Scholarly Review Explains Why HMOs Support the Early-Life Microbiome

A recent comprehensive review, published in Microbiology and Molecular Biology Reviews, provides an in-depth exploration of how human milk oligosaccharides (HMOs) contribute to the establishment and development of the infant gut microbiome. The review, titled "Linking Human Milk Oligosaccharide Metabolism and Early Life Gut Microbiota: Bifidobacteria and Beyond," surveys the complex interactions between HMOs and gut bacteria. In particular, the review focuses on the role of Bifidobacteria in early microbiome development, providing insight into how HMOs are so beneficial to infants, and what they are able to do for the microbiome in the long term.

The Critical Role of HMOs in Infant Health

Human milk oligosaccharides are a unique and highly abundant component of human breast milk. Despite being indigestible by the infant, HMOs are essential for nurturing the gut microbiome, particularly during the first critical months of life. HMOs escape digestion in the small intestine and reach the colon intact, where they serve as a food source for specific beneficial bacteria. This selective nourishment helps to establish a healthy gut microbiome, which is necessary for the infant’s overall health, including immune system development, pathogen resistance, and even cognitive development.

Bifidobacteria: The Early Colonizers

One of the central themes of the review is the relationship between HMOs and Bifidobacteria, which are among the earliest colonizers of the infant gut. These bacteria are particularly well-suited to utilize HMOs due to their specialized enzymatic capabilities.

The ability of Bifidobacteria to dominate the infant gut microbiome is partly due to their capacity to outcompete other bacteria by efficiently metabolizing HMOs. This process occurs because Bifidobacteria possess specialized enzymes that allow them to break down and metabolize HMOs more effectively than other gut bacteria. When an infant consumes breast milk, these HMOs reach the colon intact, where Bifidobacteria rapidly utilize them as a food source. This selective feeding advantage enables Bifidobacteria to proliferate and dominate the gut environment, creating a microbial landscape that favors beneficial bacteria while suppressing the growth of potentially harmful pathogens. This early colonization helps establish a healthy gut microbiome that supports the infant's overall health.

Beyond Bifidobacteria: Other HMO Utilizers

While Bifidobacteria are the primary focus, the review also considers other taxa capable of utilizing HMOs. The authors highlight that while Bifidobacteria are the most efficient at HMO metabolism, other bacteria such as Bacteroides and Lactobacillus species also play a role in this complex ecosystem. These bacteria can either directly metabolize HMOs or benefit from the metabolic byproducts produced by Bifidobacteria, a process known as cross-feeding.

These interactions between these various bacterial species contribute to the overall stability and functionality of the infant gut microbiome. Microbial diversity, fostered by the availability of HMOs, is an indispensable component of a well-balanced gut environment.

Implications for Infant Nutrition and Health

The findings presented in this review have significant implications for infant nutrition and health. The authors argue that the benefits of HMOs extend far beyond their prebiotic effects, influencing a wide range of physiological processes in the infant. By promoting the growth of beneficial bacteria like Bifidobacteria, HMOs help to protect against infections, support the development of the immune system, and even influence metabolic and neurological outcomes.

Moreover, the review suggests that understanding the specific mechanisms by which HMOs support the gut microbiome could lead to the development of more effective infant formulas. While breastfeeding remains the gold standard for infant nutrition, this research could inform the creation of formula products that more closely mimic the composition and benefits of human milk.

Repairing Our Microbiome

As we move from infancy into adulthood, the health and balance of our gut microbiome often deteriorate due to various factors such as poor diet, stress, antibiotic use, and environmental exposures. This degradation can lead to a host of health issues, including digestive disorders, weakened immune function, and even chronic diseases. The early benefits we received from HMOs during breastfeeding often seem distant as the diversity and health of our gut bacteria diminish over time.

However, emerging research suggests that HMOs could play a pivotal role in helping to repair and restore the gut microbiome, even beyond infancy. While traditionally associated with infant nutrition, the prebiotic effects of HMOs are now being realized for their benefits in adults. By selectively nourishing beneficial bacteria like Bifidobacteria, HMOs can help rebalance the gut microbiome, promoting the growth of health-supporting bacteria, the “good guys”, and inhibiting the proliferation of harmful pathogens.

HMOs offer a pathway to support our gut health at any stage of life. They can help reverse some of the damage our microbiome has endured over the years, fostering a microbial environment more akin to the one we enjoyed during our earliest days. As our understanding of HMOs continues to grow, so too does the potential for using this miracle fiber to enhance gut health, not just in infancy but throughout our lives.

Lordan, Cathy, Aoife K. Roche, Dianne Delsing, Arjen Nauta, Andre Groeneveld, John MacSharry, Paul D. Cotter, and Douwe van Sinderen. “Linking human milk oligosaccharide metabolism and early life gut microbiota: Bifidobacteria and beyond.” Microbiology and Molecular Biology Reviews 88, no. 1. 2024.