Food health Week 4 - Microbiome part 2

Gut bacteria effects of animal based lipids

• decreased bacteroides

• increased firmicutes and proteobacteria

Impact of plant based lipids

• increased lactobacillu, bifidobacteria and A muciniphila

Impact of animal based protein

• decreased firmicutes

• increased Bacteroides

Impact of plant based protein

decreased bacteroides

increased bifidobacterium and lactobacillus

Impact of animal based carbs

increased bifidobacterium and lactobacillus

Impact of plant based carbs

• increased bifidobacterium and bacteroides.

Strongest dietary contributor to microbiome structure and function

Dietary fibre

Carbohydrate Active Enzymes (CAZymes)

Enzymes that can interact with plant dietary fibre. Humans have very few, but gut microbiota have thousands, allowing them to break down dietary fibre into SCFAs and gasses.

How many CAZymes does the human body have compared to gut microbiota?

Human body: 17

Gut microbiome: 11,000

Microbiota Accessible Carbohydrates (MACS)

Dietary fibre and resistant starch that are mostly undigestible by human enzymes.

• Fermented by gut bacteria in large intestine to produce SCFAs.

What are the most abundant SCFAs in the gut?

Acetate, Proprionate and Butyrate

Functions of SCFAs in the body

• fuel gut microbiota

• Butyrate is a major energy source of intestinal cells.

• SCFAs can enter blood circulation and function as signal molecules involved in glucose, lipid and cholesterol metabolism

Why may SCFA effects be quite short lived?

• they are quite volatile and reactive.

• Short lived effects mean that regular fibre intake is important.

How SCFAs are produced

• Microbiota break down dietary fibre into monosaccharides.

• These monosaccharides are processed through different pathways to produce each SCFA

Effect of low MAC diet on gut microbiome

• Low MAC common in Western diets

• simple carbohydrates broken down in small intestine

• Low MACs in diet mean microbiota diversity is lowered (less food) and less SCFAs are produced.

• Low microbiota diversity and metabolic products is linked to western diseases.

Effect of high MAC diet on gut microbiome

• MACs fermented by large intestine microbiota, releasing SCFAs that improve body health as well as increasing microbiota diversity.

• Increased metabolic products from gut microbiota such as SCFAs is linked to protection from western diseases.

Impact of SCFAs in the cells of the large intestine (colonocytes)

• reduces pH, inhibiting pathogen growth

• increase mucus secretion helping maintain a healthy gut barrier

Impact of SCFAs in the liver

• increase glucose sensitivity

• decrease inflammation

• increase fatty acid oxidation

Effect of SCFAs that enter portal circulation

• immune modulation.

Where dietary fibre comes from in plant cells

The cell wall. During food processing, a lot of dietary fibre is often removed.

Gelatinised starch

• soluble starch that is often cooked.

• Digested easily in upper digestive system.

• gelatinisation occurs when starch interacts with water, reforming starch structures.

Starch

• granules found in plant cells for storage of sugar

Ungelatinized starch

• Insoluble and resistant starches

• often uncooked starches

• Sometimes when cooked starches are cooled down they regelatinize and form characteristics of resistant starch.

• these form resistant starches and are fermented by microbes in the large intestine.

Physiochemical characteristics of fibre

• solubility

• viscosity

• fermentability

What functions do all types of fibre perform in the GI tract?

• micronutrient availability

• Gut transit time

• Stool formation

• Microbial specificity

Mucin as a non-dietary MAC

Mucin is a molecule secreted by human goblet cells that forms a protective mucus layer over intestinal cells.

• Mucin can provide nutrients for microbes living in the mucus layer.

• These microbes help maintain the mucus layer.

• microorganisms good for mucus layer include bifidobacteria and lactobacillus.

• However some microorganisms can degrade mucin layer, leading to systemic disease (eg: cholera).

Impact of adding Akkermansia Muciniphila to mucus barrier

• Akkermansia degrades mucin which releases growth factors that help other microbiota grow.

• Akkermansia helps strengthen the host’s intestinal barrier, modulate mucin turnover and therefore immune responses?

Ways the transition from hunter-gatherer diet to modern food production may be “starving our microbes”

• more sanitation of food products, decreasing microbial diversity

• antibiotic use

• C sections and baby formula disrupting normal microbial colonisation of babies.

• Western low MAC diet.

Findings of a paper comparing US diets with diets of Malawian people and Amerindian people.

• Children below age 3 have similar gut microbiomes in all 3 cultures

• With introduction of solid food, gut microbiome becomes increasingly different.

• May be due to different stable starch based foods (Amerindians eat Cassava while Malawians eat corn).

Enterotype

A signature composition of microbes that is similar to communities in other individuals based on the presence and relative abundance of certain species.

What enterotypes can be useful for

• Making associations between gut outcomes, health, other factors

• broadly classifying people and inferring what sorts of treatments might be helpful

• can be predictive in some cases

Downsides of enterotypes

• Broad and can lack precision

• don’t provide function

Study where participants went from low fat to high fat diet over 10 days

Showed significant change to enterotypes.

Study where people were put on plant based diets for a few days

gut microbiome changed quite quickly to the change in diet, but went back to baseline when participants went back to their original diet.

How stable is the adult microbiome?

It is quite stable, and takes major disturbance to alter.

• we don’t know what changes would be needed to change to a different enterotype.

Probiotic

A live microorganism that provides a health benefit to the host when ingested in adequate amounts.

• majority of probiotics are gram positive and lactic acid producers. eg: Bifidobacteria and Lactobacillus species.

• Probiotics survive transit through stomach and small intestine.

Common probiotics

• Lactobacillus

• Bifidobacterium

• Streptococcus

• Enterococcus

• Saccharomyces

Probiotic fermented foods

Fermented food that has been fermented with a microbe that is proven to be a probiotic, or has had probiotics added at adequate amounts to confer a health benefit.

eg: yoghurt

Fermented food

A food that has been made with intentional microbial growth and enzymatic conversion of food components.

• The microbes may be alive or dead. Do not need to have a documented health benefit.

eg: sauerkraut, kombucha, leavened bread.

Prebiotic

A substance that is specifically used by a microorganism that confers a health benefit on its host (a probiotic).

Synbiotic

A mixture that includes live microorganisms that can confer a health benefit on the host and a substance that is selectively utilised by those microorganisms.

Postbiotic

Inanimate microbes or their components that confers a health benefit on the host.

What was a connection found between eating fermented foods and levels of conjugated linoleic acid in the gut?

People with higher conjugated linoleic acid (CLA) ate fermented foods.

effects of polyphenols on intestinal cells

• Increase barrier function

• Increased anti-inflammatory effects

• Increased antioxidant effects

Systemic organs that can be impacted by bioactive metabolites created when polyphenols interact with gut microbes

Lungs: decreased inflammation and oxidative stress

Brain: increased cognitive function, neuroprotection, peripheral blood flow, decreased inflammation

Heart: increased endothelial function, decreased oxidative stress and inflammation

Immune modulation

Polyphenols

A component of plant foods that impact digestion, and also give food their colour and taste. Polyphenols often interact with gut microbes, influencing them to produce metabolites that can be beneficial for the body. Polyphenols can also bind directly to cell membranes and have positive effects.

Benefits of polyphenols binding to cell membrane of intestines

• Increased inhibition of pathogenic bacteria growth

• Increased Quorum sensing inhibitors

• Increased antimicrobial agents.

Microbes that polyphenols often interact with

• Bifidobacterium

• Akkermansia

• Lactobacillus