1. Lecture 3
Ch. 5 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. 104
Suns energy + water + CO > O2 + carbohydrate
Process of Photosynthesis
simple sugar produced is metabolized to more complex forms for storage
Carbon, Hydrogen and Oxygen
sugars, starches and dietary fiber

4. Mono and Di Saccharides
Mono - one ; Di - two
glucose - major form, all converted to glucose for use in our bodies
(glucose-glucose) is maltose
(glucose-fructose) is sucrose
fructose - fruit sugar
galactose - combined with glucose is lactose, milk products

5. Complex Carbohydrates
Starches and dietary fiber (polysaccharides)
highly recommended forms of food intake
starches - digestible polysacch.
amylose - straight chains of glucose (veg., bread, pasta, rice, beans…)
storage in plants
Glycogen - branched glucose
more chains, increases breakdown
animal storage in liver (blood glucose) and muscle (movement)

6. Dietary Fiber Insight p. 111-115 Indigestible polysaccharides.
Insoluble fibers -
cellulose, hemicellulose, lignin
structural part of plants
do not dissolve in water
Soluble Fibers -
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, see table 3-4 p. 114
MODERATION

9. Carbohydrate Digestion
Begins with cooking
salivary amylase (enzyme)
mixes with food, begins break down of starch
stops in stomach due to acid
pancreatic amylase (enzyme)
released into small intestine to breakdown to monosaccharides
Sucrase, Maltase, Lactase (enzyme)
enzymes in wall of S I produce mono from disaccharides.

10. 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.

11. 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
red blood cells and brain, glucose is only source of fuel
recommend minimum 55 % of caloric intake

12. 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

13. Blood Glucose Regulated very tightly
liver controls entry into body via portal vein
hyperglycemia - too high
released in urine, diabetes
hypoglycemia - too low
irritable, headache, hungry
Mainly controlled by hormones from the pancreas and adrenal glands

14. Blood Glucose Pancreatic hormones (fig. 4-8)
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

15. 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
Multifaceted Control System

16. Recommendations No RDA, minimum 50 - 100 g 55 % of total calories
reduce fat, increase fiber
sugar intake below 10 %
average ~ 16 %
only a problem if nutrient rich food is ignored in favour of sweet foods
MODERATION

17. Sweeteners Nutritive Alternatives Sucrose high fructose corn syrup
sugar alcohol -
sorbitol, mannitol, xylitol, 3 kcal /g
Saccharin - (1879)
link with cancer, no ban
Aspartame - (1981)
amino acids and methanol, 200 times sweeter than sucrose
damaged by cooking
PKU (phenylketonuria)

18. Sweeteners Alternatives Sucralose -(1998) WHY? Acesulfame-K - (1988)
no energy value
can be cooked
Sucralose -(1998)
excreted, not used for energy
WHY?
Diabetics, calories, dental