Dietary fibre

Dietary fibre

Q. What is dietary fibre?

Dietary fibre or ‘roughage’ comprises the edible parts of plant that cannot be digested or absorbed in the small intestine and passes into the large intestine intact. This includes non-starch polysaccharides, oligosaccharides (e.g. inulin), lignin and associated plant substances (e.g. waxes).

The term dietary fibre also includes a type of starch known as resistant starch (found in pulses, partly-milled seeds and grains, some breakfast cereals) because it resists digestion in the small intestine and reaches unchanged the large intestine.

Official definition of dietary fibre differs a little among different institutions:

Organization (reference)	Definition
Institute of Medicine	Dietary fiber consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plants. Functional fiber consists of isolated, nondigestible carbohydrates that have beneficial physiologic effects in humans. Total fiber is the sum of dietary fiber and functional fiber.
American Association of Cereal Chemists	Dietary fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine, with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin, and associated plant substances. Dietary fibers promote beneficial physiologic effects including laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation.
Codex Alimentarius Commission	Dietary fiber means carbohydrate polymers with ≥10 monomeric units, which are not hydrolyzed by the endogenous enzymes in the small intestine of humans.

Q. Write the Classification of Dietary fibre?

Dietary fibres are parts of plant foods that your body can’t digest. There are two types of fibre—

1.     Soluble fibre:-Soluble fibre dissolves in water to become gummy or viscous, promotes the excretion of fatty substances such as cholesterol and helps to regulate the body’s use of sugars.

Features of water-soluble fiber

Viscosity	Adsorptive property	Fermentability
Diet with water-soluble fiber transits slowly through the stomach and intestines because of its viscosity, reducing hunger and helping prevent overeating. It suppresses spikes in blood sugar after eating by slowing the absorption of sugar.	Water-soluble fiber adsorbs bile acid and cholesterol, aiding their excretion outside the body.	When water-soluble fiber ferments and decomposes in the large intestine, bifidobacteria and other good bacterium increase, improving the intestinal environment, which has an intestinal healing effect.

Soluble fibre is found in varying quantities in all plant foods, including:

·         legumes (peas, soybeans, lupins and other beans)

·         oats, rye, chia, and barley

·         some fruits (including figs, avocados, plums, prunes, berries, ripe bananas, and the skin of apples, quinces and pears)

·         certain vegetables such as broccoli, carrots, and Jerusalem artichokes

·         root tubers and root vegetables such as sweet potatoes and onions (skins of these are sources of insoluble fiber also)

·         psyllium seed husks (a mucilage soluble fiber) and flax seeds

·         nuts, with almonds being the highest in dietary fiber.

 Insoluble fibre:-Insoluble fibre  does not dissolve in water, but adds bulk and softness to stools. Thus, insoluble fibre promotes bowel regularity.

Features of water-insoluble fibre

High water retention	Fibrous, honeycombed, and spongy	Fermentability
Water-insoluble fiber swells up as it absorbs water in the stomach and intestines, stimulating the intestine, activating peristalsis, and promoting bowl movement.	Water-insoluble fiber is chewed well when eaten, helping prevent overeating, strengthening the jaw, and improving teeth alignment.	When water-insoluble fiber ferments and decomposes in the large intestine, bifidobacteria and other gut flora increase, improving the intestinal environment, which has an intestinal regulation effect. (Generally, water-insoluble fiber is less fermentable than water-soluble fiber.)

Sources of insoluble fibre include:

·         whole grain foods

·         wheat and corn bran

·         legumes such as beans and peas

·         nuts and seeds

·         potato skins

·         lignans

·         vegetables such as green beans, cauliflower, zucchini (courgette), celery, and nopal

·         some fruits including avocado, and unripe bananas

·         the skins of some fruits, including kiwifruit, grapes and tomatoes^.

Q.Write the property of dietary fibre.

Physicochemical properties

Dietary fiber has distinct physicochemical properties. Most semi-solid foods, fiber and fat are a combination of gel matrices which are hydrated or collapsed with microstructural elements, globules, solutions or encapsulating walls. Fresh fruit and vegetables are cellular materials.

·         The cells of cooked potatoes and legumes are gels filled with gelatinized starch granules. The cellular structures of fruits and vegetables are foams with a closed cell geometry filled with a gel, surrounded by cell walls which are composites with an amorphous matrix strengthened by complex carbohydrate fibers.

·         Particle size and interfacial interactions with adjacent matrices affect the mechanical properties of food composites.

·         Food polymers may be soluble in and/or plasticized by water. Water is the most important plasticizer, particularly in biological systems thereby changing mechanical properties.

·         The variables include chemical structure, polymer concentration, molecular weight, degree of chain branching, the extent of ionization (for electrolytes), solution pH, ionic strength and temperature.

·         Cross-linking of different polymers, protein and polysaccharides, either through chemical covalent bonds or cross-links through molecular entanglement or hydrogen or ionic bond cross-linking.

Cooking and chewing food alters these physicochemical properties and hence absorption and movement through the stomach and along the intestine

Physiological Properties:

1.     Decrease intestinal transit time

2.     Increase stool bulk

3.     Fermentable by colonic microflora

4.     Reduce blood total cholesterol

5.     Reduce blood LDL cholesterol

6.     Reduce post prandial blood glucose

7.     Reduce blood insulin levels.

Q. Writes the physiological effects of Dietary fibre.

The main physiological effects attributed to dietary fibre concern:

• Bowel function
Dietary fibre, particularly insoluble fibre, helps prevent constipation by increasing stool weight and decreasing gut transit time. This effect is enhanced if fibre intake is paralleled by an increase in water intake.
The short chain fatty acids, produced when fibre is fermented by gut bacteria, are an important source of energy for colon cells and might inhibit growth and proliferation of gut tumour cells.
By improving bowel function, dietary fibre can reduce the risk of diseases and disorders such as diverticular disease or haemorrhoids, and may also have a protective effect on colon cancer.

• Blood glucose levels
Soluble fibre, may slow digestion and absorption of carbohydrates and hence lower the rise in blood glucose that follows a meal (postprandial) and insulin response. This can help people with diabetes improve control their blood glucose levels.

• Blood cholesterol
Results of epidemiological studies identify another role for dietary fibre in the prevention of coronary heart disease (CHD) that of improving blood lipid profiles. Clinical trials confirm the results of these epidemiological studies. Isolated viscous fibres such as pectin, rice bran or oat bran lower both total serum cholesterol and low density lipoprotein (LDL or bad) cholesterol levels. At the same time, research continues to show that diets high in a mix of dietary fibre also protect against CHD.

• Other
While prevention of constipation, improved blood glucose levels, and blood lipid profiles predominate as beneficial outcomes of a diet high in dietary fibre, other benefits are worth noting. For example, because fibre provides bulk in the diet, without added calories, it can have a satiating effect on appetite; helping in weight management.

Q. Write the health benefit of different types of dietary fibre.

Types of Fiber	Soluble or Insoluble	Sources	Health Benefits
Cellulose, some hemicellulose	Insoluble	Naturally found in nuts, whole wheat, whole grains, bran, seeds, edible brown rice, skins of produce.	"Nature's laxative": Reduces constipation,lowers risk of diverticulitis, can help with weight loss.
Inulin oligofructose	Soluble	Extracted from onions and byproducts of sugar production from beets or chicory root. Added to processed foods to boost fiber.	May increase "good" bacteria in the gut and enhance immune function.
Lignin	Insoluble	Found naturally in flax, rye, some vegetables.	Good for heart health and possibly immune function. Use caution if you have celiac disease or are gluten intolerant.
Mucilage, beta-glucans	Soluble	Naturally found in oats, oat bran, beans, peas, barley, flaxseed, berries, soybeans, bananas, oranges, apples, carrots.	Helps lower bad LDL cholesterol, reduces risk of coronary heart disease and type 2 diabetes. Use caution if you have celiac disease or are gluten intolerant.
Pectin and gums	Soluble (some pectins can be insoluble)	Naturally found in fruits, berries, and seeds. Also extracted from citrus peel and other plants boost fiber in processed foods.	Slows the passage of food through the intestinal GI tract, helps lower blood cholesterol.
Polydextrosepolyols	Soluble	Added to processed foods as a bulking agent and sugar substitute. Made from dextrose, sorbitol, and citric acid.	Adds bulk to stools, helps prevent constipation. May cause bloating or gas.
Psyllium	Soluble	Extracted from rushed seeds or husks of plantagoovata plant. Used in supplements, fiber drinks, and added to foods.	Helps lower cholesterol and prevent constipation.
Resistant starch	Soluble	Starch in plant cell walls naturally found in unripened bananas, oatmeal, and legumes. Also extracted and added to processed foods to boost fiber.	May help manage weight by increasing fullness; helps control blood sugars.
Wheat dextrin	Soluble	Extracted from wheat starch, and widely used to add fiber in processed foods.	Helps lower cholesterol (LDL and total cholesterol), reduces risks of coronary heart disease and type 2 diabetes. Avoid if you have celiac disease or are gluten intolerant.

Fiber contents in some food

Dietary fibers are found in fruits, vegetables and whole grains. The exact amount of fiber contained in the food can be seen in the following table of expected fiber in USDA food groups/subgroups

Food group	Serving Mean	fiber g/serving
Fruit	0.5 cup	1.1
Dark-green vegetables	0.5 cup	6.4
Orange vegetables	0.5 cup	2.1
Cooked dry beans (legumes)	0.5 cup	8.0
Starchy vegetables	0.5 cup	1.7
Other vegetables	0.5 cup	1.1
Whole grains	28 g (1 oz)	2.4
Meat	28 g (1 oz)	0.1