Carbohydrates

Question 1

What is the role of Carbohydrates in the body?

Answer 1

• Energy
• Components of RNA and DNA (deoxyribose and ribose)
• Glycoproteins and glycolipids
• cell signalling
• Gastrointestinal health - non digestible carbohydrates

Question 2

What happens to excess Carbohydrates?

Answer 2

• synthesise fatty acids via the Acetyl-CoA pathway

- synthesise non-essential amino acids

Question 3

How are carbohydrates formed?

Answer 3

Monosaccharides (e.g. glucose, fructose) join together via a condensation reaction to form a disaccharide (maltose, sucrose). The bond formed is a glycosidic bond. Polysaccharides are formed by condensing 10 or more monosaccharide units.

Question 4

What is the difference between oligosaccharides and polysaccharides?

Answer 4

• Oligosaccharides - 3-9 monosaccharides, occur naturally in legumes, onions, sweetness diminishes as chain length increases, resist digestion in SI and fermented in colon to SCFA.
• Polysaccharides - 10 or more monosaccharides, storage: starch, glycogen (digestible), structural (cellulose, pectin, chitin, indigestible)

Question 5

What is the difference between intrinsic and extrinsic sugars?

Answer 5

Intrinsic - contained within intact cell; Non-cariogenic (not causing tooth decay); fructose and glucose in fruit and veg.
Extrinsic - free in solution/added sugar, cariogenic, fruit juices (by juicing the fruit the sugars escape from the cell wall so they are very easily absorbed by the diet)

Question 6

What is Glycaemic Index? What is it influenced by?

Answer 6

GI is the extent to which blood glucose rises after ingestion of a carbohydrate food.
Influenced by the rate of intestinal absorption (i.e. how quickly we can access the glucose in food). Influenced by other nutrients e.g. fat and protein slow gastric emptying so lower GI.

Question 7

What foods are low glycemic Index and why?

Answer 7

• Unprocessed grains - wholegrain, oat, quinoa, brown rice…
• Foods high in soluble fibre e.g. fruit and vegetables especially with peel on. Soluble fibre forms a gel-like barrier which slows digestion
• Higher fat content - slows gastric emptying
• Mixed meals - Fat and protein undergo more complex digestion and slow gastric emptying.

Question 8

Explain why with high GI foods there is a rapid rise in blood glucose and then a sugar crash can occur.

Answer 8

With high GI foods the glucose is very easily absorbed so blood glucose rises rapidly. Often with these foods the pancreas doesn’t know exactly how much insulin to release so releases a lot and this can bring blood glucose levels too low.

Question 9

What does soluble fibre do?

Answer 9

Soluble fibre:

• soluble
• dissolves in water and GI fluids and turns to a gel-like substance.
• is digested by bacteria in the large intestine releasing gas and a few calories
• slows gastric emptying - increasing satiety
• binds to cholesterol reducing absorption

Question 10

What does insoluble fibre do?

Answer 10

Insoluble fibre:

• Does not dissolve in water and GI fluids.
• Not digested by bacteria
• binds water in the colon increasing faecal bulk
• reduces GI transit time so increases passing of faeces. Beneficial to remove any potential carcinogens that are in faeces which may otherwise hang around and increase the risk of colorectal cancers

Question 11

What are sources of soluble fibre?

Answer 11

• Oats
• Beans
• Fruits
• Vegetables
• particularly fruit and vegetable skins

Question 12

What are the sources of insoluble fibre?

Answer 12

• wheat bran
• wholegrains
• vegetables

Question 13

What counts as high fibre and what counts as a ‘source of fibre’?

Answer 13

High fibre > 6g/100g

‘Source of fibre’ > 3g/100g

Question 14

What are some high fibre foods?

Answer 14

Raspberries
Oats
Wholemeal flour
Nuts (Almonds, brazils, peanuts)
Linseed
Bran flakes