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Foundations In Human Nutrition > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

What is a carbohydrate?

A

Organic molecule with the general formula (CH2O)X

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2
Q

What are carbohydrates classified by, give the 3 categories

A

Classified by the degree of polymerisation

Sugars (mono and disaccharides) (DP 1-2)

Oligosaccharides (DP 3-9)

Polysaccharide (DP >9)

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3
Q

Explain what degree of polymerisation (DP) is

A

The degree of polymerisation or DP, is the number of monomeric units in a macromolecule or polymer or oligomer molecule

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4
Q

Explain alpha and beta linkage and where they are found, explain the strength

A

The linkage found in disaccharides, oligosaccharides and polysaccharides are classified as alpha or beta. These are the bonds between two monosaccharides

The alpha-linkages are easily digested by the human body

Beta-linkages are stronger because they are more stable and are not easily digested by the human body

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5
Q

Explain the structure of lactose and why type of carbohydrate is it

A

Lactose is a disaccharide found in milk and it consists of a beta D-galactose that is attached to an alpha D-glucose. The linkage between these two sugars is a beta- 1-4, glycosidic bond

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6
Q

Name the sub-groups of Oligosaccharides (3-9) and give examples

A

Malto-oligosaccharides (alpha-glucans): Maltodextrins

Non-alpha-glucan oligosaccharides: Raffinose, Stachyose, Polydextrose, Inulin

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6
Q

Name the sub-groups of Polysaccharides (>9) and give examples

A

Starch (alpha-glucans): Amylose, Amylopectin, Modified starch

Non-starch polysaccharides: Cellulose, Hemicellulose, Pectin, beta-glucan, Plant gums, Mucilage

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7
Q

Name the sub-groups of Sugars (1-2) and give examples

A

Monosaccharides: Glucose, Fructose, Galactose

Disaccharides: Sucrose, Lactose, Maltose, Trehalose

Polyols (sugar alcohols): Sorbitol, Mannitol, Lactitol, Xylitol, Isomalt

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8
Q

Explain what polypols are and where they are found

A

A specific group if sugar alcohols that are formed via the catalytic hydrogenation of CHOs. They are found naturally in certain fruits, vegetables, and mushrooms; however, they are also used as sugar-free sweeteners in products such as chewing gum, candies, and beverages

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9
Q

Name the 2 classification of carbohydrates based on physiological behaviour and explain both

A

Glycaemic carbohydrates - provides glucose for metabolism as a result of digestion and absorption in the small intestine

Non-glycaemic carbohydrates - fermented to short-chain fatty acids, CO2, H2 and methane in the large intestine

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10
Q

Explain absorption of glycaemic and non-glycaemic carbohydrates

A

Glycaemic - absorbed from the small intestine and provide CHO for metabolism

Non-glycaemic - not ingested in the small intestine but pass into the large intestine. They do not increase the blood concentration of glucose

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11
Q

Explain the function of Glycaemic Carbohydrates

A

Provide 3.8 kcal/g energy

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12
Q

Explain the function of Non-Glycaemic Carbohydrates

A

Prebiotic

Heart function

Helps to prevent constipation and stomach pain

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13
Q

Explain what a prebiotic and probiotic is

A

Probiotics are foods or supplements that contain live microorganisms intended to maintain or improve the “good” bacteria (normal microflora) in the body. Prebiotics are foods (typically high-fiber foods) that act as food for human microflora.

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14
Q

Define total carbohydrate, dietary fiber, and total sugar

A

Total Carbohydrate = All types of CHO found in the food or beverage

Dietary fiber = Dietary fiber is the part of plants that you eat but don’t get digested in your small intestine

Total Sugar = Sugars that occur naturally and are added artificially

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15
Q

Explain the process of digestion and absorption of carbohydrates

A

Entering the mouth:

A mixture of mono, di, oligo, and polysaccharides

Different susceptibility to digestion in the small intestine

Digestion and Absorption

Entering the bloodstream:

Mainly glucose

Small traces of fructose and galactose

Traces of other monosaccharides

16
Q

Explain the action of alpha-amylase in digestion

A

The action of alpha-amylase:

Produced by salivary glands and pancreas

Activity inhibited by a low pH in the stomach

Digested alpha-1,4 links in amylose and amylopectin

Does not hydrolyze bonds at the end of molecules or those next to alpha-1,6 branch point

Amylose into maltose

Amylopectn into Oligosaccharides

17
Q

Explain the different methods of absorption in the small intestine

A

Sugar transporters on enterocytes:

Apical membrane
Glucose and galactose - Sodium-glucose transporter protein-1 (SGLT1)

Fructose:
GLUT5 protein (passive transport)

Basolateral membrane

Glucose, Galactose, and Fructose
GLUT2 protein
Monosaccharides are thus transported to blood vessels linking to the portal vein to liver

18
Q

Explain how the different transporter protein works in the small intestine during absorption

A

SGLT1:

Glucose and Na+

Glucose is transported from the intestinal lumen to epithelial cells to a GLUT2 transporter protein

Sodium is transported from the intestinal lumen to epithelial cell to a Na+/K+ Pump

GLUT2:

Glucose is transported from epithelial cell to portal blood

GLUT5:

Fructose is transported from the intestinal lumen to epithelial cells and then into another GLUT5 transporter at the epithelial cell to transport the fructose to the portal blood

19
Q

Explain how glucose is actively transported in the small intestine

A

Active transport of sodium across basolateral membrane (Na+/K+-ATPase)

Decreased sodium inside the cell draws sodium across the apical membrane with glucose (SGLT1)
glucose passes across the basolateral membrane into blood vessels by facilitated transport (GLUT2)

20
Q

Explain the facilitated diffusion of fructose in the small intestine

A

Across the apical membrane (GLUT5)

Across the basolateral membrane (GLUT2)

21
Q

Explain why some carbohydrates undergo the process of fermentation

A

Enzymes are needed to digest the CHO that are not present in the small intestine

Enzymes can not gain access to the CHO trapped inside plant cell walls

Enzymes do not digest the CHO rapidly enough (affected by particle size and transit time)

Or monosaccharide transporters do not exist or are functional at a high enough rate

22
Q

Explain the process of fermentation of carbohydrates

A

Virtually all CHO that enter the large intestine will be fermented by bacteria

Bacteria produce hydrolytic enzymes that break disaccharides, oligosaccharides, and polysaccharides into monosaccharides

Bacteria internalize monosaccharides

CHO is metabolized to pyruvate by the glycolysis pathway

Pyruvate fermented to short-chain fatty acids (SCFA)

Anaerobic process

Butyrate = energy source for colonic epithelial cell

Propionate = absorbed and transported to the liver

Acetate = is absorbed and passes to the liver and then the bloodstream - metabolized by skeletal and cardiac muscle and the brain

The total energy provided by fermentation in humans is about 5%

23
Q

Explain the bacteria in the colon and explain what a symbiotic relationship is

A

Colon contains a complex ecosystem of over 400 known species of bacteria

Symbiotic relationship – they obtain substrates for growth from the host and return bi-products of their metabolism to the host

24
Q

Name the digestive enzymes

A

Lactose

Sucrase

Maltase

25
Q

How are glucose, galactose, fructose, and sugar alcohols absorbed?

A

Glucose and Galactose - active transport

Fructose-facilitated diffusion

Sugar alcohols - simple diffusion

26
Q

Guve the dietary requirement for total carbohydrates, free sugars, intrinsic, milk sugars, starch, and dietary fiber according to SACN

A

Total Carbohydrates = 50% of dietary energy

Free sugars = < 5% of total energy

Intrinsic, milk sugars and starch = 45% of total energy

Dietary fibre = 30g/day

27
Q

Name some of the carbohydrates in order of increasing cariogenicity

A

Sucrose (highest)

Fructose, Glucose, Maltose

Lactose, Galactose

Maltodextrins, Polysaccharides

Sorbitol, Xylitol

28
Q

Name the conditions low dietary fiber is associated with

A

Constipation

Diverticular disease

Hiatus hernia

Bowel cancer

29
Q

Name the characteristics of dietary CHO and functional GI tract (FGI) carbohydrates and give examples of the carbohydrates that have these characteristics and describe 1 problem of these CHO

A

Fermentable

Oligosaccharides

Disaccharides

Monosaccharides

Polyols

Include: Fructose, Lactose, Fructans, Galactans, Sorbitol, Mannitol, Xylitol, Malitol

Problem: Poorly absorbed in the small intestine, small and cosmetically active molecules, rapidly fermented by GI bacteria

30
Q

Explain the symptoms of consuming too many FGI CHOs

A

Osmotic load

Increased water delivery

Increased gas production

Motility change

Bloting

Pain and discomfort

Wind

Foundations In Human Nutrition (17 decks)

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