The human body is home to 10-100 trillion microorganisms, from the surface of our skin to the lining of our intestines. These microorganisms aren't just helpful, they are vital to maintaining our health in many ways. The largest population of microorganisms in the body lives in the gut – collectively called the gut microbiota. These microorganisms influence everything from digestion to how the body fights off gastrointestinal (GI) infections.1-3 Science is now beginning to understand how the gut microbiota forms and changes throughout an individual's lifetime.

What is the Human Microbiota?

The human microbiota includes microorganisms (composed of bacteria, fungi, protozoa, and viruses) that live inside and on the body in areas like the mouth, skin, GI tract, and lungs. These microorganisms help keep us healthy and our bodies provide them nutrients and a home.3 Microbiotas are unique, like a fingerprint, and different for everyone – even among family members.4,5

Most of the research on the human microbiota has focused on the GI tract. These microorganisms help maintain health in many ways, including:1,3,6

  1. Building and regulating the immune system
  2. Protecting the GI tract from harmful bacteria and viruses (pathogens) 
  3. Digesting food and extracting nutrients
  4. Producing vitamins the body can't make on its own
  5. Producing health-promoting short-chain fatty acids

How Is the Gut Microbiota Formed?

Although infants are born with very few microorganisms, they soon develop a gut microbiota that is uniquely their own.1,7 Infants get their first dose of bacteria and other microbes from their mothers and from their newborn diets. 

  1. Mode of delivery. An infant delivered vaginally will have gut microbiota found in the mother's vaginal microbiota; whereas, an infant delivered by Caesarean section will have gut microbes that resemble the mother's skin microbiota.8
  2. Feeding type. Breastfed infants have different gut microorganisms than formula-fed infants because breastmilk contains bacteria that establish a baby's gut microbiota.9 Formula can be supplemented with prebiotics and other additives to help develop a newborn's gut microbiota.10

Babies continue to develop gut microbiota as they age. The people who an infant has contact with and their surrounding environment further determine a baby's unique gut microbiota.1,11

  1. Family. Children acquire microbes from the individuals they are physically closest to, such as parents, siblings, family members, friends, and caregivers.12 
  2. Environment. Children pick up microbes from things they touch, such as toys and surfaces.12 

What Affects the Gut Microbiota’s Development?

Gut microorganisms rapidly increase in diversity and total number as a child ages. Initially, this occurs when breastfeeding ends and solid foods are introduced. By about age three, the gut microbiota stabilizes and begins to resemble that of an adult. Other factors that shape the gut microbiota include:1,8

  1. Diet. What you eat has a direct impact on your gut microbiota. For example, the microorganisms in the gut of a person who eats a plant-based diet are different from a person who eats meat. Throughout the life cycle, it appears that diet is the biggest external factor affecting gut microbial content.1,13
  2. Hygiene practices. Children are likely to eat a piece of candy off the floor or forget to wash their hands after using the bathroom. This means frequent contact with microbes that might make them sick and influence gut microbiota composition.12,13
  3. Weight. Obesity is associated with less Bacteroidetes, a beneficial type of bacteria that protects the gut from pathogens and provides nutrients.14,15
  4. Antibiotic use. Antibiotics reduce the diversity and quantity of gut microbes, which  can cause diarrhea, nausea, and other GI issues, such as C difficile infection.1,11
  5. Inflammatory conditions. Individuals with inflammatory bowel disease (IBD) like ulcerative colitis and Crohn's disease have different gut microbiota than those who do not have IBD.1,14,15

What Happens to the Gut Microbiota in Old Age?

Although the gut microbiota is relatively stable throughout adulthood, aging is associated with a decline in the diversity of gut microorganisms. There are many factors that likely contribute to this change. In part, the decline in diversity is linked to changes experienced by the elderly, such as lifestyle modifications, increase in infection rates and diseases, and medication needs. In addition, the aging process and its effects on the body impact microorganism function. Although these aspects affect the composition and activity of the gut microbiota, the course and mechanisms behind these changes are not completely understood.16,17

What Keeps the Gut Microbiota Healthy? 

A balanced gut microbiota is more likely to be a healthy gut microbiota. Imbalances in the microorganisms of the GI tract (called dysbiosis) are associated with conditions like inflammatory bowel disease and can lead to infection by a common pathogen called Clostridioides difficile, which causes severe diarrhea and colitis (inflammation of the colon).1,18

You can adopt the following lifestyle habits that promote a balanced, healthy gut microbiota:1,19-24 

  1. Don’t overuse antibiotics. Only take an antibiotic when necessary and prescribed by your doctor.
  2. Enjoy a diverse diet. Eating a wide variety of foods is associated with diverse gut microbes, which is associated with a healthier microbiota. 
  3. Eat plenty of fruits, vegetables, whole grains, and beans. These foods contain fiber, which serve as food for the bacteria living in your gut.
  4. Eat fermented foods. Foods like yogurt, sauerkraut, and kimchi contain beneficial bacteria that can support your gut microbiota.
  5. Keep added sugars to a minimum. Diets high in sugar are associated with an unhealthy gut microbiota.

A healthy gut microbiota is essential to maintaining overall health. The scientific world continues to expand its knowledge about the microorganisms that compose a healthy gut. In doing so, we hope to discover how microorganisms and a healthy gut microbiota can shape new approaches to wellbeing.

Information Provided by Thorne

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