by Mary Jessica Hammes
October 12, 2008

Breast milk is a mystery.

No, really—even scientists think so.

A recent Chemical & Engineering News article reports that while scientists know many of the components of breast milk, they still don’t fully understand how they work.

Breast milk is most abundant in lactose and lipids, and in the article, J. Bruce German, a food science professor at the University of California, Davis, makes the following analogy: “For lipids and membranes the science is approximately where proteins were in the 1920s, back before researchers really had any clear understanding of the sequence and structure of individual proteins.”

Milk fat exists in globules of varying sizes, and German is heading up research that aims to understand the composition and function of individual milk globules, studying a globule’s particle composition. So far, his team has found that larger particles have qualities that suggest they are made of triglycerides and cholesterol—but that smaller globules seem to have few or no triglycerides.

What does this mean? Well, first of all, the UC-Davis team suggests calling the smaller globules “lactosomes.” They also think that the lactosomes are formed differently from globules, and—here comes the mystery—might have a function apart from delivering nutrient fat.

The article also features some fascinating information on the role of oligosaccharides, and what all of this research means for both formula-fed babies and adults who drink cow’s milk.

Some tidbits:

• The way that globules deliver fat nutrients might contribute to the type of fat that develops in the body. This could be big news for food science, as homogenization of cow’s milk breaks down the globules—German suggests that if they were left intact, more nutritional benefits might be derived.

• While plant- and animal-based fat storage systems have a single layer of phospholipids, milk fat globules have that plus an extra bilayer of phospholipids and glycolipids—a “conspicuous excess” of material, German says in the article; globules and lactosomes might be delivering membrane components in addition to fat.

• Free oligosaccharides are the third most plentiful ingredient of breast milk—but babies can’t digest those compounds. Carlito B. Lebrilla, a chemistry professor at UC Davis, suggests that the sugars must play some important role in infant health. Some research already shows that oligosaccharides encourage healthy microbes to colonize infants’ digestive tracts, which in turn can prevent E. coli infection. Also, research shows that mothers’ breast milk has evolved to produce the exact components to encourage specific, “good” gut-dwelling bacteria. (Since formula-fed infants have more “adult-like” intestinal microbes in their digestive tracts, the article says, researchers are already working to synthesize oligosaccharides found in breast milk to put in formula.)

• Oligosaccharides also keep human immunodeficiency virus from binding to cells, which helps explain why many babies breastfed by HIV-positive mothers do not develop the disease themselves.

The ending quote from German is priceless. Breast milk is “a remarkable fluid,” he says. “It’s extremely embarrassing how little we still know about it.”