There has been a mountain of research conducted in recent years linking a host of medical conditions to the activities and balance of our gut flora. For years, science has paid little attention to the 100 trillion microbes that inhabit the dark corners of our gut. But now the floodgates have opened as researchers realize that our gut bacteria are not simply a passenger in our gut, but interact with our body, help regulate just about every aspect of our physiology. To put it simply, gut bacteria are so important that if there is a gut flora imbalance, the system fails. In this article, we review the diseases and conditions that are now thought to be caused by a gut flora imbalance and identify the roles played by human gut bacteria. Quite frankly, you will be shocked by how extensive the list is.
The development of our gut ecosystem
Of the 100 trillion microbiota that inhabits your gut, over 300 different species have been identified with close to 2 million unique genes. This means that there are ten times more individual strands of bacteria in your gut than there are human cells in your entire body. The gut bacteria are more than just a colony; it is an entire ecosystem.
But our gut didn’t start this way. For when a baby is born, its intestinal tract is completely sterile. Gut bacteria starts to colonize a baby’s gut as soon as it is born. The composition of the bacterial colony is influenced by diet, sanitation, the method of delivery and the baby’s level of exposure to antibiotics.
At this early stage, there is very little diversity to the baby’s intestinal gut flora but by the age of three, a child’s gut flora will closely resemble that of an adult.
It is vital for the child’s long-term health that the initial microbial colonization happens properly. Any manipulation of a child’s gut flora after the initial seeding stage may be too late to make any difference. Any gut flora imbalance in an adult may have started while the adult was an infant.
The Composition of the Virtual Organ
Certain gut bacteria prefer certain areas of your gut. Your stomach and small intestine experience a high volume of bile and pancreatic excretions which have antimicrobial properties. The gut bacterial colonies in these areas are relatively small because of this.
In contrast, the colon contains densely-populated bacterial colonies where most the different bacterial types reside.
Likewise, some bacteria prefer to stay in the lumen while some bacteria prefer to hang onto the intestine’s mucosal layers. The bacteria on the mucosal layer interacts heavily with the host’s immune system, and those in the lumen are responsible for metabolic reactions with food.
Diseases From a Gut Flora Imbalance
Gut bacteria are known to play a vital role in keeping the human body in tip-top shape. Gut bacteria interact with our immune system, digest our food, play a part in the bodies metabolism, release proteins and toxins. Subtle changes in how these processes play out or changes in the balance between the different types of gut bacteria can cause huge problems in our general health. In fact, the balance of our gut flora is so important that it should really be considered an organ in its own right, and when it fails all sorts of diseases and conditions follow. Here we have listed 19 of the most serious diseases linked to a gut flora imbalance and identify the roles played by human gut bacteria.
1. Immune system
When most people think about the immune system, vaccines, glands and white blood cells spring to mind. Most would be surprised to learn that our intestines are where the real action takes place as they contain more immune cells that the rest of the body put together. Not only do our gut bacteria help digest food, but it is postulated that there is ‘cross-talk’ between the microbes in our gut and other cells in the body responsible for the immune system and metabolism. When there is a gut flora imbalance, this feeds through to our immune system, leaving the body open to pathogens and autoimmune diseases. (1), (2)
2. Irritable Bowel Syndrome
The symptoms vary between individuals and affect some people more severely than others. They tend to come and go, with symptoms lasting a few days to a few months at a time.
Overgrowth of gut bacteria in the intestines and the subsequent gut flora imbalance has been linked to the condition. The study that proved this studied small bowel cultures from the intestines of people suffering from irritable bowel syndrome. Of the 320 people involved in the study, over 30% of the subjects had an overgrowth of bacteria as compared to ten percent in people without irritable bowel syndrome. (3)
3. Inflammatory bowel disease
Inflammatory bowel disease (IBD) is considered an autoimmune disease which describes two similar conditions, Crohn’s disease, and ulcerative colitis. Both are long term conditions involving the inflammation of the gut. Crohn’s disease can affect any part of the digestive system while ulcerative colitis usually only affects the large intestines.
Symptoms of the disease include stomach cramps, weight loss, tiredness and chronic diarrhea.
Research has shown that certain gut bacteria interact with the lining of the gut wall and influence how the wall regenerates. This regeneration is called epithelial cell shedding, and the process is vital to maintaining a healthy gut lining. The bacteria help regulate how quickly new cells replace old cells. However, in patients with IBD, the shedding process happens faster than cells can be replaced, leading to a ‘leaky’ gut barrier.
Research has shown that patients with inflammable bowel syndrome typically have less biodiversity in their gut bacteria, and are depleted in certain bacterial species. But until now, we have had only limited insights as to why this is important in the context of disease. (4),(5)
4. Infant Colic
Colicky babies are babies who cry for more than three hours a day for no apparent reason. Nobody knows what makes some babies colicky while others aren’t. However, a study run on colicky babies showed that they had a higher volume of Proteobacteria in their gut than babies without colic. This bacteria is known to produce gas which was probably why the babies cried so much. (6)
Diabetes is a condition where the body has trouble processing food for energy. Patients with diabetes either produces insufficient insulin or develop insulin resistance, a hormone used to convert food to energy.
The current consensus is that the major contributor to insulin resistance is excess weight and a sedentary, inactive lifestyle. However, recent research has now linked a gut flora imbalance to insulin resistance, a precursor to type 2 diabetes. (7), (8)
6. Metabolic Syndrome
Studies involving both humans and mice have confirmed that gut flora have a direct effect on metabolic syndrome. The bacteria in your gut is responsible for balancing out how your gut metabolizes and absorbs food. An imbalance between the host’s immune system and the bacteria that lines the gut results in inflammation and insulin resistance which wreck havoc on host’s metabolic rates. (9),(10)
An ever-increasing number of scientific studies is showing that gut bacteria can have a direct effect on a person’s weight. One of these studies showed that obese people have a gut flora imbalance and in particular, less diversity to their gut bacteria than lean people do. The prevalence of Firmicutes and lower levels of Bacteroidetes, in particular, is found among obese people. (11)
Separate studies run on mice suggest the same thing. One study such study transplanted fecal samples from obese mice and transplanted them into lean mice. After the transplant, the formerly lean mice gained mass rapidly.
8. Heart Disease
When gut flora digests certain foods such as beef and eggs, they produce compounds which increase your chances of heart disease. This compound is called TMAO, and it can cause blocked arteries. Patients with high levels of TMAO in their bodies are two times more likely to have a heart attack or suffer from a stroke.
The gut bacteria of omnivores and vegans was also compared, and researchers found increased production of TMAO in omnivores.
Results to support this claim are still preliminary however it reinforces what we know about how eating certain animal products. The research though does suggest that the link between red meat consumption and heart disease is related to a gut flora imbalance. (12), (13)
9. Brain development and function
Research on gut flora is producing mounting evidence that there is an interaction between the functioning of the gut and brain development and activity. It has even been dubbed the gut-brain axis!
There is increasing evidence pointing to a relationship between the central nervous system and the balance of the gut flora. A gut bacteria called Lactobacillus rhamnoses is suspected of having a direct effect on neurotransmitter receptors in the nervous system.
Studies showed that gut bacteria could activate the immune and central nervous systems. It is believed that gut microorganisms are capable of producing and delivering neuroactive substances into the bloodstream.
Specifically, depression has been associated with elevated levels of lipopolysaccharide (LPS), an inflammatory toxin produced by bacteria in the gut. Similarly, bacteria have also been associated with the production of serotonin and gamma-aminobutyric acid, two compounds that affect the central nervous system and which are also linked to depression.
These findings have led to the term ‘psychobiotics’ to describe the use of probiotics for psychological treatments. Indeed, clinical psychiatry in the future may involve manipulation of the balance of our gut flora for the treatment of certain conditions such as depression. Research so far in rodents has suggested that certain probiotics may have antidepressant and anxiolytic activities. (16)
Current studies of patients support the finding that gut dysfunction may be the driving force for the onset of schizophrenia. Research has found links between the schizophrenia and bowel inflammation, food intolerances and Toxoplasma gondii gut parasite. All of these conditions are linked to a gut flora imbalance. (17),(18)
13. Alzheimers disease
Alzheimer’s disease is the most common form of dementia in the western world. Currently, there is no known cure. There is plenty of experimental and clinical evidence linking gut bacteria to a number of brain and neurological disorders, but until recently, the impact of gut bacteria on Alzheimer’s was unknown.
Researchers have now found that the gut bacteria of mice suffering from Alzheimer’s are different to a healthy control group without the disease. What’s more, mice with sterile guts had significantly less beta-amyloid plaque in the brain, which are the lumps that form on nerve fibers in patients with Alzheimer’s.
The study suggests now a direct link between the disease and gut bacteria composition. (19)
14. Parkinson’s Disease
Doctors have suspected for a long time that problems associated with Parkinson’s are always preceded by digestive system problems such as indigestion and bloating. In most cases, these symptoms show up years before Parkinson’s starts to affect their motor skills.
To prove this claim, scientists transferred fecal matter from humans with Parkinson’s into mice with the mouse model of the disease and found that the mice suffered further loss of motor function. Mice that received fecal transplants from healthy humans stayed the same.
The scientists believe that the gut bacteria could be secreting chemicals that over stimulates parts of the brain, leading to damage. (20)
A wide range of evidence now supports a role for gut microbes and the development of cancers. Research has been focussed on finding particular ‘smoking gun’ bacteria that are thought to cause cancer. But now, it thought that disturbance in gut bacteria could cause cancer through more indirect routes.
It is thought that changes in gut bacteria change the ability of what the gut can and cannot digest. As a result, the gut may digest previously inaccessible nutrients, or it may also start metabolizing carcinogens which were previously left undigested. Similarly, changes in gut bacteria change how the gut wall is regenerated, allowing potential carcinogens and toxins into the blood stream. (21)
Rheumatoid arthritis is an autoimmune disease and chronic inflammatory disorder. Sufferers feel pain, swelling, loss of function and stiffness in joints. It is caused by the bodies own immune system attacking the membranes that line the joints.
Research has found differences in gut bacteria composition between sufferers and healthy patients. In particular, a microbe called Collinsella was over-represented in arthritic patients. As yet the mechanism by which this microbe stimulates an autoimmune response is as yet unknown. (22),(23)
Lupus is a chronic autoimmune disease. The immune system becomes over-active and begins to attack healthy tissues, resulting in inflammation and swelling as well damage to kidneys, blood, heart, lung and skin. Lupus is nine times more common in women than it is in men.
Again research is now suggesting that a gut flora imbalance could be playing an important role in its onset. Research conducted on mice have shown that the introduction of the bacteria Lactobacillus, a species common in yogurt, alleviated the symptoms of Lupus. Similarly, the introduction of a bacteria called Lachnospiraceae aggravated the symptoms.
They also found different combinations of these bacteria between female and male mice. If these differences are similar in human subjects, gut bacteria composition would explain the prevalence for women to contract the disease. (24), (25)
18 Multiple Sclerosis
Multiple Sclerosis is also an autoimmune disease where the immune system attacks the nervous system. However, there is still some debate as to whether it is an autoimmune disease, as the protein that the immune system is mistakenly attacking has not yet been identified.
As the disease attacks the nervous system, the symptoms are chronic and acute such as difficulty speaking, numbness, poor muscle coordination, and fatigue to name a few.
According to the “hygiene hypothesis”, it is thought that reduced exposure to infections, increased use of antibiotics as well as sterile home environments in childhood, may increase the risk of allergic and autoimmune diseases. (26),(27)
As with other autoimmune diseases, recent research is starting to point the finger at a link to gut bacteria. While the link between MS and gut bacteria is yet unproven, gut bacteria composition has been shown to be different between sufferers and healthy subjects and again a gut flora imbalance is a suspected cause of the disease. (28)
19 Liver disease
Non-alcoholic fatty liver disease describes several conditions where there is a build-up of fat in the liver. It is most common in patients that are obese. Healthy livers contain little or not fat, and while a small amount of fat in the liver is harmless, if it is allowed to build, it can lead to more complicated conditions such as diabetes, strokes and heart attacks.
Recent research has shown a link between the build-up of certain pathogenic bacteria in the small intestine and liver disease. Nonalcoholic liver disease has been linked with an increase in pathogenic bacteria within the small intestines.
Likewise, patients with liver disease were much more likely to suffer from leaky gut walls (another symptom of unbalanced gut bacteria), further pointing the finger at a gut flora imbalance as a potential cause of liver problems (29), (30)
Do’s and Don’ts of Gut Bacteria
- Regular exercise promotes the biodiversity of your gut flora. (31), (32)
- Eat lots of fiber which is the main food source that healthy bacteria prefers.
- Sleep more. Lack of sleep significantly damages your gut flora. (33)
- Eat fermented food. Probiotics seed your gut bacteria and should be the cornerstone of any diet
- Do not over clean and sterilize.
- Eat food rich in polyphenols. (34)
- Always breastfeed if possible to seed your infant’s gut bacteria
- Use antibiotics unless absolutely necessary
- Eat excessive amounts of red meat which can cause overgrowth of Bilophila bacteria linked to inflammation (35)
- Avoid artificial sweeteners as they upset the balance of your gut bacteria (36)
- Over clean and sterilize everything. A little uncleanliness is good.