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NUTRITION
Chapter 18
WHY DO YOU EAT?
• Your body requires energy to do all of the tasks you must perform in a day
• Walking, playing, sleeping, and, ironically, eating, all require you to burn energy
• Even playing video games or sitting and watching TV require a certain amount of
energy
• Your body requires energy to keep your heart beating, and to keep your brain
functioning
• Food provides the energy that you need by providing nutrients
• Nutrients are substances in food that provide the energy and materials for you to
function and grow
ENERGY NEEDS
• The amount of energy present in a food is measured in Calories (Cal).
• A Calorie is the amount of heat necessary to raise the temperature of 1 kg of
water by 1 degree C.
• NOTE: THIS DEFINITION WILL BE USED IN PHYSICAL SCIENCE, BIOLOGY, AND CHEMISTRY!
• Calories vary in foods based on the types of nutrients they provide
• Empty calories
• Calories from fats and sugars
• Add very few other nutrients, so are not the best choices
• Nutrient-Dense foods
• Foods that provide many nutrients, but few calories
• Contain vitamins and minerals
CLASSES OF NUTRIENTS
• 6 types of nutrients
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Proteins
Carbohydrates
Vitamins
Minerals
Fats
Water
• Foods containing fats, carbohydrates, and protein need to be digested
• Vitamins, minerals, and water are all directly absorbed into blood without
being digested
PROTEIN
• Large molecules that contain Hydrogen, Carbon, Oxygen, and Nitrogen
• Composed of Amino Acids
• Your body needs amino acids in order to build your own proteins
• Most Amino Acids are made by cells
• 8 must be acquired from the foods you eat
• Called essential amino acids
• Complete proteins provide the amino acids that you need
• Eggs, milk, cheese, meat
• Incomplete proteins are missing one or more amino acid
• Fruits, grains
CARBOHYDRATES
• Usually the main source for energy in your body
• Composed of Carbon, Hydrogen, and Oxygen bonded together
• When you digest the food, you break the bonds and release the energy
• 3 types of Carbohydrates
• Sugar
• Simple carbohydrate
• Sugar, fruits, honey, milk
• Starch
• Complex carbohydrate
• Potatoes, pasta
• Fiber
• Complex carbohydrate
• Grains, vegetables, beans
• You cannot actually digest fiber, but it keeps your digestive system “regular”
FATS
• Also called lipids
• Provide energy and help your body absorb nutrients
• Also protect internal organs and help build cell membranes
• Fats contain 2x as much energy as carbohydrates
• Your body stores fats for later use
• 2 types?:
• Saturated fats
• Solid at room temperature
• Raises blood pressure and can lead to heart attacks and stroke
• Unsaturated fats
• Liquid at room temperature
• Not as bad for you as saturated fats, but can still lead to problems if eaten in excess
VITAMINS
• Nutrients needed for growth, bodily functions, and prevention of disease
• Found in many foods, though no food has them all (there are 10+)
• A well-balanced diet gives you what you need
• Supplementation (taking multivitamins) is usually unnecessary, and can have negative health
impacts
• Common ones that come from certain foods:
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C-Oranges
A-Liver, lettuce, carrots, milk
B12-Meat
K-Spinach, egg
• You can overdose on vitamins
• Too much vitamin C can cause kidney stones
• Too much Vitamin A can lead to anything from nausea to hair loss and bone fractures
• Ask a doctor before beginning vitamin supplementation
MINERALS
• Nutrients that lack carbon
• Regulate many chemical reactions in your body
• You require 14 minerals for everyday tasks
• Building cells, clotting blood, building muscles, transmitting nerve impulses,
carrying oxygen, etc.
• Calcium and phosphorus are the most used
• Trace minerals are needed in small amounts
• Copper, iodine, iron, etc.
• You get minerals from fruits, vegetables, cereal, meats, and many other
foods
WATER
• Critical for survival
• You can live a couple weeks without food, but only a few days without water
• You can only get minerals from food if water is present
• They must be dissolved in water to be used
• 2/3 of your body’s water is located in your cells
• You lose water to breathing, using the bathroom, and sweating
• You need to consume approximately 2 liters of water per day to replace it
• More if you do a lot of physical activity
• You get much of the water that you need from foods
• The rest you drink in the form of liquids
• Your body tells you that you are thirsty when it senses that you need to replace some
water
NUTRITION GUIDELINES
• MyPlate Replaced the old food pyramid guidelines
• The food pyramid was way too confusing…
• Emphasizes that ½ of your meal should be fruits and veggies, and the other ½
healthy grains and protein
• Another guideline was released by Harvard School of Health
• Their research suggests limiting milk in favor of water, and having about ¼ of the
meal be fruit, ¼ veggies, ¼ protein, ¼ grains (picture next page)
THE DIGESTIVE SYSTEM
• 4 steps
• Ingestion (eating the food)
• Digestion (breaking the food down into smaller molecules so that they can be
used)
• Absorption (nutrients entering the blood and being distributed to the cells)
• Elimination (removal of wastes and unused portions of food)
INGESTION
• The mouth chews food and mixes in saliva
• Saliva contains an enzyme called amylase that helps break down food
• The food and saliva becomes a soft mass called a bolus that is moved by
the tongue to the entrance of the esophagus
• There is it swallowed and passes into the esophagus
• Food moves down due to peristalsis
• Series of involuntary smooth muscle contractions
DIGESTION
• Food passing through the esophagus passes over a structure called the
epiglottis
• This structure covers the opening to the windpipe to prevent food getting in
• Mucous in the esophagus keeps the bolus moist so it continues moving
• Smooth muscle pushes the food down into the stomach
• It takes less than 10 seconds from swallowing to reach the stomach
• In the stomach, food is mixed with enzymes, such as stomach acid and
pepsin, which creates a liquid called chyme (kime)
• The chyme moves into your small intestines
• In the duodenum (the first 25 cm of the small intestines), emzymes are released from
the pancreas, gallbladder, and liver
• Pancreas releases enzymes that break down carbs, proteins, and fats, and also neutralize
the stomach acid
• The liver releases enzymes that break down fat.
• These enzymes are stored in the gallbladder
ABSORPTION
• Food stays in the small intestine for 3-5 hours
• Peristalsis moves the chyme slowly down
• Structures, called villi, line the intestines and absorb nutrients from the chyme
• The nutrients enter the blood stream and are carried away to do their jobs
• The chyme moves into the large intestine (aka colon), which absorbs water,
leading to a more solid mass
ELIMINATION
• After the water has been removed, you are left with a soft (usually), solid
(usually) material
• 18-24 hours later
• The rectum pushes it down to the anus, and it comes out as feces
ROLE OF BACTERIA
• Throughout the process of digestion, bacteria serve important roles
• They help break down the food
• They are able to break down materials that we cannot
• They aid in the release of nutrients
• In doing so, they produce gas, embarrassing you and displeasing those around you
• They are critical to your survival