Lecture 16: Carbohydrate nutrition, digestion and absorption

Question 1

What are the key concepts of CHO intake?

Answer 1

• Energy stores, fuels and metabolic intermediates of ells
• Ribose and deoxyribose sugars are structural framework for RNA and DNA
• Cellulose makes up plant cells
• CHO are linked to many proteins and fats (Involved in cell interactions)

Question 2

What are the classes of sugars?

Answer 2

Monosaccharides (glucose, galactose and fructose)
Disaccharides (Sucrose(table sugar), maltose (fermentation) and lactose)
Polysaccharides; Glycogen, amylopectin

Question 3

What does CHO digestion begin with? (1-2)

Answer 3

Mouth

• Mechanical digestion
• Chewing and crushing

Saliva

• Chemical digestion (amylase begins to digests starch)
• Lubrication

Question 4

What happens to CHO in the stomach? (3)

Answer 4

Stomach acid deactivates amylase, does not breakdown CHO

Question 5

What happens to CHO in the SI? 4-5

Answer 5

Pancreas
- Releases Maltase, sucrase, lactase, pancreatic amylase i.e pancreatic enzymes (breakdown polysaccharides, disaccharides into monosaccharides

SI
- absorbs the now monosaccharides

Question 6

Describe how absorption takes place in the SI;

Answer 6

Active transport (glucose) (Na+ transport system)
Facilitated diffusion (Fructose)
Secondary active transport (Glucose and galactose)

Once in the enterocyte the monosaccharides enter the intestinal villi blood vessel because of facilitated diffusion via various transporters. Then travel to the portal vein.

Question 7

What happens to the monosaccharides once they reach the liver via the portal vein?

Answer 7

Galactase and frutose are converted to glucose.

Possibly stored in liver and some muscles as glycogen

Question 8

Describe carbohydrate malabsorption in relation to lactose;

Answer 8

Lactose intolerance is where lactose is not absorbed because theres no lactose enzyme etc and thus becomes fermented (large intestine) in the gut forming gas, acids, flatulance, abdominal pain, irritation of the large intestine.

Can also cause osmotic gradient and osmotic diarrhoea

Crohns can cause it due to just bad absorption.

Question 9

Why is being careful about CHO important?

Answer 9

Simple sugars are absorbed quicker and are less satiating, more readily stored etc

Question 10

Whats good about soluble fibre?

Answer 10

• Prolongs stomach emptying time
• Regulates blood sugar
• Binds with FA
• Lowers total cholesterol and LDL cholesterol
• Fermented by bacteria

Question 11

What is good about insoluble fibre?

Answer 11

• Softens stool
• Increases bulk
• Increases rate of transit

Question 12

Whats the recommenced dietary sugar intake?

Answer 12

5% total energy

Question 13

What are added sugars?

Answer 13

Often not defined and can be;

• Brown sugar
• Crown sweetener, corn syrup,
• Fruit juice concentrates
• Malt sugar
• ‘ose’ glucose, dextrose etc

etc etc etc

Point being these all have very different characteristics and tend not to be good.

Question 14

Whats the impact of glyceamic index?

Answer 14

Higher glycemic index means that blood sugars increase more dramatically, as does insulin, the rate at which the blood sugar drops also means you get hungry earlier.

Low GI foods, generate less rise in blood sugar and insulin. Exercise also lowers insulin.