The Bitterness of the Maternal Diet Influences the Bitterness of Human Milk

  • The flavors infants taste early in life, such as from their mothers’ milk, are known to drive their later food preferences.
  • A new study finds that the consumption of bitter foods, such as vegetables, by mothers may influence the bitterness of their milk.
  • The study suggests that breastfeeding could help children accept bitter flavors and develop healthier food preferences later in life.

 

Human milk is known to provide a variety of nutrients that aid infants’ growth and development and are beneficial to their health (1). But as children grow a little older, they often don’t meet recommended dietary guidelines, particularly when it comes to eating enough fruits and vegetables (2).

Taste is often an important factor in determining food preferences and choices, especially in children (3,4). Studies have shown that these taste preferences can be influenced by the flavors that infants experience early in their life, such as from their mothers’ milk. The flavors in human milk can in turn be influenced by maternal diet (5).

A new study conducted by Dimitra Mastorakou and colleagues at Danone Nutricia Research investigated the sensory properties of human milk and how they were affected by maternal diet (6). They found that the consumption of bitter foods, such as vegetables, may influence the bitterness of human milk. “The most important finding of our study was the association between the bitterness of the mother’s diet and her milk,” Dimitra Mastorakou and colleagues at Danone Nutricia Research said in an email.

The study suggests that breastfed infants may be exposed to bitter vegetable flavors at an early age, and may thus accept these flavors more easily, leading to healthier food choices later in life. “We hypothesized that being exposed to low levels of bitterness via breastmilk could possibly contribute to bitter taste acceptance of infants, similar to the acceptance of carrots by infants after breastfeeding mothers had been eating carrots,” the researchers said (7).

Previous studies have shown that children who were breastfed are less picky and more willing to try new foods as they grow compared with children who were fed formula (8). In addition, the overall duration of breastfeeding has been shown to predict vegetable intake (9). “However, our study was exploratory and the association that we found, as well as the possible effect of varying bitterness levels of human milk on later vegetable acceptance, need further evaluation,” the researchers said.

The researchers initially set out to describe the sensory properties of human milk, of which there is relatively little knowledge (10,11). In particular, they looked specifically at differences in the sensory and analytical properties of fore milk—approximately the first 30 milliliters of milk expressed—and hind milk—the remaining milk expressed. “Since we know that certain sensory characteristics of breast milk can be influenced by maternal diet, we wanted to look at the relationship between the bitterness of her diet and the bitterness of human fore and hind milk, as an initial indication of the transference of the bitter taste to breast milk,” the researchers said.

Twenty-two lactating mothers were trained on reference samples to become familiar with the five basic tastes—sweet, salty, bitter, sour, and umami—and creaminess. The mothers then kept a 24-hour food diary to assess the bitterness of their diet, followed by a sensory self-assessment of their fore and hind milks to assess how bitter they were perceived to be. The researchers also conducted analytical measurements of fore and hind milk to quantify fat, carbohydrate, total protein, and free amino acid content.

The mothers described sweetness as being the main basic taste of human milk, and it didn’t differ significantly between fore and hind milk. Human milk’s sweetness was correlated with carbohydrate content, whereas its umami was correlated with glutamic acid content.

The researchers found a significant positive correlation between the bitterness of the maternal diet consumed 24 hours before lactation and the perceived bitterness of fore milk but not hind milk. The bitterest foods in maternal diet were fruits and vegetables, caffeinated beverages, and cheeses, with vegetables being particularly bitter.

It’s still unclear why the bitterness of the maternal diet was correlated with the bitterness of fore milk but not that of hind milk, and future studies will be needed to further explore this question. The researchers suggest that the answer may lie in the differences between fore and hind milk, with fore milk being significantly less creamy, less fatty, and more watery than hind milk. Previous studies have shown that fatty acids present in human milk can mask the bitterness of certain bitter solutions (12).

The study suggests that consumption of bitter foods in the maternal diet may influence the bitterness of human fore milk, and could thus serve as an additional factor in children’s flavor learning. “Our study was exploratory but it has added to our hypothesis that the bitterness of human milk could potentially be an influencing factor on children’s later vegetable acceptance,” the researchers said.

“The taste of human milk is difficult to study, and we hope that this paper will inspire additional research that will help to further develop the knowledge of the importance of the maternal diet during breastfeeding, taking into consideration the international nutritional recommendations for lactating mothers,” they said.

 

1. Ballard O., Morrow A.L. Human milk composition: nutrients and bioactive factors. Pediatr Clin North Am. 2013 Feb;60(1):49-74.

2. Yngve A., Wolf A., Poortvliet E., Elmadfa I., Brug J., Ehrenblad B., Franchini B., Haraldsdóttir J., Krølner R., Maes L., Pérez-Rodrigo C., Sjostrom M., Thórsdóttir I., Klepp K.I. Fruit and vegetable intake in a sample of 11-year-old children in 9 European countries: The Pro Children Cross-sectional Survey. Ann Nutr Metab. 2005 Jul-Aug;49(4):236-45.

3. Drewnowski A. Sensory preferences for fat and sugar in adolescence and adult life. Ann N Y Acad Sci. 1989;561:243-50.

4. Drewnowski A. Sensory control of energy density at different life stages. Proc Nutr Soc. 2000 May;59(2):239-44.

5. Mennella, J. A. 2007. The chemical senses and the development of flavor preferences in humans. Pages 403–14 in Textbook on Human Lactation. Hale Publishing, Plano, TX.

6. Mastorakou D., Ruark A., Weenen H., Stahl B., Stieger M. Sensory characteristics of human milk: Association between mothers’ diet and milk for bitter taste. J Dairy Sci. 2019 Feb;102(2):1116-30.

7. Mennella J.A., Daniels L.M., Reiter A.R. Learning to like vegetables during breastfeeding: a randomized clinical trial of lactating mothers and infants. Am J Clin Nutr. 2017 Jul;106(1):67-76.

8. Galloway A.T., Lee Y., Birch L.L. Predictors and consequences of food neophobia and pickiness in young girls. J Am Diet Assoc. 2003 Jun;103(6):692-8.

9. de Wild V.W., Jager G., Olsen A., Costarelli V., Boer E., Zeinstra G.G. Breast-feeding duration and child eating characteristics in relation to later vegetable intake in 2-6-year-old children in ten studies throughout Europe. Public Health Nutr. 2018 Aug;21(12):2320-28.

10. Spitzer J., Doucet S., Buettner, A. The influence of storage conditions on flavour changes in human milk. Food Qual Prefer. 2010 Dec;21(8):998-1007.

11. McDaniel M.R., Barker E., Lederer C.L. Sensory characterization of human milk. J Dairy Sci. 1989 May;72(5):1149-58.

12. Ley J.P. Masking bitter taste by molecules. Chemosens Percept. 2008 Mar;1(1):58-77.

 

Contributed by
Dr. Sandeep Ravindran
Freelance Science Writer
Sandeepr.com