Gut microbiota are a collection of microbes (bacteria, Achaea, viruses and eukaryotes) that colonize the guy of humans. There are more than 1000 types, but each individual only contains about 150-170 in their gut. So yes, there is a ton of variation from human to human, especially based on events occurring as early as birth. The two major types are Firmicutes (which are present in 64% of us) and Bacterioidetes (present in fewer of us, just 23%), then Proteobacteria (8% of us contain these) and Actinobacteria (bifidobacteria) (3% of us). Interestingly, when we think of "what makes us human", the answer is actually not what you would think. We are 90% microbial cells, and only 10% "us".
Gut microbiota are found in our gut, as the word suggests. They help the body to digest foods that have escaped digestion in the small intestine. They produce Vitamin B and K as an accessory function, as well as help combat pathogenic bacterial growth, and they play a part in the immune system (barrier and training the immune cells).
What situations help us develop a healthy gut microbiota profile?
- Vaginal delivery allows healthy bacteria vs C section has worse outcomes - Hospital deliveries vs at home delivery (better exposure to good bacteria at home - hospitals often have an assortment of bad bacterias formed from oversterilization) - Smaller family size (having siblings could make you better off, as you will likely have more diversity in bacteria) - Birth weight (low body weight or prematurity could result in a poorer microbiota profile) - Use of antibiotics (early in life it can be very bad to use antibiotics, as it will raise the child's risk for asthma and obesity) - Good hygiene (we have over sterilized everything to the point of harming our microbiota rather than making ourselves more healthy) - Differences in maternal diet (not only affects her own gut, but babies too) - Breast-fed babies (vaginal births show a predominance of bifidobacteria - the gold standard bacteria!) - Formula-fed babies and cesarean (Greater bacterial diversity - more resembled adult-like bacteria which is not desirable).
How does dysbiosis come about?
- Cesarean accompanied by exposure to hospital/maternal skin microbes rather than maternal birth canal microbes
What does C section increase the risk of?
- Respiratory distress, Upper Respiratory Tract Infections (URTIs), asthma and allergies, obesity, type 1 diabetes. Also low microbial diversity (reduced species richness) is associated with several immune-disorders and/or metabolic-disorders such as inflammatory bowel disease, allergies, intestinal cancers, autoimmune
What are the two main bacteria phyla? How does a profile change in an obese individual? Can this be corrected?
Bacteriodetes, and Firmicutes. In obese there are more Firmicutes than Bacteriodetes (bad profile to have). Fecal transplant from lean to obese mice can reduce body weight and fat mass (haven’t developed this into human obesity treatments for sale yet; but has been tried for clostridium difficile infection with a 94% cure rate. Also has been tested in Parkinsons disease, MS, myoclonus dystonia and chronic fatigue syndrome).
Which other diseases are microbial compositions implicated in?
Allergic disease, Asthma, Inflammatory bowel disease, Obesity, Type 1 and 2 diabetes, Neurological development and mental health: autism, psychiatric disorders
What feeds the microbiota?
- Dietary fibre (20-45%) - Simple sugars and oligosaccharides (10%) and starch (<8%) - 5-15g protein and 5-10g lipid
How does a high fat/sugar diet cause dysbiosis?
Increases the FIrmicutes to Bacteriodetes ratio which is the undesirable microbiota profile. It also promotes more microbes that cause inflammation and decreases healthy bifidobacteria. Artificial sweeteners (aspartame) alter microbiota also, and impair glucose control.
Greenhalgh, K., Meyer, K., Aagaard, K., Wilmes, P. (2016). The human gut microbiome in health: establisment and resilience of microbiota over a lifetime. Journal of Environmental Microbiology, ‘Accepted Article’, doi: 10.1111/1462-2920.13318.
Pihl, A., Fonvig, C., Stjemholm, T., Hansen, T., Pedersen, O., Holm, J.-C. (2016). The Role of the Gut Microbiota in Childhood Obesity. Journal of Childhood Obesity, DOI: 10.1089/chi.2015.0220