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Carbohydrates
Carbohydrates Contain the Elements:
■Carbon
■Hydrogen
■Oxygen
They Are Split Into Four Groups Known As:
■Monosaccharides(Monomers)
■Disaccharides(Dimers)(2)
■Oligosaccharides(2-10)
■Polsaccharides(Polymers)(<10)
Carbohydrates
•Many carbohydrates are soluble in water.
•The usual chemical test for the simpler
carbohydrates is heating with Benedicts
solution.
•The formula for a carbohydrate is (CH2O)n
•The n represents the number of times the
CH2O unite is repeated.
Monosaccharides
(monos)
The Most Important Monosaccharide Is
Glucose.
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A Monosaccharide is made up of 1 sugar unit.
Monos are reducing sugars.
Fructose and Galactose are all so
Monosaccharides, They all have the same
chemical formula but different structures.
The Structural Differences between
Glucose, Galactose, and Fructose
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Three nutritionally important monosaccharides
➢ Glucose
➢ Fructose
➢ Galactose
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Glucose
• Blood glucose and blood sugar in the body
• Most abundant monosaccharide in the body
- Is the preferred and main source of energy
for the brain and red blood cells
• Part of every disaccharide
• Only monosaccharide in starches
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Fructose
• Sweetest of natural sugars
• Found abundantly in fruits
• Part of high-fructose corn syrup
Galactose
• Commonly occurs as part of
dissaccharide lactose
Disaccharides
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Three Disaccharides
• Sucrose
- Most common
• Lactose
• Maltose
- Least common
- Formed from digestion of
starches
Monosaccharides Link to Form
Disaccharides
Glycosidic Bond
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This is when two monosaccharides join to
form a Disaccharide.
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The reaction is similar to condensation.
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The reaction involves the water been given
off.
Glycosidic Bond
Above is the structures of a
Glycosidic bond.
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It forms a Disaccharide
Hydrolysis
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This is the breaking down of a glycosidic bond.
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Instead of water been taken away water is
added.
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Lysis means splitting.
Polysaccharides
➢ Starch
• Plants store glucose in chains of starch
- Amylose
- Straight chain
- More resistant to digestion
- Resistant starch
✓ May improve heStarcalth of digestive tract
✓ May improve glucose tolerance
✓ May stimulate growth of beneficial intestinal
bacteria
- Amylopectin
- Branched chains
- Easier to digest
Polysaccharides
■ Fiber
◆Nondigestible polysaccharides
◆Provides no energy
◆Classification
♦ Soluble
• Pectins, beta-glucan, some gums, mucilage
• Easily fermented by intestinal bacteria
–Carbon dioxide, methane, some fatty acids
♦ Insoluble
• Cellulose, lignin, some hemicelluloses
• Not easily fermented
Fiber Health Benefits
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Soluble fibers
◆Slow gastric emptying and may delay
absorption of some nutrients
♦Helps reduce serum cholesterol
♦Improve appetite control
♦Normalize blood glucose levels
◆May help protect against colon cancer
Insoluble fibers
◆Relieves constipation
Most plant foods contain both soluble and
insoluble fibers
Polysaccharides
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Glycogen
◆Storage form of glucose in animals
◆Long, branched chains of glucose
◆Stored in liver and muscle
◆Liver glycogen response to blood glucose (BG)
levels
↓ BG → glycogen breakdown → ↑ BG
◆Muscle glycogen can be broken down for
energy for the muscle
The Comparison of Starch and Glycogen
Molecules
Oligosaccharides
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Similar in length to simple carbohydrates
Similar in makeup to polysaccharides
Humans lack the enzymes necessary to digest
them
Intestinal microflora digest and ferment them
◆Cause bloating, discomfort, and flatulence
Food sources
◆Legumes, beans, cabbage, brussels sprouts,
broccoli
Carbohydrates
Carbohydrates can also be classified as
Reducing Sugars
1. Possess a free aldehyde(-CHO) or ketone (-C=0) Group.
2. Can reduce the Cu2+ cupric ions (blue)in Fehling’s or Benedict’s Solution to
Cu+ cuprous ions (reddish) that precipitate out as Cu2O(cuprous oxide).
3. Maltose. lactose, melibiose, gentiobiose, cellobiose, mannotriose..
Non-reducing
1. A free aldehyde or ketonic group is lacking.
2. No such reaction.
Benedict test
Benedict's Test for non-reducing Sugars is a test which
determines the presence of non-reducing sugars in a test
solution.
Benedict test video
Benedict test
Iodine Test
The Iodine test is used to test for the presence of starch.
Iodine solution — iodine dissolved in an aqueous
solution of potassium iodide — reacts with the starch,
producing a purple-black colour
Iodine test video
Carbohydrates can also be separated into groups based on
the Glycemic Index, which measures how high and how
quickly blood glucose levels change after eating
carbohydrates. The higher the Glycemic Index, the
higher the rise in blood sugar and the longer it takes to
return to normal. For a healthy diet, it is best to focus on
foods with a low Glycemic Index (e.g., whole grains,
oats, and whole wheat pasta). Foods with a high
Glycemic Index have been linked to elevated risks of
heart disease and diabetes.
A low-GI food will release glucose more slowly and
steadily, which leads to more suitable postprandial (after
meal) blood glucose readings. A high-GI food causes a
more rapid rise in blood glucose levels and is suitable for
energy recovery after exercise or for a person
experiencing hypoglycemia.
Glycemic Index
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Classifies the effects of carbohydrate-containing
foods on blood glucose
May be helpful for diabetics
Glycemic index (GI) refers to the measured
upward rise, peaks, and falls of blood glucose
following consumption of high-carbohydrate
food
◆Ranks foods according blood glucose
Glycemic Load
■ Glycemic load (GL) of food is a number that estimates
how much the food will raise a person's blood glucose level
after eating it. One unit of glycemic load approximates the
effect of consuming one gram of glucose.
■ Glycemic load (GL) – adjust GI by taking into account the
amount of carbohydrate consumed in a typical serving of food
■ Factors affecting GI
◆Ripeness of fruit
◆Cooking
◆Processing
◆Size of food pieces
◆Amount of fiber
◆Combinations of food eaten
Glycemic Index and Glycemic Load
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Usefulness of GI and GL for disease
prevention and weight management is
controversial
Is helpful in educating people about
◆Carbohydrate content of foods
◆Portion sizes
◆Serving numbers
Carbohydrate Digestion and Absorption
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Disaccharides and starches are digested to
monosaccharides
Monosaccharides are easily absorbed
Fiber passes through the GI tract undigested
Lactose Intolerance
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Deficiency of lactase, the enzyme that digest
lactose
◆Maldigestion – inability to digest lactose
due to low levels of the enzyme
◆Intolerance
♦Maldigestion resulting in nausea,
cramps, bloating, flatulence, and
diarrhea
Absorption of Carbohydrates
■ Once digested to monosaccharides
◆Absorbed through the intestinal cell mucosa
◆Transported to the liver via the portal vein
◆Metabolic needs direct fate of the monosaccharides
♦ Galactose and fructose
• Used by the liver for energy
• Converted to glucose
♦ Glucose
• Used for energy
• Converted to glycogen through glycogenesis
• Converted to glycerol and fatty acids for storage
in addipocytes
Functions of Carbohydrate
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Provide energy
◆4 kilocalories per gram
Maintain blood glucose
◆Carbohydrate intake
◆Glycogenolysis > 4 hours after a meal
Spare protein
◆Prevents the need for glyconogenesis
Prevents ketosis
How to Maintain Blood Glucose Levels
■ Goal for blood glucose is 70–100 mg/dl
■ Insulin – lowers blood glucose levels
◆Needed for glucose to enter the cell from the blood
stream
♦ Exception: liver, kidney, and brain cells
◆Helps convert glucose to glycogen through
glycogenesis
◆Helps convert glucose to fatty acids through
lipogenesis
◆Inhibits lipolysis
■ Glucagon – increases blood glucose levels
◆Stimulates the release of glucose into the blood
◆Stimulates glycogenolysis
◆Stimulates gluconeogensis
Insulin and Glucagon Regulate Glucose
Metabolism
Dietary Fiber
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Benefits
◆Helps lower risk of
♦Bowel irregularity
♦Obesity
♦Heart disease
♦Cancer
♦Diabetes mellitus
Quick Review
■ Glycemic index (GI) ranks foods according to effects on
glucose levels compared to white bread or pure glucose
■ Glycemic load adjust for serving size
■ Foods that contain high fiber or are eaten with protein and
fat generally have a lower GI.
■ High-fiber diet health benefits include reduced risk of
◆Constipation
◆Diverticulosis
◆Heart disease
◆Obesity
◆Diabetes Mellitus
◆Cancer
Food Sources of Carbohydrates
Quick Review
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◆Fresh fruits and vegetables
◆Whole grains
Excellent sources of fiber are
◆Whole grains
◆Fruits
◆Vegetables
Packaged foods can be good sources of starch and
fiber
◆Read label carefully
◆Avoid too much sugar, fat, and kilocalories
Natural versus Added Sugar
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Naturally occurring sugar
◆Sugars such as fructose and lactose found
naturally in foods
◆Tend to be nutrient dense
Added sugar
◆Sugars added to processed foods and sweets
◆Empty calories
Slices of an Orange versus Orange Slices
Added Sugar
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Reasons sugar is added to foods
◆To keep product moist
◆To turn pastries a golden brown
◆Preservative
◆Thickening agent
◆Make yeast rise
◆Make foods taste sweet
Finding Added Sugars on the Label
Health Effects of Sugar
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Sugar can contribute to
◆Dental carries
◆Elevated level of fat in the blood
◆Lowing of HDL cholesterol
Sugar does not cause
◆Increased risk of diabetes
◆Hyperactivity in children
Sugar is not considered an addictive substance
How many carbohydrates do I need in my
diet?
Carbohydrates should account for 45% - 65% of the
calories in your diet, which is roughly 225 g – 325 g of
carbohydrates for someone on a 2000-calories diet.
Putting It All Together
■ Carbohydrates are an important part of a healthy diet
■ Whole grains, fruits, vegetables, and lean dairy products
◆Provide carbohydrates and vitamins and minerals
◆Should be the predominant source of carbohydrates
■ Whole grains, fruits, and vegetables are a good source of
fiber and phytochemicals
◆Adequate amounts of these can prevent many chronic
disease
■ Sugary foods should be eaten in moderation