A case study on three chronic diseases thought to be caused by changes in gut microbiota.
Written by Kavya, Akshaya, Haritha
The increase in chronic disease worldwide can be attributed partly to changing gut microbiota. Here, we discuss the effect of gut microbiota on three chronic diseases: Alzheimer’s, Diabetes and Irritable Bowel disease.
Alzheimer’s Disease
Alzheimer’s disease affects around 44 million people in the world (3). Associated with older age, Alzheimer’s is considered a progressive disease that results in the inability to recall their memories. As the disease progresses, the neural connections in the brain are destroyed, resulting in dementia and eventual loss of vital mental functions (4). Recently, there has been a lot of research on preventing Alzheimer’s and possible treatments. One such study conducted connected the gut microbiota to the progression of the disease and a potential treatment.
In the study, the researchers were able to connect the dysbiosis of the gut microbiota and its impact on the neuroinflammation in those who had Alzheimer’s (5). The dysbiosis results from a change in the person’s microbiota composition. The researchers were able to deduce that there was an increase in the production of two amino acids (building blocks of proteins) phenylalanine and isoleucine. The increased production came from the dysbiosis in the microbiota. When these two amino acids are in higher concentrations, they induce the production of immune cells that are neurodegenerative (destroy). These immune cells attack our brain cells and cause inflammation, resulting in the loss of memory and mental function (5). The researchers took it one step further to see if there were any dietary supplements that would decrease the production of the two amino acids. They found that the consumption of sodium oligomannate (GV-971) showed relief of symptoms as it decreased the production of the amino acids, phenylalanine and isoleucine. This further prevented neuroinflammation. These studies were conducted in mice; however, further research must be conducted over longer periods of time to confidently see its results. The treatments proposed for Alzheimer’s and other chronic diseases should be viewed from various angles to combat their progression overall.
One thing to note is that a lot of the chronic diseases can be related to dysbiosis of the microbiota and the resulting inflammation. This study also highlights the important relationship between the gut and the brain, reinforcing the fact that what we ingest can heavily influence our neurological activities.
Diabetes
Another chronic disease which is influenced by the dysbiosis of the gut microbiota is diabetes. Individuals with this long-lasting condition tend to have higher blood sugar levels. This is because diabetics are unable to produce or use insulin, which can be categorized into Type 1 and Type 2 Diabetes. Those with Type 1 are unable to produce the hormone whereas those with Type 2, which is the more common form of diabetes, cannot respond to it well. Carbohydrates that we consume are broken down into glucose and used for energy, with the help of insulin in order for the glucose to move from the bloodstream to the cells (1). To manage this chronic health condition, fitness and a healthy diet are important.
Similar to Alzheimer’s, diabetes can be a result of the microbiome’s influence on the individual through the loss/gain of bacteria. These bacteria, as we have noted from previous posts, can promote the health of the host, but can also lead to disease. Dysbiosis, as mentioned before, is the imbalance of various bacteria in our microbiome, more specifically of the gut, which can lead to inflammation or diseases such as diabetes. The role of the gut microbiota in diabetes has been further examined in many studies. One study, on the effects of gut microbiota on Type 2 diabetes has shown that the immune and metabolic systems of the bacteria have a close relationship (2). Even though a nutritious diet is a well-known way of managing Diabetes, the microbiome can influence the extent to which this can help as it can be used to estimate “...how quickly [the] blood sugar would increase in response to eating a particular food,” (2). Going back to dysbiosis, which affects the diversity of the gut microbiota, we can see that this can have an impact on metabolic activities which include obesity and other disorders like diabetes. In an attempt to reduce hunger hormones which can increase a person’s risk of obesity and diabetes, researchers have worked to create probiotics which change the compositions of the bacteria in order to control the blood sugar levels (2).
Another study involved in researching the dysbiosis of the gut microbiota and its effects on Diabetes observed the key indicators and causes of Diabetes in individuals. Research shows that gut microbiota is “...a major environmental determinant of obesity and [Type 2 Diabetes], and gut dysbiosis plays a central role in … the pathogenesis of insulin resistance,” (7). In the study, researchers found that the gut bacteria can move past the intestinal barrier. This is because the intestine is more permeable than other areas of the body, and it is suspected that the bacteria found in individuals with higher risk of Diabetes and obesity came from their intestines (8). Additionally, it is predicted that these bacteria from the microbiome create the inflammatory process and restrict the function of insulin from being able to regulate the blood sugar levels (8).
Since we now know that the gut microbiota influences how cells can respond to insulin and lead to Diabetes, specifically Type 2 Diabetes, treatments mainly focus on altering the bacterial composition of the gut microbiota.
Irritable Bowel Disease
Irritable bowel disease (IBD) is a group of chronic inflammatory diseases of the gastrointestinal tract including Crohn’s disease and Ulcerative colitis that are associated with gut microbiota and affect around 1.5 million Americans (6). IBD is thought to be on the rise since diets have been changing worldwide. Changes in the gut microbiome are found to have an effect on the onset of this condition along with other conditions such as genetics, antibiotic use and diet (6). The human gut is populated by various bacteria such as Bacteroides, Actinobacteria, Proteobacteria, Firmicutes and Prevotella. A ‘western diet’ is thought to lead to the onset of IBD and is characterized by high levels of animal fat and low fiber as well as high levels of Bacteroides and low levels of Prevotella. An imbalance in the levels of ‘good’ bacteria and the levels of ‘bad’ bacteria in the intestine is thought to lead to increased pathogenicity (6). One theory suggests that people living in western countries are exposed to fewer types of bacteria and hence their immune systems develop in a way that causes them to be unable to handle different types of microorganisms later in life, thereby causing inappropriate immune system activation (6).
Studies were conducted to observe how changing a person’s diet would affect the severity of IBD. Exclusive enteral therapy (EEN), an alternative to pharmacological agents, was one method used to treat these diseases wherein different formula diets were given to patients either orally or through a nasogastric tube (6). In the short term, this therapy was shown to have positive effects. However, limited data made it difficult to determine the effectiveness of this treatment in the long term (6).
Several diets have shown to be effective in managing IBD. However, mechanisms of action have not been studied. Overall, patients whose diets are rich in animal fat and protein such as eggs, meat, protein and increased alcohol consumption saw a relapse of the disease. Those on semi-vegetarian or vegetarian diets did not see as much of a relapse (6). However, for the management of IBD through altering diets, more studies need to be conducted.
In recent years, more and more chronic diseases have been diagnosed worldwide. These can be attributed to the drastic changes in our lifestyles, specifically diet. There is a lot of evidence that suggests that the gut microbiota and its composition have a great effect on the overall health of the host. Therefore, more studies have to be conducted in order to better understand the relationship as it will aid in creating treatments.
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