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Human Nutrition
(Cambridge Biology Chapter 4)
First of all…
• Why do we need to eat?
• Why do we need to eat a balanced diet?
Nutrition is:
• From Latin: “nutrire” = “nourishing”
• Obtaining organic substances and mineral ions
from which organisms obtain their energy and
raw materials for growth and tissue repair.
6 Types of Nutrients
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Carbohydrates
Proteins
Fats
Vitamins
Inorganic Ions (“Minerals”)
Water
Organic vs. Inorganic Nutrients
Organic
• Molecules contain Carbon
• Typically components of
plant or animal tissues.
• For example: Pepper
(ground plant fruits)
Inorganic
• No Carbon
• Typically “stand-alone”
substances.
• For example: Salt
(mineral of NaCl)
Organic or Inorganic?
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Sugar
Iron
Wood
Water
Oxygen
Alcohol
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O
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Why Do Humans Need Nutrients?
• To give us ENERGY!
– We need energy for heat, movement, and
chemical reactions in our bodies.
– Carbs + Fats.
• To give us Building Materials:
– We need to build the cells in our bodies.
– Proteins.
Why Else?
• To give us Chemicals for Reactions
– We need chemicals to make chemical reactions
take place in our bodies.
– Proteins, vitamins, minerals, and water.
Carbohydrates
• Carbo = carbon
• Hydrate = water = hydrogen and oxygen
• So “carbs” are molecules of C, H, and O.
I bet you can do this…
• What’s a saccharide?
• “sugar”
• A monosaccharide?
• “one sugar”
• A disaccharide?
• “two sugars”
• A polysaccharide?
• “many sugars”
Simple Sugars: Monosaccharides
• A single ring of C, O,
and H.
• Glucose (yum!) 
• Fructose
• Galactose
Complex Sugars: Disaccharides
• Two sugar rings linked
together.
• Glucose +
• Galactose =
• Lactose
Complex Sugars: Polysaccharides
• 3 Types:
– Cellulose
• Makes up plant cell walls
– Starch
• Stored as food reserve in plant cells
– Glycogen
• Stored as food reserve in animal liver and muscle cells
Cellulose
Starch
Glycogen (in liver cells)
Why do we need Carbs?
• One reason: Energy!
• Plants take energy from the Sun, and turn it
into carbohydrates.
• Animals eat plants and use the energy to do
work (survive).
• Extra carbohydrates are changed into Fat.
What is a Low-Carb Diet?
• Low-carbohydrate diets restrict caloric intake
by reducing the consumption of carbohydrates
to 20 to 60 g per day (typically less than 20
percent of the daily caloric intake). The
consumption of protein and fat is increased to
compensate for part of the calories that
formerly came from carbohydrates.
• … but what are calories?
Calories
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Energy in food is measured in Calories.
Average need is 2,000 calories per day.
Carbs have lots of energy (lots of calories).
Going on a low-carb diet means you get less
energy out of your food.
• Is that a good idea?
Proteins
• A long molecule made of smaller molecules
called amino acids.
Amino Acids
• There are only 20 different amino acids.
• They can be linked in any order.
• A protein’s “identity” is based on the number
and order of amino acids.
Amino Acids
Protein Chains
Protein Molecules
Where Do We Get Proteins?
• We make them from amino acids.
• When we eat proteins, the molecules are
chopped up into amino acids.
• Then we put them back together to make the
proteins we need.
Sources of Proteins
Why Do We Need Proteins?
• Building Blocks for our cells:
– Cell membranes
– Muscle: for cells to produce movement
– Bones/Skin: Collagen
– Hair/Nails: Keratin
Keratin
Proteins are also…
• Enzymes!
(remember those?)
– Help chemical reactions take place
• Hemoglobin
– Red stuff in our blood; carries Oxygen
• Antibodies
– Attack bacteria and viruses
• Hormones – like Insulin
• Energy – but not usually
Hemoglobin
Amino Acids in Food
• Nonessential AA’s
– Our body can make them on its own.
• Essential AA’s
– Body can’t make them; they must come from
foods we eat.
– Meat, milk, and eggs contain all the essential
amino acids we need.
– Fruit, grains, and vegetables contain only some.
What about Vegetarians?
• They just have to make
sure they get all the
essential amino acids
from a diet that
includes a lot different
kinds of foods,
especially grains and
legumes (beans, etc.)
Fat
• One Fat molecule is made of:
– 1 molecule of Glycerol
– 3 fatty acids
Sources of Fat
From Animals
• Lard (pig fat)
• Fish Oil
• Butter (from milk)
From Plants
• Peanut Oil
• Olive Oil
• Corn/ Vegetable Oil
• Saturated Fats
• Unsaturated Fats
Saturated vs. Unsaturated Fats
Why Do We Need Fats?
• Energy!
– We can use it or store it.
– Fat contains more energy than carbohydrates.
– 1 gram of Fat = 2x the energy in 1 gram of Carbs
• Cell Membranes
• Heat Insulation
Fat as Insulation
Vitamins
• Organic substances that we only need in very
small amounts in our diet.
Vitamin C
Vitamin C
• Helps make the protein Collagen.
• Collagen is part of bones, skin, and blood
vessels.
• Without Vitamin C, skin and blood vessels
become weak due to lack of Collagen.
• Without enough Vitamin C, you can get a
disease called Scurvy!
– Bruises and ulcers on skin; weak gums
Scurvy
Vitamin D
Vitamin D
• Helps us absorb Calcium from food to make
bones and teeth.
• We can eat it from both plants and animals.
• We can also make it when we get enough
sunshine.
• Without enough Vitamin D, you can get a
disease called Rickets!
– Bone is soft and grows into bent shapes
Rickets
Vitamin A
• Helps with a LOT of functions in the body.
• Without enough Vitamin A, impaired vision or
blindness can occur.
Vitamin A
Inorganic Ions
• Sometimes called Minerals.
• We only need them in small amounts.
Iron
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Helps us make Hemoglobin.
Makes our blood red!
Carries Oxygen in our blood.
Without enough Iron, you can get a disease
called Anemia!
– Feel tired very easily
Iron in Blood
Calcium
• Our bones and teeth are made of calcium
salts.
• Without enough calcium…?
• Need Vitamin D to absorb it.
Calcium
Sources of Calcium
So… Why do we need a Balanced
Diet?