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Secrets of Gut Microbes

Updated: Mar 30, 2021

By Nathan Park Class of 2023

What are gut microbes

The gut microbe is the word used to describe the population of microbes living inside human intestines. It is made up of trillions of different microorganisms including bacteria, viruses, and fungi. It also contains more than 3 million genes which is 150 times more than the amount of genes humans have in our bodies.

"Mental health is just as important as physical health. Remember that."

Because of their massive population, the gut microbes itself can weight up to 2 kilograms, about 4 pounds. Although all of this may sound incredibly dull and monotonous, due to recent studies, gut microbes have been discovered to have profound effects on the nutrition, mental health, and also diseases of the human body. The importance of these new effects is that, with these abilities, scientists are developing ways in which these microbes can be used as a medicine to help humans in both their mental and physical health.

How does gut microbes affect your weight

Gut microbes contain large amounts of bacteria that all have different functions such as breaking down food, creating amino acids, and also making vitamins for the body. Published by the journal Science, a recent experiment was conducted that showed hints of gut bacteria’s ability to determine if an individual was lean or obese. In this experiment, scientists found pairs of twins in which one of them was obese while the other was lean. While looking into the gut community of each twin, they discovered that the obese individual’s gut community was less diverse and was more nuritent-loaded whereas the lean individual’s gut community was filled with a variety of species of bacteria. One example of a common bacteria that was present in the lean individual was bacteroidetes which was a group of microbes that helped break down plant starches and fibers for the body to use as energy. In proceeding with the experiment, scientists used two sets of mice in which one set of them recieved the gut bacteria of the obese twin and the other of the lean twin’s. Both sets of mice continued with the same diet, yet the mice that had the gut bacteria of the obese twin, began to gain more weight and had more body fat than the mice with the bacteria of the lean twin. When looking into the gut microbes of the obese mice, as discussed before, there were less species of bacteria inside the mice’s gut.

Figure 3: Depending on which gut microbe they received, each set of mice became either lean or obese, imitating the person that the gut microbe was taken from.

Shortly after this experiment, Dr. Gordon, the senior investigator for the study, and his team set up another experiment, but with a little twist. While still having the two sets of baby mice with gut bacteria from both twins, they put both sets of mice together in the same cage. The result was that both mice beame lean. It showed that the mice who were destined to become obese had picked up some of the bacteria from their lean peers through the digestion of their feces, a common and normal behavior for mice. The obese mice had developed more varieties of bacteria including a variety of bacteroidetes. This experiment showed that when put in a cage together, the bacteria from the lean mice overcomes the bacteria in the obese mice forcing all of the mice to become skinny.

Although it may sound like by just having the gut bacteria of a skinny person in someone who is obese can immediately make them skinny, Gordon’s last experiment emphasizes on the importance of one’s diet in shaping one’s gut system. Gordon and his colleagues created two types of mouse food pellets: one was high in fat and low in vegetables and fiber while the other was rich in fiber and vegetables and low in fat. The obese mice who were given the food high in fat, continued to grow fatter even while staying in the same cage as the lean mice. The lean mice only became lean again when given a diet rich in vegetables and fiber with no fat. The unhealthy diet filled with fat prevented the gut bacteria of the lean mice from having effect on the obese mice.

Although these experiments involved mouse subjects rather than human subjects, they raise many questions about how scientists may be able to use gut bacteria in the future to treat obesity and even prevent it. Factors such as variation in human bodies or one’s environments are yet to be considered, but to this day, scientists are developing ways in which gut bacteria can help treat obesity. There are over 39.6% (70 million) of Americans who obese and 30% of these people go on to have diabetes. More than one in every ten adults (over 20) have diabetes and with diabetes being the 7th leading cause of death, gut bacteria can be a helpful treatment that can possibly save hundreds of lives.

How do gut microbes affect your brain?

Mental Health

Proven by the previous experiments, gut microbes are capable of changing one’s physical state such as enabling them from having a lean body to have an obese body. In addition to this, gut microbes have been proven to be able to affect an individual’s mental health as well. Many scientists have begun to find gut bacteria inside the microbiome that are able to regulate how people think and feel. They have found thousands of different species of bacteria that may be responsible for playing a big role in common mental disorder such as anxiety, depression, autism, and more. The reason why scientists began to look into the connection between the human brain and gut microbes is because, for decades, researchers and also parents have seen a common pattern between people with autism and gastrointestinal disorders (relating to stomach and intestines). It was found that three quarters of people with autism had digestive issues, food allergies, or any disorders related to their stomach. Scientists have also found that the microbiomes of people with autism are different from those of control groups.

To examine this potential connection, microbiologist Sarkis Mazmanian from the California Institute of Technology, and his team identified a chemical called 4-ethylphenyl sulfate, or 4EPS, which they thought might hold a possible link to autism. They discovered that mice with symptoms similar to autism had levels of 4EPS that were 40 times higher than those of regular mice. Although it was still unsure whether 4EPS had a connection with autism, when injecting the mice with this compound, they developed autism-like symptoms. Mazmanian and his team saw this as “‘potential breakthrough’ in understanding how microbes contribute to autism and other neurodevelopmental disorders” (The Atlantic). Based off of what was seen in the mouse experiment, they think that there may be a chance of somehow turning off whatever is producing compounds like 4EPS forcing the symptoms to disappear from the body.

Not only does gut microbes play a crucial role in autism, but it also influences anxiety and depression. In another experiment conducted by Stephen Collins, a gastroenterology researcher at McMaster University in Hamilton, Ontario, he and his colleague gathered gut bacteria from mice that seemed to have anxious behavior and then transferred them into mice who were rather calm and tranquil. These mice began to develop anxiety-like behavior, thus proving the bacteria’s effect on anxiety disorders. Along the way, Collins found two species of gut bacteria: lactobacillus and bifidobacterium, that seemed to reduce anxiety-like behavior in mice.

Using these microbes, Mayer, a UCLA Researchers, conducted a human study where he had a group of 25 women, all healthy, and had 12 of them eat yogurt every day for four weeks. Yogurt is a food that contains live bacteria including bifidobacterium and lactobacillus, the bacteria that reduced the stress levels of mice. Before the women began the study, they were given a series of images that contained facial expressions such as sadness, happiness, etc. and their responses to them were recorded. After the four weeks, they did the same thing, and what happened was that the group that ate the yogurt had a much more tranquil reaction to the pictures than the control group; it was a significant difference. Although the reasoning for this is unclear, it is clear that the certain bacteria in our guts can have significant effects on our mental states.

Figure4: Gut microbes have significant effects on our mental health and if not taken care of with a healthy diet, one's mental health can begin to be affected negatively as well.

Figure 4: Gut microbes have significant effects on our mental health and if not taken care of with a healthy diet, one's mental health can begin to be affected negatively as well.

Microbes have the possibility of dominating the world of medicines with their ability to treat and prevent both mental and physical disorders. Scientists and researchers are constantly experimenting and finding ways in which we can use these gut microbes, in the future, to get rid of these common disorders in order to create a safer and healthier environment. Because there are so many species of these gut bacteria in our system, it can be difficult to identify which one does which, but with technological advancements, microbes may be the next solution to our problems.

How to maintain healthy gut microbes

Because gut microbes and one’s mental health are directly related and can affect one another, having long-term stress can actually damage the bacteria living inside an individual’s gut. Long-term difficult situations can reduce the diversity of the bacteria in one’s gut and instead increase the number of bad bacteria that cause disorders like anxiety, depression, etc.

Because of this, when an individual is left with only bad bacteria, his or her brain can become more prone to disorders such as depression, compelling the person to feel sad, guilty, and full of negative emotions. To prevent this, in order to maintain a good mental health, one needs to take care of not only their brain, but more importantly their digestive systems. A balanced diet that includes water, fish, fruits, vegetables, and overall nutritious foods is essential to keeping healthy bacteria in our bodies that leads to us being in a good mood. One’s diet can seem irrelevant when it comes to helping someone’s mental health, but because of the discovery of gut microbes, one can see that it is important to take care of his or her digestive to help prevent them from mental disorders.








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