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TRANSCRIPT
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”