One of the major revelations of life science research in the past decade has been the recognition that the trillions of bacteria that reside in our gut, and in other parts of our body, share a mutually dependent bond with us. The gut microbiome, in particular, has been linked to nutrition and immunity. Disturbances in this friendly force have been related to an increased susceptibility for several health disorders.
Truly, human physiology can no longer consider itself distinctively separate from the microbiome that resides as a collective colony within us. While the specific composition of the microbiome varies from person to person and changes over life, associations of different microbiome profiles are now being associated with health or disease across populations.
Recently published scientific studies have thrown light on the role of the microbiome in childhood malnutrition and also provide a link to malnutrition in the mother. These studies, conducted by researchers in Bangladesh, Malawi, France and the US, were published in February this year, in leading international journals, Science and Cell. The animal models employed were mice and piglets, while young children and lactating mothers provided the human link.
The studies were stimulated by an observation that germ-free mice do not grow well. What about humans? This question led the scientists to compare the microbiomes of poorly nourished and well-nourished infants and young children. Gut microbiomes were isolated from fecal samples of malnourished and healthy children. The microbiome was “immature” and less diverse in malnourished children compared to the better developed “mature microbiome” found in healthy children of the same age.
When the immature microbiome from malnourished children was introduced with food into specially bred “germ free” mice, they failed to thrive and had impaired growth. When similar mice received the mature microbiome from healthy children, while being fed an identical diet, they had good muscle and bone growth. When the malnourished mice subsequently received the mature microbiome from the healthy mice, good growth was restored in them.
The mechanism by which the friendly bacteria help child growth is still to be elucidated, but it appears that they may influence the activity of growth hormones produced in the human body. The growth of brain, liver, muscle and bones are thereby affected by changes in the microbiome. Interestingly, other studies have implicated the microbiome in the development of obesity.
How is the microbiome of the young infant shaped? Passage through the natural birth passage of the mother provides the first gift of protective bacteria, something which babies born through Caesarean section would not receive. Immediately thereafter, mother’s milk seems to provide the stimulus for the growth and maturation of the infant’s microbiome. Studies of the chemical composition of mothers’ milk have shown the presence of a modified sugar (sialylated oligosaccharides). This is not utilised by the baby for its own nutrition.
However, the bacteria constituting the infant’s microbiome thrive on this sugar which serves as their food. Malnourished mothers have low levels of this sugar in their milk. Consequently, the microbiomes of their infants fail to mature. That, in turn, leads to malnourished babies. Malnutrition begets malnutrition, not just in one human baby but in trillions of living forms!
Giving these oligosaccharides to malnourished young mice or piglets helps improve their growth, suggesting a potential pathway to remediation in malnourished children with immature microbiomes.
Mother Nature offers us some big lessons through this fresh glimpse of its operation. First, mother’s milk is highly protective, yet another reminder that there is really no substitute. Second, multiple life forms are highly interdependent; some of the lowly and much derided bacteria are essential allies for health throughout our life course. Third, malnutrition in children may have several causes but one preventable cause that must be addressed with urgency is the prevention of malnutrition in mothers. This must begin from the time the future mother is a girl child but particular attention must be paid to the period of pregnancy. Finally, as more of the mysteries of life are opened up by modern science, we must regard nature with both awe and humility.