The cereal and toast you had for breakfast made a new home for bacteria in your gut. That does not mean that this made you sick! We tend to think of bacteria as something that make you sick, but only a small number of bacteria directly cause infection leading to disease. Every person is host to billions of bacteria, many of which live in our intestines and are a critical part of digestion. These bacteria help you break down different types of food including complex carbohydrates, proteins and lipids, and without which you would starve. These bacteria make up what is called called your “microbiome”.
The types of species of bacteria living in each person’s gut is unique – a sort of microbiome fingerprint. We are beginning to understand that the type (or species) of bacteria living in your gut makes a profound contribution to overall health. There are hundreds of different species of bacteria that make up the microbiome, and these are as different from one another as the creatures in a forest, which spans everything from insects to trees to frogs to bears. Much like the ecosystem of a forest changes over time with the type of food that is available – you won’t have many bears in a forest if what they eat is not available – the bacteria of the microbiome also change with the type of food that is available to them, which is determined by what you eat. What factors make certain types or species of bacteria grow better than others to occupy more space in a person’s gut, and how does this impact a person’s health?
You have probably heard of the idea of “probiotics” – a component of food that is meant to keep the bacteria in your microbiome in top shape. The reality is that there is currently very little actual evidence that these impact a person’s microbiota and gut health, and studies that examine this directly are of high importance.
A team of researchers led by a group from Washington University School of Medicine recently examined this question, and uncovered some important factors that control how the microbiome can change depending on the food in one’s diet. These scientists used a sophisticated method that involved tagging four different species of bacteria that are usually found in the human gut with a form of “DNA barcode”. By tracking these DNA barcodes in the feces of animals, they were able to track the amount of specific bacteria in the gut of mice, and how this changed over time. This method also allowed them to track how variations in genes of these bacteria gave them advantages to growing under different conditions – in other words, getting a profile of what makes bacteria more “fit” to live in your gut based on different types of diets you might eat.
They discovered that what someone eats does indeed change the types of bacteria living in the gut. This phenomenon is complex, but one example highlighted by this study is the ability of a carbohydrate called arabinoxylan, which is found in wheat and found in food such as cereal and bread, to change the amount of a type of bacteria called Bacteroides cellulosilyticus living in the gut. This change in this species as well as other types of bacteria caused by what you eat could persist over time. In other words, the bacteria in your gut have a “memory” of what you ate.
This study is an important step forward in understanding the factors that provide each of us with our “microbiome fingerprint” – the makeup of the species of bacteria that live in our guts and do useful things like help us digest different foods and also impact development of diseases such as diabetes.