Human Milk Oligosaccharides: Next-Generation Functions and Questions.

Human milk oligosaccharides (HMOs) are the third most abundant component of human milk. So far, more than 150 different and structurally distinct HMOs have been identified. HMO composition varies substantially between women, but remains fairly constant over the course of lactation in the same woman. Which maternal genetic and environmental factors drive the interindividual variations in HMO composition remains poorly understood, and it is currently unknown whether or not a woman's characteristic HMO composition has evolved to match her own infant's specific needs. A combination of preclinical, cohort, and clinical studies is required to fully assess the many effects, functions, and potential claims associated with HMOs. In some cases, individual HMOs exert a certain effect and, while there might be some redundancy, the effects are often highly structure-specific. In other cases, a combination of different HMOs in specific ratios to each other is required to be effective, and future research needs to assess whether or not the administration of individual HMOs alone may be counterproductive and potentially harmful to the infant's short- and long-term health. Overall, the personalized complexity of HMOs cannot be mimicked in artificial infant formula and provides yet another powerful reason to protect, promote, and support breastfeeding.