What is Dietary Protein?

S. Mithra

Proteins are made of strings of amino acids that form chains known as peptides. Our bodies need dietary protein to accomplish many basic functions, such as building bones, moving muscles, and repairing tissue. Dietary protein, an essential nutrient, comes from meat, dairy, and certain grains and beans.

The structure of leucine, an essential amino acid.
The structure of leucine, an essential amino acid.

Proteins differ by the types and order of amino acids they contain. Even though there are only 20 amino acids, they create almost endless variations in chains as long as 500 links. Proteins form inside animals (including humans) and plants through processes that synthesize peptides. For humans, we cannot synthesize certain "essential protein," and so we must ingest them through food. These essential proteins are made of phenylalanine, threonine, methionine, tryptophan, leucine, isoleucine, lysine, and valine amino acids.

Milk is a complete protein food.
Milk is a complete protein food.

Food from plants, like corn, have incomplete protein, which means they do not contain all the necessary amino acids. Only food from animals, such as cheese and fish, provide complete protein, and don't need to be combined with other protein sources. Examples of complete protein foods are milk, cheese, yogurt, butter, poultry, pork, or any meat. Incomplete proteins include oats, wheat, pasta, lentils, nuts, rice, soy, pears, and seeds. Eating a combination of complementary protein sources, such as grains mixed with legumes, results in a diet of essential protein. This is how vegetarians and vegans maintain health without eating meat or dairy.

Plant-based foods, like corn, contain incomplete proteins.
Plant-based foods, like corn, contain incomplete proteins.

As building blocks for our tissue and a catalyst in metabolism, dietary protein's jobs are almost too many to enumerate. Our digestive system breaks down protein to its amino acid constituents. They're involved in the nervous system, repairing and maintaining tissue such as bones and skin, and bringing energy to cells. Dietary requirements vary from 1.4-2.5 oz (40-70 g) of protein per day. Too much protein might deplete calcium, while too little causes a form of malnutrition called kwashiorkor. Insufficient protein weakens the heart and other muscles, eventually leading to death. Incidentally, proteins are responsible for most food allergies.

Beans, which are a good source of dietary protein.
Beans, which are a good source of dietary protein.
Nuts are an incomplete protein.
Nuts are an incomplete protein.
Lentils are an incomplete protein.
Lentils are an incomplete protein.
Pears are high in protein.
Pears are high in protein.
Although it's not a diet food, butter is a source of dietary protein.
Although it's not a diet food, butter is a source of dietary protein.
Oats can be included as a supplement in a diet of essential protein.
Oats can be included as a supplement in a diet of essential protein.
Children who live in poor, rural areas and developing countries are at an increased risk for kwashiorkor due to the lack of protein sources available to them.
Children who live in poor, rural areas and developing countries are at an increased risk for kwashiorkor due to the lack of protein sources available to them.
Beans, such as black beans, are considered good sources of protein.
Beans, such as black beans, are considered good sources of protein.

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Discussion Comments

Heavanet

@talentryto- Though I like beans and other types of plant-based protein, I agree that eggs are also a good source when you want to cut back on meat. I think that eggs are also more satisfying and filling that plant-based protein sources, which sometimes leave you feeling hungry even after you eat a them.

Talentryto

The protein in my diet primarily comes from eggs. Though I'm not a total vegetarian, I try to eat as little meat as possible, I have found that eggs are a good substitute, and provide high quality protein that is easily digestible.

To compensate for not eating meat, I often make egg sandwiches, quiches, and egg salads. I get the protein I need without eating meat.

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