposure to flavors in breast milk will make babies like a food. But it does support a more fundamental idea -- that babies begin learning about food flavors long before they start eating solid foods.
That shouldn't surprise us, not if we consider the evidence for prenatal learning about food. Babies develop the ability to taste and smell before they are born, and food flavors can pass through the placenta and into the amniotic fluid. Studies indicate that newborns are more accepting of flavors they have encountered during gestation. Read more about the fascinating research in my article, "Prenatal learning: Do "pregnancy foods" affect babies' eating habits?"
The caraway study didn't support a short-term exposure effect, but it did underscore a difference between breastfed and formula-fed babies: Regardless of whether or not their mothers had consumed carroway, breastfed babies showed a higher initial acceptance of the carroway purée than formula-fed infants did (Hausner et al 2010).
That's consistent with other research showing that breastfed infants are more likely to accept new foods, and more likely to have varied diets as they get older. For instance, research suggests that infants are less likely to become picky eaters later in life (Forestell 2017). And the longer babies breastfeed, the more likely they are to consume vegetables during early childhood (de Wild et al 2018).
Could this be because the experience of tasting many different foods -- experiencing many different flavors in breast milk -- prepares babies to sample a variety of solid foods? If so, this could be an important benefit of breastfeeding.
Formula might never taste like garlic or carrots, but different formulas have somewhat different flavors, and these, too, may influence the development of food preferences.
In an experiment on preschoolers, Djin Gie Liem and Julie Mennella asked kids to taste a variety of juices, each characterized by different levels of sweetness and sourness.
The researchers found that kids who'd consumed sour-tasting, protein hydrolysate formulas as babies preferred higher concentrations of citric acid in their juice (Liem and Mennella 2002). Kids who'd used a different formula were less likely to enjoy sour juice.
A similar study found that kids who had consumed soy-based formulas were more likely to enjoy a bitter-tasting juice (Mennella and Beauchamp 2002).
And other experiments suggest that babies fed hydrolysate formulas are less likely than babies on milk-based formulas to consume pureed broccoli or cauliflower (Mennella et al 2006)
So it appears that a child's food preferences aren't purely idiosyncratic or arbitrary. They aren't just a reflection of individual genetics, or media hype, or even childhood experiences. They are influenced by prenatal events and encounters during infancy -- exposure to flavors in breast milk and formula (Forestell 2017).
What else is in breast milk? Read about the nutrients in breast milk here.
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Content of "Flavors in breast milk" last modified 2018
image credits for "Flavors in breast milk":
image of Thai meal by Vera & Jean-Christophe / flickr
image of baby nursing by Jessica Merz / flickr
image of toddler grabbing lemon slice from salad plate by Quinn Dombrowski / flickr
Small portions of this article appeared in a previous, older article about flavors in breast milk.