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Food for Life - Proteins for Growth

DK PublishingDK Publishing 2/07/2014 DKBooks
Photo: Changing requirements - Protein needs are greatest during periods of growth, such as childhood, pregnancy, and convalescence. © Provided by DKBooks Changing requirements - Protein needs are greatest during periods of growth, such as childhood, pregnancy, and convalescence.

Changing requirements - Protein needs are greatest during periods of growth, such as childhood, pregnancy, and convalescence.

Proteins for Growth

These are a major component of every cell in our bodies.

Like fats and carbohydrates, proteins are complex compounds that contain the elements carbon, hydrogen, and oxygen. They are also rich in the element nitrogen, which makes up about 16 percent of their total weight. The building blocks of proteins are called amino acids.

How we use protein

Every type of tissue in the body, including bones, skin, muscles, and organs, has its own set of proteins that help it perform its characteristic functions. Proteins help give structure to our cells and are important in cell growth, repair, and maintenance. Like carbohydrates and fats, they can also serve as an energy source. In addition, enzymes, hormones, and antibodies are all different types of proteins.

The protein that we eat has to be broken down, or digested, into amino acids and peptides (chains of amino acids) and absorbed into the bloodstream. This pool of amino acids provides most of the elements that are needed to build new proteins.

Good sources

When we think of dietary protein, we tend to think of animal meats. While these are rich sources of this vital dietary element, protein is also found in plant foods, such as grains and legumes, and in eggs and dairy products, such as milk and yogurt. In order to obtain the full range of essential amino acids, you should eat a variety of protein foods. Many people choose red meat (beef, pork, lamb, and veal) as their main source of protein, and eat it regularly through the week. However, we suggest that you eat no more than one serving of red meat a week. Examples of one serving of red meat include a small burger, steak, or cutlet.

Studies have shown that people who eat less red meat and eat more fish and chicken lower their risk of developing cardiovascular disease and colorectal cancer. In addition, fish provides a range of key nutrients that can help boost health, and legumes and grains are a useful source of fiber.

What are amino acids?

Just as the letters of the alphabet can be combined in different ways to form an endless variety of words, amino acids can be linked together in varying sequences to form a huge variety of proteins. The unique shape of each protein determines its function in the body.

Essential amino acids

Our bodies require about 20 amino acids for normal functioning. Nine of these are considered essential—that is, your body cannot make them by itself and must get them from food. The essential amino acids are lysine, histidine, isoleucine, phenylalanine, leucine, methionine, tryptophan, threonine, and valine.

Nonessential amino acids

The remaining 11 amino acids are nonessential; although you can obtain them from food, the body can also synthesize them as needed.

How much protein do you need?

According to the recently updated Dietary Reference Intakes guidelines, the recommended daily consumption of protein for adult men and womenis the following:

The difference is due to the fact that, in general, men’s bodies have more muscle mass than those of women.

How much protein you need in your daily diet is determined, in large part, by your overall energy intake, as well as by your body’s need for nitrogen and essential amino acids. Physical activity and exertion increase your need for protein. Requirements are also greater during childhood for growth and development, during pregnancy or when breast-feeding in order to nourish your baby, or when your body needs to recover from malnutrition or trauma or after an operation.

Because the body is continually breaking down protein from tissues, even adults who do not fall into the above categories need to include adequate protein in their diet every day. If you do not take in enough energy from your diet, your body will use protein from the muscle mass to meet its energy needs, and this can lead to muscle wasting over time.

Women aged 19–70 need to consume 46g of protein per day.

Men aged 19–70 need to consume 56g of protein per day.

Is deficiency common?

Protein deficiency is rare in developed countries, but it can occur in people who are dieting to lose weight, or in older adults, who may have a poor diet. Convalescent people recovering from surgery, trauma, or illness may become protein deficient if they do not increase their intake to support their increased needs. A deficiency can also occur if the protein you eat is incomplete and fails to supply all the essential amino acids.

Can you eat too much?

Since the body cannot store protein, it has to break down and dispose of any excess obtained from the diet. The liver removes nitrogen from amino acids, so that they can be burned as fuel, and the nitrogen is incorporated into urea, the substance that is excreted by the kidneys. These organs can normally cope with any extra workload but if kidney disease occurs, a decrease in protein will often be prescribed.

Excessive protein intake may also cause the body to lose calcium, which could lead to bone loss in the long-term. Foods that are high in protein (such as red meat) are often high in saturated fat, so excessive protein intake may also contribute to increased saturated fat.

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