Are there foods that flavour breast milk?

25 July 2010

Question

Hello Naked Scientists,

I really enjoy your shows. I listen to the podcasts while I work the night shift at a hotel here in Fairbanks.

The other day I was talking with a pregnant friend of mine while walking through the dairy section of a store and I got to wondering; I know that some foods can make urine smell and so, as another bodily fluid, are there foods that make breast milk smell or taste differently? If women eat a lot of sweets, will their breast milk be any sweeter, or have a higher fat content if they ingest a large amount of fat?

Well, I love all of your shows. Keep up the good work.

William Baker
Fairbanks, AK, USA

Answer

Chris: - Well we have looked at this as a news item on the Naked Scientists a couple of years ago. There was a paper we reported. I actually gave it the exciting title of "Fulsome flavours on offer at the "breastaurant". It was a piece of work done by a lady called Helene Hausner who is from the University of Copenhagen. It was a paper published in the Journal of Physiology and Behaviour in 2008. What she did was to investigate this very phenomenon because women, including my wife, who have had babies, often report that the certain things they eat will affect whether or not the baby is very enthusiastic to breastfeed or not.

To get to the bottom of this sort of transmission between food and breast milk flavourants, this group recruited 18 women who were breastfeeding at the time and they got them to give some milk samples before and then milk samples after they gave them some capsules containing various flavourants. The flavourants they tested were menthol - we all know what that is - and also a chemical called d-carvone. Carvone is the stuff that makes caraway seeds have that very aromatic flavour to them. They also tested a chemical called 3-methyl acetate which is a banana flavour, and trans-anethole which is a sort of a liquorice taste. It's the thing that makes star anise and Ouzo have the liquorice taste the way it does. By feeding the women these things and then taking breast milk samples from them for certain amounts of time after, up to 8 to 10 hours, and then measuring the volatiles (the smells) above the breast milk, they could work out roughly how much of these flavourants were getting into the breast milk. It wasn't trivial. In fact, they found that different times elapsed for different flavours. The menthol took about 4 to 6 hours to peak, d-carvone and the trans-anethole took about 2 hours to reach peak levels, but the banana flavour, the 3-methyl acetate, didn't come through at all.

The interesting thing was that there was an 80% difference in the levels of these different smells and taste between different groups of the women. So if you look at one woman and compare another woman for the same flavour, you might detect 80% more or less of that flavour in her breast milk compared with the other woman. And if you do the test more than once on the same woman, you might find more than 50% variation in the levels of these different flavourants in their breast milk. What this shows you, therefore, is that it makes a very big difference from one person to the next and it makes a very big difference even in the same person.

But the bottom line is that things that you eat definitely can end up going into your breast milk, and it's not just small molecules and flavourants; it's also whole proteins. Researchers back in the '70s did studies by radioactively labelling proteins and amino acids, sending them through in the diet, and tracing them out into breast milk, showing that they do then end up going out and going into the baby. So, people who say their babies do develop tastes for things based on what mum's been eating are absolutely right.

Ben: - How well developed is a baby's sense of taste? Do you think that babies can actually taste this?

Chris: - It's almost certain that they can. If you think about it, the baby, when it comes out, is very under-developed and tends to prioritise the development of the systems that enable it to succeed when it's little. So it tends to develop first the things that will be most essential to survival. That includes knowing when something is good for you and bad for you, and how to alert mum with a cry. And babies, if you want to encourage them to eat something, they've got to like what they're eating. It's a sort of reinforcing thing, isn't it? The brain has to say, "I like this. I want to do it more" which makes sure the baby feeds regularly. So it's almost certain that babies do get hooked on these flavours.

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