1. Lecture 3
Ch. 4 Carbohydrates

2. Overview Carbohydrates
Sources of Carbohydrates
Simple Sugars
Complex Carbohydrates
Dietary Fiber
Digestion and Absorption
Functions
Blood glucose regulation
Dietary sweeteners

3. How do we get Carbohydrates ?
Figure p. 110
Process of Photosynthesis in Plants
Requires the elements Carbon, Hydrogen and Oxygen
Suns energy + 6water + 6CO > 6O2 + glucose (C6H12O6)
simple sugar produced is metabolized to more complex forms for storage
Sugars, starches and dietary fiber

4. Mono and Di Saccharides (simple sugars)
Figure 4.1
Mono = one
Glucose, galactose and fructose
Di = two
Sucrose, lactose and maltose
glucose - major form, all others converted to glucose for use in our bodies
fructose - fruit sugar
galactose - combined with glucose is lactose found in milk products
(glucose-glucose) is maltose
(glucose-fructose) is sucrose

5. Complex Carbohydrates
Figure 4.3
Starches and dietary fiber (polysaccharides)
highly recommended forms of intake
Starches - digestible polysaccharides
storage form of carbs. in plants
vegetables, bread, pasta, rice, beans
amylose - straight chains of glucose
amylopectin - branched chain starch
Glycogen - branched glucose
more chains, increases rate of breakdown - utilize energy faster
animal storage in liver (blood glucose) and muscle (movement)
Not a dietary source of carbohydrate

6. Dietary Fiber Indigestible polysaccharides. Fig 4.4
Insoluble fibers - whole grains, flax, veg
cellulose, hemicellulose, lignin(non carb)
structural part of plants
do not dissolve in water
Increase bulk of feces, decreases intestinal transit time
Soluble Fibers - citrus fruits, oat, beans
pectin, gum, mucilage
inside and around plant cells
dissolve or swell in water
fiber rich foods are a mixture of both kinds of fiber

7. Dietary Fiber
Retains water, increasing bulk of stool, stimulates peristalsis and facilitates elimination
too little fiber, small hard stool, difficulties with elimination
hemorrhoids and diverticula
insoluble fibers increase stool size the most
require high fluid intake
may play role in preventing colon cancer

8. Dietary Fiber Emphasize foods rather than fiber supplements
vitamin C, carotenoids, may be implicated in observed benefits
soluble fiber may reduce cholesterol as it attracts bile (produced from cholesterol) and leads to its elimination in stool
recommend g per day
MODERATION
Table 4-6

9. Carbohydrates in Foods
The foods that yield the highest percentages of energy from carbohydrates
Table sugar, honey, jam, jelly, fruit, baked potatoes
Rice bread and noodles are all high ~75% carbohydrate
Peas, broccoli, oatmeal, beans, french fries and skim milk all contain moderate amounts
Fig 4.5
Emphasize grains, pastas, fruits and vegetables
Contain other beneficial nutrients

10. Sweeteners Nutritive - provide energy
Sugars - all mono and disaccharides
Consumption of sucrose pounds per person in one year in US
high fructose corn syrup
sugar alcohols -
sorbitol, mannitol, xylitol, kcal /g
Alternative- provide little energy
Saccharin - (1879)
300 times sweeter than sucrose
Aspartame (nutrasweet/equal)- (1981)
amino acids and methanol, 200 times sweeter than sucrose
damaged by cooking
PKU (phenylketonuria)

11. Sweeteners Alternatives Sucralose -(1998) WHY ALTERNATIVES?
Acesulfame-K - (1988)
200x sweeter than sucrose
no energy value
can be cooked
Sucralose -(1998)
600 times sweeter than sucrose
excreted, not used for energy
WHY ALTERNATIVES?
Diabetics, calories, dental

12. Carbohydrate Digestion
Figure 4-6
Begins with cooking
salivary amylase (enzyme)
mixes with food, begins break down of starch
Digestion stops in stomach due to acidic environment
pancreatic amylase (enzyme)
released into small intestine to breakdown starch and small chains of glucose into maltose (disaccharide)
Sucrase, Maltase, Lactase (enzymes)
enzymes in wall of S I produce mono from disaccharides.

13. Carbohydrate Digestion
Undigested disaccharide's used by bacteria in LI, produces acid and gas (abdominal discomfort)
Lactose intolerance
people lack sufficient lactase, usually avoid dairy
can reintroduce lactose into diet slowly, small amounts are OK.

14. Carbohydrate Absorption
Single sugars, actively absorbed by cells in wall of SI (energy)
travel via portal vein to liver, to be converted into glucose
used mainly for energy 4 kcal/g or stored as glycogen
For red blood cells and nervous system, glucose is the only source of fuel
recommend minimum 55 % of caloric intake

15. Functions of Carbohydrates
Energy source
Protein sparing effect
too little carbohydrate, leads to breakdown of body protein for energy
Ketosis
Low carbohydrate prevents proper metabolism of fats
production of ketones, altering acid/base balance and body functions
sweetener

16. Blood Glucose Regulated very tightly
liver controls entry of glucose into body
Stores glucose from GI that comes via portal vein
Hyperglycemia -too high-125 mg/100ml
Glucose released in urine, diabetes
hypoglycemia - too low - 40 mg/100ml
irritable, headache, hungry
Mainly controlled by hormones from the pancreas and adrenal glands

17. Blood Glucose Pancreatic hormones (fig. 4-7)
Insulin - released with onset of eating and increase in blood glucose
stimulates liver to synthesize glycogen and cells to take up glucose from the blood
Glucagon - released when blood glucose drops
stimulates breakdown of glycogen to glucose and its release from liver into the blood stream

18. Blood Glucose Adrenal Gland Epinephrine (aka adrenaline)
released in response to stress
increases blood glucose, promoting quick mental and physical action
Balance of all these hormones is necessary to maintain blood glucose
Exercise also stimulates uptake of glucose by working muscle
Multifaceted Control System

19. Recommended Carbohydrate Intake
No RDA, minimum g
55 % of total calories
reduce fat, increase fiber intake
sugar intake below 10 %
average ~ 16 %
only a problem if nutrient rich food is ignored in favour of sweet foods
Glycemic Index(GI) -blood glucose response in body - higher insulin release
Long term may have health impact - diabetes
Table High GI foods - baked and mashed potatoes, short grain white rice, honey, jelly beans, bagels
Avoid overeating high GI and sugar
Combine with lower GI foods
Exercise regularly