6: Carbohydrates Flashcards
What are the three main types of carbohydrates?
Sugars, starches, and fibre
Why is fibre unlike other carbohydrates?
fibre has monosaccharides bonded together in a way that humans cannot digest
Define intrinsic sugars and give examples
Sugars naturally found in many foods
- Fruits and milk
Define extrinsic sugars (added sugars)
Sugars added to foods by the food industry to enhance the flavour of processed foods
What are the three main monosaccharides (single sugars) found found in food
Glucose (most common), fructose, galactose
Monosaccharides (Single Sugars):
Define Glucose
- building block of most other longer carbohydrates like starch and fibre
- main monosaccharide found in the blood (blood sugar)
Monosaccharides (Single Sugars):
Functions of Glucose
- fuel the needs of all cells in body, (brain cells, red blood cells), both have an absolute requirement for glucose
- Glucose can be metabolized into ATP, the body’s main energy currency
Monosaccharides (Single Sugars):
Where is Fructose found
- fruit sugar, found in many fruits as well as some vegetables and honey
- significantly sweeter than glucose and other sugars. Therefore added to processed foods to increase perceived sweetness
Monosaccharides (Single Sugars):
Where is Galactose found
- milk sugar because it’s found in milk
- similar in sweetness to glucose
Disaccharides (Double Sugars):
What are the three most common disaccharide in the diet?
sucrose, maltose and lactose
How are Disaccharides (Double Sugars) made, what is its structure
sugars with two monosaccharide units
Disaccharides (Double Sugars):
Sucrose (Table Sugar)
Glucose + Fructose = Sucrose
- typically white or brown
Disaccharides (Double Sugars):
What enzyme breaks down sucrose
Enzyme Sucrase
- breaks down sucrose into its respective two sugars, then absorbed at the villi of the small intestine
T/F: brown sugar is healthier than white sugar
False, no clear advantage to consuming brown sugar over white.
- Brown sugar is white sugar mixed with molasses
- very similar nutritionally
Disaccharides (Double Sugars):
Maltose (Malt Sugar)
- Starch, formed from a long chain of glucose molecules
- Mouth enzymes break down longer starch chains, forming glucose-glucose disaccharide maltose
Disaccharides (Double Sugars):
What enzyme breaks down Maltose
Enzyme Maltase
- in the small intestine, enzyme maltase breaks down maltose into glucose molecules, which can then be absorbed
Disaccharides (Double Sugars):
Lactose (Milk Sugar)
Glucose + Galactose = Lactose
- main sugar found in milk
- enzyme lactase breaks it down
What is Lactose Intolerance
Condition where people lack the enzyme lactase that helps separate glucose and galactose molecules in lactose
What are Extrinsic Sugars
- added sugars into food by manufacturers to increase sweetness
What are Intrinsic Sugars
Naturally found in foods
Both brown and white sugar are sucrose that originates from what foods
Sugar cane or beets
T/F: Both Intrinsic and Extrinsic Sugars Must be Grouped Together on an Ingredients List
False, only extrinsic sugars are grouped together on an ingredients list
Oligosaccharides (Few Sugars)
- between 3 and 10 monosaccharides in their chain
- considered fibres, because humans lack enzymes needed to digest them
- Most common oligos = fructooligosaccharides (FOSs) and galactooligosaccharides (GOSs)
Why are Oligosaccharides prebiotic
- cannot be broken down by enzymes in small intestine, bacteria in the large intestine can ferment them
- prebiotics because bacteria use them for food and growth
What are Polysaccharides (Many Sugars)
- chains of monosaccharides greater than 10 units in length
- composed of long glucose chains
- 2 types of polysaccharides (starches and fibre)
Polysaccharides (Many Sugars):
Starch
- long glucose chain, either straight (amylose) or branched (amylopectin)
- get starch from eating plant foods
- Amylopectin, most common carb in the human diet
How are Polysaccharides: Starch, digested
- broken down into oligosaccharides
- then into disaccharides
- eventually into monosaccharide glucose
- then absorbed
Polysaccharides (Many Sugars):
What is Fibre
Composed of long chains of glucose molecules like starch
- Fibre = PLANT substances such as cellulose, dextrin and inulin that human enzymes cannot break down
T/F: No chemical digestion of fibre in the small intestine
True, fibres reach the large intestine predominantly undigested.
- bacteria ferment certain fibres into short-chain fatty acids. Short-chain fatty acids are then absorbed and contribute to our energy intake
T/F: Fibres are predominantly composed of glucose, and is a source of glucose to the body
False. Even though fibres are predominantly composed of glucose, fibre is not a source of glucose to the body. Instead, it is potentially a source of short chain fatty acids
Whether fibre can or cannot be fermented into short chain fatty acids primarily depends on what
whether it is soluble or insoluble fibre
Soluble Fibre
Dissolves in water to form a gelatinous solution
- Bacteria in large intestine can ferment soluble fibre to produce short-chain fatty acids
- provides 2-3 kcal/g
Foods that have Soluble Fibre
Oats, apples, beans, peas, citrus fruits, barley and psyllium
Soluble fibre has what health benefits
- may improve cardiovascular health
- regulate blood glucose
- lower blood cholesterol
Insoluble fibre
- Does not dissolve readily in water
- Passes through digestive tract virtually unchanged, not fermented by bacteria in large intestine
Health benefits of Insoluble fibre
May promote digestive health
High sources of Insoluble fibre in food
Wheat, bran, beans, potatoes, cauliflower
Glycogen
- synthesizing long chains of glucose mlcs with the aim of storing them
- glycogen stored in our muscles and around our liver
- only store so much carbohydrate – typically around 0.5-2 kg