FNH 350: Fiber - Definition, Properties, Physiological Effects, and Chronic Diseases

What is fiber?

the non-digestible portion of planers

what are novel fibers?

fibers manufactured in labs as food additives

what is the difference between dietary fiber and functional fiber?

→ Dietary fibers are non-digestible CHOs and lignin that’re naturally present in intact plants

→ Functional fibers are isolated, non-digestible CHOs that provide health benefits

what are the main components of plant cell walls?

1. cellulose

2. hemicellulose

3. lignin

4. pectin (found between and around cell walls)

what are the functions of lignin and pectin?

lignin provides structural support in specialized plant cells and pectin acts like an intercellular cement that holds plant cells together

what is the composition of dietary fiber influenced by?

1. plant species

2. part of the plant (leaf, root, stem)

3. plant’s maturity

what fibers are abundant in cereals and wheat bran?

1. hemicellulose

2. lignin

3. cellulose

what fibers are abundant in fruits and vegetables?

1. cellulose

2. pectin

How can functional fiber be consumed or used?

Functional fiber can be taken as a supplement, such as a tablet or powder, or added to foods as a food additive

what are the different classes of fiber?

1. cellulose

2. hemicellulose

3. pectin

4. lignin

5. gums

6. beta-glucans

7. resistant starch

8. fructans

9. chitan and chitosan

10. psyllium (mucilages)

what is the structure of cellulose?

glucose units linked through beta 1-4 glycosidic bond

cellulose are ___ and ___ fiber

dietary and functional

what fiber is the main component of plant cell walls?

cellulose

what are the solubility and fermentability of cellulose?

→ Water insoluble

→ poorly fermented by colonic bacteria

what are some examples of food sources rich in cellulose?

1. bran

2. legumes

3. nuts

4. peas

5. root veggies

6. cabbage family

7. skin of seeds and apples

8. whole grains

9. carrots

what is the structure of hemicellulose?

Hemicellulose is composed of 2 components: the backbone, with smaller chains of sugars (side chains) attached to it. The types of sugars in the side chains influence its properties. The units are linked through beta 1-4, alpha 1-2, and alpha 1-3 glycosidic bonds

what are the solubility and fermentability of hemicellulose?

→ Can be both water soluble or water insoluble

→ Fermentability varies depending on the side chains

what are some dietary sources of hemicellulose?

1. bran

2. whole gains

3. nuts

4. legumes

5. some fruits and vegetables

what is the structure of pectin?

pectin has a backbone of galacturonic acid linked by alpha 1-4 glycosidic bonds

pectin is a ___ and ___ fiber

dietary and functional

what are the main properties of pectin?

1. water soluble

2. ion-binding potential

3. gel-forming

4. completely metabolized by bacteria

what are some dietary sources of pectin?

strawberries, carrots, citrus fruits, apples

what is the structure of lignin?

polymer of phenol units

what is the function of lignin?

structural component of plants

lignin is a ___ and ___ fiber

dietary and functional

what are the solubility and fermentability of lignin?

lignin is water-insoluble and poorly fermented

what are some dietary sources of lignin?

carrots, whole grains, wheat bran, strawberries

what can lignin be metabolized into?

can be metabolized by intestinal bacteria into enterolactone (phytoestrogen). Phytoestrogen has a lot of health benefits

what is the structure of gums?

galactose units with beta 1-4 and beta 1-6 glycosidic linkages

where do gums come from?

secreted at plant injury sites

what are the water solubility and fermentability of gums?

→ water soluble

→ highly fermented by bacteria

what can gums be used as?

gelling, thickening agent

what is the structure of beta-glucan?

consists of glucose units linked by beta 1-3 and beta 1-4 linkages

what are the water solubility and fermentability of beta-glucans?

→ water-soluble

→ highly fermentable

what are the health effects of beta-glucans?

they can help reduce serum cholesterol and post-meal blood glucose

what do beta-glucans form?

viscous gels within GI tract

what are the main dietary sources of beta-glucans?

barley, oat

what is resistant starch?

starch which cannot be easily enzymatically digested and absorbed by humans

what are the types of resistant starches? dietary or functional?

1. RS1- dietary

2. RS2 - dietary

3. RS3 - functional

4. RS4 - functional

what are sources of RS1?

starch that is physically inaccessible to digested enzymes, found in whole or partially milled grains and seeds

what are sources of RS2?

starch granules that resist digestion, found in foods like potatoes, unripe (green) banana, maize, some legumes (tight packaging)

where does RS3 come from?

cooked/cooled starchy foods (gelatinized starch, potatoes, rice, etc)

what are the potential benefits of RS3?

RS3 can allow growth of beneficial bacteria and improve glycemic response

where does RS4 come from?

chemical modification of starch

what is the fermentability of RS3 and RS4?

partially fermentable by gut bacteria

what is the structure of fructans?

fructose units

what are examples of fructans?

inulin, oligofructose, fructooligosaccharides

what are fructans considered?

they’re considered prebiotic as they’re used as fuel to promote growth of beneficial gut bacteria, including bifidobacteria (by doing this, they also take up space within the gut that could have been taken up by other potentially less beneficial bacteria)

what are some dietary sources of fructans?

artichokes, asparagus, bananas

are chitan and chitosan soluble or insoluble? dietary or functional?

insoluble and could be functional fiber

what do chitan and chitosan do?

bind dietary lipids in the stomach, including unesterified cholesterol and phospholipids promoting their excretion in feces.

what are the potential health effects of chitan and chitosan?

have been observed to reduce serum cholesterol and triglycerides. Additionally, may have some immune-enhancing functions; may reduce adverse side effects of cancer drugs

what are some dietary sources of chitan and chitosan?

seafood crustaceans like shrimp and lobster

what are the main properties of psyllium (mucilages)?

functional fiber, binds water and adds viscosity/thickening

what is the structure of psyllium similar to?

the structure of gums

what are the physiological effects of psyllium?

promotes bowel regularity through its laxative effects and can help reduce serum lipids

why does psyllium have to be taken with sufficient liquid?

bc it absorbs water and expands, therefore insufficient liquid increases the risk of choking or obstruction

what are the major physiological effects of fiber?

1. some fibers form a gel which delays the passage of chyme through the GI tract and lowers the accessibility of our enzymes to the CHOs, calories, and energy that is retained in the food that we just consumed; they delay and lower nutrient absorption as well as allowing us to feel full more quickly (earlier satiation)

2. some fibers speed up digestion and reduce absorption time (goes through GI tract quicker so enzymes have less time to act on the CHOs)

what properties of fibers affect physiological and metabolic effects?

1. solubility in water

2. water-holding capacity and viscosity

3. adsorption or binding ability

4. degradability or fermentability (by intestinal bacteria)

what are the physiological effects of soluble fiber?

Soluble fiber can form gels, delay gastric emptying, slow the movement of food through the GI tract, increase fullness, and decrease or delay nutrient absorption, including glucose absorption

what are the physiological and metabolic effects of insoluble fiber?

insoluble fiber increases fecal bulk and speeds up movement through the GI tract, reducing transit time. It can also decrease nutrient absorption

what is water-holding capacity and viscosity?

it is the ability of fiber to bind water as it moves through the GI tract. It describes how much the fiber is able to act as a sponge

what can water holding capacity be impacted by?

1. pH of GI tract/bolus/chyme

2. size of particles

3. level of food processing

what are the effects of water holding capacity?

1. Delayed gastric emptying

2. Reduced mixing of chyme with digestive enzymes

3. reduced enzyme function

4. decreased nutrient diffusion

5. transit time delayed

How does the water-holding capacity of fiber affect gastric emptying and satiety?

Fibers with high water-holding capacity can form gels that delay gastric emptying, slowing the movement of food from the stomach into the small intestine. This can slow digestion and help a person feel full for longer

how does certain water holding capacity reduce mixing of chyme with digestion enzymes?

gel act as a physical barrier preventing digestive enzymes from accessing the food

how does certain water holding capacity reduce enzyme function?

high water-holding capacity causes gels to form in the stomach. Digestive enzymes (e.g., peptidases, lipases) may be functionally depressed by gel forming fibers.

how does certain water holding capacity decrease nutrient diffusion and absorption?

1. increase thickness of water layer on surface of enterocytes causing for less movement of nutrients into enterocytes

2. decreased peristaltic movements (convective movements) therefore less nutrients brought from lumen to epithelial surface

3. decreased absorption of amino acids and fatty acids

4. decreased glucose absorption, decreased blood glucose (benefit for diabetic patients)

what is the adsorption or binding ability of fiber?

it is the ability of fiber to bind to organic and inorganic substances in the GI tract, including FAs, cholesterol, bile acids, nutrients, and enzymes

adsorption/binding ability of certain fibers result in:

1. diminished absorption of lipids

2. increased fecal bile excretion

3. lowered serum cholesterol concentrations

4. altered mineral, carotenoid, and phytochemical absorption

Which fibers diminish the absorption of lipids?

Pectin, gums, β-glucans, some hemicellulose, lignin, chitosan

how can fiber reduce lipid absorption?

fiber adsorbs and interact with FAs, cholesterol, and bile acids, preventing formation of micelles which are needed to transport lipids to intestinal cells for absorption. These can increase the amount of fat components excreted in feces

how can adsorption or binding ability of fiber increase fecal bile excretion?

fiber adsorbs bile acids preventing recirculation and use in the formation of micelles. This results in more bile acids degraded (by bacteria) and excreted

which fibers increase fecal bile excretion?

soluble fibers (especially pectin, gums, β - glucans, and some hemicellulose); lignin, chitosan

what fibers help lower serum cholesterol concentration?

Psyllium, gums, β - glucans, pectin

how can adsorption/binding ability of fiber lower serum cholesterol concentrations?

1. Increase bile/cholesterol excretion: decreases [cholesterol] in liver, leads to more LDL removed from blood to make new bile

2. Bile composition changes: liver pulls LDL from blood for new bile production, which inhibits enzyme required for cholesterol synthesis

3. Production of short chain fatty acids: inhibit cholesterol and fatty acid synthesis

how can fiber affect mineral, carotenoid, and phytochemical absorption?

fiber can either enhance or inhibit mineral absorption depending on the degree of fermentability which results in fluctuation in the absorption of minerals, carotenoids, and phytochemicals. Slowly fermented fiber may reduce mineral absorption because growing microbial cells take up minerals. Highly fermented fiber produces short-chain FAs, lowers colonic pH, and increases mineral solubility and absorption

which fibers are non-fermentable?

cellulose and lignin (some hemicellulose)

which fibers are highly fermentable?

fructans, pectin, gums, psyllium, resistant starch, beta-glucans (some hemicellulose and cellulose (slow))

what are the beneficial effects of non-fermentable fibers?

1. detoxification

2. increased fecal volume

how do non-fermentable fibers help with detoxification?

help with increased microbial scavenging of toxins thus increased excretion of toxins. Also, potential inhibition of proliferation of tumour cells and enzymes that convert pro-carcinogens to active carcinogens

how do non-fermentable fibers help with feces?

increased fecal volume, more frequent defecation (laxative), reduced transit time, decreased intraluminal pressure

what are the most effective fiber laxatives (food)?

wheat bran and rice bran

where does fiber fermentation occur?

in the colon, initiated by bacteria

what are the products of fiber fermentation?

1. gases: H2, CO2, methane (CH4)

2. SCFAs: acetic acid, propionic acid, butyric acid

what is the function of acetic acid?

can be used or ATP formation in most tissues

what is the function of propionic acid?

liver converts it to glucose

what is the function of butyric acid?

source of energy for colon cells

what’re the beneficial effects of highly fermentable fibers?

1. generation of SCFAs

2. prebiotic activity

What are the physiological benefits of short-chain fatty acids (SCFAs)?

1. increased water and sodium absorption in the colon

2. mucosal cell differentiation and proliferation

3. provision of energy: SCFAs can provide a source of energy for various body tissues

4. acidification of luminal environment in the colon

what is the effect of acidification of luminal environment in colon?

decreased pH which can result in less soluble bile and less bile conversion. Also, increased calcium binding of bile and fatty acids which can be protective in colon cancer (bile and fatty acids cause chronic inflammation in the colon epithelium which can progress to cancer)

what is the prebiotic effect of fermentable fiber?

they resist digestion in the small intestine and reach the colon, where they are fermented by beneficial gut microflora. This helps promote the growth of beneficial bacterial species such as Lactobacilli and Bifidobacterium while decreasing bad ones like Clostridium and Salmonella. Additionally, may be useful in several diseases (e.g., protective against colon cancer).

what are examples of fermentable fibers with prebiotic effects?

oligosaccharides found in beans and legumes (Raffinose, Stachyose, Verbascose)

what are prebiotics?

prebiotics provide fuel for beneficial gut bacteria rather than delivering live bacteria to the GI tract

what are probiotics and what is an important characteristic of probiotic bacteria?

probiotics are live bacteria (usually and mostly lactobacillus casei). An important characteristic is that the bacteria reach the intestine intact and are not digested.

how can probiotics be consumed?

can be consumed as supplements or in food (for example, yogurt)

what diseases can fiber help prevent/manage?

1. Diabetes mellitus

2. Heart disease

3. Obesity

4. GI disorders

5. Colon cancer

how can fiber help with diabetes mellitus?

fiber can cause hypoglycemic effect as it can lower blood glucose lvls by decreasing absorption in the intestine

how can fiber help prevent heart disease?

certain fibers lower blood lipids and cholesterol, particularly serum cholesterol, which can help reduce cardiovascular disease risk

how can fiber help with obesity?

fiber can increase satiety as high viscosity fibers can delay gastric emptying and prolong feeling of fullness, thus reduce caloric intake. Additionally, fiber can reduce absorption of macronutrients as gel-forming fibers limit enzymes’ access to carbs