Carbohydrates

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Carbohydrates
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Types of carbohydrates

• Sugars
• Starches
• Fibers

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Functions

• Provide 1/2 of energy needs of body through
  glucose and glycogen

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Chemical composition

• Carbon
• Hydrogen
• Oxygen
• Ratio 121- CH2O

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Types of carbohydrates

• Simple
• Sugars
• Monosaccharides
• Disaccharides
• Complex-chains of simple sugars
• Glycogen
• Starches
• Fibers

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Simple carbohydrates monosaccharides

• Glucose
• Found in plants and animals
• Blood sugar- essential source of energy
• Fructose
• Found in plants
• Can convert into glucose and be used by body
• Galactose
• Part of milk sugar

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Condensation reactions

• Two simple sugars can chemically join together to
  make a disaccharide through condensation reactions

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Simple sugars disaccharides

• Maltose
• Glucose-glucose
• Sucrose
• Glucose-fructose
• Lactose
• Glucose-galactose

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Hydrolysis reactions

• Disaccharides (and polysaccharides) can be broken
  into their monosaccharide components through
  hydrolysis reactions
• These monosacchrides can be metabolized by the
  body

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Complex carbohydrates

• Usually long chains of glucose
• Known as polysaccharides

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Complex carbs glycogen

• Found only in animals
• Long branched chains of glucose
• Found in muscle cells and liver cells
• Hydrolyzed when the body needs glucose
• Not a nutritionally significant source of
  carbohydrate

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Complex carbs starches

• Polysaccharides found in plants
• Grains
• Yams and potatoes
• Legumes
• Long unbranched or slightly branched chains of
  glucose
• Can be digested (hydrolyzed) by humans

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Complex carbs fibers

• Structural parts of plants
• Usually nonstarch polysaccharides
• Bonds cannot be broken by human digestion

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Soluble fibers

• Dissolve in water, viscous, form gels
• Ferment easily by colon bacteria
• Found in oats, barley, legumes, citrus
• Protect against heart disease, diabetes
• Lower cholesterol and glucose
• Includes pectin from fruit thickening agent

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Insoluble fiber

• Do not dissolve in water
• Not easily fermented
• Found in bran of whole grains and in vegetables
• Promote bowel movements and prevent constipation

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Functional fibers

• Fibers extracted from plants or manufactured and
  added to foods or supplements
• Have beneficial health effects
• For example, cellulose in supplement form to
  alleviate constipation

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Total fiber

• Sum of dietary fibers and functional fibers

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Resistant starches

• Starches that do not digest and pass into colon
• Nature of starch-no one can digest
• Reduced or lack of ability of the individual to
  digest
• Common in whole legume, raw potatoes, unripe
  bananas

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Phytic acid

• Not a fiber
• Often accompanies fibers
• Found is husks of grains, legumes, seeds
• Can bind to minerals (possibly fibers can also)
  which are then excreted in stools, and thus are
  unavailable for absorption
• Problem if mineral intake is inadequate and/or
  fiber intake very high

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Carbohydrate digestion

• Starches are broken into shorter chains, and
  eventually into glucose, which is absorbed
• Unbranched chains digest more slowly and raise
  blood glucose less than branched (glycemic index)
• Disaccarides are broken into 2 monosaccharides,
  which are absorbed
• Glucose is absorbed directly

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Carb. Digestion in mouth

• Salivary amylase breaks start into small
  polysaccharides and maltose

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Carb. Digestion in stomach

• Amylase is inactivated and carb. Digestion stops

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Carb. digestion in sm. intestine

• Pancreatic amylase converts more starch into
  short polysaccharides and maltose
• Disaccharides are broken into component
  monosaccharides by enzymes on surface of
  intestinal cells
• Maltoseglucoseglucose
• Sucroseglucosefructose
• Lactoseglucosegalactose
• Monosaccharides are then absorbed
• All digestable carbs. are processed and absorbed
  within 1-4 hours after eating

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Carb. Digestion in colon

• Only fibers left
• Bacteria ferment some fibers into water, gas, and
  short chain fatty acids
• Fatty acids can be used by cells of large
  intestine as energy source or absorbed and
  transported to liver

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Benefits of fiber

• Undigested fibers hold water, bind bile,
  cholesterol, and some minerals
• Are eliminated
• Slows absorption of glucose
• Regulates passage of food through system
• Alleviates constipation

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Absorption

• Glucose
• In mouth
• In small intestine
• Requires active transport (energy powered pumps)
• Fructose and galactose
• In small intestine
• Requires facilitated diffusion
• Slower than active and causes less rise in blood
  glucose

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Fate of galactose and fructose

• Travel to liver
• Converted usually into glucose
• NOTE All disaccarides provide one molecule of
  glucose directly and a second one indirectly

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Lacotse intolerance

• Lactose is broken by the enzyme lactase into
  monosaccharides
• If the enzyme is not present in sufficient
  amount, lactose remains undigested and attracts
  water, which leads to bloating discomfort and
  diarrhea
• It then passes into large intestine
• Bacteria utilize lactose and produce gas, and
  more discomfort and bloating and diarrhea

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Causes of lactase deficiency

• Aging
• Genetics
• Congenital
• Disease
• Medicines
• Diarrhea
• Malnutrition

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Prevalence of lactose intolerance

• Lowest in northern Europeans
• Highest in native North Americans and Southeast
  Asians

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Management

• Dietary changes-avoid lactose
• Lactase supplements
• Total avoidance of dairy could lead to
  riboflavin,vitamin D, and calcium deficiency, if
  other sources are not eaten

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Glucose

• Energy supply is primary role
• Can combine with proteins and change protein
  function
• Can combine with fats in cell membranes and
  influence ways cells recognize one another
• Sugar coated cancer cells evade the immune system
  because the immune system thinks they look
  normal
• Possibility for vaccine based on sugar

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Glycogen

• After energy needs are met, muscle, brain and
  liver covert excess glucose to glycogen
• Muscles store 2/3s of glycogen ,but use it for
  muscle energy needs
• Brain store a tiny amount for its own use-the
  brain has to have glucose at all times
• Liver store 1/3 of total glycogen breaks off
  glucose molecules and releases them into blood
  when blood sugar drops

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• Less than a days supply at rest is stored in the
  liver
• Glycogen attracts water-one of the reasons for
  large water loss during low carb. diets, once the
  glycogen has been depleted

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Glucose conversion to energy

• Cells break glucose into two smaller molecules
• These fragments are further broken down and yield
• Energy stored in the form of ATP
• Carbon dioxide
• Water

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Gluconeogenesis

• If dietary glucose is not available and glycogen
  is depleted protein is converted into new
  glucose-gluconeogenesis
• Not a good thing if extensive proteins have
  specific functions that need to be carried out,
  instead of being burned as fuel
• Carbs. Are called protein sparing

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Ketones

• During times of carbohydrate inadequacy fat
  metabolism changes and fat fragments combine to
  make ketone bodies, which can be burned for
  energy
• Excess ketone bodies result in the state of
  ketosis that shifts the acid-base balance

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Dietary needs

• 50-100 g carbs./day to prevent ketosis and
  gluconeogenesis from protein

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Excess dietary glucose

• Once energy needs are met and glycogen is
  replenished, metabolism shifts to use more
  glucose
• If glucose levels still remain high, glucose is
  converted into fat and stored in fat cells, which
  have an unlimited capacity.

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Role of glucose in body

• All cells use glucose to some degree
• Brain and nerve cells rely almost exclusively on
  glucose
• Blood in capillaries flows by body cells
• Glucose diffuses out of the capillaries and into
  the fluid that surrounds cell
• Glucose attaches to carrier proteins on cell
  surfaces and is brought into the cell to be used
  as fuel.

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Glucose homeostasis

• Normal limits during fasting are about
  70-100mg/dL
• Levels rise when glucose is absorbed from the GI
  tract and fall when glucose enters cells
• In a healthy person, hormones keep the levels
  from becoming too high or too low, and allow a
  return to normal limits

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Insulin

• When glucose enters the blood, beta cells of the
  pancreas release insulin
• Insulin signals receptors on cell membranes to
  allow glucose to enter
• Most cells take only what they need for current
  energy demands
• Liver and muscle take extra and also produce
  glycogen
• Excess glucose, after above needs have been met,
  is taken up by the liver and converted into fat
  and exported to other cells

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Homeostasis and feedback

• When blood levels of glucose drop to normal
  levels the production of insulin stops-this is a
  negative feedback system

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Glucagon

• When blood glucose levels fall below normal
  between meals glucagon is released by the alpha
  cells of the pancreas
• Glucagon signals the liver to break down gycogen
  and release glucose

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Homeostasis and feedback

• When blood glucose levels rise within normal
  limits, the production of glucagon stops-this is
  a negative feedback

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Epinephrine

• Epinephrine (adrenalin) is released in times of
  stress and emergency
• It also signals the liver to release glucose

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Balancing glucose within normal ranges

• Balanced meals at regular intervals during day
  helps to avoid large changes in glucose levels
  and puts less stress on the cell of the pancreas

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Governing of blood glucose levels

• Hormones ultimately determine the blood glucose
  levels, not the food eaten

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Type 1 diabetes

• Beta cells cease to function and insulin is no
  longer produced
• Glucose cannot enter cells, because receptors do
  not get signaled
• Blood glucose rises
• Cells must use alternative sources of fuel

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Cause of type 1 diabetes

• Possibly an activation of the immune system by
  certain viruses that results in the immune system
  destoying beta cells
• Possible genetic predisposition

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Treatment of type 1 diabetes

• Insulin injections
• Cannot be given by mouth, because insulin is
  protein-like and would be digested

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Type 2 diabetes

• More common than type 1
• Associated with obesity
• Cell receptors do not respond to insulin and /or
  in a minority of cases, there is some, but
  insufficient, insulin produced

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Treatment for type 2 diabetes

• Weight reduction
• Diet modification
• Drugs

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Hypoglycemia

• Hypoglycemia results if blood glucose levels are
  too low
• Signs are weakness, trembling, rapid heart beat,
  sweating, anxiety, hunger
• Can lead to death if not treated quickly by
  administering sugar

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Causes of hypoglycemia

• Most often occurs in poorly managed diabetics who
  have taken too much insulin for current needs
• Rare in healthy people
• Can also occur due to medications, pancreatic
  tumors, alcohol abuse, other illnesses

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Treatment

• Adjust diet if person is otherwise healthy
• In acute cases administer sugar immediately

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Glycemic index

• Method of classifying foods according to
  potential for raising blood glucose
• Not adequate scientific data
• Gycemic index is not included on food labels
• May be helpful in weight loss and prevention of
  hear disease

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Sugar intake

• Moderate amounts of dietary sugar in is
  considered not harmful
• Large amounts can lead to nutritional
  deficiencies, as sugar supplies only energy,
  obesity, and to tooth decay

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Added sugars

• Sugars are not inherent part of food, but are
  added to it
• Include sucrose, invert sugar (mixture of glucose
  and fructose from hydrolysis of sucrose), corn
  syrups and solids, corn sugar, high fructose corn
  syrup, honey
• Soft drinks and sugared fruit juices account for
  large increase in sugar consumption within the
  last several decades

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Tooth decay-dental caries

• Most common bacterial disease of man
• Mouth bacteria use maltose from starch breakdown
  or glucose and produce acid for 20-30 minutes
• Acid attacks tooth

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Recommendations

• Eat sugar over short time interval bacteria are
  tiny, so minute amounts will set off acid
  production for 20-30 minutes.
• Eat sugar with meals if possible
• Milk and milk products may reduce acid effects
  and help restore calcium in tooth enamel

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Sugared soft drinks

• Contain acid that may enhance effects of acids
  produced by bacteria

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Milk

• Lactose can be used by bacteria of mouth, but
  metabolism is slow
• Can cause severe dental caries in infants put to
  bed with bottle of milk

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Fruit juices

• Contain fruit sugar and possibly added sugars and
  can cause dental caries
• Can cause severe caries in babies put to bed with
  bottle of juice

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Sugar an health

• High sugar intakes have been linked obesity and
  heart disease
• No scientific data supports a link between sugar
  and hyperactivity or misbehaviors
• No scientific evidence supports a true sugar
  addiction, although it may raise serotonin levels
  and elevate mood
• Restricting intake may be a psychological
  component of cravings

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Recommended sugar intakes

• Try to restrict added sugars
• On average each person in US consumes 105 pounds
  of added sugar a year!
• Sugars should be considered in discretionary
  calories

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Do you have to have sugar in your diet?

• No
• Complex carbohydrates can supply glucose needs
  and stabilize blood sugar, because resulting
  glucose molecules enter blood stream a little at
  a time

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Health benefits of adequate fiber

• Fosters weight management
• Lowers cholesterol
• May help prevent colon cancer
• Help control and prevent type 2 diabetes
• Helps prevent and alleviate hemorrhoids
• Helps prevent appendicitis
• Helps prevent diverticulosis

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Health concerns of excessive fiber intake

• Displaces energy and nutrient dense foods
• Causes intestinal discomfort and distention
• May interfere with mineral absorption

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Recommended intakes of complex carbohydrate
(starch and fiber)

• About half of energy requirements

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Artificial sweeteners

• Saccharin-safe for most healthy people
• Bitter after taste
• Aspartame
• Safe for healthy people
• Contains phenyalanine cannot be used with people
  with PKU
• Produces toxic methanol and formaldehyde as
  intermediate metabolic products-amounts are very
  small, transient, and well below acceptable
  levels
• Excessive amounts may increase threshhold for
  seizures in epileptics

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• Acesulfame-K
• Passes through body unchanged
• Increases intake of potassium
• Sucralose
• Made from sugar
• Passes through body undigested and unabsorbed

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• Neotame
• Phenylalanine is blocked
• Can be used by people with PKU
• Altiame
• FDA approval pending
• Used in other countries
• Cyclamate
• Approval pending
• Does not cause cancer, but may promote it, if
  cancer is already present

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The end