Carbohydrates

Dr Shatha Hammad

Introduction

Carbohydrates

Main function is???

Preferred energy source for many of the body’s functions

As long as carbohydrate is available, used exclusively by

brain as an energy source

Should not be avoided when trying to lose weight

Portion size and balance of nutrients is important

Dietary carbohydrate

Dietary carbohydrate

Simple sugar

Monosaccharides Disaccharides

Complex

Starch Fiber

Where is it found???

Types of dietary carbohydrate

1) Sugar:

1. Monosaccharides: single sugars

Glucose also called blood sugar or dextrose

Fructose (also known as fruit sugar)

Galactose

2. Disaccharides: double sugars

Sucrose: glucose and fructose (table, or white, sugar)

Lactose: glucose and galactose (also known as milk sugar)

Maltose: two glucose units

Disaccharides

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Types of dietary carbohydrate

Most cells depend on glucose for their fuel to some extent

How about the brain and nervous system??

Fructose is the sweetest of the sugars, occurs naturally in fruits, in

honey, and as part of table sugar

Many people lose the ability to digest lactose after infancy. This

condition, known as lactose intolerance?

How about human infants???

Simple carbohydrate

Enzymes in the digestive tract

will give…??

Types of dietary carbohydrate

2) Starch and fiber are:

Polysaccharides: chains of monosaccharides, mainly glucose

for fiber and only glucose for starch

Starch: a plant polysaccharide consisted of hundreds of

glucose molecules in either occasionally branched chains or

unbranched chains. Richest source is…???

Dietary fibers: found in plant-derived foods; non-digestible

by human digestive enzymes. Structural parts of plants

The Chemist’s View of

Carbohydrates (cont’d.)

Glycogen is a polysaccharide (made of glucose) found in animals

(meats) and human body, Where is it found in the body??

When is it formed??

What is the significance of glycogen in the human body??

Is glycogen a significant food source of carbohydrate??

Split in GI

Human enzymes can digest starch, but they cannot digest

cellulose because the bonds that link the glucose units

together in cellulose are different.

Starch vs. Dietary fibers

What is “cellulose”???

The Chemist’s View of

Carbohydrates (cont’d.)

Types of dietary fiber

Soluble

Readily digested (fermentable) by

bacteria

Highly associated with lower risks of

chronic diseases

Insoluble

What is the health effect of insoluble

fiber??

The Chemist’s View of

Carbohydrates (cont’d.)

Other notes regarding fibers

Resistant starches???: classified as fibers, they escape digestion and

absorption in the small intestine

Energy/gram of fiber…….???

Some fibers: digested by bacteria in the human digestive tract

Bacterial fermentation can yield energy

Digestion and Absorption of

Carbohydrates

Goal of digestion and absorption of sugars and starches:

Break them into small molecules that body can absorb and

use

Which sugars can be absorbed by intestinal cells???

Regulation of Blood Glucose

Blood glucose homeostasis

Insulin’s role in regulating blood glucose

Facilitates blood glucose uptake by the muscles and adipose

tissue

Stimulates glycogen synthesis in the liver

Glucagon

Triggers the breakdown of liver glycogen to single glucose

molecules. The benefit of its highly branched structure??

Which organs are responsible for blood glucose homeostasis??

Health Effects of Sugars

and Alternative Sweeteners

Naturally occurring sugars: sugars that are not added to a food

but are present as its original constituents, such as the sugars of

fruit or milk.

Added sugars Dietary Guidelines for Americans ??

Consumption in recent decades is a dramatic upward trend

Leading source is soft drinks

Excessive amounts

Linked to obesity, heart disease, nutrient deficiencies, and

dental caries. How??

Added sugar and diseases

Obesity:

Most people can afford only a little added sugar in their diets if they are to meet nutrient needs within kcalorie limits

Excess sugar in the diet may be associated with more fat on the Body

Control the total energy intake will allow you to consume moderate amounts of sugar

Heart disease:

Influence the balance between the body’s fat-making and fat-clearing mechanisms

By increasing obesity

Health Effects of Sugars and

Alternative Sweeteners (cont’d.)

Recommended sugar intakes

Dietary Guidelines for Americans

Reduce the intake of kcalories from added sugars

The USDA Food Patterns

Eight teaspoons for 2200 kcal (5 – 10 percent of day’s total

energy intake)

Recognize sugar in all its forms – e.g., added sugars (Glossary)

Health Effects of Sugars and

Alternative Sweeteners (cont’d.)

Alternative Sweeteners: Sugar

Alcohols

Sugar alcohols (nutritive sweeteners)

Trigger a lower glycemic response

Two to three kcalories per gram, why?

Occur naturally in fruits and vegetables, also, in

manufactured food (to add sweetness).

What are some side effects of sugar alcohols?

Abdominal discomfort and diarrhea (due to fermentation)

Advantage: do not promote dental caries, why?

Alternative Sweeteners:

Nonnutritive Sweeteners

Nonnutritive Sweeteners

Minimal or no carbohydrate or energy

Extremely sweet

FDA endorsement

Safe over a lifetime within Acceptable Daily Intake

(ADI) levels. The level varies based on the type

U.S.-approved nonnutritive sweeteners

Aspartame, saccharin, stevia, sucralose

Alternative Sweeteners: Nonnutritive

Sweeteners

Do not cause tooth decay

Do nonnutritive sweeteners correlate with weight loss and

improved health?

When people reduce their energy intakes by replacing

sugar in their diets with nonnutritive sweeteners and

then compensate for the reduced energy at later meals,

energy intake may stay the same or increase.

Safety: read the label and use in moderation

Health Effects of Starch and Dietary

Fibers

Carbohydrates: disease prevention and recommendations:

Emphasize a variety of these foods each day: foods such as whole

grains, legumes, vegetables, and fruits supply valuable vitamins,

minerals, and phytochemicals, along with abundant dietary FIBER

and little or no fat.

Fiber-rich carbohydrate foods

May lower the risk of heart disease, cardiovascular disease, type 2

diabetes, and colon cancer. How, describe the mechanism(s)??

May enhance weight control and the health of the large intestine

Fiber & obesity:

Slows eating and stimulates the flow of saliva

Linger in the stomach, therefore, they delay gastric emptying

Provide a feeling of fullness and satiety?

Delay the absorption of nutrients (how this would affect health??)

Fermentation of viscous fiber in the large intestine generates

water, gas, and short-chain fatty acids (what the latter gives?)

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Fiber

Possible side effects of excessive

fiber consumption

Mainly in vegan

Mineral balance might be affected

May not be able to take in enough food to meet energy

or nutrient needs

Dehydration.

Health Effects of Starch and Dietary

Fibers (cont’d.)

Carbohydrates: recommended intakes

DRI advises 45 to 65 percent of energy requirement

Fiber

Adequate Intake (AI): 14 g/1000 kcal/day

roughly 25 to 35 grams of dietary fiber daily

Health Effects of Starch and Dietary

Fibers (cont’d.)

Carbohydrates: food sources

Grains

Vegetables

Fruits

Milk and milk products

Protein foods: limited to nuts and dry beans

Fibers in selected foods

Fibers in selected foods

Fibers in selected foods

Fibers in selected foods

Health Effects of Starch and Dietary

Fibers (cont’d.)

Carbohydrates: food labels

Feature

Total carbohydrate (grams)

Fiber and sugar grams: also listed separately

Total carbohydrate and dietary fiber: also expressed

as “% Daily Values”