Gut microbiota composition correlates with diet and health in the elderly
Summary
Changes in the type and quantity of the bacteria in the human gut have been linked to serious
medical conditions including obesity and inflammatory diseases. ELDERMET has previously found
that the type of bacteria found in the gut of older people is very variable, much more so than that of
younger people. This current ELDERMET research has found that the type of bacteria older people
have in their gut is influenced by where they live, even when diet is taken into consideration. People
living in long term institutional care had more limited bacterial types in their gut than people living in
the community, who had a greater diversity of bacterial types in their gut. The loss of bacterial types
commonly seen in the gut of community-dwellers was linked with increased levels of frailty and
other indicators of health. This research supports a relationship between the diet, the bacteria in
the human gut and health of older Irish people. It indicates that diet, not only has a role in
influencing what type of bacteria are found in the human gut, but that it may be possible to use diet
to change the type of bacteria living in the gut and thus affect the rate of health decline in older Irish
people.
Introduction
The bacteria in the gut (the microbiota) are crucial to maintaining good health, particularly intestinal
health, during adult life. Healthy adults have a unique and stable gut microbiota composition; the
ELDERMET team has previously found that older adults have a more varied gut microbiota
composition that differs from that of younger adults. In addition, as people age, there is a gradual
deterioration of the immune system which can lead to persistent inflammation. Serious medical
conditions, including inflammatory bowel disease, irritable bowel syndrome and obesity have been
linked to changes in the composition of the microbiota. Links have also been found between specific
types of gut bacteria and increased inflammation in adults. Finally, a small study has found that
changes in the composition of the microbiota have a link with increased levels of frailty in older
people, although this was a small group of people in a single location which may not be generally
representative.
The composition of the microbiota is affected by physical factors of ageing such as tooth loss, a
reduction in saliva production and deterioration of the digestive system which can increase the time
taken for food to move through the intestine. Diet has been shown to influence the composition of
the microbiota in animal models and small scale human studies. However, the links between diet,
the composition of the microbiota and health in large human groups was not clear.
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This research asked whether or not variation in the composition of the microbiota can influence
how quickly both the immune system and general health deteriorates in older people. A broad
range of dietary information and physical and physiological health information, including assessment
of the immune system, was collected and compared to the composition of the microbiota from 178
Irish people who ranged in age from 64 – 102 years, with an average age of 78 years. Also included
were 13 younger adults with an average age of 36 years.
Individuals taking part in the ELDERMET project were clustered by the type of diet they consumed.
Those within a particular cluster were found to have similar microbiota composition and health
status: the healthiest people lived in a community setting, ate more healthily and had a very
different microbiota composition than those living in a long-term residential care setting. This novel
research supports a link between diet, the composition of the microbiota and the rate of ageing in
older people. It suggests that changing the diet to drive a beneficial change in the composition of
the microbiota could support better health and healthier ageing in older people.
The type of bacteria in your gut differs depending on where you live
This research involved people in four main residential groups, those who were: community-dwelling
(82); attending day-hospital care (20); in rehabilitative care for less than six weeks (15); or in longterm residential care (60).
Biological samples (including stool) were taken from each individual and over five million pieces of
genetic information were generated. Over 28,000 pieces of genetic information on each individual’s
microbiota were examined using several cutting edge methods. There was a clear difference
between the composition of the microbiota from individuals living in the community, which was
similar to that of younger adults, and those living in long term residential care. This clear distinction
continued when the composition of bacterial was examined: individuals in long term residential care
had higher levels of the Bacteridetes group of bacteria while community-dwelling and younger
individuals had higher levels of the Firmicutes group and unknown bacterial species. These two
subject groups were clearly separated even when the bacterial groups were examined in more
detail; the composition of the microbiota differed depending on where the individual lived.
A measure of the activity of the bacteria in the gut
To confirm that the composition of the microbiota had a functional outcome, the activity of the
bacteria was measured using chemicals excreted by the bacteria. These compounds were examined
in individuals living in the community, those in rehabilitative care and those in long-term residential
care. A distinct difference was found between community-dwellers and those in either rehabilitative
or long-term residential care which also had strong links to the composition of the microbiota in
these groups. Those living in the community had higher levels of short chain fatty acids such as
butyrate, acetate, propionate and valerate. These major end-products of bacterial activity can
influence the immune system. Individuals living in long-term residential care differed; they had less
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short chain fatty acids and higher levels of glucose (a sugar), glycine (amino acid – a component of
protein) and fats (lipids).
To further confirm that there was more short chain fatty acid production in community-dwelling
individuals, the frequency of genes for short chain fatty acid production was examined. Of the ~2.51
million predicted genes found, significantly more were predicted in community-dwelling individuals
compared with those in rehabilitative or long term residential care, explaining the greater level of
short chain fatty acids in community-dwelling individuals. There was also far greater genetic
information for genes representing the more common markers of biological activity in communitydwelling or rehabilitative care individuals when compared to those in long-term residential care.
These data confirm that short chain fatty acids, including butyrate, which has been confirmed as
capable of influencing human health, are produced at higher levels in the intestines of communitydwelling individuals. It also confirms not only the composition of the microbiota, which differs
depending on residential location, but also that the microbiota is active in different ways.
Your microbiota is what you eat! The connection between the composition of the microbiota and
diet
When the type and frequency of food consumed by each ELDERMET individual was examined, the
greatest differences were found between the diet of individuals living in the community, and those
in long-term residential care. These differences were mostly in the consumption of vegetables, fruit
and meat, with a gradual change across the four groups from community-dwelling to long-term
residential care. When this information was compared with the composition of the microbiota in
these individuals, it was found to be linked; individuals with a similar diet had a similar microbitoa
composition. Analysis revealed four dietary types: low fat/high fibre (DG1) and moderate fat/high
fibre (DG2) which included 98% of community-dwelling and ‘day-hospital’ individuals; and moderate
fat/low fibre (DG3) and high fat/low fibre (DG4) which included 83% of individuals in long-term
residential care. Those individuals with a healthier, more diverse diet had a more diverse microbiota
composition. Both the composition of the microbiota and diet were found to be most diverse in
healthier individuals (those with a DG1 diet) and least diverse in frailer individuals (those with a DG3
or DG4 diet).
Not only was the difference in microbiota composition shown to be related to dietary group, the
duration of residence in long-term residential care was also linked to microbiota composition; those
individuals longest in long term residential care had a microbiota composition furthest from that of a
community-dwelling individual. Both diet and microbiota composition of individuals in long-term
residential care was found to move away from that of community-dwelling individuals the longer
they stayed in residential care, the diet changing most rapidly. After a month in long-term
residential care, all individuals had a residential diet but it took a year for the composition of the
microbiota to become clearly that representative of an individual in long-term residential care.
These data indicate that the composition of the microbiota is determined by the composition and
diversity of the diet.
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Microbiota –links with health
The links between measures of heath and the composition of the microbiota were investigated with
consideration for factors, such as the subject’s age or gender, which have the potential to bias the
results. The composition of the microbiota did not differ between males and females. Analyses also
took into consideration all medications, including antibiotics being taken; these were not found to
influence the microbiota-health linkages.
The composition of the microbiota from individuals living in the community was less variable than
that of individuals living in long term residential care. Individuals in long-term residential care had
significantly higher levels of markers of inflammation (as measured by increased levels of three
blood markers for non-specific immune system activation) than those living in the community.
These frailer individuals, not unexpectedly, also had poorer scores for a diverse range health
measures, including standard measure of geriatric health such as the Charlston co-morbidity index (a
measure of the influence of illnesses), the Geriatric Depression Test, the Barthel Index and
Functional Independence Measure (FIM) (both measures of independent living), the Mini-mental
State Exam (a measure of cognitive ability) and the mini-nutritional assessment (MNA – a predictor
of malnutrition risk).
There were significant links between several measures of health and the composition of the
microbiota. The strongest links were between the composition of the microbiota and the FIM,
Barthel and MNA - measures of frailty and the risk of malnutrition. In addition, links were found
with level of blood pressure and calf circumference, which may be due to the influence of the diet
and/or the microbiota on muscle mass and/or the decline in muscle mass (sarcopaenia) and
therefore frailty. These findings are supported by a link between frailty and the chemical markers of
bacterial activity; frailer individuals, as measured by FIM and Barthel, also had lower levels of the
short chain fatty acids acetate, butyrate and propionate, most commonly seen in communitydwelling individuals.
Among community-dwelling individuals, there was a strong link between the microbiota and
nutrition, as measured by the MNA. A weaker link was found with blood pressure, which has
previously been linked with the composition of the microbiota. There was no link between the ratio
of the two most common groups of bacteria (Bacteriodetes:Firmicutes) that make up the microbiota
and Body Mass Index (BMI) as has been shown in previous studies. There was however a link
between the composition of the microbiota and BMI in individuals in long term residential care.
There was also a link between the composition of the microbiota and the geriatric depression test
when individuals across all four residential locations were examined.
The difference seen in the composition of the microbiota between community-dwelling individuals
and those in residential care remained strong, even when the effect of residential setting, which can
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largely determine diet, was taken into consideration. This, coupled with the fact that there are clear
links between health and the composition of the microbiota in frailer individuals indicates that the
diet influences the composition of the microbiota, which, in turn, influences health.
The composition of the microbiota and healthy ageing
The microbiota of individuals can be allocated to one of three main clusters, each driven by a
primary bacterial type, either Bacteoides or Prevotella or Ruminococcus. Previous research has
detected only two of these clusters, Bacteroides and Prevotella, which are linked with diets rich in
protein and carbohydrate respectively. We found these same two clusters in this older population,
with community-dwelling individuals most commonly displaying a Prevotella cluster profile.
Using more extensive methods to describe the profile of the microbiota in this older population, we
found eight bacterial sub-clusters. Each of these eight sub-clusters represents a group of individuals
who have a distinct microbiota profile. The transition from healthy, community-dwelling individuals
to frailer individuals in long term institutional care is accompanied by a progressive change in the
proportion of bacterial types found in each group. As individuals move from the community setting
profile cluster to that of an individual in long term institutional care, so the dominance of Prveotella
and Ruminocuoccus bacterial groups is replaced by Alistipes and Oscillibacter bacterial groups.
Analyses showed that there were two main routes from healthier to frailer bacterial profiles.
Differences were found; individuals in pathway B had a higher risk of depression. Some markers of
inflammation (IL6 and IL8) were higher for all people in pathway A while another (C-reactive protein)
was higher in pathway B in individuals in long term residential care. Individuals in pathway A were
older but were less frail than individuals of a similar age in pathway B. As the profile of individuals
moves from that of community-dweller to that of an individual in long term institutional care, so
their muscle mass (as measured by calf circumference) and weight decreases and their level of
inflammation (as measured by IL6) increases. For individuals in long term residential care, as the
composition of their microbiota moves further away from that of a healthier community-dwelling
individual, so the level of frailty (as measured by FIM and Barthel) and inflammation (as measured by
C-reactive protein) increases and their level of cognition (as measured by the Mini Mental State
Exam (MMSE)) decreases.
Although there are many factors beyond those examined in this research that influence a decline in
health in older populations, the evidence suggests that diet influences the composition of the
microbiota which subsequently affects health in older populations. The influence of diet on the
composition of the microbiota may have more subtle impacts on younger adults, particularly those
in developed countries. The impact on health would be more difficult to assess in these younger
populations and may only manifest in older people who have a more compromised immune system.
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This research supports the important role the microbiota plays in healthy ageing and highlights the
possibility that it may play a large part in the acceleration of an ageing-related deterioration in
health. The global population is ageing and solutions to increasing health in older peoples are
required. This work supports the manipulation of the composition of the microbiota, using diets
specifically designed to promote healthier ageing. It supports the identification of biological
markers to identify individuals at risk of less-healthy ageing and the development of specific food
ingredients that promote particular components of the microbiota to promote healthier ageing.
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