Lecture 4: Carbohydrates- Sugars, Starches, and Fiber Flashcards
(57 cards)
1
Q
Carbs
A
- The brain and body’s best
fuel source - Provide 4 kcal per gram
- Broken down into glucose
molecules in the body - Made through
photosynthesis
2
Q
Classifications of Carbohydrates
A
Based on # of units linked together
Can be simple or complex
(Simple carbs: mono or disaccharides, oligosaccharides, complex carbs: polysaccharides)
3
Q
Simple Carbs
A
Monosaccharides
Disaccharides
Perceived as sweeter than complex carbohydrates
* Mix with saliva and react with taste buds
Basic unit of carbohydrates: monosaccharide
* Glucose
* Fructose
* Galactose
Disaccharides: 2 monosaccharides linked together through condensation
* Maltose
* Sucrose
* Lactose
4
Q
Complex Carbs
A
Polysaccharides
5
Q
Condensation Reactions
A
Links monosaccharides to form disaccharides
Glucose + Glucose = Maltose
Glucose + Fructose = Sucrose
Glucose + Galactose = Lactose
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Q
Complex Carbs
A
Made up of many monosaccharides linked together in
chains
* Oligosaccharides: 3-10 monosaccharides.
~In foods: Legumes, beans, cabbage, brussels sprouts,
broccoli
~Found in breast milk
* Polysaccharides
~Glycogen (animals)
~Starch, fiber (plants)
7
Q
Polysaccharides
A
Starch
~Plant glucose storage in two forms:
-Amylose
-Amylopectin
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Q
Amylose
A
Straight chain of polysaccharides found in starch
- More resistant to digestion than amylopectin – “resistant
starch” is not digested in the GI tract.
~May improve health of digestive tract
~May improve glucose tolerance
~May stimulate growth of beneficial intestinal bacteria
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Q
Amylopectin
A
Branched chains of polysaccharides found in starch
* Easier to digest
10
Q
Where to get starch from in diet?
A
- Toots and tubers
- Grain seeds
- Legumes
- Cornstarch
- Many processed foods
11
Q
Glycogen
A
- Storage form of carbohydrates in animals
- Stored in liver and muscles in limited amounts
- Source of glucose for body
- Dissipates with rigor mortis, therefore is not present in
animal products that humans consume
12
Q
Fiber
A
- Most forms of fiber are nondigestible polysaccharides and occur naturally as a structural component called cellulose.
- We cannot digest or absorb fiber
- Only found naturally in plant foods, not foods of animal origin
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Q
Dietary Fiber
A
Natural Fiber
14
Q
Functional Fiber
A
Added Fiber
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Q
Total Fiber
A
Dietary + Functional Fiber
Listed as dietary fiber on food labels
16
Q
Soluble Fiber
A
- Dissolves in water to form viscous solutions
- Can be fermented by intestinal bacteria
- Includes: pectins, beta-glucans, mucilages
- Food sources: oats, apples, beans, seaweed
Benefits:
* Helps lower cholesterol
* Slows gastric emptying
* Control appetite
* Normalizes blood sugars
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Q
Insoluble Fiber
A
- Cannot be fermented by bacteria in the large intestine
- Does not dissolve in water
- Derived from structural parts of plants such as cell walls
- Includes: cellulose, lignin, some hemicelluloses
- Food sources: wheat bran, rye bran, fruit & vegetable peels
Benefits:
* Increases bulk of stool
* Helps relieve constipation
18
Q
Apple
A
Skin= Cellulose: insoluble fiber
Inside apple= Pectin: soluble fiber
19
Q
Why is dietary fiber so important?
A
Benefits:
* Helps lower risk of
~Bowel irregularity
~Constipation and diverticulitis
~Obesity
~Heart disease
~Cancer
~Diabetes
20
Q
What can fiber help prevent?
A
Heart Disease
Diabetes
Cancer
21
Q
How does fiber prevent heart disease?
A
- Soluble fiber helps decrease blood cholesterol levels.
- Soluble fiber may reduce the rate at which fat and
carbohydrate are absorbed. - Insoluble fiber has been shown to promote heart health
22
Q
How does fiber prevent diabetes?
A
- Soluble fiber helps slow digestion and absorption of glucose,
helping control blood glucose levels. - Higher consumption of fibers from cereals has been shown to reduce the risk of developing diabetes
23
Q
How does fiber prevent cancer?
A
- Fiber helps reduce the incidence of several cancers.
~Decreases the amount of time cancer-promoting substances spend in contact with the intestinal lining
~Encourages the growth of colon-friendly bacteria and their
fermentation by-products
~Reduces concentration of bile acids in the colon
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Q
How does fiber prevent obesity?
A
- Increases satiety, resulting in reduced food intake
- Some cautions about fiber
~Introduce fiber into the diet slowly.
~Initially, a high-fiber diet can cause flatulence and bloating.
~It may reduce the absorption of some minerals
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How are carbs digested and absorbed?
* Disaccharides and starch are digested into monosaccharides.
* Monosaccharides are easily absorbed by the small intestine.
* Fiber passes through the GI tract undigested.
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Where are carbs digested?
Mouth:
~Saliva contains amylase enzyme, which starts breaking down amylose and amylopectin into smaller starch units and maltose
~Mechanical digestion of fiber
* Stomach:
~HCl inactivates salivary amylase
~Fiber delays gastric emptying
* Small intestine
~Pancreatic amylase breaks down remaining starch into disaccharides (maltose)
~Maltose and other disaccharides are broken down to monosaccharides and absorbed into blood
* Large intestine
~Fiber continues to the large intestine, where some is metabolized by bacteria in the colon and the majority eliminated in your stool
~Production of short-chain fatty acids by fiber metabolizing bacteria
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How are carbs absorbed?
After carbohydrates are digested to monosaccharides they are:
* Absorbed through the intestinal cell mucosa
* Transported to the liver via the portal vein
* Metabolic needs direct the fate of the monosaccharides
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Absorption of galactose and fructose
Used by the liver for energy
Converted to glucose
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Absorption of Glucose
* Used for energy
* Converted to glycogen through glycogenesis
* Excess glucose is converted to glycerol and fatty acids for storage in adipocytes.
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Functions of Carbs
* Provide energy
~4 kilocalories per gram
* Maintain blood glucose levels
~Glucose is the primary fuel for the brain.
~Glycogenolysis occurs 4 hours after a meal.
~Muscle glycogen cannot be used to raise blood glucose levels.
* Spare protein
~Prevents the need for gluconeogenesis
-Occurs mainly in the liver but can occur in the kidney
* Prevents ketosis
~Ketosis is an elevated number of ketone bodies in the
blood that occurs after approximately 2 days of fasting
-Protein from muscle and organs broken down to make
glucose
-Brain switches to using ketone bodies for fuel to spare
protein-rich tissues
-If fasting continues, protein reserves are depleted and
death occurs
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Ideal blood glucose level
The body wants to keep blood glucose between 70 milligrams/deciliter and 110 milligrams/deciliter to ensure availability to cells
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Hormones responsible for maintaining blood glucose level
Insulin
Glucagon
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Insulin
* Released from pancreas
* Lowers blood glucose level
~Needed for glucose to enter the cell from the bloodstream
~Liver, kidney, and brain cells can use glucose without insulin.
~Stimulates glycogenesis (liver and muscle)
~Stimulates lipogenesis (liver and adipose)
~Inhibits lipolysis
~Inhibits gluconeogenesis
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Glucagon
* Released from pancreas
* Target organ is the liver
* Increases blood glucose level
~Stimulates the release of glucose into the blood
-Stimulates glycogenolysis
-Stimulates gluconeogenesis
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Fed (postprandial) state
Blood glucose increases
* Pancreas releases insulin
* Insulin allows for the uptake of glucose by peripheral tissue (glucose travels from the blood into tissue = drop in blood glucose)
~Muscle stores glucose as glycogen (glycogenesis)
~Adipose stores glucose as fat (lipogenesis)
* Liver will store as glycogen and then fat lipogenesis; reduces glucose output
* Reduction in blood glucose signals `pancreas to reduce insulin secretion
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Fasting State
* Blood glucose drops
* Pancreas releases glucagon
* Glucagon stimulates the breakdown of glycogen into glucose (glucose travels from the tissue into blood = increase in blood glucose)
* Stimulates gluconeogenesis in the liver; increases glucose output
* Increase in blood glucose signals pancreas to reduce glucagon secretion
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Hypoglycemia
Low blood glucose below
* Occurs with excess insulin production
Symptoms:
Hunger, dizziness, feeling light-headed, confused, weak, or
beginning to sweat
Treatments:
* Eat or drinking
carbohydrate-rich foods
* Eating smaller, well-balanced meals throughout the day
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Glycemic Response
Blood glucose response
* How quickly and how high blood glucose level rises after
consuming carbs
* How quickly it returns to normal
Affected by:
* type and amount of carbohydrate consumed - refined sugars
and starches raise blood sugar levels faster than unrefined
carbohydrates and fiber
* amount of fat and protein consumed
* Genetics
* Microbiome
* Sex
* Anthropometrics
* Other environmental factors (sleep, physical activity, meal
timing)
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Glycemic Index (GI)
A rating scale of the likelihood of foods to increase the levels of blood glucose and insulin.
Concerns:
* Does not account for the amount of carbohydrate
consumed.
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Glycemic Load (GL)
The amount of carbohydrate in a food multiplied by the amount of the GI of that food.
* Adjusts the GI to account for the amount of carbohydrate
typically eaten
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DRI Carb Recommendation
130 grams/day
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MyPlate Carb Recommendation
* 6 servings of grain/day
* 3 servings of vegetables/day
* 3 servings of dairy/day
* 2 servings of fruit/day
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AMDR carb recommendation
45-65% of total kilocalories/day
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Overconsumption of carbs
Most adults in the United States consume well over the
minimum DRI: 180-330g/day (~50% kcal)
* Primarily from refined bread, soda, baked goods
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Daily Fiber recommendations
DRI: 14 grams per 1,000 kilocalories consumed
AI: 25 to 38 grams per day
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Best sources of carbs
Whole foods
Some sources are better than others such as grains, vegetables, fruits, and beans
Best choices should include:
* Nutrient-dense, low-saturated-fat foods, with low amounts of
simple carbohydrates
* Higher amounts of fiber and complex carbohydrates
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Parts of a whole grains
Endosperm
Bran
Germ
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Endosperm
Largest part of kernel.
Made up primarily of starch
Contains most of kernel's protein + some vitamins and minerals
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Bran
Outermost layer
Contains most of the fiber
Good source if many vitamins and minerals
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Germ
Located at the base of kernel
Embryo where sprouting occurs
Source of oil
Rich in vitamin E
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Whole-wheat flour
Missing folic acid
Uses who kernel
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Enriched flour
Only uses Endosperm
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Wheat flour (not enriched)
Uses only endosperm
No nutrients added back
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Enrichment
Adding nutrients back
Riboflavin
Niacin
Thiamin
Iron
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Fortification
Adding extra nutrients
Folate
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Whole Grains
* Decrease risk of stroke
* Decrease risk of dying from cancer or heart disease
* Fiber linked to lower risk of diabetes
* More satiating
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