Carbohydrates

SESSION 2: DIETARY FIBER

DR AZADEH NADJARZADEH

AZADEHNAJARZADEH@GMAIL.COM

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Adequate amounts of dietary fiber help to maintain health and reduce risks of colon cancer and coronary artery diseaseSources of dietary fiber in the food supply are:Grain productsVegetablesFruitsLegumes, nuts, and soy

Key MessagesKey Messages

Session Overview for InstructorSession Overview for Instructor

Fiber

Fiber is the structural part of plants and is found in vegetables, fruits, grains and legumes.

Most dietary fibers are polysaccharides, like starch, but they are not digestible.

The human body lacks the enzymes needed to digest and absorb fiber.

As a result fibers reach the lower intestine intact where intestinal bacteria can ferment some fiber.

Fiber

Fiber

Nonstarch polysaccharide fibers◦ Cellulose◦ Hemicellulose◦ Pectin◦ Gums◦ Mucilages

Nonpolysaccharide fiber◦ Lignins◦ Cutins◦ Tannins

Resistant Starches

Types of Fiber

There are many different types of fiber, in general fibers can be divided into two types based on their physical properties.

◦ Soluble fibers◦ Insoluble fibers

Soluble Fibers

Soluble fibers dissolve in water, form gels and are easily digested by bacteria in the lower intestine.

◦ Provides a feeling of fullness.◦ Slow down the rate food leaves the stomach.◦ May have a role with heart disease, diabetes and colon cancer

Found in legumes and fruits

Insoluble Fiber

Insoluble fibers absorb water and swell up resulting in a larger softer stool that is easier and quicker to pass.

◦ Provides a feeling of fullness◦ Helps with intestinal function◦ May help with colon cancer

Found in grains and vegetables

Fiber and Health

Both fiber types are important for health.

Fibers are beneficial for many conditions; constipation, diarrhea, diverticular disease, heart disease, diabetes and colon cancer.

Fiber is only one factor involved in these conditions.

Fiber and Health

Foods high fiber have many factors that may be factors in lowering disease risk.

◦ High fiber◦ Low in fat◦ High vitamins (antioxidants)◦ High in minerals◦ High in phytochemicals

Intestinal Function

Insoluble fibers absorb water resulting in a larger, softer stool that is faster and easier to eliminate, which can help with:

◦ Constipation◦ Hemorrhoids◦ Diverticular disease

Colon Cancer

Both insoluble and soluble fibers may protect against colon cancer◦ Insoluble fibers absorb water making a larger, softer stool which can:

◦ Dilute potential carcinogens◦ Reduce transit time so the colon is exposed to any cancer causing substance for less time.

◦ Soluble fibers can bind bile acids, potential carcinogens, and increase their excretion.

Heart Disease

As mentioned, soluble fibers can bind to bile acids and increase their excretion.

With fewer bile acids in the intestine, less fat is absorbed.

Also by increasing bile acid excretion, the liver must use its cholesterol to make new bile acids.

Diabetes

Soluble fibers may have a favorable effect on blood glucose.

Soluble fibers decrease the rate at which food is released from the stomach and delays glucose absorption into the blood.

This may help prevent wide swings in blood glucose throughout the day.

Weight Management

Foods rich in complex carbohydrates tend to be low in fat and added sugars which can help with weight management by providing fewer calories.

In addition, as fibers absorb water they swell up creating a feeling of fullness and delaying hunger.

How Much Fiber

The National Research Council set a Dietary Reference Intake (DRI) for dietary fiber.

An adequate Intake (AI) for dietary fiber was set at 14 grams dietary fiber per 1,000 calories.

◦ Thus for a reference 2,000 calorie diet recommended intake would be 28 grams per day.

Too Much Fiber

Dietary fiber can bind some minerals and decrease their absorption. However, if mineral intake is adequate a recommended dietary fiber intake will not compromise mineral balance.

Fiber intake is like all nutrients - “more” is not always “better.” Consuming a diet that provides a variety of nutrients is the key.

Food Sources of Fiber

Foods are the best source of fiber, get both soluble and insoluble fiber.

Food sources of fiber include fruits, vegetables, whole grain products, legumes, nuts and seeds.

Cooking processing and removing peels can lower fiber content.

Tips for Increasing Fiber

Increase fiber slowly. Increasing fiber too fast may cause bloating and gas.

Since some fiber absorbs water it also is important to drink plenty of fluids when increasing dietary fiber.

Tips for Increasing Fiber

Because fibers absorb liquids drink plenty of fluids when increasing fiber.

As with all nutrients, “more” is not “better.” Moderation is the key.

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Summary of Dietary Fiber Classes

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Other Sweeteners Nutritive sweeteners

◦ Sugar alcohols (sorbitol, mannitol, xylitol)

Nonnutritive sweeteners◦ Artificial sweeteners in food

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Sweetness of Sugars and Artificial Sweeteners

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Energy Function of Carbohydrates

Basic fuel supply◦ Energy for physical activities and all work of body cells

Reserve fuel supply◦ Provided by glycogen◦ Maintains normal blood glucose level

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Special Tissue Functions of Carbohydrates

Liver◦ Glycogen reserves protect cells from depressed metabolic function

Protein and fat◦ Carbohydrates regulate proteins and fat

(Cont'd…)

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Special Tissue Functions of Carbohydrates(…Cont’d)

Heart◦ Glycogen is vital emergency fuel for heart muscle

Central nervous system◦ Brain dependent on minute-to-minute supply of glucose

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Food Sources of Carbohydrates Starches

◦ Provide fundamental complex carbohydrates

Sugars◦ High-sugar diets carry health risks

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Carbohydrate Content of Foods

(Cont'd…)

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Carbohydrate Content of Foods(…Cont’d)

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Digestion of Carbohydrates Mouth

◦ Mechanical or muscle functions break food mass into smaller particles

Stomach◦ Peristalsis continues mechanical digestive process

(Cont'd…)

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Digestion of Carbohydrates(…Cont’d)

Small intestine◦ Peristalsis continues mechanical digestions◦ Pancreatic secretions◦ Intestinal secretions

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Summary of Carbohydrate Digestion

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Body Needs for Carbohydrates Dietary Reference Intakes

◦ 45%-65% of adult’s total caloric intake should come from carbohydrate foods◦ Limit sugar to no more than 25% of calories consumed

Dietary Guidelines for Americans◦ Does not outline specifics for caloric consumption or where kilocalories should come from

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Daily Recommendations of Dietary Fiber Daily Recommendations of Dietary Fiber Needed* by Age/GenderNeeded* by Age/Gender

Years Grams Years Grams Years Grams

*Recommendations, in grams, are based on *Recommendations, in grams, are based on Estimated Average Requirements (EARs).Estimated Average Requirements (EARs).

Children Males Females

1-3 19 9-13 31 9-18 26

4-8 25 14-50 38 19-50 25

51+ 30 51+ 21

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The Institute of Medicine of the National Academy of Sciences publishes the Dietary Reference Intakes (DRI) for dietary components, including macronutrients, vitamins, minerals, and fiber. The DRIs consist of the RDAs, EARs, AIs, and ULs.

Recommended values are provided for each life cycle group—from birth through childhood, sexual maturity, midlife, and old age.

Supplemental InformationSupplemental Information

Background Information on the Background Information on the Dietary Reference IntakesDietary Reference Intakes

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Recommended Dietary Allowance (RDA) The average daily intake level sufficient to meet the nutrient requirements of 97 to 98 percent of healthy individuals.

Nutrient Values Provided by theNutrient Values Provided by theDietary Reference IntakesDietary Reference Intakes

Tolerable Upper Level (UL)

The highest level of daily nutrient intake that is likely to pose no risks of adverse health effects to almost all individuals in the general population.

Supplemental InformationSupplemental Information

Dietary Reference Intakes, continuedDietary Reference Intakes, continued

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Supplemental InformationSupplemental Information

Dietary Reference Intakes, continuedDietary Reference Intakes, continued

Estimated Average Requirement (EAR) The nutrient intake value sufficient to meet the requirements of half the healthy individuals in a group. The Nutrient Content of the U.S. Food Supply Series uses this DRI for nutrient comparisons.

Adequate Intake (AI) The recommended daily intake based on approximations of nutrient intake by a group (or groups) of healthy people. It is used when the RDA cannot be determined.