Topic 8 - Diet, the gut microbiome, & human health (PART 2) Flashcards
What factors influence your microbiome?
- age
- diet
- antibiotic use
- genetics
- physiology
Which of the 5 important factors impacts microbiome the most?
Probably diet – dietary changes are profound; occur over a short time and can dramatically affect the diversity and function of the gut
Differences in the fecal microbial communities of Malawians, Amerindians, and US children and adults
- Malawians have diet rich in corn
- Amerindians have diet rich in cassava
- US have more protein + animal based protein
all have big differences in their microbiomes (esp US & the other two)
Extreme diet change can lead to . . .
extreme microbiota change over a short period of time
Differences in microbiota over 3 day study
- volunteers changed their diet dramatically for 3 days
- the vegan diet caused a little change, but the meat and cheese diet caused big changes, almost over night
- specifically, there was an increase in bacteria linked to cardiovascular disease like hemophela
KEY FINDINGS:
- short-term diet alters the gut microbiota
- plant based diet increases the production of SCFAs
How are SCFAs produced?
- produced when microbiota start to break down dietary fibre
- the SCFAs produced are used as energy sources but also have signaling pathways
What happens when a person shifts to having an increased access to complex carbohydrate with a background on increased diversity,
the metabolic output will be increased
If more complex carbohydrates but reduced amount of fibre complexity (or decreased amount of bacterial diversity). . .
you will have dif metabolic output
Why is mucous important?
- maintains the integrity of the barrier in the membrane
- it is here that the microbes start to interact with the body
- new modulators + peptides are secreted
Features of the bacteria species Akkermansia muciniphila
- can feed off mucous
- to be able to have very localized and important effects on the health of the gut microbiota system
- direct inoculation of this bacteria means that SCFA production is increased
- this has secondary effects, which are able to help modulate the effect of the rest of the microbiota + the bilayer
Define probiotic
live microorganisms which, when ingested in adequate amounts, confer a health benefit on the host
most are Gram+, lactic acid producers
Some features of probiotics
- bifidobacterial species & lactobacillus species
- survive transit through stomach and duodenum
others include non-pathogenic streptococci, enterococci, etc.
What is a prebiotic?
something a gut microbiota uses to support its own growth & in acids
Specialized plant fiber that acts as food for the good bacteria
Are foodborne microbes detectable in the gut?
Yes
The metabolome of fermented food consumers was enriched in with . . .
conjugated linoleic acid (CLA), a putatively health-promoting molecule
cross-omic analyses between metagenomic sequencing and mass spectrometry suggest that CLA may be driven by taxa associated with fermented food consumers
How to enhance diet for gut microbiota
- cutting down on ‘discretionary foods’
- gradually increasing your intake of FIBRE
- eating a diet rich in fibre, colourful plant foods and probiotic foods like onions, garlic, Jerusalem artichoke, kombucha, and yoghurt may have benefits for the gut and subsequently for the brain
What are MACs?
- microbiota-accessible carbohydrates such as dietary fibres and resistant starch, that pass through the upper gastrointestinal tract without being digested
- when they reach the large intestine, they are fermented by gut bacteria to produce SCFAs
What are SCFAs?
- organic acids consisting of one to six carbons
- are the main metabolites produced by gut bacteria during anaerobic colonic fermentation of non-digestible MACs such as dietary fibres and resistant starch
- acetate, propionate, and butyrate are the most abundant SCFAs in the human gut
What are the 3 main functions of SCFAs?
- a necessary waste product required to balanced oxygen levels in the large intestine
- butyrate is a major energy source for colonocytes
- enter the host’s systemic circulation to affect lipid, glucose, and cholesterol metabolism is various organs as signal molecules
High microbiota + accessible carbohydrates =
- high microbiota diversity
- high metabolic output
- protection from western diseases
You eat a broccoli. It has few simple sugars. What happens in production of SCFAs?
- a high-MAC diet that has few simple sugars
- major contribution of carbohydrates to host metabolism is in the form of the SCFA fermentation end-products of the microbiota
- in addition to calories, these molecules play diverse regulatory roles in human physiology, including protection from many Western diseases
You eat cake. It has the many sugars.
- a low-MAC Western diet results not only in a loss of beneficial metabolites such as SCFA, but also in a selection of distinct microbiota that may seem foreign to the host
- increased representation of mucus-utilizing microbes, decreased gut motility, and increased calories in the form of sugar and fat may synergize to cause Western disease
MACs include. . .
carbohydrates from diet,
host secretion (e.g. mucin glycans),
or other resident microbes that serve as a metabolic input for members of the microbiota
What is a citizen science?
a derived pool of gut microbiome data that could yield valuable insights about health & disease
What is the evidence base for ‘leaky gut’?
- no evidence that the intestinal permeability is increased in some diseases like IBD or celiac
- no evidence that restrictive diets can ameliorate intestinal permeability in positive way
What does ‘leaky gut’ refer to?
involves defective tight junctions in the intestine and entry of bacteria and toxins into the bloodstream with widespread physiological effects
not a medical condition
Does short-term dieting impact the gut microbiome?
- Evidence from mouse models shows short-term dieting may be more detrimental to weight and metabolic health than not dieting at all
- In one recent study, mice who had gained weight on a high-fat diet and then normalized their weight on a
regular diet were predisposed to gaining weight more rapidly the second time they switched to a high-fat diet, compared with mice that had never
dieted - The mechanism was found to be related to the gut microbiota: obesity followed by short-term dieting had left mice with a gut microbial signature that predisposed them to faster weight regain upon re-exposure to a high-fat diet; this was confirmed by transferring the post-dieting gut microbiota to germ-free mice
Negative effects of low-carb diets
A high-protein (~138 g/day),
low-carbohydrate (22 g/day) weight loss diet provided to 17 obese men resulted in a decrease in total fecal short-chain fatty acid (SCFA) concentrations, with a disproportionate reduction in amount of butyrate
The increased intake of dietary protein resulted in a shift toward protein fermentation in the colon, with a marked increase in fecal N-nitroso compounds (which are known carcinogens).
Positive impacts of eating a diet high in MACs
a diet high in fermentable
carbohydrates with a balanced macronutrient profile shifted an obesityassociated dysbiotic gut microbiota to a structure with relatively lower
levels of bacteria that produce potentially toxic metabolites from the fermentation of dietary fats and proteins, and with higher levels of bacteria
(Bifidobacterium spp.) supported by the fermentation of carbohydrates
Negative consequences of gluten-free diet
- decrease in potentially health-promoting bacteria
- lower production of immune factors (?) like TNF-a
- A more recent
study using 16S rRNA gene sequencing in healthy subjects following a
gluten-free diet for 1 month revealed that the diet induced changes in
gut microbial composition - specifically affected were bacteria involved in carbohydrate and starch metabolism
- still uncertain about overall effects
What does low FODMAP diet involve?
eliminating foods high in fermentable
but poorly absorbed carbohydrates and polyols, usually for 6–8 weeks
Negative impacts of low FODMAP diet
- may have negative impacts on gut microbiome due to reduced prebiotic content
- When the gut microbiota of people on a diet was compared with that of people on a typical Australian diet, the low-FODMAP diet was associated with lower absolute abundance of total bacteria, butyrate-producing bacteria, and Bifidobacterium
Positive impacts of high FODMAP diet
- A recent study examining
the colonic microbiota in IBS demonstrated that consumption of a low FODMAP diet resulted in higher bacterial richness, specifically Firmicutes - still unclear whether results are POSITIVE or NEGATIVE
What is the Paleolithic diet?
The modern-day paleo diet pattern consists of unlimited intake of vegetables, fruit, lean meats, tofu, nuts, and seeds; however, dairy products, cereal/grain products, and legumes are prohibited
focused more on consuming whole foods and less on eliminating all carbohydrates
Describe the evolutionary discordance hypothesis
changes to the traditional nutrition activity patterns of human hunter-gatherer ancestors have contributed to the endemic chronic diseases of the modern day
Should processed foods be reduced to improve gut health?
a study examining emulsifiers in rodents found they had a detrimental influence on the gut microbiota and reuced intestinal mucosal thickness
noncaloric artificial sweeteners when fed to rodents, resulted in much higher glucose intolerance and were associated with increased abundance of bacteria (bad bacteria ?)
yes it’s bad
Intake of fermented foods has been associated with. . .
weight maintenance, a reduced risk of type 2 diabetes, and cardiovascular disease
fermented food could in theory inhibit the growth
of pathogens in the gut, improve food digestibility, or enhance vitamin synthesis or absorption
What is resistant starch?
a form of dietary fiber that resists digestion in the small intestine and reaches the colon, where it is metabolized by the microbiota, resulting in SCFA production
Best sources of resistant starch
unripe banans, pasta, pulses, potatoes (esp wholegrain)
How do fruits & veg improve gut microbiota?
Fruit and vegetables, rich in both polyphenols and fiber, likely assist in modulating the gut microbiota toward a more health-promoting profile by increasing lactobacilli and bifidobacteria.
What Types of Fats Should be Consumed for Optimal Gut Health?
Research in rodent models suggests olive oil and
flaxseed/fish oil result in the most diverse intestinal microbiota.
more research needed
Does Protein Derived From Animals Have a Particular Impact on Gut Health?
Bacteroides are highly associated with animal
proteins and variety of amino acids, whereas Prevotella is highly associated
with increased intakes of plant protein
Interventional studies have demonstrated that high-protein diets result in reductions to fecal butyrate concentrations and butyrate-producing bacteria, which have negative impacts on gut health
Good vs Bad diet for microbiome
A “Western” diet with high consumption of fast foods or processed foods,
high levels of omega-6 polyunsaturated fatty acids, and high sugar intake—
with low fiber—is associated with negative changes to the microbiome and
health.
A diet rich in fiber, mainly from fruit and vegetables, low in red meat,
and rich in omega-3 polyunsaturated fatty acids increases health-associated
microbiota characteristics, with more Bacteroidetes and Bifidobacterium.
Define dysbiosis
an imbalance in bacterial composition, changes in bacterial metabolic activities, or changes in bacterial distribution within the gut
Bacteriodetes vs Fermicutes optimal ratio
a higher ratio of Bacteriodetes to Firmicutes is associated with better health
Whether the ancient microbiota is a better microbiota is debatable; however, at least two arguments support this idea. What are they?
1) our human genome lacks the plasticity that our microbiota possesses and therefore has not been able to keep pace with the
recent profound changes brought on by our modern lifestyle, such as the consequences of a diet very low in microbiota-accessible carbohydrates (e.g., low diversity microbiota, less
SCFA production)
(2) traditional societies typically have much lower rates of Western diseases
What can dysbiosis (gut microbiota imbalance) lead to?
- gastrointestinal disorders
- obesity
- metabolic diseases
How can dysbiosis occur?
- due to a poor diet high in processed foods, low in fiber, an lacking in diversity
Dietary fiber acts as. . .
prebiotic
provides nourishment for beneficial bacteria & promotes their growth
Fiber-rich foods, such as fruits, vegetables, whole grains, and legumes, should be included in the diet to support a diverse gut microbiota.
Polyphenols & bacteria
Polyphenols, found in foods like berries, tea, and cocoa, have been shown to have prebiotic-like effects, selectively stimulating the growth of beneficial gut bacteria.
Examples of prebiotics
Prebiotics, such as inulin and fructooligosaccharides, are non-digestible carbohydrates that promote the growth of beneficial bacteria in the gut.
A high-salt diet is one of the major risk factors in the development of. . .
hypertension
kideny injury
CVDs
gastric cancer
Are microorganisms in traditional fermented foods considered probiotics?
No (bc they are ‘uncharacterized’)
Many fermented food products have no evidence that their live microbial component provides health benefits and the precise microbiological content is rarely defined. Without this level of characterization, they should not be labelled as “containing probiotics”
4 classes of possible side effects of probiotic use:
- systemic infections
- detrimental metabolic effects
- cytokine-mediated immunologic adverse events in susceptible individuals
- transfer of antibiotic resistance genes
2 issues with studies on probiotics
1) METHODOLOGICAL ISSUES
2) a mechanism of action involving the gut microbiota is not confirmed most of the time (don’t know what happens in b/w)
Gastrointestinal function of probiotics
1) improves diarrhea and constipation
2) IBD, ulcerative colitis, Pouchitis, but NOT Crohn’s disease
3) IBS (improvement in symptoms overall, but individual symptoms were not reliably affected)
4) CVD (reduced LDL) + improve blood pressure
Improvements in IBS were associated with. . .
single probiotic species, lower doses, and short durations of treatment
