We humans, as well as all life on earth, make use of the energy that is stored in the chemical bonds of different types of sugars to sustain ourselves. Sugars come in many forms and shapes — from one ringed simple sugars such as glucose and fructose to disaccharides, that are two simple sugars linked together (e.g. table sugar — sucrose is a disaccharide of glucose and fructose) and on to complex chains of simple sugars that form fibers such as cellulose and starch.
Lactose, a disaccharide found in milk produced by all mammals, has gained over the last few decades a bad reputation for the digestion problems it causes for some individuals. The ability of adult humans to digest lactose has evolved fairly recently (in evolutionary terms), and is common mostly in people of European descent. The rest of us have to take a supplement, usually a pill, containing lactase, an enzyme that breaks down lactose, together with our ice cream to avoid the negative side effects of lactose intolerance.
This reputation, however, is unjustified. Lactose and its derivatives have an important contribution to an infant’s health, a contribution that is a subject of intense research for the last 100 years. It is no longer considered “just” an energy source like other types of sugars, but rather, a molecular scaffold that is the basis of a unique class of molecules called “Human Milk Oligosaccharides”, abbreviated — HMOs.
Of all the constituents of mother’s milk, HMOs are the third most abundant solid component, and it is left mostly undigested until it reaches the lower part of the digestive tract. Over the years its function was shrouded in mystery — why would the human body go to such a great extent to synthesize complex molecules that neither the producer (the mother) nor the consumer (the infant) can digest?
Up until the start of the 20th century, the infant mortality rate was estimated to be around 30% (For comparison, the current infant mortality in Israel is estimated to be 2.4 per 1000 births, and ~ 5.7 per 1000 births in the US), but major differences were observed between the mortality rates of infants that were breastfed and infants that were not breastfed.
Although reliable data about breastfeeding and infant mortality before the 20th century is scarce, we know that even today, with modern medicine babies who are breastfed have a 21% lower risk of death in their first year, compared with babies never breastfed. The reduction in risk rises to 38% if babies are breastfed for 3 months or more. It is easy to imagine that the rates would have been much higher before the discovery of antibiotics and vaccines.
In particular, gastrointestinal infections that on many occasions resulted in widespread epidemics led to vast increases in infant mortality. Such an epidemic took place in 1884 in Naples and resulted in 7000 deaths, many of those are small children. A German pediatrician named Theodore Escherich, who witnessed and later studied that epidemic, was one of the first scientists to study the contribution of breastfeeding to infant health and its relationship to gut microbe populations. His research culminated in a detailed study named “Enterobacteria of infants and their relation to digestion physiology” (translated from german). Among other topics, this paper described a bacterium which he called “bacterium coli commune” that was very common in human feces. This bacteria was later renamed — Escherichia coli — and today it is the most studied organism on the planet.
Escherich was a true pioneer in the field of pediatrics. For example, he demonstrated that meconium was sterile and that bacterial intestinal colonization is attributable to the infant’s environment (including milk) within 3–24 h after birth, Moreover, he showed that, under anaerobic conditions, the growth of the “bacterium coli commune” population was totally dependent on carbohydrate fermentation.
Building on Escherich’s research, a french pediatrician named Henry Tissier who was working in the Pasteur Institute in Paris added a critical element to Escherich’s findings — he was able to grow in a culture a population of anaerobic bacteria found in healthy breastfed infants. Anaerobic (obligatory) bacteria are organisms that react negatively or even die if free oxygen is present, therefore, they require unique growing conditions, which Tissier was able to formulate. Using his newly discovered culturing methods, Tissier showed that “Bacterium coli commune” was not the major component of the intestinal flora of healthy infants as previously thought, but that a newly found bacterium, which based on its Y shape he named Bacillus bifidus communis (in Latin, the word bifid translates to cleft, forked, split halfway down into two equal parts), was the most abundant one. The Bifidobacterium genus is currently one of the most common bacteria in probiotics, is highly abundant in the gut flora of breast-fed infants until the introduction of solid foods, while it is less common in the feces of bottle-fed infants, and much less common when infants suffer from diarrhea.
By the turn of the 20s century, the link between breastfeeding, bacterial flora, and infant health was starting to solidify. In parallel to the observations made by pediatricians at the turn of the 19th century, chemists were also starting to take interest in breast milk and its constituents. By then, it was known that lactose is the most common type of sugar in milk, but gradually, researchers have noticed that milk contained other forms of molecules containing lactose in many shapes and sizes.
Why? And what does it have to do with the mother’s blood type?
That will be the topic of our next post.