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Dietary Fibre

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Eat more fiber. You've probably heard it before. So what is dietary fiber and how does it benefit you? Also called bulk or roughage, dietary fiber is a substance in plants. It is in fruits, vegetables and grains. It is the part of the plant that your body can't digest. Yet it is an important part of a healthy diet. It adds bulk to your diet and makes you feel full faster, helping you control your weight. Fiber helps in digestion and prevents constipation.

Contents

[edit] Composition

A common misconception about fiber is that it is not digested by enzymes in the body and therefore provides no calories or nutrients. But the category “fiber” includes chemicals that are not fibrous, materials that can be dissolved, and some substances that can be digested partially. We eat quite a complex mixture of fibers. Dietary fiber is a broad generic term and includes following chemicals, which form the structural components of plants, including many of the plant foods we eat :

  • cellulose
  • hemicellulose
  • lignin
  • pectin
  • mucilage
  • gums

The above are classified into two categories: first three are insoluble fiber that don't dissolve in water, but absorb and hold water in the digestive system. Others are soluble fibers which are partially broken down in digestion to a gel like substance which also retains water.

Insoluble Fiber: This type of fiber increases the movement of material through your digestive system and increases stool bulk. It can be of benefit in conditions of constipation or irregular stools. Whole-wheat flour, wheat bran, nuts and many vegetables are good sources of insoluble fiber.

Soluble Fiber: This type of fiber dissolves in water to form a gel-like material. It can help lower blood cholesterol and glucose levels. It also slows digestion and nutrient absorption from the stomach and intestine. Soluble fiber is found in good quantities in oats, peas, beans, apples, citrus fruits, carrots and barley.

Many commonly used plant sources of fiber contain both soluble and insoluble fibers. Psyllium husks, for example, contain a mixture of 70% soluble and 30% insoluble fibers. Until very recently, the functions of a specific type of fiber were determined by whether or not the fiber was classified as soluble or insoluble. Despite the widespread use of the terms "soluble" and "insoluble" to describe the health benefits of dietary fiber, many medical and nutrition experts contend that these terms do not adequately describe the physiological effects of all the different types of fiber. These experts are now proposing the use of the terms "viscous" and "fermentability" in place of soluble and insoluble to describe the functions and health benefits of dietary fiber.

[edit] Health Benefits

People earlier used fiber for the normal clearing of bowel. Later in 1970s the role of dietary fibers started getting importance in the daily diet when reports by some British clinician showed that there is a relationship between these fibers and many diseases. People with high intake of these fibers showed low incidence of diverticular disease (small pouches in the colon), irritable colon, haemorrhoids, cancer of colon (mixed evidence), obesity, coronary heart disease, diabetes mellitus and gall stones.

Reducing Cholesterol Levels

Soluble fibers lower serum cholesterol by reducing the absorption of dietary cholesterol. In addition, these also complex with bile acids, which are compounds manufactured by the liver from cholesterol that are necessary for the proper digestion of fat. After complexing with bile acids, the compounds are removed from circulation and do not make it back to the liver. As a result, the liver must use additional cholesterol to manufacture new bile acids. Bile acids are necessary for normal digestion of fat. Soluble fiber may also reduce the amount of cholesterol manufactured by the liver. Oats and guar gum are found in lowering blood cholesterol.

Normalizing Blood Sugar Levels

Fibers also help normalize blood glucose levels by slowing the rate at which food leaves the stomach and by delaying the absorption of glucose following a meal. These also increase insulin sensitivity. As a result, high intake of fibers plays a role in the prevention and treatment of type 2 diabetes. In addition, by slowing the rate at which food leaves the stomach, fibers promote a sense of satiety, or fullness, after a meal, which helps to prevent overeating and weight gain.

Promoting Bowel Regularity

Certain types of fiber are referred to as fermentable fibers because they are fermented by the "friendly" bacteria that live in the large intestine. The fermentation of dietary fiber in the large intestine produces a short-chain fatty acid called butyric acid, which serves as the primary fuel for the cells of the large intestine and helps maintain the health and integrity of the colon.

Beneficial in Constipation

Dietary fiber increases the weight and size of your stool and softens it. A bulky stool is easier to pass, decreasing your chance of constipation. If you have loose, watery stools, fiber may also help to solidify the stool because it absorbs water and adds bulk to stool.

Weight Loss

Eating a high-fiber diet may also help with weight loss as it tends to make a meal feel larger and linger longer. As a result, you stay full for a greater amount of time. High-fiber diets tend to be less "energy dense," which means they have fewer calories for the same volume of food.

[edit] Recommended Intake

In its most recent 2005 public health recommendations for fiber (published as the Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients), National Academies Press, 2005), the National Academy of Sciences established an Adequate Intake (AI) level of 38 grams of total daily fiber for males 19-50 years of age and 25 grams for women in this same age range. Children aged 3-18 years need less fiber than adults.

[edit] Toxicity

Intestinal obstruction: Intake of dietary fiber in excess of 50 grams per day may cause an intestinal obstruction in susceptible individuals. In most individuals, however, this amount of fiber will improve (rather than compromise) bowel health.

Dehydration: Excessive intake of fiber can also cause a fluid imbalance, leading to dehydration. Individuals who decide to suddenly double or triple their fiber intake are often advised to double or triple their water intake for this reason.

Mineral deficiencies: In addition, excessive intake of non fermentable fiber, typically in supplemental form, may lead to mineral deficiencies. This takes place by reducing the absorption of minerals such as iron, zinc, magnesium, and calcium. However, this effect usually does not cause too much concern because high-fiber foods are typically rich in minerals.

Gas, distention and /or diarrhoea: Eating a large amount of fiber in a short period of time can cause intestinal gas, bloating and abdominal cramps. This usually goes away once the natural bacteria in the digestive system get used to the increase in fiber in the diet. Adding fiber gradually to the diet helps in reducing gas and diarrhoea.

[edit] High Fiber Intake

The following suggestions can help include more fiber in your diet:

  • Substituting whole cereal grain for refined foods. For example, whole grain breads. These breads list whole wheat, whole-wheat flour or another whole grain as the first ingredient on the label.
  • Eat more beans, peas and lentils. Add kidney beans to a green salad.
  • Eat fruit at every meal. Apples, bananas, oranges, pears and berries are good sources of fiber.
  • Fresh and dried fruit, raw vegetables, and low-fat popcorn and whole-grain crackers are all good choices for snacks.
  • Bran can be added to daily diet. This addition should be gradual. 1-2 tablespoon can be mixed to the flour while making chapatti.

[edit] References

  • Dietary Fiber
  • fiber, dietary
  • Benefits of Dietary Fiber