When Fat is Fabulous: Mother’s Milk & Infant Neurodevelopment

Fat is back, baby!  After a pretty extensive smear campaign, fats are now recognized to be necessary for a healthy, balanced adult diet. But for infants,  LL Cool J said it best- “Don’t call it a comeback, I’ve been here for years!” Fats have always been an essential constituent in mother’s milk and in the last decade specific fatty acids have been added to commercial formula. The lion’s share of research effort in the topic of early nutrition has been dedicated to fatty acids and cognition. This is because fatty acids, made from phospholipids and triglycerides, are critical structural components of the brain.

More to the Story: Phospholipids                  

A recent pilot study conducted by colleagues in Japan suggests that formula fortified with a particular phospholipid may confer some benefits for infant neurodevelopment and function. Sphingomyelin is a phospholipid, and in rats, contributes to myelination of the brain. In our brains, neurons send “messages” to one another through electrical signals. These signals travel down a long cable coming from the neuron- known as an axon. When axons are wrapped in a sheath of lipids, called myelin, the signal travels even more quickly between neurons. Its sort of like highway tunnels that allow us to bypass cities without distractions. Importantly, in humans, much of our myelination occurs after we’re born, so fats in milk, and particularly sphingomyelin, are really important during this critical  period of post-natal neurodevelopment. 

 scientists' representation

In their pilot study, Tanaka et al. (2012) provided sphingomyelin-enhanced formula to infants that were getting a mix of breast-milk and formula. Of the phospholipids in the experimental formula, 20% were sphingomyelin while in the control formula, only 13% of the phospholipids were sphingomyelin. Twelve pre-term infants were randomly assigned to the experimental group and twelve were assigned to the control group. Infants who received the sphingomyelin fortified milk had slightly higher levels of sphingomyelin in their blood, and performed slightly better on some cognitive tests than the control group. There were a number of constraints on interpreting the data: a small sample size, many outcome measures, and many statistical tests, and no ability to control for breast-milk consumption. Despite these significant caveats, the general pattern suggests that greater consumption of sphingomyelin has the potential to improve neurodevelopment.

artist's representation

BUT the really interesting thing is that sphingomyelin makes up MUCH more than 20% of phospholipids in human breast milk. In 1984, Bitman and colleagues. investigated sphingomyelin in the milk of US women who delivered at term (37+ weeks, N=6), 1-2 weeks pre-term (31-36 weeks, N=28), and very preterm (26-30 weeks, N=18). Specifically, he investigated the sphingomyelin concentration in colostrum, transitional, and mature milk. At all time points, among all groups, sphingomyelin was >30% of the phospholipid  content and was usually closer to 40%. More recently, Wang and colleagues (2000) demonstrated that among Japanese women delivering full-term infants, sphingomyelin was 31% of the phospholipid content. Both research teams also reported some variation among mothers around the mean values. Hmmm, have you noticed that pretty much all constituents vary in their concentration among mothers to some extent?! Importantly, the sources of that variation remain poorly understood, especially for micro-constituents. Diet? Genes? Body condition? Parity?

         A Complex System                              

The key take-home message from the growing body of literature is that one main research imperative is to comprehensively investigate what constituents are in breast milk and their concentrations among mothers and populations as well as across lactation (Neville et al., 2012). Randomized trials that fortify formula one by one with different constituents thought to be bioactive in the newborn are going to constrain our understanding of breast-milk (and therefore slow-down improvements to formula). This is because few, if any, milk constituents exert their bioactivity in a vacuum from other constituents. Those complex interactions are going to be overlooked, compromised, or misattributed by a reductionist approach.

If I wanted to understand how a plane flies, I wouldn’t one by one add rivets to secure the wing to the plane, awaiting that magic rivet that makes flight possible.  No one rivet is responsible for securing the plane wing, just as no single constituent in milk determines neurodevelopment and cognition. It’s an exquisitely, magnificently complex system.

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References cited.                          

Bitman J, Wood DL, Mehta NR, Hamosh P, Hamosh M. Comparison of the phospholipid composition of breast milk from mothers of term and preterm infants during lactation. Am J Clin Nutr. 1984 Nov;40(5):1103-19.

Neville MC, Anderson SM, McManaman, Badger TM, Bunik M, Crume T, Dabelea D, Donovan S, Forman N,  Frank DN, Friedman JE, German JB, Goldman A, Hadsell D, Hambidge M, Hinde K, Horseman ND, Hovey RC, Hovey RC, Janoff E, Krebs N, Lebrilla C, Lemay DG, MacLean PS, Meier P, Morrow A, Neu J, Nommsen-Rivers, Raiten DJ, Rijnkels M, Seewaldt V, Shur BD, VanHouten J, Williamson P. 2012. Lactation and neonatal nutrition: defining and refining the critical questions. Journal of Mammary Gland Biology and Neoplasia. DOI: 10.1007/s10911-012-9261-5.

Tanaka K, Hosozawa M, Kudo N, Yoshikawa N, Hisata K, Shoji H, Shinohara K, Shimizu T. 2012. The pilot study: Sphingomyelin-fortified milk has a positive association with the neurobehavioural development of very low birth weight infants during infancy, randomized control trial. Brain Dev. [Epub ahead of print]

Wang L, Shimizu Y, Kaneko S, Hanaka S, Abe T, Shimasaki H, Hisaki H, Nakajima H. Comparison of the fatty acid composition of total lipids and phospholipids in breast milk from Japanese women. Pediatr Int. 2000 Feb;42(1):14-20.