Digestion and Nutrition

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Digestion and Nutrition

• Starr/McMillans
• Human Biology
• Fourth Edition
• Chapter 6

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• The typical American diet is high in fat
• Body fat relative to total tissue should be
• female 18-24 (under 30 years old)
• male 12-18
• Obese refers to a person who carries gt25 of
  their weight as fat
• obesity increases the risk of developing
  diabetes mellitus, stomach and esophageal cancer,
  and colon disorders
• As a result of our evolutionary adaptation, we
  have fat-storing cells in our adipose tissue to
  use as energy reserves
• once those cells form, they are here to stay
• variations in food intake only determine how
  full or empty each cell gets

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• When we diet, the brain calls for a metabolic
  slowdown
• The lack of food is seen as starvation
• Energy is used more efficiently thus we do more
  with less
• Skeletal muscles burn less energy than before
• Dieting does no good without a long-term
  commitment to exercise
• If and when you stop dieting, the depleted fat
  cells quickly refill
• For most people, the only way to keep weight off
  is through consistently moderate food intake and
  regular exercise

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food, water intake
oxygen intake
DIGESTIVE SYSTEM
RESPIRATORY SYSTEM
elimination of carbon dioxide
nutrients, water, salts
oxygen
carbon dioxide
CIRCULATORY SYSTEM
URINARY SYSTEM
water solutes
elimination of food residues
rapid transport to and from all living cells
elimination of excess water salts, wastes
Fig. 6.2, p. 113
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Key Concepts

• Nutrition encompasses the processes by which we
  take in and digest food then absorb nutrients
• The digestive system has specialized parts for
  food transport, processing, and storage.
• The digestive system mechanically breaks food
  apart, chemically breaks it down, absorbs
  nutrients, and eliminates residues

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Key Concepts

• To maintain weight and health, energy intake must
  balance energy output
• Digestion and absorption of food makes a vital
  contribution to homeostasis
• Adequate nutrition requires vitamins, minerals,
  amino acids and fatty acids

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Overview (6.1)

• The digestive system is made up of
• The gastrointestinal tract (GI)-the tube food
  passes through from mouth to anus
• Also called alimentary canal
• Accessory organs-not a part of the tube, but
  contribute to the process of digestion
• Nutrients do not enter the body until diffused
  from the tube into the bloodstream
• The space inside the tube is the lumen

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Continued.

• The GI tract is 6.5-9 meters (21-30 ft.) long in
  an adult
• Mucus-coated epithelium lines all surfaces facing
  the lumen
• The mucus protects the walls of the tube
• Also enhances diffusion
• Substances advance in one direction

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Human Digestive System
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Digestive System Tasks

• Mechanical processing and motility
• Secretion
• Digestion
• Absorption
• Elimination

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Accessory structures

• Accessory organs secrete enzymes and other
  substances that have essential roles in digestion
  or absorption
• Salivary glands
• Liver
• Gall bladder
• Pancreas
• Also glands in the wall of the GI tract

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Layers of the Digestive Tube
Serosa (Outermost) Smooth muscle Submucosa Muc
osa (Innermost)
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lumen
mucosa
submucosa
circular muscle
smooth muscle layer
longitudinal muscle
serosa
Fig. 6.4, p. 115
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Digestion

• Digestion is actually a combination of physical
  and chemical processes
• Physical includes mechanical digestion and the
  actual movement of the food material
• Peristalsis-
• wavelike muscle contractions that move food
  forward,
• rings of circular smooth muscle contract behind
  food
• Segmentation-
• oscillating movements that constantly mix the
  contents,
• rings of smooth muscle repeatedly contract and
  relax,
• this also forces material against wall for
  absorption

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Motility

• Peristalsis
• Stomach
• Wave-like contractions

Segmentation Small Intestine Oscillating
movement
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Fig. 6.5b, p. 115
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GI Tract Organs an overview

• Mouth
• physical (mechanical) digestion by chewing,
• chemical digestion by amylase (begins breakdown
  of starch)
• Esophagus
• physical movement (peristalsis) of food into
  stomach
• Stomach
• Physical by peristalsis
• Chemical by numerous enzymes

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• Small intestine three sections
• Duodenum 1st third of s.i.
• Jejunum middle 3rd
• Ileum last portion, most absorption occurs here
• Large intestine (colon)
• all that is left is water and waste, water is
  reabsorbed (most)
• Rectum
• temporary storage
• Anus
• elimination

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Chewing and swallowing- mechanical digestion
(6.2)

• In the oral cavity (mouth), both physical and
  chemical digestion begin
• Physical (mechanical), the actual chewing
• Chemical begins with the enzyme amylase, which is
  in saliva, which digests starch
• Amylase is produced by the salivary glands
• Parotid-located in front of each ear
• Submandibular-floor of mouth
• Sublingual-under the tongue
• Saliva is mostly water and also contains mucins,
  proteins which help bind food into the bolus

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Teeth
Molars (12) Premolars (8) Canines (4) Incisors
(8)
upper jaw
lower jaw
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molars (12)
premolars (8)
canines (4)
incisors (8)
LOWER JAW
UPPER JAW
enamel
crown
dentin
pulp cavity
gingiva
root canal
root
peridontal membrane
bone
Fig. 6.6a, p. 10
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Salivary Glands and Saliva
Salivary glands Parotid gland Submandibular
gland Sublingual gland Saliva Mostly
water Salivary amylase Bicarbonate Mucins Heim
lich maneuver
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parotid gland
submandibular gland
sublingual gland
Fig. 6.6b, p. 116
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VOLUNTARY PHASE
INVOLUNTARY PHASE
hard palate
food bolus
epiglottis
Contracted muscles close off esophagus.
Larynx rises trachea closes, and muscle
contractions squeeze food into esophagus.
trachea (airway) open
Fig. 6.7a, p. 117
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• Esophagus
• physical movement (peristalsis) of food into
  stomach
• Epiglottis covers air tube when you swallow so
  food and liquid go down the food tube toward
  the stomach
• If not, Heimlich manuever

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foreign mass in trachea
base of rib cage
fist of rescuer
navel
Fig. 6.8, p. 117
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Stomach and small intestine (6.3)

• Stomach and small intestine are main
  food-processing organs
• Both organs have layers of smooth muscle for
  physical digestion and enzymes for chemical
  digestion (table 6.1, page 119)
• Both organs have a highly folded inner lining for
  increased surface area
• Stomach-called rugae
• Small intestine-tiny, finger-like projections
  called villi

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Stomach

• Three main functions
• Mixes and stores food (holds about a quart for
  about four hours)
• Its secretions help dissolve and start chemical
  digestion, especially proteins
• Controls passage of food into small intestine
• Contains sphincter muscles at both ends
• Cardiac sphincter at bottom of esophagus, top of
  stomach, keeps food in stomach
• Heart burn
• Pyloric sphincter at entrance to small intestine,
  keeps food in stomach proper length of time

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The Stomach
Cardiac sphincter
Muscular, expandable sac
Esophagus
Pyloric sphincter
Main Functions Mix and store food Chemical
breakdown Control passage into small intestine
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muscles relaxed
Circular muscles contract, squeezing bolus
toward the stomach.
muscles relaxed
food bolus
Lower esophageal sphincter opens and food enters
stomach.
stomach
Fig. 6.7b, p. 117
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Stomach

• Stomach wall facing lumen is lined with glandular
  epithelium
• Secretes
• HCl-hydrochloric acid
• Mucus
• Pepsinogens-will be pepsins to digest proteins
• Intrinsic factor-a protein required for B12
  absorption
• All these plus water make up gastric fluid
• The gastric fluid, along with contractions,
  converts food into chyme
• This highly acid fluid requires a gastric mucosal
  barrier to protect the stomach lining, includes
• Control mechanisms
• Buffers
• mucus

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The Small Intestine

• 6 meters long
• Three sections
• Duodenum
• Jejunum
• Ileum

Circular muscle
Longitudinal muscle
Intestinal wall smooth muscle layers are oriented
in different directions
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blood vessels
mucosa
submucosa
serosa
gut lumen
longitudinal muscle
circular muscle
mesh of nerves (plexus)
Fig. 6.9, p. 118
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Small intestine

• The stomach, pancreas, liver, and gall bladder
  contribute about 9 liters of fluid to the
  duodenum, most is absorbed
• Chyme entering duodenum trigger enzyme secretions
  from pancreas which act on all organic compounds
• Also secrete bicarbonate (buffer), which maintain
  chemical environment

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Major Digestive Enzymes
Carbohydrate Digestion Salivary
Amylase Pancreatic Amylase Disaccharidases Prot
ein Digestion Pepsins Trypsins and
chymotrypsin Carboxypeptidase Aminopeptidase
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Major Digestive Enzymes
Fat Digestion Lipase Also requires
bile Nucleic Acid Digestion Pancreatic
nucleases Intestinal nucleases
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Bile and Fat Digestion

• Bile is secreted by liver, contains
• Salts, cholesterol, lecithin, pigments
• Stored in gallbladder, held in by sphincter
• Emulsifies fats because fats are insoluble in
  water and therefore tend to clump, they must be
  held in small droplets in order for enzymes to
  digest them (increase surface area)

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Major Components
Accessory Organs
MOUTH (ORAL CAVITY)
SALIVARY GLANDS
PHARYNX
ESOPHAGUS
STOMACH
LIVER
GALLBLADDER
SMALL INTESTINE
PANCREAS
LARGE INTESTINE (COLON)
RECTUM
Fig. 6.3, p. 114
ANUS
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serosa
esophagus
longitudinal muscle
circular muscle
pyloric sphincter
oblique muscle
submucosa
mucosa
Fig. 6.5a, p. 115
duodenum
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Absorptive Structure of the Small Intestine (6.4)
One villus
villi
glands
artery
lymph vessel
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Absorption Mechanisms
Water moves by osmosis Mineral ions are
selectively absorbed Some nutrients absorbed
directly Active transport of monosaccharides and
amino acids across plasma membranes Facilitated
diffusion into bloodstream (some molecules get
help)
INTESTINAL LUMEN
carbohydrates
monosaccharides
amino acids
proteins
EPITHELIAL CELL
INTERNAL ENVIRONMENT
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Remember.

• Because of emulsification, fat globules are
  broken down into fatty acids and monoglycerides
• Bile salts in the bile are also very important in
  this difficult process
• Fatty acid and monoglyceride molecules have
  hydrophobic regions therefore they do not
  dissolve in the watery chyme

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Absorption Mechanisms

• They clump together with bile salts, cholesterol,
  and other substances and form droplets, each
  called a micelle
• If the concentration gradient is favorable when a
  micelle contacts the lining surface
• the nutrients will diffuse out into the
  epithelial cell,
• reunite into triglycerides,
• combine with proteins into microscopic particles
  called chylomicrons,
• enter tissue fluid,
• enter lymph vessels called lacteals, which
  eventually drain into blood vessels, whew!!

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Aborption Mechanisms
bile salts
free fatty acids,

FAT GLOBULES (triglycerides)
MICELLES
mono- glycerides
EMULSIFICATION DROPLETS
triglycerides proteins
CHYLOMICRONS
Exocytosis of chylomicrons
To Lacteal
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submucosa
mucosa
muscle layers
serosa
blood capillary
villi
lymph vessel
glands
artery
lymph vessel
Fig. 6.10a, p. 120
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cytoplasm
microvilli at free surface of absorptive cells
phagocytosis lysozyme secretion
mucus secretion
hormone secretion
absorption
Fig. 6.10b, p. 120
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INTESTINAL LUMEN
bile salts

MICELLES
carbohydrates
monosaccharides
EMULSIFICATION DROPLETS
FAT GLOBULES (triglycerides)
free fatty acids, monoglycerides
proteins
amino acids
EPITHELIAL CELL
CHYLOMICRONS
INTERNAL ENVIRONMENT
Fig. 6.11, p. 121
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Click to view animation.
animation
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Liver Functions (6.5)
Secretes bile Converts glucose to
glycogen Removes toxins Inactivates
hormones Converts ammonia to urea
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(inferior vena cava)
hepatic vein
(liver capillary beds)
liver
stomach
gallbladder
(spleen)
hepatic portal vein
pancreas
ascending colon of large intestine
descending colon of large intestine
small intestine
appendix
rectum
Fig. 6.12, p. 122
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Major liver diseases

• Cirrhosis liver scarring caused by long-term,
  heavy alcohol use
• Hepatitis 5 types caused by viruses that infect
  and damage the liver
• A and E are transmitted by contaminated food or
  water
• Symptons nausea, abdominal pain, jaundice
• B and C are transmitted sexually or in
  contaminated blood
• B can cause cirrhosis, increases chance of liver
  cancer, C produces mild symptons but can be
  chronic and cause serious damage
• D infects people who already have B, but becomes
  chronic with devastating long-term effects.

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The Large Intestine (6.6)

• By the end of the small intestine all nutrients
  should be absorbed
• Therefore, all thats left is waste
• Undigested/unabsorbed material
• Indigestable material
• Water (mostly reabsorbed)
• Bacteria (makes up about 30 of dry weight of
  feces)

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Continued

• About 1.2 meters long (5 feet)
• Begins as cecum (a blind pouch), this is where
  the appendix can be a problem
• Cecum merges with colon, which is divided into 4
  regions in an inverted U shape
• The ascending colon goes up the right side of the
  abdomen
• The transverse colon goes across to the left
• The descending colon turns downward on the left
  side
• the sigmoid colon makes an S-curve and connects
  with the rectum

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Fig. 6.13, p. 123
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Cecum and Appendix
ascending portion of large intestine
last portion of small intestine
cecum
appendix
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The Large Intestine
Absorbs water and salts from food residues
Begins as cecum Becomes colon Ascending
colon Transverse colon Descending
colon Sigmoid colon Connects with rectum
cecum
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Problems of the large intestine

• Appendix
• Appendicitis
• peritonitis
• Constipation
• Diarrhea
• Eating a diet that contains dietary fiber will
  help decrease the chance of these problems
  developing

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Controls and nutrient turnover (6.7)

• Controls over the digestive system act before
  food is absorbed into the internal environment
• These controls respond to the volume and chemical
  makeup of the material in the lumen
• Controls made up of
• Nervous system
• Nerve networks in digestive tube walls
• Endocrine system

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CENTRAL NERVOUS SYSTEM
sight, smell, taste of food
emotional states
LONG REFLEX PATHWAYS
sensory neurons
motor neurons
sensory receptors
nerve network
smooth muscle or gland
gut wall
SHORT REFLEX PATHWAYS
Stimulus
Response
gut lumen
change in food volume, composition in lumen
gut wall moves or substances secreted into the
lumen
Fig. 6.14, p. 124
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Nutrient turnover and organic metabolism

• Once nutrients enter body they are shuffled and
  reshuffled depending on needs
• Nervous and endocrine control this
• Carbs, proteins, and lipids are broken down then
  used for energy or building
• Eating builds up pools of organic compounds
• Excess carbs and other dietary molecules are
  transformed into fats (mostly) and stored in the
  adipose tissue
• Some carbs are converted to glycogen in the liver
  and muscles
• When organic molecules are absorbed and stored
  most cells use glucose as their main energy source

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Continued

• During a meal, and for several hours after,
  glucose moves into cells to be used as an energy
  source
• When a person fasts or exercises (is active), the
  glucose becomes depleted
• The body taps into the fats stored for energy
• Fat stored in the adipose tissue is broken down
  to glycerol and fatty acids, which are released
  into the blood
• Glycerol is converted to glucose in the liver
• Cells take up circulating fatty acids and use
  them to make ATP

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What we need food for

• Energy -catabolism-break down to use for energy
  burned off as heat
• Carbohydrates
• Lipids
• Protein

• Building -anabolism- build new cells for growth,
  repair, replacement
• Protein
• Lipids
• Carbohydrates

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Disorders that disrupt absorption

• Disorders can result from not producing needed
  enzymes or not absorbing properly
• Ill effects can range from gas, to diarrhea, to
  malnutrition
• Malabsorption disorder-anything that interferes
  with nutrients entering lining of small intestine
• Lactose intolerance-lack the enzyme lactase
• Cystic fibrosis-cannot digest and absorb fats
• Crohns disease- inflammatory bowel disease
• intolerance to gluten in wheat
• Food allergies also disrupt digestion and
  absorption
• These are skewed responses of the immune system
• These can lead to electrolyte imbalances

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Nutritional Requirements (6.8)

• Carbohydrates
• Should be bulk of caloric intake
• Bodys preferred energy source
• Should be complex carbs
• Lipids
• No more than about 30 percent of calories
• Energy reserves and cell membranes
• Proteins
• Remainder of calories
• Provide essential amino acids

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ADDED FATS AND SIMPLE SUGARS
Read additional information on page 126!!
Reduce and restrict this group as much as possible
MILK, YOGURT, CHEESE GROUP
Also low fat types
LEGUME, NUT, POULTRY, FISH, MEAT GROUP
Should be lean!
FRUIT GROUP
Goes with the vegetable group!
VEGETABLE GROUP
This level minimum of 5 servings a day!!!
BREAD, CEREAL, RICE, PASTA GROUP
Remember, these should be complex carbs, not
processed and refined, but whole grain
Fig. 6.16, p. 126
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Food intake
dietary carbohydrates, lipids
dietary proteins, amino acids
POOL OF CARBOHYDRATES AND FATS (carbohydrates
fats)
POOL OF AMINO ACIDS
NH3
structural components of cells
storage forms
specialized derivatives (e.g., steroids,
acetylcholine)
used as cellular energy source
nitrogen-containing derivatives (e.g., hormones,
nucleotides)
components of structural proteins, enzymes
urea
some surface secretion, cell sloughing
cell activities
excreted as CO2 via lungs
excreted in urine
cell activities
some cell sloughing
Fig. 6.15, p. 125
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isoleucine leucine lysine methionine phenylalanine
threonine tryptophan valine
Fig. 6.17a, p. 127
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Fig. 6.17b, p. 127
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Vitamins and minerals (6.9)

• Vitamins organic substances that are essential
  for growth and survival (no other substances can
  play their metabolic roles)
• 13 are essential (see page 128)
• Many chemical reactions use several types of
  vitamins so the absence of one can affect others
• Minerals inorganic substances essential for
  growth and survival (see page 129)
• You should get all you need of both from eating a
  good, balanced diet of whole foods
• Sometimes supplements are needed
• Metabolism varies from person to person
• Remember, too much of anything is bad for you!!

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Vitamins and Minerals (6.9)

• Vitamins
• Fat Soluble
• A, D, E, K
• Water Soluble
• B1, B2, Niacin, B6, Folate, Pantothenic acid,
  B12, Biotin, C

• Minerals
• Calcium, Chloride, Copper, Fluoride, Iodine,
  Iron, Magnesium, Zinc, Phosphates, Potassium,
  Sodium, Sulfur

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Food energy and body weight (6.10)

• Obesity, or any weight gain, is usually caused by
  an imbalance between caloric intake and energy
  output
• Carrying extra weight is a health risk
• Roughly 300,000 people die each year from
  preventable, weight-related causes (see page 130)
• BMI (body mass index) weight (pounds) x 700
• 
  height (inches)2
• if value is 27 or higher, the risk increases
  dramatically
• BMR (basal metabolic rate)amount of energy
  needed to sustain body when resting, awake, and
  has not eaten for 12-18 hours

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Continued.

• Remember again, peoples metabolic rates vary
• Other factors that affect energy output include
• Differences in physical activity
• Age
• Hormone activity
• Emotional state
• To figure kilocalories needed for you, see page
  130
• Your set point and your genes also play a role
• Genes affect hormone and enzyme production, there
  is a connection proven by research
• Ex. leptin
• Remember, you cant starve yourself to lose
  weight for the long term, exercise is essential
• Moderate reduction in caloric intake with
  increased physical activity will work best!!
  Slow but sure

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Food and Body Weight
To maintain weight, caloric input must be
balanced with energy output
Basal Metabolic Rate (BMR) Amount of energy it
takes to sustain the body when a person is
resting, awake, and has not eaten for 12-18 hours
BMR varies from person to person
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Weight Guidelines for Women
Weight Guidelines for Men
Starting with an ideal weight of 100 pounds for a
woman who is 5 feet tall, add five additional
pounds for each additional inch of height.
Examples
Starting with an ideal weight of 106 pounds for a
man who is 5 feet tall, add six additional pounds
for each additional inch of height. Examples
Fig. 6.18, p. 130
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Malnutrition and Undernutrition (6.11) This is a
blue section so remember to read through this for
information!!
Fig. 6.19, p. 132