WHAT IS PROTEIN?
Proteins are part of every cell, tissue, and organ in our bodies. These body proteins are constantly being broken down and replaced. The protein in the foods we eat is digested into amino acids that are later used to replace these proteins in our bodies.
Proteins are compounds composed of carbon, hydrogen, oxygen , andnitrogen , which are arranged as strands of amino acids . They play an essential role in the cellular maintenance, growth, and functioning of the human body. Serving as the basic structural molecule of all the tissues in the body, protein makes up nearly 17 percent of the total body weight. To understand protein’s role and function in the human body, it is important to understand its basic structure and composition.
Protein is found in the following foods:
- meats, poultry, and fish
- legumes (dry beans and peas)
- nuts and seeds
- milk and milk products
- grains, some vegetables, and some fruits (provide only small amounts of protein relative to other sources)
DIFFERENT KINDS OF PROTEIN
The quality of protein depends on the level at which it provides the nutritional amounts of essential amino acids needed for overall body health, maintenance, and growth. Animal proteins, such as eggs, cheese, milk, meat, and fish, are considered high-quality, or complete, proteins because they provide sufficient amounts of the essential amino acids.
Plant proteins, such as grain, corn, nuts, vegetables and fruits, are lower-quality, or incomplete, proteins because many plant proteins lack one or more of the essential amino acids, or because they lack a proper balance of amino acids. Incomplete proteins can, however, be combined to provide all the essential amino acids, though combinations of incomplete proteins must be consumed at the same time, or within a short period of time (within four hours), to obtain the maximum nutritive value from the amino acids. Such combination diets generally yield a high-quality protein meal, providing sufficient amounts and proper balance of the essential amino acids needed by the body to function.
Protein from animal sources, such as meat and milk, is called complete, because it contains all nine of the essential amino acids. Most vegetable protein is considered incomplete because it lacks one or more of the essential amino acids. This can be a concern for someone who doesn’t eat meat or milk products. But people who eat a vegetarian diet can still get all their essential amino acids by eating a wide variety of protein-rich vegetable foods.
For instance, you can’t get all the amino acids you need from peanuts alone, but if you have peanut butter on whole-grain bread, you’re set. Likewise, red beans won’t give you everything you need, but red beans and rice will do the trick.
The good news is that you don’t have to eat all the essential amino acids in every meal. As long as you have a variety of protein sources throughout the day, your body will grab what it needs from each meal.
ALL PROTEIN ISN’T ALIKE
Protein is built from building blocks called amino acids. Our bodies make amino acids in two different ways: Either from scratch, or by modifying others. A few amino acids (known as the essential amino acids) must come from food.
- Animal sources of protein tend to deliver all the amino acids we need.
- Other protein sources, such as fruits, vegetables, grains, nuts and seeds, lack one or more essential amino acids.
Vegetarians need to be aware of this. People who don’t eat meat, fish, poultry, eggs, or dairy products need to eat a variety of protein-containing foods each day in order to get all the amino acids needed to make new protein.
PROTEIN PROCESSING: DIGESTION, ABSORPTION, AND METABOLISM
Protein digestion begins when the food reaches the stomach and stimulates the release of hydrochloric acid (HCl) by the parietal cells located in the gastric mucosa of the GI (gastrointestinal ) tract. Hydrochloric acid provides for a very acidic environment , which helps the protein digestion process in two ways: (1) through an acid-catalyzed hydrolysis reaction of breaking peptide bonds (the chemical process of breaking peptide bonds is referred to as a hydrolysis reaction because water is used to break the bonds); and (2) through conversion of the gastric enzyme pepsinogen (an inactive precursor) to pepsin (the active form). Pepsinogen is stored and secreted by the “chief cells” that line the stomach wall. Once converted into the active form, pepsin attacks the peptide bonds that link amino acids together, breaking the long polypeptide chain into shorter segments of amino acids known as dipeptides and tripeptides. These protein fragments are then further broken down in the duodenum of the small intestines. The brush border enzymes, which work on the surface of epithelial cells of the small intestines, hydrolyze the protein fragments into amino acids.
The cells of the small intestine actively absorb the amino acids through a process that requires energy . The amino acids travel through the hepatic portal vein to the liver, where the nutrients are processed into glucose or fat (or released into the bloodstream). The tissues in the body take up the amino acids rapidly for glucose production, growth and maintenance, and other vital cellular functioning. For the most part, the body does not store protein, as the metabolism of amino acids occurs within a few hours.
Amino acids are metabolized in the liver into useful forms that are used as building blocks of protein in tissues. The body may utilize the amino acids for either anabolic or catabolic reactions. Anabolism refers to the chemical process through which digested and absorbed products are used to effectively build or repair bodily tissues, or to restore vital substances broken down through metabolism. Catabolism , on the other hand, is the process that results in the release of energy through the breakdown of nutrients, stored materials, and cellular substances. Anabolic and catabolic reactions work hand-in-hand, and the energy produced in catabolic processes is used to fuel essential anabolic processes. The vital biochemical reaction of glycolysis (in which glucose is oxidized to produce carbon dioxide, water, and cellular energy) in the form of adenosine triphosphate, or ATP, is a prime example of a catabolic reaction. The energy released, as ATP, from such a reaction is used to fuel important anabolic processes, such as protein synthesis.
The metabolism of amino acids can be understood from the dynamic catabolic and anabolic processes. In the process referred to as deamination , the nitrogen-containing amino group (NH2) is cleaved from the amino acid unit. In this reaction, which requires vitamin B6 as a cofactor, the amino group is transferred to an acceptor keto-acid , which can form a new amino acid. Through this process, the body is able to make the nonessential amino acids not provided by one’s diet. The keto-acid intermediate can also be used to synthesize glucose to ultimately yield energy for the body, and the cleaved nitrogen-containing group is transformed into urea, a waste product, and excreted as urine.
6 Primary Functions of Proteins
- 1. Repair and Maintenance
Protein is termed the building block of the body. It is called this because protein is vital in the maintenance of body tissue, including development and repair. Hair, skin, eyes, muscles and organs are all made from protein. This is why children need more protein per pound of body weight than adults; they are growing and developing new protein tissue.
- 2. Energy
Protein is a major source of energy. If you consume more protein than you need for body tissue maintenance and other necessary functions, your body will use it for energy. If it is not needed due to sufficient intake of other energy sources such as carbohydrates, the protein will be used to create fat and becomes part of fat cells.
- 3. Hormones
Protein is involved in the creation of some hormones. These substances help control body functions that involve the interaction of several organs. Insulin, a small protein, is an example of a hormone that regulates blood sugar. It involves the interaction of organs such as the pancreas and the liver. Secretin, is another example of a protein hormone. This substance assists in the digestive process by stimulating the pancreas and the intestine to create necessary digestive juices.
- 4. Enzymes
Enzymes are proteins that increase the rate of chemical reactions in the body. In fact, most of the necessary chemical reactions in the body would not efficiently proceed without enzymes. For example, one type of enzyme functions as an aid in digesting large protein, carbohydrate and fat molecules into smaller molecules, while another assists the creation of DNA.
- 5. Transportation and Storage of Molecules
Protein is a major element in transportation of certain molecules. For example, hemoglobin is a protein that transports oxygen throughout the body. Protein is also sometimes used to store certain molecules. Ferritin is an example of a protein that combines with iron for storage in the liver.
- 6. Antibodies
Protein forms antibodies that help prevent infection, illness and disease. These proteins identify and assist in destroying antigens such as bacteria and viruses. They often work in conjunction with the other immune system cells. For example, these antibodies identify and then surround antigens in order to keep them contained until they can be destroyed by white blood cells.
HOW MUCH PROTEIN DO YOU NEED?
This will depend on your level of activity. Yes there are a lot of people who go on a protein diet and lose weight without exercise. That’s not something I would recommend. Simply because exercise is good for your overall health. Your health should be your first concern always. A great looking body is the result of working out and eating well.
With that in mind, here’s a simple rule of thumb. Most experts agree that eating between 1 and 1.8 grams of protein per pound is good. Now if you’re not working out regularly, you can reduce that to 0.8 per pound of body weight.
The nitrogen balance index (NBI) is used to evaluate the amount of protein used by the body in comparison with the amount of protein supplied from daily food intake. The body is in the state of nitrogen (or protein) equilibrium when the intake and usage of protein is equal. The body has a positive nitrogen balance when the intake of protein is greater than that expended by the body. In this case, the body can build and develop new tissue. Since the body does not store protein, the overconsumption of protein can result in the excess amount to be converted into fat and stored as adipose tissue . The body has a negative nitrogen balance when the intake of protein is less than that expended by the body. In this case, protein intake is less than required, and the body cannot maintain or build new tissues.
A negative nitrogen balance represents a state of protein deficiency, in which the body is breaking down tissues faster than they are being replaced. The ingestion of insufficient amounts of protein, or food with poor protein quality, can result in serious medical conditions in which an individual’s overall health is compromised. The immune system is severely affected; the amount of blood plasma decreases, leading to medical conditions such as anemia or edema; and the body becomes vulnerable to infectious diseases and other serious conditions. Protein malnutrition in infants is called kwashiorkor , and it poses a major health problem in developing countries, such as Africa, Central and South America, and certain parts of Asia. An infant with kwashiorkor suffers from poor muscle and tissue development, loss of appetite, mottled skin, patchy hair, diarrhea, edema, and, eventually, death (similar symptoms are present in adults with protein deficiency). Treatment or prevention of this condition lies in adequate consumption of protein-rich foods.
The nutritional values for shakes can vary widely. Typically from 24g and up. It depends on the brand and serving size.
VEGETARIAN PROTEIN SHAKES
There are hundreds of protein bars available in a wide range of protein grams. When choosing a protein bar read the label carefully. You want to avoid those with a high amount of sugar. Aim for sugar below 5 grams.
PROTEIN & MUSCLE BUILDING
Skeletal muscle demonstrates extraordinary mutability in its responses to exercise of different modes, intensity, and duration, which must involve alterations of muscle protein turnover, both acutely and chronically. Here, we bring together information on the alterations in the rates of synthesis and degradation of human muscle protein by different types of exercise and the influences of nutrition, age, and sexual dimorphism. Where possible, we summarize the likely changes in activity of signaling proteins associated with control of protein turnover. Exercise of both the resistance and nonresistance types appears to depress muscle protein synthesis (MPS), whereas muscle protein breakdown (MPB) probably remains unchanged during exercise. However, both MPS and MPB are elevated after exercise in the fasted state, when net muscle protein balance remains negative. Positive net balance is achieved only when amino acid availability is increased, thereby raising MPS markedly. However, postexercise-increased amino acid availability is less important for inhibiting MPB than insulin, the secretion of which is stimulated most by glucose availability, without itself stimulating MPS. Exercise training appears to increase basal muscle protein turnover, with differential responses of the myofibrillar and mitochondrial protein fractions to acute exercise in the trained state. Aging reduces the responses of myofibrillar protein and anabolic signaling to resistance exercise. There appear to be few, if any, differences in the response of young women and young men to acute exercise, although there are indications that, in older women, the responses may be blunted more than in older men.
Whether running sprints, long-distance swimming or lifting weights, athletes expend more energy than the average person and their bodies need additional nutrients to recover from intense physical activity. Protein plays an important role in an athlete’s diet as the nutrient helps repair and strengthen muscle tissue. High protein diets are popular among athletes — especially those seeking a leaner, more defined physique. But how much protein is really necessary?
While protein is critical in building muscle mass, more is not necessarily better. Eating large amounts of lean protein will not equate with a toned body.
When determining protein requirements for athletes, it’s important to look at the athlete’s overall diet. About 10 to 15 percent of an athlete’s total calories should come from protein, with the remaining calories coming from carbohydrates and fat. Athletes who consume diets adequate in both these nutrients end up using less protein for energy than those who consume a higher protein diet. This means that protein can go toward building and maintaining lean body mass. Athletes need to ensure that they are also meeting needs for carbs and fat, not just protein.
IS THERE ANY BENEFIT TO GETTING PROTEIN FROM BARS OR SHAKES INSTEAD OF WHOLE FOODS?
No. Shakes and protein bars might make it easier to meet your daily protein requirements, but in the end, high-protein foods like meat, eggs, peanut butter, and nuts may actually be more satisfying because they have higher fat content and take longer to digest than shakes or bars.