The human microbiota is composed .by all the microorganisms living in the gut, which have essential roles for the human body. We know that they turn certain undigested foods into nutrients we need, such as fiber, into some essential fatty acids, but they have many more roles than that!
In 2017, during the "Microbiota for Health World Summit" in Paris, with more than 400 scientists presenting the latest research, the famous "you are what you eat" was proposed to be updated by "you are what your gut microbes do with what you eat." Right, that means a lot.
Some examples of the topics presented during these conferences are gut-brain communication, the use of certain probiotics to improve depression, the proposal of new therapies based on diet, and the balance of the gut microbe for autoimmune conditions, obesity, behavioral problems, intolerances, or IBS. You can read more here .
Everyone has a different and unique bacteria population, like a fingerprint, and those differences can actually make someone more or less prone to develop certain diseases. And this uniqueness is such that some studies even suggest that identifying people from their microbiome data could be feasible!  In any case, whatever your fingerprint is, you can still do a lot to improve it!
So, which factors determine this flora?
Its composition is established during the first years of life in children and tends to stay fairly stable, but it also changes by dietary and lifestyle factors.
The process of colonisation of the gut by microorganisms starts at the moment of birth, not before. Even the way the baby is delivered, by cesarean section or naturally, or whether it is breastfed or not, will define the number and types of gut bacteria.
The early years are crucial for the prevention of possible future problems, but again, it doesn’t matter what your age is; it is always possible to make it better! As a general rule, include in your diet enough variety of fats, fibre, and some probiotics like yogurt or kefir.
 GMFH Editing Team, “Microbiota for Health - Summit Report 2017”, 2017
 GMFH Editing Team, “Your Mircrobiome is like a unique fingerprint”, www.gutmicrobiotaforhealth.com/en/your-microbiome-is-like-a-unique-fingerprint/, Jul 2015