Carbs biochemistry

1. Chapter 4
THE CARBOHYDRATES:
Sugars, Starches &
Fibers

2. Carbohydrates
(CH2O)n
• Simple carbohydrates
–Monosaccharides (single sugars)
–Disaccharides (double sugars)
• Complex carbohydrates
– Polysaccharides (many sugars)
Copyright 2005 Wadsworth Group, a division of Thomson Learning

3. Simple Carbohydrates
Monosaccharides
(C6H12O6)
Glucose
Fructose
Galactose
Copyright 2005 Wadsworth Group, a division of Thomson Learning

4. Monosaccharides
Glucose – dextrose or blood sugar
1. Primary fuel for the body
2. Found in all disaccharides &
polysaccharides

5. Monosaccharides
Fructose – fruit sugar
1. Found in fruit, honey,
syrup
2. Converts to glucose
in the body

6. Monosaccharides
Galactose – part of lactose
1. Found in milk
2. Converts to glucose
in the body

7. Simple Carbohydrates
Disaccharides
Maltose
Sucrose
Lactose
Copyright 2005 Wadsworth Group, a division of Thomson Learning

8. Disaccharides
Sucrose – table sugar
1. Glucose + Fructose
2. Refined from sugar beets &
cane

9. Disaccharides
Lactose – milk sugar
1. Glucose + Galactose
2. Lactose intolerance – missing
digestive enzyme needed to
split into two monodisaccharide
parts to absorb it

10. Disaccharides
Maltose – malt sugar
1. Glucose + Glucose
2. Found in germinating seeds &
used in fermentation to produce
malted beverages (beer,
whiskey)

11. Condensation

12. Hydrolysis

13. Complex Carbohydrates
Polysaccharides
Glycogen
Starches
Fibers
Copyright 2005 Wadsworth Group, a division of Thomson Learning

14. Polysaccharides
Glycogen – long chains of glucose
found in animals
1. Stored in liver & muscles
2. Helps maintain blood glucose
and important source of “quick
energy”, esp. during exercise
(lasts only about 12 hrs)

15. Polysaccharides
Starch – long chains of glucose
found in plants
1. Cereal grains (wheat, rice,
corn, etc.), legumes (beans &
peas), and root vegetables
(potatoes, yams)

16. Polysaccharides
Fiber – mostly indigestible CHO;
gums, mucilages, lignin
1. Component of plant cell walls
2. Classified according to solubility
in water
3. Abundant in whole grains,
legumes, fruits and vegetables

17. Fibers
Insoluble – nonviscous;
cellulose, lignins
Soluble – viscous & fermentable;
pectins, gums,
mucilages

18. Digestion
• Mouth
–Salivary amylase
• Stomach
–Fibers and satiety
• Small Intestine
-Maltase, sucrase, lactase

19. Digestion
• Pancreas
–Pancreatic amylase
• Large Intestine
-Fermentation of viscous fibers
 Water, gas, short-chain fatty
acid production

20. Carbohydrate Digestion
in the GI Tract

21. Absorption

22. Metabolism
Glucose in the Body
• Used for energy – fuels most of the body’s
cells
• Stored as glycogen – 1/3 in the liver and
2/3 in muscles
• Made from protein – gluconeogenesis
• Converted to fat – when in excess of
body’s needs

23. Constancy of Blood Glucose
• Regulating hormones – maintain
glucose homeostasis
1. Insulin – moves glucose from
the blood into cells
2. Glucagon – signals the liver to
release glucose into the blood
3. Epinephrine – released when
emergency fuel needed

24. Maintaining Blood Glucose Homeostasis

25. Constancy of Blood Glucose
• Diabetes
–Type 1 diabetes
•Failure of insulin production
–Type 2 diabetes
•Obesity
• Hypoglycemia
–Rare in healthy people
• Glycemic response
–Glycemic index

26. Glycemic Index

27. Health Effects of Sugar
• Sugar in excess
1. Contains no nutrients and may
contribute to malnutrition
2. Causes dental caries (tooth decay)
3. Does not cause, but can contribute
to: obesity, diabetes, heart
disease, & behavorial problems

28. Accusations Against Sugars
• Sugar causes
obesity
• Sugar causes
heart disease

29. Accusations Against Sugars
• Sugar causes misbehavior in children
and criminal behavior in adults
• Sugar causes cravings and addictions
–serotonin

30. Recommended Intakes of
Sugars
• DRI
–No more than 25% of total daily
energy intake
-Limit added sugars to <10% of
total energy intake
Copyright 2005 Wadsworth Group, a division of Thomson Learning

31. Health Effects
• Complex carbohydrates &
fiber may reduce
the risk of:
-Heart disease
-Diabetes
-GI health
-Cancer
-Weight
Management

32. Health Effects
How?
• Diets high in complex CHO tend to
be:
1. Lower in fat and calories
2. Higher in fiber, vitamins, &
minerals

33. Soluble Fibers
• Lower blood cholesterol by binding
dietary cholesterol so less absorbed
• Slow glucose absorption
• Slow transit of food through upper GI
tract
• Holds moisture in stools, softening
them
• Lower risk of heart disease
• Lower risk of diabetes

34. Soluble Fibers
• Gums & mucilages, pectins,
psyllium
• Sources
–Whole-grains, fruits, legumes,
seeds and husks, vegetables
–Extracted and used as food
additives

35. Insoluble Fibers
• Increase fecal weight - helps form
soft, bulky stools which improves
G.I. motility & reduces risk of
constipation, hemorrhoids,
diverticulosis & colon cancer
• Speed fecal passage through colon
• Provide bulk and feelings of fullness
(satiety)

36. Insoluble Fibers
• Cellulose, lignins, hemiculloses
• Sources
–Brown rice, fruits, legumes, seeds,
vegetables, wheat bran, whole
grains
–Extracted and used as food
additives

37. Recommended Intakes
of Carbohydrates & Fibers
• RDA for carbohydrate
–130 g/day
–45% - 65% total daily energy
intake with emphasis on complex
-Daily Value: 300 g/day
• Fiber
–Daily Value: 25 g/day
–AI: 14 g/1000 kcal/day

38. Dietary Recommendations
Example:
If 2000 kcal diet, then:
1100-1200 kcals as CHO
(275-300 grams)
with < 200 kcals as “added sugar”
(50 grams)
One 12 oz. soft drink has 36-40 gms sugar
0ne tsp. sugar weighs 4 gms = 9-10 tsps!

39. Alternative Sweeteners
Two Categories
1. Sugar Alcohols – mannitol, sorbitol,
xylitol
2. Artificial sweeteners – sugar substitutes
(calorie-free); in moderation, useful for
blood sugar & weight control

40. Alternative Sweeteners
Sugar Alcohols
1. CHOs that provide less energy than
sucrose (2-3 kcals/gm) because not
completely absorbed
2. May cause gas, abdominal discomfort,
diarrhea
3. Less cariogenic than sugar

42. Alternative Sweeteners
Artificial Sweeteners
1. Saccharin = “Sweet ‘N Low” or
“Sugar Twin”
2. Aspartame = “Equal” or “Nutrasweet”
must avoid if have phenylketonuria
3. Acesulfame-K = “Sunette” or “Sweet
One”
4. Sucralose = “Splenda”

45. Alternatives to Sugar
• Acceptable Daily Intake (ADI)
• Artificial sweeteners and weight
control
• Saccharine and cancer
• Aspartame and PKU

46. Sugar Alternatives on Food Labels

47. Alcoholic Beverages
• Rule of thumb to figure calories per
ounce for wines and distilled spirits
Wine: Multiply the “percent of alcohol by
volume” by two to obtain calories/ounce
Example: Zinfandel is 12.5% alcohol by
volume, 12.5 X 2 = 25 calories/ounce
Distilled Spirits (hard liquor): Proof minus 15
to obtain calories per ounce
Example: 80 proof whiskey – 15 = 65
calories per ounce