5 – Fibre and Monogastrics Flashcards
Role of dietary fibre
- Impacts gut health, immune system and systemic health
- Maintenance of health
- Disease prevention
- **too little or too much=NEGATIVE EFFECTS
Gut microbiota depend on dietary fiber
- Energy source to sustain or shift gut microbe populations
- Produce some essential nutrients for host (ex. Vit K)
- Produce substances that act locally and/or systemically via immune or NS and other organs
What are the main two categories of the effects of fibre on the gut-metabolic-immune system?
- Gut-microbiota dependent: local and systemic effects
- Microbiota independent: local and systemic effects
- **all of them affect health outcomes
What are some clinical applications of fiber?
- Dilute calorie intake
- Promote satiety
- Hairball control
- Alter fat or cholesterol absorption
- Affect gut motility and transit time
- Promote laxation
- Normalize fecal quality
- Treat bile-salt induced diarrhea
- Increase resistance to pathogenic bacteria
What is the definition of dietary fibre (DF)?
- Indigestible plant AND non-plant materials
- *unified by resistance to animals’ digestive enzymes
o Incapable of hydrolyzing some chemical bonds - *NOT uniform in form or function
- Most complex category of food product
What are some ‘related’ indigestible plant sources?
- Polyphenol: LIGNIN
- Non-plant sources: fungi and animal sources
- Synthetic forms
If animal enzymes can’t digest fiber, what happens to it after ingestion?
- Interacts with GIT and other digesta
- Some pass through GIT unchanged=excreted in feces OR some utilized by gut microbes and disappear (partially or entirely)=metabolites of fermentation appear
Fermentation
- Metabolic process by which microorganisms extract energy from foodstuffs
- Successful fermentation depends on presence of specific microorganism with the correct substrate in a favorable environment
What happens to the composition of digesta/feces as fiber is fermented?
- Metabolites from fermentation increase
- As fibre disappears=fecal bulk decreases
- Microbiome may maintain or shift (competition)
- Microbial mass might increase
Where does fermentation occur in monogastrics?
- Lower GIT
o Determined by interaction between individual’s microbiome and types of fiber
What are some potential by-products of fermentation?
- AA
- Vitamins (B and K)
- Gases (methane)
- ***SHORT-CHAIN FAs (C2-6)=volatile FAs
What should 90-95% of SCFAs be?
- Acetate (C2)
- Propionate (C3)
- Butyrate (C4)
What are the functions of SCFAs?
- Source of energy
- Act as signalling molecules
- Influence immune system
- Maintain or alter intestinal environment
SCFAs: maintain or alter intestinal environment
- Help maintain anaerobic environment
- Increase tight junction proteins and mucin
- **acidify pH in lumen of GIT/colon
o inhibits growth of pathogenic microbes
o ammonia trapping to be excreted in feces
SCFAs as energy source: herbivores vs. carnivores & omnivores
- Herbivores: major contributor to daily maintenance energy
- Carnivores & omnivores: negligible contribution to daily maintenance energy
o **butyrate is preferred cellular fuel of enterocytes and coloncytes
What does insufficient fermentable fibre lead to?
- Decreased microbial diversity
- **impaired intestinal health
- **Increased risk of colitis and obesity
What can an over-abundant amount of fermentable fibre cause?
- *Abdominal distention/discomfort
- *Increased/problematic flatulence
- Altered frequency of defecation
- Decreased fecal quality
What is ‘pre-biotic’ fiber?
- Inulin, FOS
- Selectively supports metabolism/growth of ‘good’ bacteria to support or improve host animal’s health
What are the 4 main descriptors for dietary fiber?
- Physiologically significant descriptors
o Viscosity
o Fermentability
- Physiologically significant descriptors
- Easily measurable descriptors
o Solubility
o Molecular weight (<10 untis=low molecular weight)
- Easily measurable descriptors
What is the importance of viscosity and fiber?
- SLOWS gastric emptying and SI transit
o Can influence diffusion, digestion, and/or absorption of nutrients
What does viscosity depend on?
- Concentration/amount of fibers present
- Conditions in GIT
- Presence of other fibers
- Overall food matrix
**Clinical utility of viscosity in upper GIT
- Enhance satiety and decrease food intake
- Modulate post-prandial glycemic response
**Clinical utility of viscosity in lower GIT:
- *depends on fermentability
- If highly fermentability: used up by gut microbiome
- If low fermentability: persists through transit of colon
o ‘normalize’ fecal consistency: water holding and gelling
What are some drawbacks with increasing viscosity amounts?
- Cause or exacerbate reflux
- Interfere with digestion
What is insoluble dietary fiber?
- Does NOT dissolve in water
- High molecular weight
- Non-viscous
- Very low fermentability in non-herbivores
- ‘bulking fiber’
o Laxation: increased fecal output
o Dilute calories: increased food volume
o +/- alter digestibility or absorption of nutrients - Ex. cellulose, hemicellulose, lignin
What is soluble dietary fiber?
- Dissolves in water
- High molecular weight
o Adds volume to food (less than insoluble)
o Absorbs water
o May or may not alter viscosity
o Variable fermentability - Ex. pectins, gums
- **all viscous fibers are soluble, but NOT all soluble fibers are viscous
What are oligosaccharides and why are they important?
- Soluble
- Low molecular weight
- *often fermentable or ‘prebiotic’
- Physiologic effect from relatively small doses
- **not included in most fiber quantifications
- Ex. inulin, FOS, dextrins
What are the roles of resistant starches in the upper and lower GIT tract?
- Upper: functions like insoluble DF (adds bulk)
- Lower: functions like soluble DF
o Most resistant starches are moderately to highly fermentable! - *most are not included in traditional measures/quantification of fiber
What is their main site of digestion/absorption?
- Small intestine
Cecum
- ‘hindgut’ fermenters
o Realtively large and retains digesta for long periods
o Major site of fermentation
Colon
- Main site of fermentation for non-herbivores
- Highly fermentable fibers quickly utilized by ileum and ascending colon
- Moderately to slowly fermentable fibers may reach descending colon
- *ileo-ceco-coli valve: prevents microbes and products form moving into SI
Monogastric herbivores: ‘hind gut fermentation’
- Relatively small stomach capacity
- Larger, complex ceca and colon
o Ferments more fibers completely - Foraging/grazing is important
o Prevent gastric ulcers and hunger
o Prevent dehydration
o Prevent torsions and colic
Cecotropes
- Cecal microbiota can synthesize essential nutrients NOT found in typical forage and are packed into cecotropes
o NEED to be re-ingested so nutrients can be absorbed in the SI (Vit B’s and K, protein and AA)
o If multiple left in environment=will have nutritional deficiencies OR something else is going on
What are the common fibres in pet foods?
- Cellulose: insoluble
- Beet pulp: mixed insoluble and soluble DF
- Psyllium husk
- Oligosaccharides and blends
- ‘hidden’ in whole food ingredients
Psyllium husk: clinically useful combination of properties
- Most soluble DF with some insoluble DF
- *Viscous and gel-forming at higher concentrations
- *SLOWLY fermentable
- Moderates fermentation of other fibers
o *Can shift fermentation towards distal colon=increased SCFAs - *helps normalize fecal quality
o Constipation=softens feces, promotes laxation
o Diarrhea=adds form and improves gut health
