The level of variation in the gut microbiome between different people and locations across the globe is astonishing.
While over 1,000 different bacterial species have been found to exist in the human gut, each individual is thought to harbor only around 160 of these.
Today, some believe that a core set of metabolic and molecular processes are at the heart of a healthy gut. Which species support these processes is less relevant than how well they are working together.
The hallmark of this functional core of gut bacteria is a set of genes that promote long-term residence in the gut and active contribution to human metabolic function.
Specifically, these microbes aid digestion, as well as the production of vitamins, hormones, and essential amino acids.
Diet is a major player in determining which microbes take up residence in our guts long-term. A Western diet, high in fat and refined sugars but low in fiber, is thought to reduce microbial diversity.
This can have detrimental effects on health.
A study published in the journal Nature investigated the mechanism.
When mice were fed a low-fiber diet for 4 weeks, the levels of 60 percent of microbial species decreased significantly. About half of these returned to normal levels when the mice were switched back to a high-fiber diet.
But even a short burst of such an unhealthful diet left long-lasting effects, or "scars," on the microbial diversity, as the researchers pointed out.