Carbohydrates - Text Book
For young adults, what percentage of the daily energy intake should come from carbohydrates? a. 15-20% b. 25-30% c. 45-50% d. 45-65%
45-65%
Identify some commonly used alternative sweeteners.
Artificial Sweeteners - acesulfame potassium, aspartame, sucralose, saccharin Herbal Products - Stevia Sugar Alcohols - Erythritol - Isomalt - Lactitol - Maltitol
Describe the risks and benefits of using alternative sweeteners.
Artificial Sweeteners: - 0 kcalories - safe for ingestion/ pregnant women - may have adverse effects at high levels - may cause longterm detrimental effects i.e. sucralose - contain Cl Herbal Product - Stevia - 0 calories - generally recognized as safe - 300 x sweet, therefore, only need a little Sugar Alcohols - alternative sugar for people with diabetes - inhibiting caries-causing bacteria - limit energy intake
What are the possible fates of glucose in the body?
- energy - metabolism - blood glucose regulation
Summarize the main steps in the metabolism of glucose.
1. Glycolysis = 1 glucose --> 2 pyruvate (net energy = low) 2a) 2 Pyruvate --> 2 Lactate (anaerobic, quick source of temp. energy) 2b) 2 Pyruvate --> 2Acetyl CoA (aerobic, generates fat or ATP)
During which metabolic process is a disaccharide made from two monosaccharides? a. digestion b. hydrolysis c. condensation d. glucogenesis
condensation
What may each of the energy-yielding nutrients first be metabolized to before entering the TCA cycle? a. ammonia b. pyruvate c. electrons d. acetyl CoA
d. Acetyl CoA
What is a significant difference between starch and cellulose? a. starch is a polysaccharide but cellulose is not b. animals can store glucose as starch, but not as cellulose c. hormones can make glucose from cellulose but not starch d. digestive enzymes can break the bonds in starch, but not in cellulose
digestive enzymes can break the bonds in starch, but not in cellulose
What is the storage form of glucose in the body? a. insulin b. maltose c. glucagon d. glycogen
glycogen
When glucose is insufficient in metabolism, what do fat fragments combine to form? a. dextrin's b. mucilages c. phytic acids d. ketone bodies
ketone bodies
What enzyme breaks a disaccharide into glucose and galactose? a. amylase b. maltase c. sucrase d. lactase
lactase Note: lactose is a disaccharide composed of the monosaccharides glucose and galactose
Which set of terms fits into the category of disaccharides? a. starch, glycogen, fiber b. amylose, pectin, dextrose c. sucrose, maltose, lactose d. glucose, galactose, fructose
maltose, sucrose, lactose
Which type of food does NOT contain carbohydrates? a. milks b. meats c. breads d. fruits
meats
Define aerobic and anaerobic metabolism. How does insufficient oxygen influence metabolism?
process does require oxygen / process does not require oxygen The anaerobic pathway yields energy quickly but cannot be sustained for long. Need of immediate energy = pyruvate --> lactate (anaerobic) Need of normal energy = pyruvate --> acetyl CoA (aerobic)
What is the protein-sparring action of carbohydrates?
the action of carbohydrate in providing energy that allows protein to be used for other purposes. if adequate amount of carbohydrates aren't available the body will begin to break down protein to glucose form the liver and skeletal muscles
What is the ultimate goal of carbohydrate digestion and absorption? a. to yield fibers b. to yield glucose c. to yield enzymes d. to yield amylase
to yield glucose
How are starch and glycogen similar and how do they differ?
Glycogen = an animal polysaccharide; storage form of glucose in the body Starch = plant polysaccharides; storage form of glucose in plants Similarities: both are built of glucose units Differences : - Glycogen = found only to a limited extent in meats and not at all in plants; food is not a significant source of glycogen; storage sites = liver and muscle cells - Starch = found to a great extent in plants - grains [richest source of starch] (wheat, rice), root crops, tubers (yams and potatoes), legumes (peas, beans)
Describe the structure of a monosaccharide and name the 3 monosaccharides important in nutrition. In what foods are these sugars found?
Monosaccharides are most important in nutrition, each contain 6 carbons, 12 hydrogens, 6 oxygens (C6H12O6). The Three Monosaccharides: - Glucose - Fructose - Galactose Foods monosaccharides are found in? - Glucose (blood sugar, dextrose) - Fructose (naturally = fruits, honey; Other: soft drinks, cereals, desserts) - Galactose (milk and dairy foods) Note: also known as a simple carbohydrate
How can these alternative sweeteners be classified?
Non-nutritive = provide no energy - artificial sweeteners - stevia (herbal product) Nutritive = provide energy - sugar alcohols
Describe the structure of polysaccharides and name the ones important in nutrition.
Polysaccharides contain many glucose units and in some cases a few other monosaccharides; they are long chains of monosaccharides also known as complex carbohydrates. Polysaccharides in Nutrition: - glycogen - starch - fiber
How does the body maintain its blood glucose concentration? What happens when the blood glucose concentration rises too high or falls too low?
Regulating Hormones: - Insulin = for when blood sugars are HIGH; insulin moves blood glucose into cells - Glucagon = for when blood sugars are LOW; stimulates liver to to bring glucose out of storage and to release it into the blood stream - Epinephrine also signals the liver to release glucose in times of stress
What foods provide starches and fibers?
Starch: - grains (wheat, rice) - root crops -tubers (yams, potatoes) - legumes (peas, beans - resistant starch) - starch is found in all plants Soluble Fibre: - whole grains (barley, oats, bran, rye) - fruits (apples, citrus) - legumes, seeds, husks, vegetables Insoluble Fibre: - brown rice - fruits - legumes - seeds - vegetables (cabbage, carrots, brussel sprouts) - wheat bran - whole grains
How do starch and glycogen differ from other polysaccharides?
Strarch and Glycogen can be digested and absorbed by digestive enzymes, whereas, fiber is not digested nor absorbed and instead are: a. digested by bacteria in the colon (soluble fibers) b. pass through the body and are excreted (insoluble fibers) Note: because fiber is not digested nor absorped - passes through the body as is - they contribute no monosaccharides, thus, little to no energy a
Name the 3 disaccharides commonly found in foods and their component monosaccharides. In what foods are these sugars found?
The Three Disaccharides: - Maltose (Glucose + Glucose) - Sucrose (Glucose + Fructose) - Lactose (Glucose + Galactose) Foods disaccharides are found in? - Maltose (barley) - Sucrose (fruits, vegetables, grains) - Lactose (milk) Note: also known as a simple carbohydrate
What does the pancreas secrete when blood glucose rises? When blood glucose falls? a. insulin: glucagon b. glucagon:insulin c. insulin:glycogen d. glycogen:epinephrine
a. insulin[high]:glycogen[low]
For complete oxidation, which process does acetyl CoA enter? a. glycolysis b. TCA cycle c. Cori cycle d. the electron transport chain
b. the TCA cycle
Which of the following statements about glycolysis is correct? a. glycolysis always requires oxygen b. glycolysis generates abundant energy c. glycolysis converts glucose to pyruvate d. glycolysis produces ammonia as a by-product
c. glycolysis coverts glucose to pyruvate
Which of the following is correct about the pathway from pyruvate to acetyl CoA? a. it produces lactate b. it is known as glucogenesis c. it is metabolically irreversible d. it requires more energy than it produces
c. it is metabolically irreversible
Describe carbohydrate digestion and absorption.
Digestion: In the mouth salivary amylase begin to break down polysaccharides to disaccharides to monosaccharides. Very little carbohydrate digestion takes place in the mouth. In the stomach the food mixes with stomach acid and protein-digesting enzymes which inactivate salivary amylase. Fibers linger in the stomach and delay gastric emptying thereby provide a feeling of fullness (satiety) In the small intestine a great deal of carbohydrate digestion takes place. Pancreatic amylase enters the small intestine and breaks down polysaccharides to disaccharides. Then specific enzymes come in to break down specific disaccharides Lactase breaks down lactose into- galactose and glucose Maltase breaks down maltose into 2 glucose molecules Sucrase breaks down sucrose into fructose and glucose In the large intestine within 1-4 hours all sugars and most of starches have been digested. Only fibers remain in the digestive tract. Fiber attracts water in the large colon and bacteria will attempt to break down some of the fiber content. Absorption: Some glucose is absorbed through the lining of the mouth but for the most part nutrient absorption takes place in the small intestine. Glucose + Galactose = active transport Fructose = facilitated diffusion As blood travels from small intestine to liver cells take up the sugars they need.
What role does fiber play in digestion and absorption?
Fiber delays gastric emptying, creates a feeling of fullness (satiety), attracts water in the large intestine (drink lots of water).
What are the health effects if starches and fibers? What are the dietary recommendations regarding these complex carbohydrates?
Foods rich in starch and fiber offer many health benefits a. protect against heart disease - lower BP, improve blood lipids, reduce inflammation - oatmeal reduces cholesterol and thus risk of heart disease - foods rich in soluble fibers lower blood cholesterol by binding with bile acids in the GI tract and thereby increasing their excretion - bacterial by products of fiber fermentation in the colon inhibit cholesterol synthesis in the liver b. high fiber foods reduce the risk of T2DM by slowing glucose absorption in the GI tract c. dietary fibers enhance the health of the large intestine; cleanse colon, alleviate constipation, prevent several GI disorders - prevent hemorrhoids, appendicitis, diverticulosis d. increasing dietary fiber protects against colon cancer high fiber and whole grain foods help maintain weight. Rich fiber foods create feeling of satiety thus prevent weight gains and promote weight loss ** harmful effects of excessive fiber** - energy/ nutrient needs unmet on high fiber diet - abdominal discomfort, gas, diarrhea , obstructio of GI tract - dehydration DRI: - carbohydrates = 45-65% of energy requirement (900 kcal/ 2000 kcal; 225-325g/day; min (RDA) = 130 g/day) - Fiber = men = 38 g; 50+ men = 30g; women = 25 g, 50+ 21 g
What are the health effects of sugars? What are the dietary recommendations regarding concentrated sugar, "added" sugar intakes.
When consumed in moderate amounts sugars do not harm health. When consumes in excess amounts sugars can be detrimental: a. cause nutrient deficiencies by supplying kcalories without nutrients b. contribute to tooth decay and dental caries Dietary recommendation for "added" sugar = <25% of the days total energy intake WHO = free sugars = <10% of total energy intake American Heart Association = - women = 6 tsp/day - men = 9 tsp/day Sources of Natural Sugar = milk, fruits, vegetables, grains
What happens in a condensation reaction?
a chemical reaction in which water is released as two reactants combine together to form one large product
What happens in a hydrolysis reaction?
a chemical reaction splits a molecule into 2, with H added to one and OH added to other (from water). this reaction typically takes place during digestion