Dietary fibre

• Cellulose


  Most common organic polymer. Large polysaccharide composed of a linear chain of many β-1,4 linked d-glucose units
• Lignin


  A crosslinked polymer mainly comprised of three constituent monomers arranged in a hyperbranched topology with no regular repeating structure
• CODEX Alimentarius


  International body that sets guidelines for national regulatory authorities, founded in 1963 as part of the WHO/FAO
• CODEX Alimentarius reached consensus upon a definition of dietary fibre after almost 20 years of deliberation


  2009
• Dietary fibre


  Polysaccharide polymers more than 10 units that are not hydrolysed in the small intestine
• Edible carbohydrate polymers


  Naturally occurring in the food consumed
• Carbohydrate polymers


  Obtained from food raw material by physical, enzymatic or chemical means and which have been shown to have a physiological benefit to health, as demonstrated by generally accepted scientific evidence to competent authorities
• Synthetic carbohydrate polymers


  Have been shown to have a physiological benefit to health, as demonstrated by generally accepted scientific evidence to competent authorities
• Dietary fibre


  • Carbohydrate polymers with 10 or more monomeric units
  • Not hydrolysed by the endogenous enzymes in the small intestine of humans
• -         A clear and transparent definition is needed to guide international harmonisation for food labelling and food composition tables.
• Types of dietary fibre

  New/emerging dietary fibres: hydrocolloids, by-products

  Traditional cereals, fruits, and vegetables:

  • INSOLUBLE: celluloses, hemicelluloses, ligins
  • SOLUBLE (high molecular weight): gums, pectins
  • Included in AOAC method: resistant starches, dextrins
  • SOLUBLE: beta-glucans, psyllium, pentoses
  • LOW MOLECULAR WEIGHT, PREBIOTICS: inulins, fructo-, galacto-oligosaccharides.
• Non-starch polysaccharides (NSP)


  Insoluble DF and soluble DF compounds (apart from lignin) are known collectively as non-starch polysaccharides.
• Sources of various types of fibre:

  A) Cellulose

  B) Hemi-cellulose

  C) Lignin

  D) Gum, mucilages

  E) Pectins

  F) B-glucans

  G) resistant starch

  H) Cereal grains

  I) endosperm

  J) fruit and veg

  K) oats and barley

  L) legumes, unripe bananas

  M) potato

  N) most plants

  
• FOOD SOURCES OF Dietary fibre

  -        Grains –cellulose, hemicellulose, Arabinoxylans, 

  -        Fruit & veg –cellulose, hemicellulose, pectin

  -        Legumes –hemicellulose, pectin, resistant starch 1

  -        Potatoes – resistant starch
• Where does AOAC fibre come from?

  Meat: 9.6%

  Fruit: 10.6%

  Cereals: 41.7%

  Vegetables and potatoes: 26.7%

  Other: 11.4%
• Recommended dietary fibre intake: AOAC 30g/day, Englyst (NSP) approx.. 24g/day (excl lignin)
• DF CONTENT PER 100g

  A) 2

  B) 1.9

  C) 3.1

  D) 4.2

  E) 2

  F) 2

  G) 4.5

  H) 7.4

  
• History of fibre


  •       High meat & high vegetable/fruit fibre (>100g/day) in hunter gatherer times

  change in fibre source from F&V to cereal – shift from more soluble types of fibre to insoluble types
• Stone Age Hunter-Gatherers (HG)

  Humanity's genes were selected when ancestors lived as HGs, consuming heavily fibrous, uncultivated fruits and vegetables with a low glycemic index
• Modern optimal nutrition should mimic the diet of early humans from around 50,000 years ago
• Paleo diets


  Excluded wheat, rice, and corn, only fibre from F&V, which were low glycaemic index
• Despite agricultural and industrial advances, there have been few genetic changes since the Stone Age
• Interest in dietary fibre

  Emerged in the 1970s, which was previously seen only as roughage or waste
• T. L. Cleave: 'Linked increased intake of refined sugar and starch to diseases (1974), indirectly suggesting high refined sugar + start diets = low-fiber diets'
• Trowell (1971): 'Defined dietary fibre as plant cell material resistant to digestion by the gastrointestinal enzymes, a definition that became accepted and helped clarify fibre's role in diet'
• Early methods for measuring fibre

  Measured "crude" fibre, missing significant components like cellulose and hemicellulose
• Current definition of dietary fibre

  Nonstarch polysaccharide material
• Difficulties distinguishing fibre's direct protective effects from its displacement of harmful foods
• Studies on fibre's role in cholesterol absorption, increased bile acid excretion, and heart disease have mixed results
• Many of these studies were on fruit and veg intake, not fibre, vegetarian lifestyle was found to correlate with reduced heart disease, but not fibre
• Fibre influences intestinal flora, potentially affecting the metabolism and formation of various compounds, including oestrogens, impacting diseases like breast cancer
• Primitive humans likely consumed much higher fibre levels (100-200 grams/day) than modern populations
• Significant changes in fibre intake occurred during key developmental periods like the "Neolithic transition"
• where is fibre digested?

  Mouth, stomach, small intestine, colon
• Potential beneficial mechanisms of fibre?

  Increased stool bulk:

  • Decreased transit time
  • Dilute carcinogens

  Binds with bile acids etc:

  • Excrete potential carcinogens

  Reduce cholesterol:

  • Reduced absorption
  • Fermentation by fecal flora to short chain fatty acids (SCFA).

  Slow glucose absorption, improve insulin sensitivity:

  • Form diffusion barrier due to increased viscosity
  • Inhibit amylase and absorption of sugars

  Increase satiety:

  • Soluble types

  Affect estrogen metabolism:

  • Inhibit reabsorption
  • Inhibits synthesis.

  Lower blood pressure, promote weight loss, anti-inflammatory
• Higher levels of fermentable fibre in the gut are associated with improved insulin sensitivity (b glucans)

  Higher wholegrain may reduce inflammatory markers such as C Reactive protein (and increase in anti-inflammatory factors).
• Short Chain Fatty Acids (SCFA) are produced as a result of the microbial fermentation of dietary fibre. These seem to be key mediators of the beneficial effects seen in the gut microbiome.
• SCFA directly modulate health through a range of tissue-specific mechanisms related to gut barrier function, glucose homeostasis, immunomodulation, appetite regulation and obesity. 
• Modifications in gut microbiota composition as a result of digesting fibre may also have an impact on risk of certain cancers such as cancer of the colon.
• -        Fibre intake was associated with gut microbiota composition but not diversity in generally healthy adults. 

  -        Fibre from specific food sources may yield differential effects on gut microbiota. 

  -        In this analysis, greater fibre intake, particularly from beans, was associated with greater abundance of beneficial bacteria (e.g. F. prausnitzii, which has demonstrated anti-inflammatory activity) and has potential to reduce cancer of the colon risk.