Basic Nutrition Lesson Two - Proteins

An Introduction to Proteins

Proteins are necessary for the structural components of the human body, such as muscles and organs. You also need proteins for your immune system, to synthesize neurotransmitters and for the creation and signaling of hormones, as well as a lot of other reasons. Your diet supplies you will all of the protein you need. Meats, eggs and dairy products are significant sources of protein; however you can also get protein from a variety of grains, legumes, nuts and seeds.

Just a Tiny Bit of Protein Chemistry

Proteins tend to be large molecules made up of several building blocks called amino acids. The general structure of any amino acid molecule includes a carboxyl group of atoms and an amine group. The carboxyl group contains a carbon atom, 2 oxygen atoms and a hydrogen atom. The amine group contains a nitrogen atom with 2 hydrogen atoms attached to it.

There are 20 different amino acids, and all amino acids contain the carboxyl group, the amine group, and a side chain. All 20 amino acids have different side chains, which vary in shape including straight chains of atoms, branched chains of atoms and rings of atoms. The side chains may include carbon atoms, hydrogen atoms, sulfur, nitrogen and oxygen.

Amino acids are linked together to form peptides, which are small chains of amino acids. The peptides are then linked together to form larger proteins. In the human body, there are thousands of different proteins that carry out a large number of jobs. Even though there are so many different proteins at work in your body, you don’t have to worry about consuming each individual protein from the foods you eat. Your body will make those proteins. All you need to do is to make sure your body has a healthy supply of all 20 of the different amino acid “building blocks.” Having enough of those amino acids is pretty easy because your body can make 11 of them from other compounds already in your body. That leaves eight amino acids that you must get from your diet. Those 8 amino acids are called “essential amino acids.”

Non Essential and Essential Amino Acids

The 11 non-essential amino acids are not called "non-essential" because they are not important. They are very important and your body requires those amino acids for several functions. Those amino acids are called "non-essential" because you don't need to get them from your diet. Your body can build those twelve amino acids from chemicals already present in your body. The non-essential amino acids include:

• Alanine
• Arginine
• Asparagine
• Aspartic Acid
• Cysteine
• Glutamic Acid
• Glutamine
• Glycine
• Proline
• Serine
• Tyrosine

The amino acids arginine, cysteine, glycine and tyrosine are sometimes also considered to be conditionally essential. That means you should get enough from your diet, but there may be different conditions that would necessitate additional ingestion of those amino acids.

The 9 essential amino acids are called "essential" because you can't manufacture them, you have to eat proteins that contain those amino acids. Those essential amino acids include:

• Histidine
• Isoleucine
• Leucine
• Lysine
• Methionine
• Phenylalanine
• Threonine
• Tryptophan
• Valine

Do you really need to worry about essential amino acids when you plan your daily meals? Not really. Animal sources of protein such as meat, eggs and dairy products are complete proteins. Those foods contain all of the amino acids you need. Those of you who are vegetarian and especially vegan may need to pay closer attention to the proteins you eat. Plant proteins are called incomplete proteins because plants do not contain all 9 of the essential amino acids. That is OK, though, because all 9 of the essential amino acids are available in plant sources and with a little careful planning, vegetarians and vegans can get all of the amino acids you need. We will get back to this later in the lesson.

Protein Functions in the Body

Since there are many different proteins in your body, there are many different functions too. Proteins functions include:

• Enzyme activity that promotes chemical reactions in the body.
• Signaling cells what to do and when to do it.
• Transporting substances around the body.
• Keeping fluids and pH balanced in the body.
• As building blocks for hormone production.
• Components that are important for blood clotting.
• Antibody activity that controls immune and allergy functions.
• As structural components that give our body parts their shapes.

Protein Digestion and Metabolism

The digestion of protein begins in the mouth with chewing. Chewing not only makes food easier to swallow, it also helps with digestion by chopping food up into smaller bits. Remember that it really is important to chew your food thoroughly; don’t gulp your food down in huge bites.

Protein digestion continues in the stomach with the release of hydrochloric acid and pepsinogen. Hydrochloric acids convert pepsinogen into pepsin, which begins to break down the bonds between the amino acids. This process takes place while the muscles surrounding the stomach squeeze and squish the foods and stomach fluids together.

The next step occurs in the small intestine where the hydrochloric acid is neutralized with bicarbonates released from the pancreas. The pancreas also releases an enzyme called trypsin. Trypsin continues to break apart the amino acids, which are then absorbed into the blood stream. Once in the blood stream, the amino acids are carried to the cells in various parts of your body. Your body uses the individual amino acids that were broken down during digestion to build the proteins needed for the various functions in your body.

Protein and Diet

You may not think of protein as an energy source, but proteins do contribute calories to you diet. Those calories need to be acknowledged if you are watching your weight. Each gram of protein you eat has four calories. The USDA suggests that you get about 20 percent of your calories from protein. For someone who needs 2000 calories per day, that would come to 100 grams of protein.

It isn’t difficult to get enough protein in your diet. One chicken leg alone will provide you with about 30 grams of protein. One salmon fillet has about 40 grams of protein, one cup of oatmeal has 6 grams of protein and a cup of asparagus even has two grams of protein. Since most people get enough protein from their diet, any protein deficiency is rare in developed countries.

In under-developed countries, protein deficiency is more common and severe protein deficiency is called kwashiorkor. Children with kwashiorkor tend to have very thin arms and legs and large, distended bellies. Lack of protein can cause growth failure, loss of muscle mass, a depressed immune system, lung problems, heart problems and death.

Your body only requires that about 20 percent of your calorie intake come from proteins; however there may be some good reasons for increasing your protein intake while decreasing some of your fat and carbohydrates. Protein digestion takes longer than carbohydrate digestion. It takes longer for proteins to be broken down so proteins stay in the stomach longer. This means you feel full longer, which may make it easier for you to reduce your total calorie intake by reducing or eliminating between-meal snacking.

A diet with more protein and fewer carbohydrates will also reduce your body’s need to produce insulin. Some experts believe this will help you to lose weight and it is certainly important for people with diabetes or metabolic syndrome.

If you don’t get enough of your daily calories from carbohydrates, your body will use protein as a fuel. This is the basis for ketogenic diets like the Atkins diet. “Ketogenic” refers to the ketones that your body makes when protein is used as a fuel. Proponents of these high protein, very low carbohydrate diets claim that this type of dieting is a safe and healthy way to lose weight, control cholesterol and keep blood sugar level. Opponents of the ketogenic diets point to possible kidney problems, liver problems, calcium loss, lack of fiber and dehydration as potential problems for followers of these diets.

Healthy Protein Choices

Making healthy protein choices is more about the fats that accompany the proteins and the preparation methods than it is about the actual protein. This means looking for protein sources that are lower in saturated fats, higher in healthier unsaturated fats and prepared in healthy ways. A fish fillet baked with lemon and almonds is an example of a healthy protein choice. Baking a chicken breast and topping it with salsa would also be another healthy example. A porterhouse steak is full of protein and tastes delicious, but is not as healthy as poultry or fish due to all of the saturated fats normally found in red meat. For most people, it is a good idea to limit red meat consumption to only a couple of meals each week. Processed meats like lunch meats and hot dogs are poor sources of protein too, because of the fats and ingredients used to make them have been linked to cancer.

Of course, fish and chicken may not always be healthy. Fish sticks or fried chicken are not good protein choices because the cooking methods add unhealthy fats and extra calories. Breaded and fried meats should be only be eaten rarely.

Other healthy protein sources include legumes, nuts and seeds. Vegetables and grains also contain some protein. These plant sources contain polyunsaturated fats, some of which are very beneficial to your health. We will learn more about the different types of fats next week.

How Much Protein Do You Need Each Day?

The USDA suggests that you need about 20 percent of your daily calorie intake to come from proteins. If you need 2000 calories per day, then about 400 calories should come from protein. One gram of protein has four calories so that means you would need 100 grams of protein each day. One ounce of protein is about 28 grams, so you need about four ounces of protein each day. One cup of diced chicken breast meat has about 45 grams of protein, or just less than two ounces. Three ounces of canned tuna has 20 grams of protein, or about 2/3 of one ounce of protein.

So how do you turn this into the right number of portions and portion sizes? For now, it is good to know that one serving of meat is usually about 3 ounces, or about the size of a deck of cards, and in general, three ounces of meat will have around 20 grams of protein. One cup of low fat milk has about eight grams of protein. Twelve almonds have about three grams of protein. We will discuss portion sizes and meal planning in later lessons.

Vegetarians and Incomplete Proteins

Remember the incomplete and complete proteins from the section on amino acids? Complete proteins contain all of the essential amino acids and incomplete proteins are missing one or more of the individual essential amino acids. Proteins from animal origin contain all of the essential amino acids, however proteins from plant sources do not. This means that a diet based on plant protein requires the right combinations of protein sources to get enough of all of the essential amino acids.

People who regularly eat meat, dairy and eggs don't need to be concerned with combining proteins since meat, eggs, fish, poultry and dairy products all contain complete proteins. Vegetarians and vegans may need to pay closer attention to the foods they eat to be sure they get a complete blend of amino acids.

A vegetarian or vegan diet that includes legumes, whole grains, nuts and seeds will supply all of the essential amino acids. Soy protein is a complete protein and eating soy will provide you with all of the essential amino acids too.

This Week's Assignment

There are quite a variety of ways to get healthy protein into your diet, and I would like you to concentrate on making healthy choices for your protein needs. This means protein sources that aren’t high in saturated fat or prepared in such a way that more fat and calories are added to the protein. At least three times this week, I would like you to substitute a healthy protein source for an unhealthy one. Here are some examples:

• Choose lean sliced turkey for a sandwich instead of a hot dog or hamburger.
• Bake a fish fillet with some almonds and lemon instead of frying your fish.
• Spread some peanut butter, almond butter or cashew butter on whole grain toast for breakfast instead of eating sausage or bacon.
• Order a grilled chicken sandwich rather than a breaded deep-fried chicken sandwich.
• Try a vegetarian dish with legumes such as black beans, pinto beans or navy beans.

this Week's Quiz

You can test your knowledge of proteins with this quiz: Quiz Two - Proteins

Read More About Protein

Proteins - Harvard School of Public Health

Proteins - How Stuff Works

Protein Makes You Feel Fuller

Vegetarian Protein Combining

This is lesson two of the About Nutrition Basic Nutrition Course. You may sign up for the whole e-course at About Nutrition