Our gut contains trillions of microbes that accompany us throughout our lifespan. However, they transition with us through every stage of our lives and are influenced by many factors. In this blog, we explore the science behind how and why our guts change throughout our lives.
The Gut Through Life Stages
Did you know that at birth, the diversity of gut bacteria is extremely limited, but by the time we are adults, we have trillions of microorganisms living in our gut? The time in between these two periods is packed with important stages in the life cycle of the gut microflora (1, 2).
The gut transitions through three distinct stages- the infant stage, the adult (maintenance) stage, and the elderly stage. This blog will look at each of these stages to see how they influence the gut microbiome. The goal is to also highlight why a varied diet is important throughout life.
Different Life Stages of The Gut
The gut is critical for the proper functioning of our immune system and metabolism. It has its own microbiome, one that changes with age, and so do the genes that encode its gut flora (3, 4). Let us embark on a scientific journey to see how our gut evolves over time.
Birth and Infancy
In the human life cycle, the period of a foetus growing in the uterus (the gestation period) is considered sterile, which means the foetus remains immune to the maternal bacteria. However, a few researchers have confirmed the presence of some bacteria in the uterus, but the number and diversity were too low to have any effect on infant gut colonisation (4).
The type of birth, vaginal or caesarean section (C-section), greatly influences the gut composition during infancy and childhood. During vaginal delivery, the colonisation of the bacteria comes from the mother’s birth canal. In this case, the gut bacteria of the babies and mothers are somewhat similar. Studies have demonstrated the presence of Lactobacillus, followed by Prevotella and Sneathia species in infants born with vaginal delivery (5).
In the case of C-section delivery, the bacteria colonisation comes from the mother's skin. These infants have less common gut bacteria than their mothers. In addition, species like Staphylococcus, Propionibacterium, and Corynebacterium, and high numbers of Clostridium difficile and Escherichia coli were found in the guts of the babies delivered through C-section (4, 5).Moreover, some studies have found that these babies have a higher risk of allergies or obesity later in life (6, 7).
Then comes an important phase after birth: breastfeeding. It plays a significant role in providing nutrition to the baby. Breastmilk the only source of good nutrients and prebiotics for a child and also helps strengthen the immune system. During this phase, prebiotics derived from breast milk promote the growth of Bifidobacteria species. It is one of the reasons for their abundance in the guts of babies, which aids in the breakdown of sugars found in mothers' milk (8).
Following breastfeeding, the introduction of solid foods leads to a marked escalation in the structural and functional diversity of the infant microbiota, resembling that of an adult. The dominant species present at this stage include Bifidobacteria, Ruminococcus, and Bacteroides, which help the child degrade complex carbohydrates and produce short-chain fatty acids. Experts recommend that mothers introduce plant-based and fiber-rich foods that are gut-friendly at this stage for a healthy gut(4, 9, 10 ).
In the case of bacterial infections, a prescription for antibiotics is generally given by medical experts. However, their use is linked to disrupting the child’s gut microbiome (3). Evidence supports the use of probiotic supplementation to restore the gut community after an antibiotic course (11). Adding probiotic-rich foods such as curd, kefir, and other fermented foods can be helpful too.
Adolescence is a transition toward adulthood associated with major physiological changes related to sexual maturation and is predominantly driven by hormones. There is also intense inter-organ crosstalk, including organs like the skin, brain, and genitalia. It is indeed a fascinating stage where potential hormones affect the gut microbiome.
Moreover, at this stage, due to hormonal fluctuations, mood swings take over the lives of teenagers. Furthermore, it is intriguing to learn that certain compounds produced by gut bacteria regulate the synthesis and release of neurotransmitters known to influence mood. In particular, adolescents have significantly higher levels of Bifidobacteria and Clostridia compared to adults.
Adolescence marks the onset of several mood disorders like anxiety, psychosis, depression, schizophrenia, and eating disorders. Therefore, it is necessary to keep a watch on the dietary habits during this stage. At this stage, make sure to support the diet with more fibre and plant-based foods to improve mental health and enhance gut health (3, 11).
The adult microbiota is relatively more stable compared to that of early life. But it is still susceptible to environmental changes. Even a small shift to either a plant-based or animal-based diet can dramatically change the composition and functionality of the adult gut microbiome.
Moreover, environmental shifts, like temperature fluctuations or seasonal variations, have a great impact on the gut microbiota. Urban factors like having processed foods, irregular sleep, stress, unhealthy lifestyle (excessive partying, drinking and no physical activity) and fluctuations in weight play an important role in shaping your gut in the wrong way (3, 12).
Furthermore, when it comes to pregnancy, a major alteration in the composition of the gut microbiome occurs. There is an increased abundance of Proteobacteria and Actinobacteria species.
Researchers believe that changes in gut microbiome composition, combined with dramatic changes in hormonal dynamics during pregnancy and the early postpartum period, may affect mothers' psychiatric balance and well-being and, in some cases, predispose them to develop psychiatric problems such as anxiety and depression.
Moreover, the use of antibiotics affects the mother’s gut health. Stomach issues like constipation are normal during pregnancy and can be managed by consuming enough fibre and water.
Another stage in women’s lives is menopause, marked by a decline in estrogen levels that results in a progressive loss of muscle mass, strength, and bone density. It is one of the factors that may disrupt the microbiome configuration in a woman’s life. In such cases, giving probiotics to postmenopausal women could restore an improved balance within their bodily systems (3).
As humans age, there is a gradual loss of functioning of multiple organ systems related to growth, energy homeostasis, metabolism, and immunity. There is a significant dysbiosis in the gut microbiota with age, together with the use of antibiotics and lack of nutrition.
The elderly are prone to several conditions, including mobility problems, heart diseases, and dementia, and therefore the use of medications increases. A significant loss of teeth and less salivary function limits the nutrient intake and, thus, impacts microbial growth (4).
Additionally, our ability to produce bile decreases as we age. Bile is a fluid that is made and released by the liver and stored in the gallbladder. It plays an important role in emulsifying fats for digestion and absorption and maintaining a balance of the gut bacteria (13, 14). A lack of bile acids in the gut has been linked to bacterial overgrowth and inflammation, which in turn can negatively affect our gut structure and composition (15).
Further, our brain is also subject to age-related unwanted changes, causing neurodegenerative disorders like Parkinson’s disease (PD) or Alzheimer’s disease (AD). Research has suggested that PD is associated with alterations in gut microbiome composition, particularly in the genus Prevotella and enterobacteria through thegut-brain axis (16).
To summarise, reduced motility, digestion and absorption significantly reduce appetite and lead to malnutrition. In older adults, this is the major factor that affects the growth of gut microbes which in turn could contribute to an impaired immune system.
Given the gut microbiome's ever-increasing impact on the immune system, it's reasonable to speculate that restoring age-related decline in gut-microbial richness and function—whether through personalised nutrition or supplements—could serve as a preventive measure to combat functional decline in immune fitness (17).
Treatment interventions for a healthy gut like probiotics, prebiotics, and other nutrients that target the microbiome are considered potentially attractive future modalities during all these life stages. We’ll be discussing these interventions soon! Until then, monitor the state of your gut and keep it healthy with a well-balanced diet and lifestyle to stay on top of your game.
- Khan S, Hansen R, Scott K, et alG116(P) The human gut is probably sterile at birthArchives of Disease in Childhood 2015;100:A50-A51
- Turnbaugh, P., Ley, R., Hamady, M. et al. The Human Microbiome Project. Nature 449, 804–810 (2007). https://doi.org/10.1038/nature06244
- Parag Kundu, Eran Blacher, et al. Our Gut Microbiome: The Evolving Inner Self, https://doi.org/10.1016/j.cell.2017.11.024
- Ravichandra Vemuri, Rohit Gundamaraju, et al. Gut Microbial Changes, Interactions, and Their Implications on Human Lifecycle: An Ageing Perspective 26 Feb 2018. https://doi.org/10.1155/2018/4178607
- Clemente, Jose C et al. “The impact of the gut microbiota on human health: an integrative view.” Cell vol. 148,6 (2012): 1258-70. doi:10.1016/j.cell.2012.01.035
- Bager, P et al. “Caesarean delivery and risk of atopy and allergic disease: meta-analyses.” Clinical and experimental allergy : journal of the British Society for Allergy and Clinical Immunology vol. 38,4 (2008): 634-42. doi:10.1111/j.1365-2222.2008.02939.x
- Yuan, Changzheng et al. “Association Between Cesarean Birth and Risk of Obesity in Offspring in Childhood, Adolescence, and Early Adulthood.” JAMA pediatrics vol. 170,11 (2016): e162385. doi:10.1001/jamapediatrics.2016.2385
- Lawson, M.A.E., O’Neill, I.J., Kujawska, M. et al. Breast milk-derived human milk oligosaccharides promote Bifidobacterium interactions within a single ecosystem. ISME J 14, 635–648 (2020). https://doi.org/10.1038/s41396-019-0553-2
- Zafar, Hassan, and Milton H Saier Jr. “Gut Bacteroides species in health and disease.” Gut microbes vol. 13,1 (2021): 1-20. doi:10.1080/19490976.2020.1848158
- Flint, Harry J et al. “Microbial degradation of complex carbohydrates in the gut.” Gut microbes vol. 3,4 (2012): 289-306. doi:10.4161/gmic.19897
- Chen, Yijing et al. “Regulation of Neurotransmitters by the Gut Microbiota and Effects on Cognition in Neurological Disorders.” Nutrients vol. 13,6 2099. 19 Jun. 2021, doi:10.3390/nu13062099
- Martinez, Jason E et al. “Unhealthy Lifestyle and Gut Dysbiosis: A Better Understanding of the Effects of Poor Diet and Nicotine on the Intestinal Microbiome.” Frontiers in endocrinology vol. 12 667066. 8 Jun. 2021, doi:10.3389/fendo.2021.667066
- Bertolotti, M et al. “Age-related changes in bile acid synthesis and hepatic nuclear receptor expression.” European journal of clinical investigation vol. 37,6 (2007): 501-8. doi:10.1111/j.1365-2362.2007.01808.x
- Ramírez-Pérez, Oscar et al. “The Role of the Gut Microbiota in Bile Acid Metabolism.” Annals of hepatology vol. 16,Suppl. 1: s3-105. (2017): s15-s20. doi:10.5604/01.3001.0010.5494
- Ridlon, Jason M et al. “Bile acids and the gut microbiome.” Current opinion in gastroenterology vol. 30,3 (2014): 332-8. doi:10.1097/MOG.0000000000000057
- Scheperjans, Filip et al. “Gut microbiota are related to Parkinson's disease and clinical phenotype.” Movement disorders : official journal of the Movement Disorder Society vol. 30,3 (2015): 350-8. doi:10.1002/mds.26069
- Bosco, Nabil, and Mario Noti. “The aging gut microbiome and its impact on host immunity.” Genes and immunity vol. 22,5-6 (2021): 289-303. doi:10.1038/s41435-021-00126-8