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FNH 250 > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

What are simple carbohydrates?

A
  • monosaccharides (MS)
  • disaccharides (DS)
  • “sugars” -plant & animal sources
  • “simple sugars” -plant & animal sources
  • refined: table sugar
  • unrefined: fruits, dairy, honey
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2
Q

What are complex carbohydrates?

A
  • polysaccharides (PS)
  • “starch” -plant sources
  • “dietary fibres” -plant sources
  • “glycogen” -animal sources
  • refined - white flour, white rice
  • unrefined - whole grains, starchy vegetables, legumes
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3
Q

What are monosaccharides?

A

Single sugar units

a. GLU – glucose (blue)

  • found in all 3 disaccharides and polysaccharides
  • starch – major food source of energy in the world
  • glycogen – form of energy storage in body
  • often called ‘blood sugar’
  • mildly sweet on tongue
  • ex., starchy vegetables, grains, legumes

b. FRU – fructose (pink)

  • intensely sweet on tongue
  • ex., fruits, honey, maple syrup, high fructose corn syrup

c. GAL – galactose (green)

  • mildly sweet on tongue
  • ex., milk, few milk products
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4
Q

What are disaccharides?

A

2 monosaccharides linked via condensation reaction

a. Sucrose – SUC = GLU + FRU

  • table sugar
  • maple syrup, honey, sugar cane and beets

b. Lactose – LAC = GLU + GAL

  • milk sugar
  • can account for 30-50% of energy from milk

c. Maltose – MAL = GLU + GLU

  • germinating grains = partial breakdown of starch
  • partial digestion of starch in humans
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5
Q

What is glycogen?

A
  • storage form of carbohydrates in animal tissues (muscle, liver)
  • highly branched chains of mostly glucose, fast source of energy due to multiple branch ends, highly hydrated
  • sources – negligible amount in meats; not found in plant foods
  • A glycogen molecule contains hundreds of glucose units in highly branched chains.
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6
Q

What is glycogenolysis?

A
  • Rapid enzymatic breakdown of glycogen, surge of glucose available as source of energy
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7
Q

What is starch?

A
  • storage form of carbohydrates in plants
  • amylose = unbranched chains of GLU units
  • amylopectin = occasionally branched chains of GLU units
  • resistant starch – starch not hydrolyzed by digestive enzymes
  • sources – Grains: wheat (NA, Europe), rice (Asia), corn (CA, SA), millet, rye, barley, oats; Legumes: beans, peas, lentils, peanuts; Tubers: potatoes, yams, cassava; Veggies
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8
Q

What is a whole grain?

Provide examples

A
  • three parts (bran, germ, endosperm) present

Examples:

Amaranth*

*gluten-free Barley

Buckwheat*

Bulghur
Corn*
Cornmeal

whole* Kamut

Millet*
Oatmeal*
Oats, whole*
Popcorn*
Quinoa*
Rice – brown & coloured*

Sorghum*
Spelt
Triticale
Whole rye
Whole or cracked wheat

Wheat berries
Wild rice*

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9
Q

What is dietary fibre?

A
  • structural form of carbohydrates in plants
  • heterogeneous group of polysaccharides
  • mostly GLU units linked in b-1,4 bonds which are resistant to human enzymatic hydrolysis in digestive tract
  • common classification system: water soluble & water insoluble
  • most fibre-containing foods are a mixture of soluble and insoluble fibres
  • feed gut bacteria - ‘prebiotics’
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10
Q

Compare the structure of starch and fibre.

A

Starch

  • alpha-1,4 bonds – hydrolyzed by humans

Fiber

  • ß-1,4 bonds – not hydrolyzed by human digestive enzymes
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11
Q

Describe the health effects, components, and food sources of water-soluble fiber.

A
  • Greatest effect in small intestine
  • Viscous, more fermentable
  • Dissolves or swells in water, delays gastric emptying.
  • contributes to satiety
  • Slows glucose absorption.
  • Slows transit time through GI tract.
  • Lowers serum cholesterol.
  • Metabolized by bacteria in colon to produce gases and short chain fatty acids.
  • components: pectins, gums, mucilages Hemicelluloses
  • food sources: citrus fruit, apples, legumes, oats, barley, cereals, vegetables
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12
Q

Describe the health effects, components, and food sources of insoluble dietary fibres.

A
  • greatest effect in large intestine
  • Non-viscous, less fermentable
  • Contribute to satiety
  • Not dissolved in water, but attracts H2O. § Accelerates transit time through GI tract.
  • Increases fecal bulk, softens stool.
  • Not metabolized by bacteria in colon.
  • Carbohydrate components: Cellulose, Hemicelluloses
  • Carbohydrate food sources: Whole wheat, cereals, legumes, vegetables
  • Non-carbohydrate components: Lignan
  • Non-carbohydrate food sources: Vegetables
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13
Q

Describe digestion of carbohydrates in the mouth.

A
  • salivary amylase starts the digestion of starch to shorter PS and to DS (maltose) level
  • fibre: slows eating, increases saliva production
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14
Q

Desribe digestion of carbohydrates in the stomach.

A
  • salivary amylase – not acid-stable, denatured, no CHO digestion in stomach
  • fibre: delays gastric emptying (esp. soluble), contributes to satiety
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15
Q

Describe digestion of carbohydrates in the small intestine.

A
  • Secretin, hormone produced in small intestine, stimulates pancreas to release juices into lumen, that include pancreatic amylase – digests polysaccharides to discaccharide level
  • Crypt glands secrete intestinal enzymes, sucrase, maltase & lactase, digest disaccharides into constituent monosaccharides
  • Fibre – not digested: slows absorption of monosaccharides, blunts blood insulin, high intakes can bind minerals
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16
Q

Describe digestion of carbohydrates in the large intestine.

A
  • minimal, if any digestion
  • insoluble fibres attract water, soften stool, easier elimination, fewer/lower GI tract conditions
  • soluble fibres fermented by bacteria – produce SCFA (2-4 carbons) and gases (CO2, CH4, H2)
  • resistant starches (found in legumes, unripe bananas, cooked and cooled potatoes…) and undigested disaccharides (i.e., lactose) pass through the small intestine into the colon where they are fermented by bacteria to produce SCFA and gases, or are excreted
  • SCFA can be used as a source of energy by the body
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17
Q

Describe the absorption and transport of carbohydrates.

A
  • glucose & galactose (a.t./f.d.)
  • fructose (f.d./f.d.)
  • monosaccharides (MS) cross the intestinal cells to enter the blood capillaries in the absorptive villi, then travel directly to the liver, entering through the portal vein
  • once MS enter the liver, they are almost entirely converted to glucose for use by the body
  • fibre, resistant starches and undigested lactose are not absorbed
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18
Q

Describe liver metabolism of dietary carbohydrates.

A

In the liver GLU can:

  • be used as an immediate source of energy for the liver itself
  • be transported out of the liver through the hepatic vein in the bloodstream for use by other cells
  • be stored as glycogen for later use as GLU
  • if in excess to body needs, be converted into fat then transported to and stored in the adipose cells
19
Q

What are the 5 main functions of carbohydrates?

A
  1. Fuel Source
  2. Potential Energy – as CHO (glycogen)
  3. Storage of Excess CHO kcal as Body Fat
  4. Endogenous Sources of CHO
  5. Maintenance of Blood Glucose Level
20
Q

Describe the catabolism of glucose.

A
  • anerobic respiration
  • lactic acid builds up in muscle cells, decreases pH, increases pain, slows activity, if increased O2 available then switch to aerobic metabolism
  • lactic acid travels from muscle to liver, converted into pyruvate (Cori cycle), then to glucose through the process of gluconeogenesis, and travels back to muscles for aerobic metabolism into immediate energy (ATP) + CO2 + H2O
21
Q

Describe the storage of carbohydrates in the liver.

A
  • Liver – holds ~300-400 kcal of energy as GLU in the form of glycogen
  • ~1/4 of body CHO stores
  • when at rest, liver stores of glycogen can supply GLU for ~24 hours
  • when active, glycogen stores can supply GLU for as little time as a few hours
  • free GLU available to other tissues because liver has glucose 6-phosphatase enzyme activity (not active in muscles)
22
Q

Describe the storage of carbohydrates in muscle.

A
  • capacity for storing ~1400 kcal of energy as GLU in the form of glycogen (trained athlete)
  • more typical stores ~500-700 kcal
  • can represent ~3/4 of body CHO stores
  • GLU only used internally by each muscle cell
23
Q

Describe the storage of carbohydrates in the bloodstream.

A
  • Not a true storage site
  • ~20-80 kcal continuously streaming in and out of blood
24
Q

What does the body rely on for long term energy reserves?

A

The body relies on fat – a relatively water-free energy storage system – very large amounts can be stored.

25
Q

How long do glycogen stores last?

A
  • holds 3 grams of water for each gram of glycogen, bulky energy storage system, therefore limited supply of energy stored as glycogen (hours)
26
Q

What is lipogenesis?

A
  • body energy needs are met, glycogen stores are full and still excess CHO kcal entering body
  • liver catabolizes GLU to smaller fragments and uses them to synthesize fat, called LIPOGENESIS
  • fat travels to adipose cells for storage § virtually unlimited fat storage
27
Q

Describe risk of fat gain due to overeating carbohydrates.

A
  • generally, excess quantities of CHO kcal are not consumed over long term when choosing higher quality dietary CHO (unrefined, fibre-containing): increased bulk, feeling of fullness sooner, greater satiety, lower fat/kcal intake
  • excess quantities of CHO kcal may be consumed when choosing lower quality dietary CHO (refined, concentrated sugars, often containing fat)
28
Q

What are endogenous sources of carbohydrates?

A

a. PROTEIN (Gluconeogenesis)

  • proteins in muscles & other organs – only C-skeleton portion of amino acid used
  • proteins needed for own functions, over time can lead to reduced functioning of organs (e.g., heart, muscles, liver, kidneys)
  • adequate dietary CHO intake “spares” body protein

b. FAT

  • only glycerol portion of TG available for GLU synthesis
  • when adequate CHO present, fat is completely oxidized to CO2 and H2O
  • “FAT burns in a fire of CHO”

c. Lactate

  • lactate that is produced from the anerobic glycolysis in RBC and active muscle (low O2) travels to liver where it is converted to GLU
  • Gluconeogenesis of GLU from lactate costs metabolic energy (ATP) and cannot be sustained indefinitely
  • GLU enters blood and returns to RBC or muscle for metabolic use
29
Q

What is ketosis?

A
  • if inadequate CHO present, fat is not completely oxidized leading to formation of KETONE BODIES
  • ketone bodies can be used as an energy source by the brain, heart, muscle and kidneys under conditions of low CHO intake (adaptive mechanism)
  • fruity smell on breath
  • ketones suppress appetite and cause dehydration
  • without this short-term adaptive process during periods of low/no CHO intake, body would be forced to greatly increase degradation of body proteins to supply GLU
  • ketosis may change blood pH, making it more acidic, which in the long term may damage organs
  • need to consume 50-100g CHO/day to spare body proteins and prevent ketone formation
30
Q

How is blood glucose level affected?

A
  • normal BGL ranges between 80-120 mg/dL (4-6 mmol/L)
  • BGL fluctuates in response to fed or fasted conditions
  • hyperglycemia: consistently >120 mg/dL
  • hypoglycemia: consistently <80 mg/dL
  • pancreatic hormones – main regulators of BGL:
  • insulin – lowers BGL
  • glucagon – raises BGL
31
Q

What hormones are the main regulators of blood glucose levels/?

A

Pancreatic hormones:

  • insulin – lowers BGL
  • glucagon – raises BGL
32
Q

Which hormone lowers blood glucose levels?

A

Insulin

33
Q

Which hormone raises blood glucose levels?

A

Glucagon

34
Q

Describe the function of insulin.

A
  • at high BGL – circulating insulin contacts receptors on cell membranes which opens channels through which GLU enters cells
  • most cells move the amount of GLU that is needed as an immediate source of energy
  • as BGL drops, turn to liver stores to maintain BGL in normal range
35
Q

Describe the function of glucagon.

A
  • at low BGL – Glucagon released from pancreas, acts on liver to enhance GLYCOGENOLYSIS
  • GLU released from glycogen stores in liver, enters bloodstream to raise BGL
  • GLU travels to other body cells for use as fuel

Note: during stress or exercise, epinephrine (adrenalin) also acts similar to glucagon to cause release of GLU from glycogen stores for use as energy

36
Q

What are the health implications of sugar intake?

A

Dental cavities

  • bacteria in mouth ferment sugars in food to produce acids, acids erode the enamel to cause cavities
  • increased frequency of intake, especially of sticky sugary foods, increases exposure time of enamel to acid and increases risk of dental cavities

Reduced nutrient density and relationship to risk of obesity

  • increased intakes of simple sugars, especially if combined with fat (lower quality dietary CHO) can displace more nutrient-dense foods in diet
37
Q

What are the health implications of starch intake?

A

A diet low in refined simple sugars and high in unrefined, complex CHO is often:

  • lower in fat
  • lower in energy
  • higher in fibre
  • higher in vitamins & minerals
  • this type of diet may assist in decreasing risk of obesity, diabetes, heart disease, cancer, dental caries, malnutrition
  • higher fibre intake increases diversity in gut microbiota – may help with weight control
38
Q

What are the positive health implications of dietary fibre?

A

Weight Control

  • slows eating, increases saliva production
  • delays gastric emptying – fullness, satiety
  • draws water into GI tract – fullness
  • sources: fruits, vegetables, legumes, whole grains – economical, nutritious, tasty

Improved Function/Health of GI Tract

  • taken with plenty of water, prevents impaction
  • insoluble fibres attract water, increased stool size, easier elimination
  • prevents GI disorders including:
  • constipation
  • hemorrhoids
  • diverticulosis

Lowered Blood Cholesterol

  • water-soluble fibres bind bile in small intestine making it unavailable for re-absorption in ileum – prevents ENTEROHEPATIC CIRCULATION of bile – bile exits in feces
  • decreased bile may lead to decreased fat and cholesterol absorption and lower cholesterol in the blood
  • with little bile being recycled to the liver, liver has to synthesize more bile
  • liver pulls cholesterol from blood to make bile

Slows Glucose Absorption

  • soluble fibre slows release of chyme from stomach into small intestine
  • blunted insulin response to slower and smaller amounts of GLU entering bloodstream

Reducing Risk for Colon Cancer

  • some populations with high intakes of fibre have shown reduced rates of colon cancer
  • dilution and/or binding of carcinogens, and/or rapid removal from colon
  • bacterial fermentation of resistant starches and fibres may reduce pH – protective effect?
39
Q

What are the negative implications of dietary fibre intake?

A

Bulk

  • high fibre intakes can provide satiety without adequate energy/nutrient intake
  • elderly, children, malnourished at risk

Abdominal Discomfort

  • rapid increase in fibre intake, gases produced, bacteria need time to adapt
  • gradually increase fibre from a variety of sources along with plenty of fluids

Impaction

  • high fibre intake without adequate fluid intake can dehydrate feces and cause blockage of GI tract
  • may need surgery to remove blockage

Quicker Passage through GI Tract

  • limited absorption of some nutrients
  • insoluble fibres bind minerals (e.g., Ca, Zn, Fe)
  • increased fibre intakes usually associated with increased mineral intake
40
Q

What is diverticulosis?

A

Diverticula may develop anywhere along the GI tract, but are most common in the colon.

41
Q

What is Enterohepatic Circulation?

A

Enterohepatic circulation refers to the circulation of biliary acids, bilirubin, drugs or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte and transport back to the liver.

42
Q

What are food sources of carbohydrates?

A
43
Q

What are the dietary recommendations for overall carbohydrate intake?

A

* choose unrefined simple and complex CHO from a variety of sources whenever possible

  • aim for <10% of total energy intake from “free sugars”; current Canadian intake ~11%
  • current Canadian intake of “total” sugars ~21%

DRI-RDA

  • all adults: 130 g/day
  • based on energy needs of the brain

DRI-AMDR

  • 45-65% of your total energy intake
44
Q

What are the dietary recommendations for dietary fibre?

A
  • key = moderation (not too much or too little)
  • recommended 14 g mixed dietary fibre/1000kcal § DRI-AI
  • adult woman: 25 g/day
  • adult male: 38 g/day
  • children: age + 5 = total grams dietary fibre/day
  • select from a variety of sources – plant foods only – whole grains, legumes, vegetables, fruit
  • eating breakfast is a good way to add to your dietary fibre intake for the day
  • consume plenty of fluids with dietary fibre

FNH 250 (11 decks)

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