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CARBOHYDRATES. Chapter 5. Carbohydrates. Made of carbon, hydrogen, and oxygen in a 1:2:1 ratio Primary fuel source for body cells Divided into two main classes: Simple sugars Complex sugars. MONOSACCHARIDES. GLUCOSE. Also called hexose or dextrose

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CARBOHYDRATES


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carbohydrates

CARBOHYDRATES

Chapter 5

carbohydrates1
Carbohydrates
  • Made of carbon, hydrogen, and oxygen in a 1:2:1 ratio
  • Primary fuel source for body cells
  • Divided into two main classes:
      • Simple sugars
      • Complex sugars
glucose
GLUCOSE
  • Also called hexose or dextrose
  • Principle building block of all other carbohydrates
  • Typically exists in the ring form
fructose
FRUCTOSE
  • Also called levulose
  • Isomer of glucose
  • Metabolized into glucose by the liver
  • Small amounts are converted into glycogen, lactic acid, or fat
  • Found in fruit, honey, and high fructose corn syrup
galactose
GALACTOSE
  • Not usually found free in nature in large quantities
  • Isomer of glucose
  • Typically found as a subunit of lactose
  • Converted to glucose by the liver
  • Used as an immediate energy source or is stored as glycogen
other monosaccharides
Other Monosaccharides
  • Ribose
      • Five carbon sugar
      • Used in the formation of RNA
      • Very little present in our diet
  • Deoxyribose
      • Five carbon sugar
      • Used in the formation of DNA
      • Not considered a nutrient of our diet since our bodies can make all that it ever needs.
maltose
MALTOSE
  • Constructed by a condensation reaction
  • Composed of two glucose molecules
  • Possesses an alpha bond
  • Commonly produced by fermentation reactions called malting
  • Most maltose digested is the result of starch digestion
sucrose
SUCROSE
  • Constructed by a condensation reaction
  • Composed of one glucose and one fructose
  • Possesses an alpha bond
  • Commonly called table sugar and is found in plants such as sugar cane and maple syrup
  • Purified to form brown, white, and powdered sugars
lactose
LACTOSE
  • Constructed by a condensation reaction
  • Composed of one glucose and one galactose
  • Possesses a beta bond
  • Beta bonds are difficult to digest
  • Primary sugar in milk and milk products
oligosaccharides
OLIGOSACCHARIDES
  • 3-10 monosaccharides: raffinose and stachyose
  • Found in beans and legumes
  • Not digested by the body
  • Metabolized by bacteria in the large intestine
  • Raffinose=galactose+glucose+fructose
  • Stachyose=galactose+galactose+

glucose+fructose

polysaccharides
POLYSACCHARIDES
  • Digestible polysaccharides:
    • Starch
      • Amylose
      • Amylopectin
    • Glycogen
  • Non-digestible polysaccharides: fibers
    • Soluble fiber
    • Insoluble fiber
starches
STARCHES
  • 3000 monosaccharides
  • Contain alpha bonds
  • Amylose is straight chain
  • Amylopectin is branched chain
  • High Glycemic Index
glycogen
GLYCOGEN
  • Storage form of glucose in animals and humans
  • Structure is similar to amylopectin but with more complex branching
  • Numerous alpha bonds
  • Found in liver (400 kcal) and muscles (1400 kcal)
fiber
Fiber
  • Dietary fiber= fibers found naturally in foods
  • Functional fibers= fiber added to foods that has shown to provide health benefits
  • Total fiber= dietary fiber + functional fiber
chemical composition of fibers
Chemical Composition of Fibers
  • Contain beta bonds
  • Insoluble: not fermented
    • Cellulose
    • Hemicellulose
    • Lignin*
  • Soluble: 1.5-2.5 kcal/g
    • Gum
    • Pectin
    • Mucilage
within the mouth
Within the Mouth
  • Saliva contains amylase
  • Converts polysaccharides, starch, into oligosaccharides, maltose, and glucose
  • Broken down by hydrolysis reaction
within the stomach
Within the Stomach
  • The acidic environment of the stomach inhibits the action of salivary amylase
within the small intestines
Within the Small Intestines
  • Pancreatic amylase
    • Converts oligosaccharides to disaccharides
  • Intestinal cells release
    • Maltase
    • Lactase
    • Sucrase
carbohydrate absorption
CARBOHYDRATE ABSORPTION
  • Monosaccharide absorption occurs in the duodenum
  • Glucose and galactose by active absorption
  • Fructose by facilitated diffusion
carbohydrate absorption1
CARBOHYDRATE ABSORPTION
  • Portal vein transports absorbed monosaccharides to the liver
  • Liver can then:
    • Transform them to glucose
    • Release them back to the blood stream
    • Store it as glycogen
functions of carbohydrates
FUNCTIONS OF CARBOHYDRATES
  • Supplies energy
  • Protein sparing
  • Prevents ketosis
  • Food sweeteners
    • Fructose
    • Sucrose
    • Glucose
    • Maltose
    • Galactose
functions of dietary fiber
FUNCTIONS OF DIETARY FIBER
  • Promotes regularity and softer, larger stool
  • Reduces hemorrhoids and diverticula
functions of dietary fiber1
FUNCTIONS OF DIETARY FIBER
  • Promotes regularity and softer, larger stool
  • Reduces hemorrhoids and diverticula
  • Aids weight control
  • Causes a filling of fullness
  • Slows glucose absorption
  • Decrease in colon cancer
  • Reduces cholesterol absorption
  • Reduces heart disease
recommended carbohydrate intake
RECOMMENDED CARBOHYDRATE INTAKE
  • RDA is 130 g/day for adults
  • 50-100 g of CHO/day to prevent ketosis
  • Recommended: 45-65% of total kcal
  • 180-330 g of CHO/day (primarily from white bread, soda, baked goods)
  • 50% of total kcal
  • Worldwide the CHO intake is +70%
recommended fiber intake
RECOMMENDED FIBER INTAKE
  • Adequate Intake is 25 g/day for women and 38 g/day for men (14g/1000kacl)
  • Daily Value= 25g/day for 2000 kcal diet
  • Average U.S. intake= 13-17 g/day
problems with high sugar intakes
PROBLEMS WITHHIGH SUGAR INTAKES
  • Empty calories
  • Dental caries
  • Glycemic index=the blood glucose response to a given food compared to a standard
  • Glycemic load=the amount of Carbohydrate in food times the glycemic index for that food. Related to structure, fiber content, amount of processing, and macronutrient content
effects of ingesting high glycemic load foods
Effects of Ingesting High Glycemic Load Foods
  • Stimulates insulin release
      • Insulin increases blood triglyceride levels
      • Insulin increases LDL
      • Insulin increase fat synthesis
      • Increased risk for CVD
      • Muscles may become resistant to insulin
      • Increases risk of developing diabetes
  • Become hungry quicker
problems with high intakes of dietary fiber
PROBLEMS WITH HIGH INTAKES OF DIETARY FIBER
  • Too much fiber (>60 g/day) will:
    • Require extra intake of fluids
    • Bind to some vitamins
    • Develop phytobezoars
    • Fill the stomach of a young child quickly
lactose maldigestion
Lactose Maldigestion
  • Primary lactose maldigestion
    • 75% of world population
    • Begins to develop around age 3 to 5 years
  • Secondary lactose maldigestion
    • Temporary decrease in lactase production
    • 25% of North American population
    • Increases with age
food sweeteners
FOOD SWEETENERS
  • Nutritive sweeteners
    • Sugars
    • Sugar alcohols
  • Alternative sweeteners
    • Saccharin
    • Aspartame
    • Neotame
    • Acesulfame-K
    • Sucralose