How Gut Microbiome Affects Your Health
We have over 7 trillion microbes in the human GI tract. In fact, the human body is made up of more microbes than human cells. There are bacteria, viruses and fungi that make up the human gut microbiome. Studies have shown the 2 predominant bacteria species in humans are Bacterioides and Firmicutes. The ratio of these differ based on one’s diet. People who are vegetarians and vegans tend to have more Bacteroides than Firmicutes, and those who eat meat have the opposite ratio. People who have excess weight also have more Firmicutes compared to more Bacteroides in leaner individuals.
What do these microbes do? They function in various ways including digestion of food products, synthesize vitamins, affect immune system proteins, produce short chain fatty acids, maintain a tight junction in the cell lining to block toxic substances from being absorbed, and have been found to affect brain function and mood as well.
This is an exploding area of research currently and it’s fascinating to think how these tiny microbes can affect so much in our body. Let me share with you one study done in mice. There’s a strain called “germ free” mice which have been born by c section in a sterile environment. They continue to be raised in a sterile environment. Scientists took stool from a conventionally raised mouse and rubbed it on the back of the germ free mouse. Now, they have a hybrid of sorts, and when they studied these 3 types of mice, after 2 weeks, the germ free mouse weighed the least, the hybrid mouse weighed the most and the conventional mouse was in between. The conventional mouse increased body fat by 42% despite eating 29% fewer calories and the hybrid mouse increased body fat by 57% despite eating 29% fewer calories AND having a higher metabolic rate by 27%. So the germ free mouse who got the gut bacteria from the regular mouse ate less calories and had a higher metabolic rate yet gained the most weight. The only difference was introduction of a different gut microbiome.
So how can this happen? We are learning that some bacteria such as the Firmicutes are able to extract more calories and break down more of what we ingest than others such as the Bacteroides bacteria. These are called hyper-harvesters. When we have more Firmicutes in our gut, we are able to extract more calories from our food, compared to someone who has less Firmicutes. These extra calories then can lead to weight gain. Scientists have verified this by measuring the nutrient content in the stool of mice fed the same diet. The stool of those that have more Firmicutes have less calories compared to the stool of those that have more Bacteroides in their gut. It’s no surprise then that when the gut microbiome of lean vs individuals with excess weight were analyzed, Bacteroides species predominate in the lean individuals. They did not harvest as much nutrients from food as those individuals that had more Firmicutes in their gut. This leads to more calories from the same amount of food eaten based on the gut microbiome composition.
Our microbiome can change with our diet. As I mentioned previously, a diet higher in plant foods favors more Bacteroides in the gut. Weight loss itself can also shift the balance towards Bacteroides, sometimes as early as a 2% weight loss. We know that a diet high in plants provides the fiber and nutrients that supports the growth of these particular microbes.
Besides nutrient absorption, these microbes also have an affect on the lining of the cells. You may have heard of the “leaky gut”. Our intestinal lining is a potent barrier to toxins and harmful organisms. There are gaps, however, in the lining called tight junctions that allow water and nutrients to be absorbed while blocking harmful substances. If our gut microbiome is not healthy and certain microbes predominate, these tight junctions can be impaired allowing passage of toxins into our body that affect our immune system (possible autoimmune diseases like celiac, IBS, food allergies and others) and create inflammation in our body causing cell damage. Certain bacteria have been found to directly affect these tight junctions making our guts leaky and exposing us to unhealthy substances.
Our gut microbiome is unique to each individual and the more diversity we have in our gut, the better. More and more health conditions are being linked to these microbes, and research indicates that a diet with plenty of fruits, veggies, and whole grains will better support a healthier gut.