Carbohydrate nutrition, digestion and absorption in the small intestine

Question 1

Approximately what percentage of our daily energy intake is from carbohydrates?

Answer 1

Approx 40-60% carbs of which only 10% should be simple sugars. (around 50% should be complex carbs)

Question 2

what are the two main branches of carbohydrates?

Answer 2

Complex and simple

Question 3

What are the branches of complex carbs?

Answer 3

Starches:
eg potatoes, rice, bread

Fibre:
insouble eg bran
soluble eg lentils, beans, oatmeal

Question 4

What are the branches of simple carbs?

Answer 4

Sugars:
monosaccharides - glucose, fructose, galactose
disacchardies - sucrose, maltose, lactose

Question 5

What is the end product of both complex and simple sugars?

Answer 5

Glucose

Question 6

What is the polysaccharide most commonly stored in humans and where is it stored?

Answer 6

Glycogen - in the liver and skeletal muscle

Question 7

How much glycogen do we have stored in our body? What happens when we run out?

Answer 7

Enough to last 12-14 hours. Once all of this is broken down we start to break down protein and muscle to get glucose. Fat can also be used as it can be converted to ketones which can be used an energy source but if they are not used up and they accumulate then it results in ketosis - an acid/base imbalance.

Question 8

Discuss the steps of STARCH carbohydrate digestion from the time food enters the mouth to when it enters the small intestine.

Answer 8

1. When food enters the mouth the salivary amylase along with the chewing of teeth starts to hydrolyse and break down starch
2. Once in the stomach the acid inactivated the amylase and so digestion is halted/not much occurs in the stomach
3. As chyme enters the small intestine the acidity stimulates the secretion of digestive enzymes from the stomach and pancreatic amylase starts to break down the starch into small polysaccharides
4. Disaccharidases produced by the microvilli break down the small polysaccharides and disaccharides into monsaccharidases which can then by absorbed by the intestinal cells.
5. Glucose and galactose are absorbed via active transport whereas fructose is transported via facilitated diffusion
6. These monosaccharides move into the hepatic vein from the venule in the villi and then on to the liver

Question 9

Describe the digestion of dietary fibre from the moment it enters the mouth

Answer 9

1. The chewing of the teeth and movement of the tongue start to tear and rip apart the dietary fibre
2. In both the stomach and the small intestine there is no digestion of fibre and so it delays gastric emptying and then prolongs the absoroption of other nutrients
3. Once in the large intestine the bacteria can start to digest the dietary fibre and break it down into short chain fatty acids/gas and the rest of the dietary fibre binds water and bile and cholesterol and transports it out of the body through the faeces.

Question 10

What are the two types of sugars?

Answer 10

Intrinsic - mainly fructose in fruits and veges and lactose in milk

Added free sugars - mainly sucrose (fructose + glucose) that we have added to food eg fruit drinks

Question 11

What is NZ’s daily recommendation of sugar?

Answer 11

5% of daily carbs (6 teaspoons of sugar) note a coke is already 10 teaspoons.

Question 12

What is the function of insoluble fibres eg bran in terms of colon health?

Answer 12

It absorbs water and so it softens stools so prevents constipation. Note: enough water must be consumed with the fibre for the swelling of faeces to occur.

Question 13

What is the function of soluble fibre eg oatmeal, lentils in terms of bowell health?

Answer 13

It binds to fatty acids and bile and cholesterol (LDL) to prevent them from being absorbed and excretes them in the faeces. It is also able to be digested/fermented by bacteria which produces short chain fatty acids which “feed” the enterocytes and keep them healthy.