Proteins are large molecules consisting of amino acids which our bodies and the cells in our bodies need to function properly. Our body structures, functions, the regulation of the body's cells, tissues and organs cannot exist without proteins.
The human body's muscles, skin, bones and many other parts contain significant amounts of protein. In fact, protein accounts for 20% of total body weight.
Enzymes, hormones and antibodies are proteins. Proteins also work as neurotransmitters and carriers of oxygen in the blood (hemoglobin).
What are proteins?
Imagine proteins as machines; machines which make all living things, from viruses, bacteria, butterflies, jellyfish, plants and humans function. The human body is made up of approximately 100 trillion cells - each one has a specific function. Each cell has thousands of different proteins, which together make the cell do its job - the proteins are tiny machines within the cell.
Amino acids and proteins - protein is made up of amino acids; amino acids are the building blocks of protein, there are 20 of them. Imagine there are 20 different types of bricks, and a much larger number of different types of houses which we could name according to the way we combined the bricks (their sequence). The bricks are the amino acids and the houses are the proteins.
According to the U.S. National Library of Medicine1, the 20 different amino acids are: alanine, arginine, asparagines, aspartic acid, cysteine, glutamic acid, glutamine, glycine - histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine.
These 20 amino acids can be arranged in millions of different ways to create millions of different proteins, each one with a specific function in the body. Amino acids are organic molecules - they are made out of carbon, hydrogen, oxygen, nitrogen and sometimes sulphur.
There are three types of nutrients that are essential as energy sources for the human body:
One gram of protein or carbohydrate contains 4 calories, while one gram of fat has 9 calories.
Jons Jacob Berzelius (1779-1848), a Swedish doctor and chemist, introduced the word protein into science. Dutch chemist Gerhardus Johannes Mulder had already described proteins beforehand, but had not introduced the word as we know it today.
The Greek word protos means "first" and the Greek word proteios means "the first quality". As European scientists believed it was essential to life (a primary/first quality for life, a raw/primary material), they created a new word from the original Greek one.
The function of proteins
In virtually every biological process proteins are playing a role. According to a report published in the journal Molecular Biology2, some of the main functions of proteins in the human body are to:
- Build, strengthen and repair/replace things, such as tissue. Examples include keratin (strengthens protective coverings, such as hair), collagen and elastin (both provide support for connective tissue).
- Make antibodies for our immune system
- Make hormones, which help cells send messages and coordinate bodily activities
- Muscle contractions - actin and myosin, two types of proteins, are involved in muscle contraction and movement.
- Make enzymes. An enzyme facilitates a biochemical reaction.
- Carry things - hemoglobin, a protein, transports oxygen through the blood.
- Mediate cell response - rhodopsin is a protein in the eye which is used for vision
- Store things - ferritin is a protein which stores iron in the liver
Recent developments on protein function from MNT news
High protein diets may help promote weight loss. The International Food Council Foundation found that a high percentage of women who eat more protein do not only avoid weight gain, but also report weight loss.
A high protein diet may be good for bone health. An investigation published in the Journal of Clinical Endocrinology and Metabolism, revealed that a calorie controlled diet lower in carbohydrates and higher in protein along with daily exercise has a significantly positive impact on bone health in overweight individuals as well as obese young women.
Dietary requirements of protein
Nobody seems to agree on how much protein we can eat; experts from industry, government agencies, diet companies and nutritional organizations have a varying list of assertions.
An individual's daily protein requirement depends on several factors, including:
- Age - a growing child's needs will not be the same as an individual aged 80 years
- Sex - males generally require more protein than (non-pregnant or non-breastfeeding) females
- Weight - an individual who weighs 200lbs will require more protein compared to somebody who weighs 120lbs. In fact, recent studies indicate that weight matters more than age when determining dietary protein requirements.
- Muscular exertion - an individual who earns his living delivering pianos will require more protein than a computer programmer of the same age and height
- Muscle mass - a muscle-bound weight trainer will need more dietary protein than a marathon runner
- Health - a person who is convalescing after an illness or medical procedure may need more dietary protein than other people
The Institute of Medicine, part of the National Academy of Sciences, USA, which created the DRI (Dietary Reference Intake), a system of nutrition, recommends the following for dietary protein intake:3
Percentage of energy that should come from protein:
- Infants (7 - 12 mo) - 11 grams per day
- Infants (0 - 6 mo) - 9.1 grams per day
- Teenage boys (14 - 18 y) - 52 grams per day
- Teenage girls (14 - 18 y) - up to 46 grams per day
- Adult men - approximately 56 grams per day
- Adult women - approximately 46 grams per day
- Pregnant or lactating (breastfeeding) women - about 71 grams per day
According to the U.S. Centers for Disease Control and Prevention4, protein intake should be:
- Children ages 1 to 3 - 13 grams per day
- Children ages 4 to 8 - 19 grams per day
- Children ages 9 to 13 - 34 grams per day
- Girls ages 14 to 18 - 46 grams per day
- Boys ages 14 to 18 - 52 grams per day
- Women ages 19 to 70+ - 46 grams per day
- Men ages 19 to 70+ - 56 grams per day
In some developing countries protein deficiency is a major cause of illness and premature death. Protein deficiency can lead to mental retardation and reduced IQ, according to a study published in the journal Food and Nutrition.5
In most parts of the world where protein deficiency is common, total food energy consumption is also too low - i.e. people are not getting enough food in general. Protein deficiency can lead to:
- Growth problems
- Wasting and shrinkage of muscle tissue
- Fatty liver
- Swollen belly
- Swollen legs
- Weaker immune system, leading to a higher susceptibility to infections and diseases
In several countries where protein deficiency is a serious problem, the leaves and other parts of the Moringa tree can help provide dietary protein.
In developed countries, especially Western Europe where the dietary requirements of poorer people are very carefully monitored and resolved, protein deficiency is quite rare. In developed nations, protein deficiency is more likely to occur among people on crash diets, or among very elderly individuals who do not eat properly.
Some studies indicate that protein deficiency and general malnutrition is probably worse than people realize, especially in the USA among poor people, convalescing patients, and the elderly. The difference in the nutritional content of a Japanese/Finnish state school lunch, compared to one in the USA would shock most Finnish or Japanese nutritionists.
Sources of dietary protein
- Fish and fish eggs
- Dairy products
- Seeds and nuts
- Soy products
- Quorn - a fungus extract, popular in the UK/Ireland. Egg-white is used as a binder, so it is not a vegan source.
- Grains, vegetables and legumes also have protein (less per kilo of total weight)