By Elena Voropay

It's hard to overemphasize the importance of protein in the body's quest for rebuilding and regenerating healthy tissues. Theoretically it is possible to eat enough meat, fish, poultry, soy, dairy and eggs to get the protein you need. But most people find it difficult to do so. It takes time to buy products, fix meals, and even more time to eat them and clean the dishes. If you are physically active, you might need to double the amount of food and time to just meet the demand. If you are a bodybuilder, thripple all of the above, and you end up living in the kitchen. So, what do you do? Supplements, good old protein powders and meal replacements come to your door to save your life. What are they? What's the difference? Which ones are best?

Without protein, life would cease to exist. The word is derived from the Greek "proteios," meaning "of prime importance." The derivation clearly shows that protein's significance to bodily health, and to life itself, has been a long-recognized fact. Every single cell of the human organism contains some protein. It is estimated that there are between 10 000 and 50 000 different kinds of protein in the human body.

Brain cells, for example, are 10 percent protein. Muscle and red blood cels have as much as 20 percent. Overall, protein is the second largest building material of the human body (preceded only by water) comprising approximately 15% by weight.

Protein promotes new cell growth throughout the body. Existing in a constant state of growth and repair, the body uses protein to create and replace hair, skin and nails. Built of amino acids, proteins are needed to form most hormones, muscle fibers, tendons and ligaments.

Protein propels the body's catabolism/anabolism cycle. No doubt that you know how crucial this cycle is to your physically active body. Exercising causes muscle tissue to be broken down in a process called catabolism, and restored in a process called anabolism. Increasing protein intake in the anabolic mode helps the body form new muscle tissue as well as repair/rebuild existing tissue. (Rest and recovery also contribute greatly to the effectiveness of exercising.) Amino acids are responsible for the production of all the body's 15 000 enzymes that are involved in most of the chemical reactions including catabolic and anabolic cycling. Participating in regular exercise without consuming sufficient protein can move the body into a catabolic (muscle wasting) state.

Protein increases metabolism. The process of digestion, absorption and storage of food increases your metabolic rate by an average of 10 percent. Certain amino acids found in protein directly stimulate these after-meal cellular processes. A high-protein meal raises metabolism about 25%, compared with a 5% boost after a high-carbohydrate meal.

Protein helps monitor water balance, regulate fluid volume and even the composition of body fluids. The water comprising the majority of the body is found between and within cells as well as inside the vascular system (i.e., capillaries, veins and arteries). Proteins are are attracted to water, meaning they are hydrophilic and exert osmotic pressure . Some proteins work as special transporters in cell membranes called 'pumps' that move molecules in and out of cells. A very important example is the sodium-potassium pump that regulates the concentrations of these minerals in the body fluids. Sodium-potassium pump maintains the function of nerves and muscles. A diet deficient in protein results in depleted proteins in the blood. Without enough protein to attach to water in the vascular spaces, the water leaks out into the spaces between the cells, causing edema, or water retention, due to the kidney's inability to excrete it. Disturbed mineral and electolyte balance may have devastating consequences.

Protein strengthens the immune system producing antibodies, which live in the blood and combat disease. When the body is attacked by viruses, bacteria or other foreign intruders, antibodies deactivate the intruders, thereby preventing the disease. Amazingly, the body's cells retain a molecular memory of the antibodies used in an invasion, to be used the next time that infection sets in. Thus, once protein helps the body fight off disease the first time, it continues to thwart that condition in the future.

Proteins make up some of the chemical messengers called hormones. Hormones are often described as the bodies chemical messengers that travel throughout hte body delivering instructions to our living cells. Examples of hormones that are proteins include:

insulin - increses the transport of glucose into cells lowering blood glucose levels
growth hormone - promotes growth of all body tissues, including your muscles
glucagon - increases blood glucose levels, especially important during starvation

thyroxin - regulates your metabolic rate, or the conversion of eaten food into usable energy
calcitonin - regulates serum calcium concentrations, importantly in calcium and phosphorus metabolism and the ability to decrease blood calcium levels.

Protein maintains nitrogen balance. Of the four energy nutrients - carbohydrates, protein, fat and alcohol - only protein contains nitrogen, which is critical in repairing, rebuilding, growing muscle tissue, fighting infections, handling stress and staying healthy. Nitrogen is constantly depleted in sweat, urine and feces, making it necessary to ingest enough protein to keep the body in a state of positive nitrogen balance. The maintenance of this crucial equilibrium is the foundation of many nutritionally sound, doctor-prescribed lifestyle diets prescribing the frequent intake of light, protein-rich meals throughout the day, compared with the traditional, heavier, breakfast-lunch-dinner mode. The higher the quality of the protein (as measured by Biological Value), the more nitrogen is absorbed and retained by the body.* Protein molecules maintain life making up certain enzymes and serving as important regulators of your blood pressure, blood sugar level, and your metabolism. They normalize moods, concentration, aggression, attention, sleep, and sex drive.

Essential Building Blocks

Out of 22 amino acids required for proper functioning, your body can make only 10-12 in sufficient amounts. The are alanine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, proline, serine, and tryptophan. The rest of them have to be supplied through your diet, hence the name "essential amino acids". These are tryptophan, lysine, methionine, phenylalanine, threonine, valine, leucine, and isoleucine. Semi-essential amino acids are arginine and histidine. Usually aduls can make enough of these to maintain normal balance. But children and bobybuilders need additional amounts to support muscle tissue growth and higher metabolic demands.

Chemically proteins are large complex molecules that contain the same atoms of carbon, hydrogen and oxygen as both carbohydrates and lipids. However, amino acids differ from other nutrients in their nitrogen and sometimes sulphur containing properties. Your body needs to maintain positive nitrogen balance to support all of its needs plus some more to permit muscle growth and maintenance.

Protein Quality

Different proteins have different availability in the body. They are ranked according to Biological Value (BV) which measures how efficient a specific protein is in supporting your body's needs.Scientists feed only one given protein to ginnea piggs and measure how much nitrogen is retained. The protein has to contain all the essential amino acids mentioned earlier in order to be completely synthesised; otherwisethe nitrogen is excreted. So, the more nitrogen remains in the body, the higher the quality of protein. The number indicates a percentage of consumed nitrogen that can be retained.

The BV of some common foods:

A protein with BV of 70 or greater can support human growth if the energy intake is adequate. At the time the system was introduced eggs were given the highest BV of 100 because they are the most bio-available natural protein. Afterwards whey was isolated from milk and shown to have a higher BV, and depending on the process used can yield percentage from 104 to 154 on the scale.

Application:
BV scales are a useful tool in putting together a complete protein, but it represents only part of the picture when it comes to real life. Scientists and professionals agree that protein test environment might differ from real life environment which may show different results. And just because the protein is well retained in the body doesn't mean that it is being well utilized. A protein with high Biological Value is digested and absorbed with a lot less effort and time. The faster it is absorbed, the sooner it enters the blood stream and becomes available for tissue utilization. However, you can only utilize a limited amount of protein at any one given time. This makes consuming large amount of protein in one sitting almost useless. After all, what is not used will be wasted and/or stored in the form of fat around your waistline. So, you are better off taking smaller amounts more often when it comes to protein with high BV. Both rapid and slow proteins offer benefits to someone trying to build muscle.

Amino Acid Scoring determines the amino acid composition of any protein by comparing it with a reference protein, which is currently whole egg. All the amino acids found in the egg are calculated in mg per gram of nitrogen; then the numbers are compared with another food. This is the most simple way to evaluate protein quality and identify the limiting amino acid. The problem here is that Amino Acid Scoring, also known as Chemical Protein Scoring, doesn't predict how well the protein is digested, absorbed and utilized when it is eaten with other foods. Say, how good is your egg omelet if you cook the eggs, add vegetables with undigestible fiber, plus additional wholegrain toast which also slows down digestion and prevent absorption of certain nutrients. Many factors may inhibit the ability of the body to digest and thus absorb certain amino acids. And your digestive system has to function properly to get the most benefit, and this is not the case with most people. So, while Amino Acid Scoring is usable in calculations, it is just as applicable as your Glycaecemic Index.

Amino Acids in Whole Egg (mg/g N)

An important aspect of protein metabolism is how well or how poorly a given protein is digested by the human body. The newest measurement of a protein's quality is the PDCAAS, the Protein Digestibility Corrected Amino Acid Score. Besides completeness and quality of protein, PDCAAS measures its digestibility in the human body. In other words, PDCAAS compares the amino acid contents of a given protein with amino acid requirements of pre-school children. Since young children have high protein energy demands due to accelerated growth, this method reveals the most limiting amino acid in the given protein. The reason scientists have chosen this specific age group to provide guidelines for everybody is that if a protein will effectively support a young child's growth and development, then it will meet or exceed the requirements of adults. Protein digestibility depends on its source, what else is eaten with that protein, and other limiting factors. The downfall is that some foods naturally contain anti-nutritional factors like in some beans, or may be created as result of heating and/or cooking, and inhibit the ability of the body to digest and thus absorb certain amino acids. Research has shown the PDCAA method of scoring protein often over estimates the quality of foods containing anti-nutritional factors.

Application:
The amino acid with the lowest ratio is the first limiting amino acid. Almost all plant sources of protein have one or more limiting amino acids. Wheat protein is known to be a poor quality protein due to the fact that its limiting essential amino acid is lysine. In the case of pinto beans, for example, limiting amino acid is tryptophan showing 8.8mg/1g protein for the required 11mg/1 g protein. But amno acid score does not accout for digestibility. So, you have to put digestibility score of 79 percent in the case for pinto beans. Regardless of the amount consumed, you will utilize only about 63 percent (8.8 divided by 11 and multiplied by 79) of protein found in pinto beans. Say the food label would show that one serving provides 7 grams protein per 1/2 cup. With utilization ratio of 0.63, you will get only 4.41 grams of protein.

The Protein Efficiency Ratio (PER) is often used for evaluating protein quality and measured through the weight gain due to consumption of certain protein. Specifically, scientists feed protein to young rats and periodically weigh them to see whether there are any changes in the weight of tested rats. Then, the gain or loss in weight is divided by the amount of fed protein. This method theoretically shows the effect of certain protein on the body - how well it is digested, absorbed and utilized by all the tissues in the body.

Application: This is an inexpensive but time-consuming and inefficient technique. It overlooks two important factors: the amino acid needs of rats are not the same as those of humans, and the requirements for growth are different than for maintenance. Also, consider that in real life we don't consume one protein by itself - we combine it with other foods which directly effects the rate of protein assimilation. Other factors, such as individual biochemistry, personal needs and activity level all play a huge role in effectiveness of macronutrients. So, practically, it's just good to be aware of this type of Protein Quality measurement.