Curated by Dr. Paola Groff, Pediatrician at Aventino Medical Group, Rome The microbioma is a subject of study that holds great importance nowadays, also in pediatrics, because it plays a fundamental role in the development of the immune and metabolic systems during the early years of life. What is the microbioma? The microbioma is defined as “the collection of symbiotic microorganisms that coexist with the human body without causing harm.”It is a complex system, highly diverse, and composed of over a thousand species of bacteria.The ensemble of microorganisms that make up the intestinal microbioma, formerly known as the intestinal flora, plays a crucial role—especially in the development of the newborn’s immune system—by acting as a barrier against pathogens (viruses/bacteria/fungi).Its alteration, known as dysbiosis, can cause numerous diseases such as allergies, asthma, eczema, inflammatory bowel diseases, metabolic disturbances, obesity, and diabetes.THE FIRST 1000 DAYS OF LIFE, which include the gestational period and the first two years of life, are important not only for the growth and development of the child but also for the formation of the microbioma.The development of the microbioma begins at birth and is influenced by many factors such as the type of delivery (vaginal or cesarean), the type of feeding (breastfeeding or formula feeding), the type of diet, the use of prebiotics and probiotics, pharmacological treatments—particularly antibiotics—illnesses, and the surrounding environment.The neonatal gastrointestinal tract is considered sterile and, after birth, begins to be colonized by many microbes that will form an entirely new microbioma. In particular, during vaginal delivery, the mother’s microbioma can be one of the main elements influencing the newborn’s microbioma. What are probiotics and prebiotics? According to the World Health Organization (WHO), probiotics are “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host.”In humans, the most commonly used probiotics are bacteria of the genus Lactobacillus or Bifidobacterium.Prebiotics are indigestible substances that promote the growth and activity of beneficial bacteria. Why is breast milk important? Breast milk plays an important role in the development of the microbioma during the neonatal period.The World Health Organization (WHO) recommends exclusive breastfeeding for the first six months of life and, after the introduction of complementary foods, continuing up to two years or more.Breast milk has an extremely complex composition, rich in both protective and nutritional elements. It contains hundreds of non-pathogenic bacterial species that have beneficial effects for the newborn, such as Bifidobacteria and Lactobacilli.Moreover, breast milk contains a large amount of nutritional elements, including non-digestible HMO oligosaccharides, which promote the development of specific intestinal bacteria. Oligosaccharides are defined as a particular type of prebiotic—an important substrate that fosters the growth and activity of beneficial bacteria while limiting the growth of pathogenic ones.It is estimated that breast milk contains between 10^6 and 10^9 (colony-forming units) per ml of beneficial probiotics capable of directly modulating the immune response.Breastfed infants acquire a simple and stable microbioma as early as the first and second week of life.In cases where breastfeeding is not possible, the use of formula—with a composition very similar to that of breast milk, but with different characteristics even if supplemented with probiotics and prebiotics such as fructooligosaccharides (FOS) and galacto-oligosaccharides (GOS)—leads to the formation of a varied but less stable microbioma. How does the microbioma change during weaning? Weaning is defined by the World Health Organization (WHO) as “the process that begins when breast milk alone is no longer sufficient to meet the nutritional needs of infants, and therefore the introduction of solid and liquid foods alongside breast milk becomes necessary.”When the child begins to introduce the first solid foods, new micro- and macronutrients start to influence the microbioma.The progressive changes in dietary habits ensure that, by about three years of age, a child has an intestinal microbioma similar to that of an adult, predominantly represented by the species Bacteroidetes and Firmicutes.A gradual and balanced introduction of foods helps diversify the microbioma, thereby improving digestion and the immune response.In particular, the MEDITERRANEAN DIET—balanced and varied, rich in dietary fibers, with an appropriate supply of fats, proteins, and carbohydrates, including fresh fruits and vegetables, legumes, and whole grains, and low in refined sugars and ultra-processed foods—has the ability to positively influence the composition of the microbioma. The benefits of this diet are mainly due to the dietary fibers present in foods such as legumes, vegetables, fruits, and cereals.A balanced and varied diet, to be initiated after an exclusive breastfeeding period of about 6 months, helps prevent the development of food allergies, asthma, and allergic rhinitis.In addition to dietary habits, scientific studies indicate that factors such as the presence of siblings in the same family, living conditions, and early exposure to environmental allergens also influence the composition of the microbioma. Excessive environmental hygiene can limit exposure to the beneficial microorganisms necessary for the development of the immune system. CONCLUSIONS The intestinal microbioma is an essential element for a child’s health and proper development. Through breastfeeding, a balanced and varied diet, and gradual exposure to environmental bacteria, it is possible to foster a healthy microbioma from the very first months of life. Dr. Paola Groff, Pediatrician at Aventino MedicalGroup, is available for personalized pediatric consultations to assess your child’s health.