Human Milk Oligosaccharides and The Brain: Current Challenges

The TIG Blog invites any interested trainees to write a guest post about a topic that interests them. These blogs can be about a current issue in human milk and lactation research, a description of their own research, or simply a question of interest. This guest post was written by ISHRML trainee Stephen Fleming, who is currently in his 4th year as a doctoral student of neuroscience with Dr. Ryan Dilger at the University of Illinois at Urbana-Champaign in Champaign, IL.

Fleming Photo 2
Trainee Stephen Fleming during a science outreach event. 

We recently published a paper in Nutrients1 demonstrating that supplementation with sialyllactose did not affect cognition or gross sleep-related behaviors in piglets. Given mounting evidence that other oligosaccharides (e.g., 2’fucosyllactose,2  galactooligosaccharide,3 fructooligosaccharide,4 and chitosan oligosaccharide5) promote brain development or function in some way, this finding raised the question, “Why not this oligosaccharide?”

Human milk contains a variety of oligosaccharides in higher concentrations than the milk of any other species,6 and has presumably evolved to offer the most optimal nutrition for the human infant as possible. Providers of infant formula are looking for key ingredients and formulations that can bridge the gap between infant formula and human milk. The current approach to that task appears to be identifying nutrients or bioactive compounds in human milk that aren’t present in infant formula and adding them once there is sufficient evidence and regulatory approval. On the surface, this makes sense, however, I propose that rather than trying to create an identical formulation to human milk – which is impossible by current technological standards – the goal should instead be to recreate the functionality. However, the issue with recreating the functionality is that our understanding of the mechanisms behind feeding oligosaccharides are quite poor.

I will approach this goal from the perspective of brain development. There are many sources demonstrating that formula fed infants demonstrate fewer cognitive abilities than their breast-fed counterparts,7 however even these findings have been called into question.8 If formula fed infants, on average, operate at a level beneath that of breast-fed infants, how can we match their performance? Returning to our study, the objective was to evaluate if supplementation with sialyllatose improved performance on a recognition based behavioral task and diurnal activity patterns. We fed one group of piglets a custom-formulated milk replacer without sialyllactose and the other group was fed a formula containing 380mg sialyllactose per liter of milk replacer. We chose this amount as a previous student from our lab, Austin Mudd, published data showing that of a range between 0 and 760 mg sialyllactose/L milk, the dosage near the middle was most effective at altering MRI-related outcomes in the brain.9 From this information, we assumed the moderate dosage would be the optimal dose to assess the behavioral effects of sialyllactose supplementation. We should note, however, that another group had supplemented different forms of sialyllactose at much larger concentrations (2 or 4 g) and found a part of sialyllactose, sialic acid, was enriched in the piglet brain.10 Perhaps that may have been a better concentration to use, however such a high level of sialyllactose is uncommon in human or porcine milk.11, 12 Additionally, there is evidence suggesting that sialic acid, a monosaccharide important for cell signaling in the brain,13 is beneficial for brain development. Together with the emerging research demonstrating prebiotics positively affect cognition14 one might assume that sialyllactose, which contains sialic acid and has prebiotic-like effects,12 would be a powerful oligosaccharide with regards to supporting brain development.

There was one important issue however, the formula of our control group also contained a blend of prebiotics: polydextrose and galactooligosaccharide. We had shown in a previous paper that supplementing 2 g/L each of polydextrose and galactooligosaccharide increased exploratory behavior, improved recognition memory, and even altered the concentration of serotonin in the hippocampus.15 We note in our study with sialyllactose that perhaps the presence of polydextrose and galactooligosaccharide masked any beneficial effects we might observe from sialyllactose. Whether that is true or not, it raises a larger question. If prebiotics that aren’t found in milk can promote cognitive and brain development, what is special (regarding the brain) about human milk oligosaccharides? Perhaps nothing, which suggests my earlier proposal to make infant formula function closer to human milk, rather than make its composition the same as human milk, more feasible. Indeed, one might accomplish the goal of improving cognitive performance by using fructooligosaccharide, a plant-based oligosaccharide,16 or even chitosan oligosaccharide, an oligosaccharide found in fungi, arthropods, and insects!17 However, I don’t imagine the public would react favorably to feeding their babies an oligosaccharide from fungi or insects.

ExploreACES 2015
Trainee Stephen Fleming giving a presentation on the pig brain.

The world of prebiotics and HMO suffer from the same problems as the world of probiotics, we don’t understand how they work. We understand there is a gut-brain-axis and the microbiome is presumably an important player, but that hasn’t yet helped explain why some oligosaccharides promote brain development and others don’t. In my opinion, some of the best mechanistic work was done by simply providing 2’fucosyllactose to vagotomized rats and observing whether or not it was beneficial (it wasn’t).2

This is a long-winded way of addressing some of the issues faced when assessing the function of HMO. In my example, the use of an appropriate controls would have helped. However, when we look at work out of Dr. Shelley McGuire’s (former ISRHML secretary/treasurer) laboratory, demonstrating important global variation in the HMO content of human milk,18 are adequate controls even attainable? The second issue is given the quantity and complexity of HMO, it would be unrealistic to assume the scientific community can generate a wealth of data on each oligosaccharide and their interactions with every other one in a reasonable length of time. Third, the inability for academic labs to align in using the same prebiotics with the same dosing regimens in the same study designs impedes the ability to generalize observed effects. Lastly, and more surmountable, are the difficulties in conducting clinical research, controlling nutrition, and assessing cognitive outcomes throughout the human lifespan. Typically, this is where animal research steps in, as it provides a cheaper and more controllable source of experimentation. Of course, if we accept that human milk is unique to humans, how is measuring their function in animals relevant? Our lab has chosen to use the piglet, which offers greater similarities to the human in terms of neurodevelopment and gastrointestinal anatomy than the widely-used rodent. It still does not overcome the issue of species-specific milk profiles; however, it takes us a step in the right direction. Ultimately, I hope to see more mechanistic work completed in a variety of species, rather than continuing to describe the observable effects of feeding HMO.

Thank you, Stephen, for sharing these current trends and challenges in oligosaccharide supplementation research with us! If you’d like to contact Stephen to further discuss this piece or his research questions in brain development as it relates to human milk oligosaccharides, you can email him at or via LinkedIn. If you would like to read more about the work going on in the Dilger lab, you can do so here.

Pig wrangler by day, house-husband by night. After a hard day in the mud pits with the swine (it’s a little more glamorous than that) Stephen is usually found spoiling his cat Lucy, cooking dinner for his wife, or watching the next hit dystopian TV show. Between those endeavors, Stephen has recently taken up an entrepreneurial venture with his advisor Dr. Ryan Dilger to commercialize their work as a hybrid academic lab and contract research organization to bring research services in the piglet model to the pediatric nutrition industry and beyond.


  1. Fleming, S.A., Chichlowski, M., Berg, B.M., Donovan, S.M., Dilger, R.N. Dietary Sialyllactose Does Not Influence Measures of Recognition Memory or Diurnal Activity in the Young Pig. Nutrients. 10 (4), 395, doi: 10.3390/nu10040395 (2018).
  2. Vazquez, E. et al. Dietary 2’-fucosyllactose enhances operant conditioning and long-term potentiation via gut-brain communication through the vagus nerve in rodents. PLoS One. 11 (11), 1–14, doi: 10.1371/journal.pone.0166070 (2016).
  3. Savignac, H.M. et al. Prebiotic administration normalizes lipopolysaccharide (LPS)-induced anxiety and cortical 5-HT2A receptor and IL1-β levels in male mice. Brain Behav Immun. 52, 120–131, doi: 10.1016/j.bbi.2015.10.007 (2016).
  4. Chen, D. et al. Prebiotic Effect of Fructooligosaccharides from Morinda officinalis on Alzheimer’s Disease in Rodent Models by Targeting the Microbiota-Gut-Brain Axis. Front Aging Neurosci. 9, 403, doi: 10.3389/fnagi.2017.00403 (2017).
  5. Jia, S. et al. Chitosan oligosaccharides alleviate cognitive deficits in an amyloid-β1–42-induced rat model of Alzheimer’s disease. Int J Biol Macromol. 83, 416–425, doi: 10.1016/j.ijbiomac.2015.11.011 (2016).
  6. Bode, L. Human milk oligosaccharides: Every baby needs a sugar mama. Glycobiology. 22 (9), 1147–1162, doi: 10.1093/glycob/cws074 (2012).
  7. Horta, B.L., Loret De Mola, C., Victora, C.G. Breastfeeding and intelligence: A systematic review and meta-analysis. Acta Paediatr Int J Paediatr. 104, 14–19, doi: 10.1111/apa.13139 (2015).
  8. Girard, L.-C., Doyle, O., Tremblay, R.E. Breastfeeding, Cognitive and Noncognitive Development in Early Childhood: A Population Study. Pediatrics. 139 (4), e20161848, doi: 10.1542/peds.2016-1848 (2017).
  9. Mudd, A.T. et al. Dietary Sialyllactose Influences Sialic Acid Concentrations in the Prefrontal Cortex and Magnetic Resonance Imaging Measures in Corpus Callosum of Young Pigs. Nutrients. 9 (12), 1297, doi: 10.3390/nu9121297 (2017).
  10. Jacobi, S.K. et al. Dietary Isomers of Sialyllactose Increase Ganglioside Sialic Acid Concentrations in the Corpus Callosum and Cerebellum and Modulate the Colonic Microbiota of Formula-Fed Piglets. J Nutr. 146 (2), 200–8, doi: 10.3945/jn.115.220152 (2016).
  11. Mudd, A.T. et al. Porcine Milk Oligosaccharides and Sialic Acid Concentrations Vary Throughout Lactation. Front Nutr. 3 (September), doi: 10.3389/fnut.2016.00039 (2016).
  12. Ten Bruggencate, S.J., Bovee-Oudenhoven, I.M., Feitsma, A.L., van Hoffen, E., Schoterman, M.H. Functional role and mechanisms of sialyllactose and other sialylated milk oligosaccharides. Nutr Rev. 72 (6), 377–389, doi: 10.1111/nure.12106 (2014).
  13. Wang, B. Sialic Acid Is an Essential Nutrient for Brain Development and Cognition. Annu Rev Nutr. 29 (1), 177–222, doi: 10.1146/annurev.nutr.28.061807.155515 (2009).
  14. Kao, A.C.C., Harty, S., Burnet, P.W.J. The Influence of Prebiotics on Neurobiology and Behavior. Int Rev Neurobiol. 131, doi: 10.1016/bs.irn.2016.08.007. Elsevier Inc. (2016).
  15. Fleming, S.A., Monaikul, S., Patsavas, A.J., Waworuntu, R. V., Berg, B.M., Dilger, R.N. Dietary polydextrose and galactooligosaccharide increase exploratory behavior, improve recognition memory, and alter neurochemistry in the young pig. Nutr Neurosci. 0 (0), 1–14, doi: 10.1080/1028415X.2017.1415280 (2017).
  16. Rivero-Urgell, M., Santamaria-Orleans, A. Oligosaccharides: Application in infant food. Early Hum Dev. 65 (SUPPL. 2), 43–52, doi: 10.1016/S0378-3782(01)00202-X (2001).
  17. Muanprasat, C., Chatsudthipong, V. Chitosan oligosaccharide: Biological activities and potential therapeutic applications. Pharmacol Ther. 170, 80–97, doi: 10.1016/J.PHARMTHERA.2016.10.013 (2017).
  18. McGuire, M.K. et al. What’s normal? Oligosaccharide concentrations and profiles in milk produced by healthy women vary geographically. Am J Clin Nutr. (C), ajcn139980, doi: 10.3945/ajcn.116.139980 (2017).



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