Transcript Carbohydrates

Carbohydrates
King Saud University
Al-Riyadh Community college
By: Murad Adnan Sawalha
Outline
• Nature of carbohydrates
• Classes of carbohydrates
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- Simple carbohydrates
(monosaccharide, disaccharides)
- Complex carbohydrates
(polysaccharides)
Functions of carbohydrates
Food sources of carbohydrates
Digestion of carbohydrates
Body needs for carbohydrates
Nature of carbohydrates
• Basic fuel source:
- Energy is the power an organism requires to do
work, this energy system must have a basic fuel
supply.
- Photosynthesis: transform solar energy into
carbohydrates (the stored fuel form of plants.
- Because the human body can quickly breakdown
sugars & starches, they provide the major sources of
energy, in the form of calories.
- “Quick energy” foods.
Nature of carbohydrates
• Energy production system:
- 3 steps to produce energy from a basic fuel supply:
1) Change the basic fuel to a refined fuel that the
machine is designed to use.
2) Carry this refined fuel to the places that need it.
3) Burn this refined fuel in the special equipment set
up at these places.
- Example: (1) In human body, the body digests its
basic fuel, carbohydrates, changing it to glucose. (2)
The body then absorb & through blood circulation,
carries this refined fuel to cells that need glucose. (3)
Glucose is burned in these cells, & energy produced
through the process of metabolism.
Nature of carbohydrates
• Dietary importance:
- Carbohydrates are widely available & easily
grown
- Low cost in comparison with other food items.
- Easily stored, & they can be kept for long periods
without spoilage.
- Most of the total Kcalories in our diet come from
carbohydrates.
Classes of carbohydrates
• A carbohydrates is composed of carbon (C), hydrogen
(H), and oxygen (O).
• (CH2O)n when n = 5 then C5H10O5
• Saccharide: chemical name for sugar molecules comes
from the Latin word saccharum, meaning “sugar”.
• Carbohydrates: are classified according to the number
of sugar, or Saccharide units.
Classes of carbohydrates
• Monosaccharide: single (mono) molecules of
sugar, one sugar unit.
– They are quickly absorbed from the intestine into the
blood stream and carried to the liver.
– Glucose, fructose, lactose.
• Disaccharide: “double sugar” composed of 2
sugar unit.
- Sucrose, Lactose, Maltose.
• Polysaccharide: carbohydrates consisting of
many (poly) sugar molecules.
- Starch, Glycogen, Dietary fiber.
Monosaccharide
• Glucose:
- Is the form of sugar circulating in the blood and is
the primary fuel to the cells.
- The blood supply comes mainly from the digestion
of starch, & sometimes called dextrose.
- Is a moderately sweet sugar.
• Fructose: is found mainly in fruits, consider the
sweetest of the simple sugars.
• Galactose: comes mainly from the digestion of milk
sugar, or lactose.
Disaccharides
• Sucrose:
- Is common table sugar, its two sugar units are
glucose & fructose.
• Lactose:
- Is the milk sugar, formed in mammary glands
- Its two single sugar units are glucose & Galactose.
- Not found in plants.
- Aids in the absorption of calcium & phosphorus.
• Maltose:
- The two single sugar units that compose maltose
are double glucose molecule.
Polysaccharides
• 1) Starch:
- They are found in grains, legumes, and other
vegetables, and some fruits.
- Breakdown more slowly and supply energy over a
longer period of time.
- Most important dietary carbohydrate
- The major food sources of starch include grains in
the form of pasta, crackers, bread, and other baked
goods, legumes in the form of beans, & peas,
potatoes, rice, corn, & bulgur.
Polysaccharides
- Whole grains: is used for food products such as
flours, breads, or cereals that are produced from
unrefined grain, which is grain that still retains its
outer bran layers and inner germ endosperm and
their nutrients (i.e. dietary fiber, minerals, &
vitamins)
- Enriched grains: are refined grain products to
which key nutrients, usually minerals (i.e. iron),
and vitamins (i.e. A, C, D, thiamin, riboflavin, &
niacin), have been added.
• 2) Glycogen: found in animal muscle tissue, and
liver
• 3) Dietary fiber
Polysaccharides: Dietary fiber
• Dietary fiber: in humans there is a lack in the necessary
enzymes to digest dietary fiber, used to treat
gastrointestinal problems.
- Cellulose: helps move the food mass along, stimulates
normal muscle action in the intestine, and forms feces for
elimination of waste products, the main sources are the
stems and leaves of vegetables and the coverings of seeds
and grains.
- Noncellulose polysaccharides: they absorb water and swell to
a larger bulk, thus slowing the emptying of the food mass
from the stomach, and preventing spastic colon.
- Lignin: is a large compound that forms the woody part of
certain plants, it also combines with bile acids and
cholesterol in the human intestine, preventing their
absorption
Other sweeteners
• Used as sugar replacers
• 2 types:
1) Nutritive sweeteners:
- They are sweeteners such sugar alcohols that
contribute to total calorie intake.
- Sugar alcohols (sorbitol, mannitol, & xylitol)
- 2-3 kcalories/gram.
- Sorbitol: sucrose substitute.
- They are absorbed slowly in the small intestine.
- Use for diabetic patients
- Excessive amount= diarrhea.
- lowered risk than sugar to cause dental caries.
Other sweeteners
2) Nonnutritive sweeteners:
- Alternative sweeteners.
- Are sugar substitutes that do not have any
caloric value.
- Sweet taste without energy.
- Commonly used are aspartame & saccharin.
- Sweeter than table sugar.
Functions of carbohydrates
• 1) Primary energy function:
(a) Basic fuel supply:
- Primary fuel for the body.
- Fuel factor for carbohydrates is 4 kcal/gram.
(b) Reserve of fuel supply:
- Glycogen reserves fuel supply
- Individual must eat carbohydrate foods
regularly to meet energy demand (to maintain
blood glucose level & prevent a breakdown of
fat and protein in tissue).
Functions of carbohydrates
• 2) Special tissue functions:
- Liver: glycogen reserves in the liver &
muscles, protect cells from depressed
metabolic function.
- Protein & fat: (1) Carbohydrates protects
protein to be used in tissue growth &
maintenance (2) Prevent rapid breakdown
of fat & produce ketones (strong acid),
this action called antiketogenic effect.
Functions of carbohydrates
• 2) Special tissue functions:
- Heart: fatty acids are the regular fuel for
energy, in emergency situation glycogen.
- Central nervous system: the brain need
continues supply of glucose, otherwise low
sugar cause brain damage.
Food sources of carbohydrates
• Starches:
- Such as grain products (corn, bread), & vegetables
(tomatoes, onions).
- Provide energy for prolong period.
- Basic component in the balanced diet.
- Unrefined forms are considered sources of fiber &
other nutrients.
• Sugars:
- Such as candies, fruits, milk.
- are necessary for health but in a moderate amount.
- High sugar diets= risk for dental caries & obesity.
Digestion of carbohydrates
• Mouth: digestion by 2 types of actions:
1) Mechanical process by mastication: breakdown
food into small particles, & mixed with saliva.
2) Chemical process: specific enzymes such as
salivary amylase breaks into smaller usable
metabolic products.
Example: amylase breakdown starch into
dextrin, and disaccharides.
- Monosaccharides travel to stomach & small
intestine for absorption without further
digestion.
Digestion of carbohydrates
• Stomach:
- Peristalsis: wavelike contractions of the
muscle fiber mixes food particles with
gastric secretions.
- Hydrochloric acid: stops the action of
salivary amylase.
- In the lower part of the stomach: the food
mass become thick creamy (chyme)
- Emptying chyme to duedenum.
Digestion of carbohydrates
• Small intestine:
- peristalsis continue mechanical digestion.
- Pancreatic secretions: enter the duodenum through the
common bile duct.
Pancreatic amylase: (1) digest starch to maltose, (2)
reduces maltose to monosaccharides, (3) breakdown of
disaccharides to monosaccharides.
- Intestinal secretions: enzymes attached to “special cells
on the microvilli” (bruch border), sucrase, lactase, &
maltase convert dissaccharides (sucrose, lactose,
maltose) into monosaccharides (glucose, galactose, &
fructose)
- Lactose intolerance: inability to break lactose into
glucose & galactose (lack of lactase enzyme),
symptoms include bloating, gas, abdominal pain, &
diarrhea.
Body needs for carbohydrates (CHO)
• Dietary reference intake:
- 45%-65% of an adult total caloric intake should come
from carbohydrate foods.
- Means 225-325g of CHO for a 2000kcal/day diet
- Recommended fiber: choosing carbohydrates contain
whole grain cereals, legumes, vegetables, & fruits.
- Sugars no more than 25% of total calories.
• Dietary guidelines for americans:
- As in food guide pyramid: grains, fruits, & vegetables
are the foundation of a healthy diet.
Thank you for your listening