Pehling Plath
FScN 3612Revision of Literature Review
1. A summary of the comments and suggestions your peers made about your paper.
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They suggested it would be better to arrange our paper by article instead of by
biomarkers (LPS, insulin resistance/glucose intolerance, inflammation) to make it easier
to read and follow
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Reiterate the thesis in the introduction of the paper and not just in the abstract.
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The terms were confusing and they weren’t sure what certain things meant. They
suggested defining all of the specific words to make the paper easy to understand for
someone not in the field.
●
Add more ‘flow’ to the introduction.
2. A description of what you changed in moving from the original paper to the revised paper.
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We felt like the paper was missing a general message so we wanted to make a thesis
statement and tie it throughout the review. Forming a hypothesis or argument is helpful to
try to convey a message of whether or not the literature has come to a consensus on the
topic. Ours was to incorporate the idea that a high fat diet will have select for certain
kinds of gut microflora. Through the intervention of antibiotics, probiotics or prebiotics,
the composition of the bacteria will be affected and therefore result in changes of LPS
levels, insulin resistance/glucose intolerance and inflammation biomarkers.
●
There were too many variables in the first version of our paper. There were three
differences in the diet/genetics, three interventions and four biomarker measurements. It
was both overwhelming to write as well as read therefore we eliminated the evaluation of
the diet/genetics aspect and decided to only look at mice being fed a high fat diet in
relation to one variable change and how it effects glucose intolerance/insulin resistance,
LPS levels and inflammation changes.
●
Also, we rearranged the order of topics. Before we went from LPS, inflammation,
glucose intolerance and insulin sensitivity. Upon further thought, we decided it would be
better to switch glucose intolerance and insulin sensitivity because insulin insensitivity
results in glucose intolerance. This supported the overall flow of the paper and our thesis
statement.
●
In the discussion, we wrote about how this relates to humans and how it could be life
changing for many people. We felt by adding how our topic relates that it would help
support our “why this is important” argument.
●
Our peer reviewers felt the topic was difficult to understand, so we decided to add
paragraphs to the different sections. We thought it would help the reader understand the
information because it is presented in sections.
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We carefully reread it multiple times to catch any grammatical or spelling error.
3. A list of changes you know that you need to make in your final paper, but haven’t made yet.
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We will find the specific types of bacteria that have been linked to metabolic disorders
and see if there are any connections to the development of diabetes. If so, it could make
the review’s argument much stronger.
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Further editing to ensure correct punctuation and grammer
.
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4. A brief list of points you would like us to be looking at and specific questions and concerns
you have regarding this version of your paper.
●
Should this be written so an average person can read and understand this or is it
specifically for people who are already in the field or are familiar with the topic? We
were writing for an audience who already has background knowledge on the subject but
our peer reviewers were confused with the terms.
●
Is our thesis statement/hypothesis clearly stated and tied throughout the paper? We would
like to further incorporate it to make our argument stronger that there is in fact a
relationship.
●
Are the headings appropriate to separate the paper?
●
We were also wondering about citations. Did we properly cite our resources and
research?
The Effect of Gut Microflora on the Development of Type II Diabetes in High Fat Diets
1.
Abstract
The microbiota living in the intestinal tract is linked to metabolic disorders such as the
development of type II diabetes. The variation of microflora living in the intestinal tract can be
associated with diet. A high fat diet can stimulate growth of certain bacteria, which is associated
with increased intestinal permeability. Consequently, endotoxemia increases and triggers
inflammation leading to metabolic disorders. The purpose of this systematic review was to
determine if bacteria plays a role in initiating the development of type II diabetes. A high fat diet
may influence the composition of gut microflora to elicit an inflammatory response to promote
insulin resistance and gut permeability. A combination of “gut microflora,” “insulin resistance,”
and “high fat diet” were used in MNCAT Discover, PubMed, PLoS ONE, and Google Scholar to
find applicable sources. All six of the studies reviewed showed mice receiving either antibiotic,
probiotic or prebiotic treatment had increased glucose tolerance, reducing the rates of type II
diabetes. Five of the studies recorded insulin resistance, showing similar results of having
improved insulin sensitivity with treatment. Five out of the six studies evaluated inflammation,
finding that with treatment, there was a reduction in inflammatory markers. Lipopolysaccharide
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(LPS) was evaluated in three of the studies; all showing a positive correlation with antibiotic,
probiotic and prebiotic treatment and a decrease in LPS levels. Feeding a high fat diet was shown
to increase gut permeability, increase plasma LPS, increase endotoxemia, and increase
inflammation to result in metabolic disorders. The usage of prebiotics, probiotics and antibiotics
to selectively stimulate or inhibit the growth of certain bacteria resulted in an overall decrease in
inflammation, and thus reduction in metabolic disorders risk. Hence, recent research has shown
that high fat diet induces pro-flammatory gut microflora that is attributed to the development of
type II diabetes. Through this data, modulation of gut microbiota could be beneficial for
humans by improving glycemic control and decrease metabolic disease risk factors.
2.
Introduction
The growing rate of obesity and metabolic disorders, such as insulin resistance and
diabetes, is a major public health concern. In the United States, over 25.8 million Americans
have type II diabetes, that is, 8.3 percent of the population. (7) Low grade inflammation has been
linked to the source of the development of metabolic diseases, but the primary cause to its
development is still being investigated. Many researchers argue different theories on the source
of inflammation, including various genetic and environmental factors. For example, American’s
high intake of pro-inflammatory Omega 6 fatty acids and low intake of anti-inflammatory
Omega 3 fatty acids. However, a promising recent theory has been suggested that an individual’s
gut microbiota may play a pivotal role in the development of inflammation and therefore type II
diabetes. It has been shown that certain gut microbiota may be more inclined to stimulate LPS, a
pro-inflammatory Many theories try to explain the variation in individual’s diversity of
microbiota as a result of genetics or environment. As shown by the reviewed studies, high fat
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diets stimulate the growth of these pro-inflammatory gut microorganisms. These studies
modulated the high fat diet induced gut microflora using pro-biotics, pre-biotics and antibiotics
in mice in order to decrease inflammation and metabolic disease risk factors. Hence, recent
research has shown that high fat diet induces pro-flammatory gut microflora that is attributed to
the development of type II diabetes.
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Animal studies were the primary focus of current research on the factors that may have
influenced inflammation. All studies analyzed used mice as their subjects and fed them a high
fat diet (HFD), which tended to consist of about 45% of total calories. To analyze the effects of
gut microbiota on the development of diabetes, four major criteria were examined including
changes in LPS, inflammation, glucose intolerance, and insulin resistance in mice being fed a
high fat diet. An increase in LPS has been shown to negatively impact inflammation, which is
also correlated to increased glucose intolerance and insulin resistance. This is further discussed
below.
3.
Results
a. Lipopolysaccharide (LPS)
The exact mechanism to which gut microflora influences the development of metabolic disease
is theorized to be influenced by bacterial LPS and its impact on inflammation. Found on the
outer membrane of gram-negative bacteria, LPS can bind to CD14 receptor complexes on many
cell types to act as an endotoxin. An associated increase in gut permeability as a result of the
endotoxin may lead to inflammation. Of the six studies that were included in our research, three
of the studies did not evaluate change in LPS.
In the Carvalho et. al. study that evaluated antibiotic and high fat diet treated mice, LPS
levels increased to 1.4EU/ml in the high fat diet mice and to 0.2 EU/ml in antibiotic+ high fat
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diet treated mice. This indicates that a high fat diet may select for gram-negative bacteria with
LPS. When the mice were treated with antibiotics, it wiped out the gut microflora and resulted
in less plasma LPS compared to the high fat diet alone.
In the Everard et. al. study that evaluated the LPS results in mice that were fed high fat
diets and then treated with prebiotics. The mice that were fed prebiotics had significantly less
plasma LPS, 1.0EU/mL, compared to the mice who were not treated with prebiotics, 2.0 EU/mL.
This may indicate that prebiotic treatment after a high fat diet could modify gut microflora and
select for bacteria that do not consist of the endotoxin LPS.
Lastly, the Membrez et. al. study evaluated high fat diet in mice with antibiotic treatment
and found significantly lower plasma LPS in antibiotic treated mice (18EU/mL) compared to the
control (25 EU/mL). Results of this study may suggest that antibiotic treatment suppressed LPS
producing bacteria. This may indicate that high fat diets can select for bacteria with LPS, which
has a negative effect on inflammation, potentially contributing to type II diabetes. Overall, these
studies may indicate that high fat diet induces pro-inflammatory microorganisms in the gut that
could be adjusted through the usage of prebiotics and antibiotics. These adjustments can decrease
the LPS biomarkers and therefore may reduce the risk of the development of metabolic disease.
b. Inflammation
Recent research has been able to link metabolic diseases, including diabetes, with a lowgrade inflammatory state. Hence, investigating the inflammation response is an important
criterion when assessing the overall relationship between gut microflora and the development of
metabolic diseases, such as type II diabetes. Out of the six studies evaluated, five of the studies
examined changes in inflammation.
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Ding et. al. studied the difference between a high fat diet and a low fat diet and its
influence on inflammation. They found that mice fed a high fat diet had an increase of two
inflammatory biomarkers in the intestine, including TNF-a mRNA and NF-kB, compared to
mice fed a low fat diet. The findings of this study may indicate that high fat diet results in greater
inflammation.
In the Carvalho et. al. study, mice that were fed the high fat diet but treated with
antibiotics had lower Portal TNF- α (75pg/ml) and Portal IL-6 (14pg/ml) compared to high fat
diet without antibiotic treatment, which had Portal TNF- α (140pg/ml) and Portal IL-6 (23pg/ml).
By eliminating gut microflora, Carvalho et. al. showed a difference in inflammation which can
be attributed to the difference in gut microflora. This may indicate that modulating gut
microflora influences inflammation.
Similarly, Cani et. al. found that antibiotic treatment on mice that were fed a high fat diet
had reduced inflammation (1.2 PAI-1 mRNA levels) compared to a high fat diet with no
antibiotic treatment (2.5 PAI-1 mRNA levels). A study conducted by Membrez et. al. found
similar results with mice treated with antibiotics on a high fat diet; the inflammatory response
status diminished. Results of Membrez et. al. found that antibiotic treated mice had less
expression of jejunal TNF α-TNF (0.00005 2δCt) compared to the control (0.00010 -2δCt) who
were not given antibiotics.
Finally, a study conducted by Neyrinck et. al. treated mice with a high fat diet and
prebiotics to modulate the gut microbiota. The mice treated with prebiotics had decreased plasma
inflammatory marker concentrations: marker IL6 (53.9611.5 pg/ml in HFD and 21.967.7 pg/ml
for AX treatment) and MCP-1 (32.165.3 pg/ml in HFD and 12.362.4 pg/ml in AX treated mice).
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The results of the study showed that the prebiotics changed the gut microbiota which resulted in
a difference in the inflammatory response.
Overall, these studies may show that gut microbiota can be influenced by diet and
therefore effect inflammatory response and the development of metabolic diseases. High fat diets
have been shown to increase pro-inflammatory bacteria that increase inflammatory biomarkers.
Treatment of prebiotics can select for bacteria that can diminish the inflammatory response and
accordingly protect against metabolic diseases.
c. Insulin Resistance
The development of metabolic diseases has been shown to be influenced by low grade
inflammation. Insulin resistance is key hallmark symptom of type II diabetes and usually results
in glucose intolerance. When blood glucose levels rise in the body, insulin is released to aid in
the absorption of glucose into tissues. With insulin insensitivity, blood sugar concentrations
remain dangerously high. The analyzed studies have found that high fat diets have been shown to
decrease insulin sensitivity in mice by affecting the gut microorganisms. Through the modulation
of gut microflora, insulin sensitivity is shown to improve.
Both prebiotics and antibiotics were focused on regarding these studies in controlling the
growth of gut microbiota. Prebiotics aid in stimulating the growth of non-inflammatory bacteria
in the gut while antibiotics kill gut microorganisms including pro-inflammatory bacteria. In Cani
et. al., the mice that were given the antibiotic treatment showed improved insulin resistance
(AUC insulin 10-3) compared to the control mice (AUC insulin 10-3).
Carvalho et. al. had mice on a high fat diet exhibiting insulin resistance. The mice treated
with antibiotics showed a decrease in insulin resistance and improved insulin sensitivity (450
pmol/l in pair-fed mice and 120 pmol/l in antibiotic treated mice).
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In Ding et. al. mice fed a high fat diet became more insulin resistant (6 ng/ml) compared
to mice fed a low fat diet (1 ng/ml). These studies demonstrate that a high fat diet in mice can
increase the incidence of insulin resistance. When treated with antibiotics, there was increased
insulin tolerance, highly relating to improving type II diabetes characteristics. This research may
indicate that high fat diets induce insulin resistance that can be modulated using prebiotics and
antibiotics to influence gut microbiota.
d. Glucose Intolerance
With improved insulin sensitivity, these studies have shown that glucose tolerance subsequently
improves after the administration of antibiotics and prebiotics. Through the modulation of gut
microflora, glucose tolerance is shown to improve in mice fed high fat diets.
Everard et. al. used a prebiotic treatment for four days on mice being fed a high fat diet
for five weeks prior. At the end of the four day treatment phase, the mice fasting glycemia was
significantly lower and there was improved glucose sensitivity.
Cani et. al. fed it’s mice a high fat diet which resulted in glucose intolerance. Blood
glucose concentrations were all higher in the high fat diet mice (950 AUC 15-90 min) than the
control mice (1100 AUC 15-90 min). When treated with antibiotics for four weeks, there was
improved glucose intolerance. This shows that the bacteria in the gut may play a pivotal role in
glucose intolerance, and that it can be reversed in mice through gut microflora modulation.
These studies show that glucose intolerance in mice may be linked to the kinds of
bacteria in the gut. By using antibiotics and prebiotics, gut microorganisms can be modulated to
change glucose intolerance. Hence, the research indicates that a high fat diet may influence the
development of type II diabetes by influencing insulin resistance and ultimately glucose
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intolerance. Through this data, modulation of gut microbiota could be beneficial for humans by
improving glycemic control and decrease metabolic disease risk factors.
4.
Discussion/Conclusion
Recent evidence has proven the link between low-grade inflammation and the
development of diabetes and other metabolic diseases. This poses the question to why some
people have more inflammation than others. To answer this, the human microflora is being
investigated. Humans have trillions of bacteria living within the intestinal tract and their
interaction with human metabolism may play a vital role in the development of inflammation.
More specifically, the composition of bacteria could either promote or interfere with the
inflammatory response. Researchers have investigated this question by examining high fat diets
in rats, the use of antibiotics and the use of prebiotics.
To research this topic, six articles were reviewed based upon 4 main criteria including
change in LPS, inflammation, glucose intolerance and insulin resistance. After analyzing the
articles, our research shows that there is a change in LPS dependent on bacteria. The
composition of bacteria can change the amount of LPS found in plasma. Furthermore, the degree
of inflammation is related to the amount of LPS. Mice that were fed a high fat diet had greater
amounts of plasma LPS and more severe inflammatory markers. This may indicate that the type
of diet may influence gut microflora composition. Mice that were treated with antibiotics to wipe
out gut bacteria all showed lesser plasma LPS concentration and lesser inflammatory markers.
Additionally, the prebiotics to select for certain bacteria likewise showed a lesser LPS
concentration and lesser inflammatory markers, indicating that the species of bacteria plays an
important role.
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Additionally, glucose intolerance and insulin resistance were examined to inspect the
relationship between bacteria composition and the development of diabetes. For mice with
elevated LPS and elevated inflammatory markers, consequently greater insulin resistance and
glucose intolerance were seen. Therefore, it appears that high fat diet may influence the
composition of gut microflora to elicit an inflammatory response to promote the insulin
resistance and glucose intolerance.
The relationship between obesity and type II diabetes in America is a hot topic. It is
accepted that being overweight or obese is a risk factor for type II diabetes leading us to further
look into this relationship. If researchers are able to show there is a difference between the
microbiome of humans at a healthy weight (BMI 18.5-24.9 km/m2) compared to overweight or
obese people (BMI >25 km/m2) this could lead to a product or procedure to alter the bacteria in
the gut. Overweight or obese people could lose weight simply by selectively eliminating or
adding bacteria, which could help decrease LPS and inflammation and in turn decrease insulin
resistance and glucose intolerance. This could reduce the prevalence of metabolic disorders,
such as type II diabetes.
a. Limitations
The research being performed in this field is still fairly new, thus it is being studied
through animal studies. All of the studies that were assessed used mice so it is difficult to relate
the findings to humans. In order to take this data seriously, researchers will need to use human
subjects in future studies. Even then, it will take several studies to show that gut microbiota are
influenced by a high fat diet and in turn can have an effect on type II diabetes.
It was noticeable that some researchers were struggling to determine if a high fat diet caused
certain gut flora growth or if the mice were genetically predispositioned to the kinds of bacteria
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that would grow in the gut. Most studies cleared the entire gastrointestinal tract by administering
a high dose of antibiotics for an extended period of time. This helped show that diet heavily
affects the types of bacteria that grow in the gut, however, it is still unclear how large of a role
genetics play.
Four out of the six studies that were evaluated had a small sample size (<25 mice). This
makes it difficult to properly assess if the data is statistically significant or not. More research
needs to be conducted with a larger sample size. Only one study evaluated 50 mice, which is still
questionably small. If this research moves to humans, studies will need to have large sample
sizes to ensure the results can be accepted.
Bibliography
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endotoxemia-induced inflammation in high-fat diet-induced obesity and diabetes in mice.
Diabetes. 2008;57(6):1470-81.
2. Carvalho BM, Guadagnini D, Tsukumo DM, et al. Modulation of gut microbiota by
antibiotics improves insulin signalling in high-fat fed mice. Diabetologia. 2012;55(10):2823-34.
3. Ding S, Chi MM, Scull BP, et al. High-fat diet: bacteria interactions promote intestinal
inflammation which precedes and correlates with obesity and insulin resistance in mouse. PLoS
ONE. 2010;5(8):e12191.
4. Everard A, Lazarevic V, Derrien M, et al. Responses of gut microbiota and glucose and lipid
metabolism to prebiotics in genetic obese and diet-induced leptin-resistant mice. Diabetes.
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5. Membrez M, Blancher F, Jaquet M, et al. Gut microbiota modulation with norfloxacin and
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6. Neyrinck AM, Possemiers S, Druart C, et al. Prebiotic effects of wheat arabinoxylan related
to the increase in bifidobacteria, Roseburia and Bacteroides/Prevotella in diet-induced obese
mice. PLoS ONE. 2011;6(6):e20944.
7. U.S. Department of of Health and Human Services, National Diabetes Education Program.
The Facts About Diabetes: A Leading Cause of Death in the U.S. 2014. Available at:
http://ndep.nih.gov/diabetes-facts/. Accessed on October 22, 2014.
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