The human body is home to trillions of microorganisms known as the microbiome. Large families of bacteria, such as Bacteroides, Prevotella, Firmicutes, and Ruminococcus, are found in the gut.
Scientists used to believe that the guts of infants are nearly sterile at birth and proceed to have low-biodiversity microbiota during the first couple of months following birth. A new research, however, reshapes our understanding of infant health.
Dancing to a Circadian Rhythm
The gut microbiome was found to oscillate with a circadian rhythm, even if cultivated outside the body. This resulted from a study by a team of researchers led by microbiome expert Dirk Haller of the Technical University of Munich. The details of their research are discussed in the paper "Diurnal rhythmicity of infant fecal microbiota and metabolites: A randomized controlled interventional trial with infant formula."
The research team used a randomized controlled trial to study microbiome development in 210 infants. Infants who were exclusively breastfed were compared with infants who received different types of formula. The latter includes those who take a formula containing breast milk-derived bacteria (Bifidobacteria), a formula containing breast milk-mimicking sugars (galactooligosaccharides or GOSs), a formula containing both Bifidobacteria and GOSs and unsupplemented formula.
The team sampled the infant stools to track the microbes longitudinally. This was done while the infants were 0.5 months, one month, three months, seven months, 12 months, and 24 months old. The time of the day when the stool sample was collected was also noted.
Haller and his colleagues observed rhythmic 24-hour fluctuations in the abundance of different microbiome species. When the infant gut microbes were allowed to grow continuously in the laboratory, they settled in the same circadian rhythm, even without external light or host cues. This was the first evidence that bacteria maintain these rhythms independently.
According to Haller, these rhythms have been detected in adults, but experts were unsure when these mechanisms first appeared. The study reveals that the microbial ecosystem develops the rhythm at very early stages of gut colonization, about two weeks after birth. Then, the circadian rhythmicity becomes more pronounced with age.
Role of Diet in Gut Metabolite Profile
The study's findings also reveal that diet had only a little impact on the development of the infant microbiome. While there was a lot of variation, all infants exhibited a gradual increase in gut microbe diversity. At 24 months, there was no observable difference between the groups.
When the different types of formula were compared, it was found that GOS-supplemented infant formula was more effective at promoting sustained levels of Bifidobacteria than formula containing Bifidobacteria.
Meanwhile, when the research team compared breastfed and formula-fed infants, there were significant differences in the gut metabolite profile. This could have a fundamental role in metabolic priming and many downstream effects.
The researchers believe that age plays a more critical role. As described by Haller, diet matters, but less than the aging of the gut. This means that the human intestinal system might be a little more flexible in adapting to what the environment offers.
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