ProteinsThe Body’s Building Blocks

Which of the food groups from the Food Pyramid provide the most protein in a diet?

Answer: The meat/beans group and the milk products group

Question

Familiar Protein Sources

Other Protein Sources

It is an energy-yielding nutrient composed of carbon, hydrogen, oxygen, and nitrogen

The presence of nitrogen is what makes it differ from carbohydrates and fats

Proteins are made up of amino acids The body has at least 30,000 types of

proteins; each type does a different job

What Is Protein?

The building blocks of protein Most proteins are made up of different

patterns and combinations of 20 amino acids, which are linked in strands

The 20 amino acids are like letters in the alphabet – just as you use different letter combinations in different sequences to make different words, you combine different amino acids in different sequences to make different proteins

Amino Acids

Amino Acid Structure

Every cell contains DNA; this DNA provides the instructions for how the amino acids will be linked to form the proteins in your body

In this way, your body can take amino acids from the breakdown of foods that you eat and make the required proteins to perform required body functions, such as tissue and cell repair, disease fighting, growth and development, etc.

How do amino acids combine to make proteins?

DNA is to proteins, as ____ is to a model airplane kit

Amino acids are to proteins, as ____ are to the alphabet

Analogies

Proteins can change their shape and take on new characteristics

This is called denaturation Heat, acids, bases, and alcohol are among the

factors that can denature proteins E.g. : Frying an egg – applying heat to an egg

changes it from a runny fluid to a solid mass The shapes of the protein molecules in the egg

have changed Once a protein is denatured, it can never return to

it’s original state

Shape Changers

You need all 20 amino acids for good health Your body can synthesize 11 of the amino

acids from other amino acids The amino acids your body can make are

called nonessential amino acids The remaining 9 amino acids that your body

can’t make are called essential amino acids

Types of Amino Acids

What is the difference between essential amino acids and nonessential amino acids?

Answer: Your body can make nonessential amino acids, while it has to obtain essential amino acids from foods

Question

Bite, chew, swallow Stomach acids denature the protein Move to the small intestine, where they are

broken down by enzymes into single amino acids

Amino acids are absorbed into the bloodstream, and are carried to the body cells that need them

Protein in the Body

Your cells can use amino acids from food proteins to build new proteins

Cells can also convert amino acids to other compounds, including other amino acids

The proteins built by cells are custom designed to perform a wide range of functions

The roles proteins play depend on where they are located and how your body needs them

Proteins have 6 main functions

Functions of Proteins

As your body grows, it uses protein to help make new tissue, which is why it is important for people to get enough protein during the growth years

When you eat a nutritious diet, your body uses protein to build lean muscle mass

Protein makes up about 18-20% of the body◦ About 3% of this protein is broken down each day◦ You also need protein to maintain existing tissue

1. Build and Maintain Tissues

Your body uses proteins to make enzymes, which cause specific chemical reactions in the body (e.g. digestive enzymes for food breakdown)

Proteins are used to make some hormones, which are released in the bloodstream to control specific body processes

Your body’s immune system uses proteins to make antibodies, which defend the body against infection and disease

2. Make Important Compounds

Proteins help carry the minerals sodium and potassium from one side of cell walls to another

These minerals and other proteins control the flow of water through cell membranes

A balance of fluid inside and outside the cell is crucial

3. Regulate Fluid and Mineral Balance

Acid-base balance refers to the maintenance of the correct level of acidity of a body fluid

If blood becomes too acidic, it can be life-threatening

Proteins in the blood act as chemical buffers◦ A buffer is a compound that can counteract an

excess of acid or base in a fluid

4. Maintain Acid-Base Balance

Proteins linked with fat form lipoproteins, which are the compounds used to carry fats in the bloodstream

Proteins also transport iron and other nutrients

Oxygen transport in the blood is reliant upon protein as well

5. Carry Vital Substances

The body’s number one priority is to provide the cells with the energy they need to exist

Even though only proteins can perform cell growth and repair, the body will use proteins for energy when it lacks carbs and fats

The body will also burn proteins for energy when there is excess protein taken in; this is hard on the liver and kidneys

* A Billboard For Proteins

6. Provide Energy

Animal flesh – Beef, pork, poultry, lamb, veal, and fish

Other sources – Eggs, milk, yogurt, cheese, and ice cream

Meat and some dairy are problematic due to high fat content◦ Most of the fat is saturated◦ No fiber is obtained from these foods◦ The cost of protein from animal sources can be

high

Animal Sources of Protein

Found in grains, nuts, seeds, and legumes Legumes are peanuts, black-eye peas,

kidney beans, black beans, chickpeas, etc. Soy beans are a large source of plant

protein◦ They are a legume◦ They can be modified to form a variety of food

products, such as tofu and soy burgers

Plant Sources of Protein

Vegetarianism The practice of eating a

diet consisting entirely or largely of plant foods

Beneficial to health in that most of the fat in plant foods are polyunsaturated, plants foods contain no cholesterol, and these foods are generally high in fiber

The eating patterns of vegetarians vary greatly; there are four main types

Types of Vegetarians 1. Vegans – eat no food from animal sources;

their diet is limited to plant foods 2. Lacto-vegetarians – eat animal protein in the

form of dairy products, but no meats, fish, poultry, or eggs

3. Lacto-ovo vegetarians – eat animal protein in the form of dairy and eggs, but no meats, fish, or poultry

4. Semivegetarians – eat dairy, eggs, poultry, and seafood, but no red meat

Reasons for Vegetarianism Religious reasons – Buddhists, Hindus,

Seventh-Day Adventists, Trappist monks Health reasons – avoid fat and cholesterol,

hormones and chemicals, and foodborne illnesses

Socioeconomic reasons – eating meat is wasteful

Environmental reasons – animal grazing is hard on the land

Humanitarian reasons – can’t stand the idea of eating Bambi, Flipper, Chicken Little, etc.

Protein Quality Proteins in different foods differ in quality

◦ Plant foods provide lower quality proteins and are sources of incomplete proteins These proteins are missing one or more of the

essential amino acids◦ Animal foods have high quality proteins and are

sources of complete proteins Means that all the essential amino acids humans

need are present in the proteins Animal products such as eggs, cheese, milk and

yogurt are also complete proteins

Incomplete Vs. Complete Proteins Your body needs the right balance of all 20

amino acids to build tissues and other compounds

If one or more essential amino acids is missing your cells will not be able to make needed proteins

Have to find a way to complete the incomplete proteins

*Animal Vs. Plant Protein

Complementary Proteins You can get the amino acids missing from one

incomplete source by combining it with another incomplete source

Two or more incomplete proteins which can be combined to provide all the essential amino acids are called complementary proteins

In general, combining grains, nuts, or seeds with legumes will give you complementary proteins (e.g. peanut butter and whole wheat bread)

Can also get a complete protein when eating a small amount of a complete protein with a large amount of an incomplete protein (e.g. pork with rice)

* A Good Match

How Much Protein Do You Need? Your body does not store protein, so you

need some every day The amount depends upon your age,

gender, body size, and health◦ Children and teens need more◦ Pregnant and nursing women need more◦ Teenage boys and men need more◦ Sick and injured people need more

Why do the above groups need more?

Protein Needs Children need more protein due to rapid

growth Pregnant women need more protein for fetal

development Nursing mothers need more to make milk Males need more due to a higher amount of

muscle mass People who are sick need more in order to

make antibodies People who are injured need more to repair

damaged tissue

RDA for Protein 14-18 year old males – 52 grams per day 14-18 year old females – 46 grams per day

To meet the RDA, 10-35% of daily calories should come from protein (do the math)

Do Athletes Need More Protein? Well-trained athletes do need a little more

protein per day An extra half a glass of milk or a chicken

wing will provide the extra that athletes need

Remember – an athlete’s primary need is for energy◦ Athletes should focus on the high end of the

calorie range for carbs (~55-65%) and the low end of the range for fats (~20-25%)

◦ That leaves 10-25% of an athletes calories for protein

Protein Supplements? So much of what is out there is unproven Not enough research at this point, so long

term effects are still largely unknown (transparency)

The Risks of Too Little or Too Much Protein As with all nutrients, moderation is key Nitrogen balance is a comparison of the nitrogen a

person consumes with the nitrogen they excrete Protein is the only nutrient that provides nitrogen,

so nitrogen balance is used to evaluate a person’s protein status◦ Nitrogen equilibrium – take in as much as you excrete

(e.g. healthy adult)◦ Positive nitrogen balance – take in more than you

excrete (e.g. when you are growing tissue, such as a child or a pregnant woman)

◦ Negative nitrogen balance – take in less than you excrete (e.g. losing body tissue due to starvation)

◦ * Protein Balance

Protein Deficiency Deficiency diseases develop when you lack an

essential nutrient Common among people fighting poverty Protein-energy malnutrition (PEM) – condition

caused by a lack of calories and protein in the diet◦ Kwashiorkor – protein-deficiency disease; common in

poor countries when a mother weans one child to feed the next; characterized by stunted growth and immune system weaknesses

◦ Marasmus – calorie and protein – deficiency disease; most often affects infants in poor countries; characterized by wasting away of the body and infant mortality

Excess Proteins Most people in the U.S. consume too much protein Leads to:

◦ Liver and kidney problems – excess proteins must be excreted as nitrogen; overworks the liver and kidneys, causing them to age prematurely

◦ Calcium loss – diets high in protein from animal sources contribute to calcium loss from the bones, leading to fractures, osteoporosis, etc.

◦ Excess body fat – many high-protein foods are also high-fat foods; since the body cannot store excess protein, it converts it to fat and stores it in the adipose tissue, leading to weight gain

◦ * Not Too Little, Not Too Much

Comparing Protein Sources 4 ounces extra-lean ground beef patty

290 calories 112 mg cholesterol High in saturated fat 0 g fiber

44% protein 56% fat 0% carbohydrates

½ cup pinto beans

116 calories 0 mg cholesterol Low in saturated fat 7 g fiber

24% protein 1% fat 75% carbohydrates

Review Questions What is the difference between an essential

and a nonessential amino acid? What role do stomach acids play in protein

digestion? How can a diet low in carbohydrates and

fats affect the way the body uses proteins? Name three specific animal sources and

three specific plant sources of protein.

Review Questions About what percentage of daily calories

should come from protein? What type of nitrogen balance would

describe the protein status of a healthy teen?

What are the 3 problems associated with high-protein diets?