Protein and Its Impact on Nutrition, Food Properties, and Health

Nutritional Role of Protein
Protein accounts for about 10–15 percent of energy in human diets and is indispensable for life. It forms the structure of all cells and contributes to enzymes, transport molecules in the blood, and certain hormones. Globally, the challenge of ensuring adequate protein supply is second only to the overall food problem, as population growth continues to strain food systems.

Protein in Foods
Proteins also shape the sensory qualities of food, influencing taste, aroma, and texture. Animal-based foods such as meat, poultry, fish, eggs, milk, yogurt, and cheese are rich in high-quality protein. Plant-based sources—beans, lentils, nuts, grains, and vegetables—contain smaller amounts, but when eaten in combination, they can supply essential amino acids. A classic example is rice paired with beans, which together form a complete protein source.

Food Quality and Functionality
Protein levels often serve as quality indicators. In wheat and flour, for instance, protein content is the best single measure of bread-making performance. Proteins frequently combine with carbohydrates and fats to form glycoproteins and lipoproteins, which influence the flow and texture of food solutions. These compounds also have technical uses in the food industry, acting as natural emulsifiers in products like dressings and baked goods.

Effects of Cooking
Cooking alters proteins in significant ways. Heat can degrade amino acid side chains or cause them to react with sugars, producing desirable flavors through the Maillard reaction. This reaction is responsible for the appealing browning of roasted and baked foods. However, excessive heating may damage essential amino acids, reducing the overall nutritional value of the protein.

Protein Quality and Health
Protein quality plays a central role in human development and health. High-quality proteins provide all essential amino acids in the right proportions, supporting growth in children and maintenance in adults. Low-quality proteins, by contrast, may lack one or more key amino acids. Digestibility and amino acid composition are the two main factors that determine protein quality. With rising demand, sustainable sources such as plant-based proteins, cultured meat, and even insect protein are increasingly being developed to meet global nutritional needs.
Protein and Its Impact on Nutrition, Food Properties, and Health

Hordein – prolamin glycoprotein in barley

Prolamins are the endosperm storage proteins of cereal grains. The prolamins are monomeric polypeptide chains with molecular weights between 30 to 80 kDa depending on the type of cereal. They are rich in proline and glutamine (20 - 55 %).

Prolamins present different names depending on the type of cereal from which are extracted. Prolamins in wheat which are known as gliadins, in barley as hordeins, in rye as secalins, and in oats as avenins are main triggering factor in celiac disease.

Barley prolamins are the main storage protein in the grain, and major protein in barley by-product. The barley prolamins, hordeins as the main storage protein fraction in barley seeds constitute approximately 50–80% of total grain proteins.

Hordeins accumulate in the starchy endosperm cells of developing barley grains, during grain filling. Hordein synthesis proceeds linearly from approximately 10 to 30 days post-anthesis.

Four sub-units are classified based on their electrophoretic mobilities, B-hordein of 35–46 kD, C-hordein of 55–75 kD, γ-hordein of less than 20 kD and D-hordeins of more than 100 kD.

B-hordein consists in the major fraction of hordein (70–80%) and are sulfur-rich. C-hordein it is the second most important fraction (10–20%) and are sulfur-poor. D-hordein considered a protein with high molecular weight (HMW) and γ -hordein (1%–5%) with the smallest polypeptides.

Scientists study the effect of B, C and D hordeins on malting quality of northern European barleys and found that the B fraction had some effect on malting quality through changing adjusting diastatic power.

The hordeins are amongst the triggers of coeliac disease (CD), a well characterized T-cell mediated disorder suffered by approximately 1% of most populations. In coeliac disease the immune system mounts an inappropriate reaction to particular peptide sequences in dietary gluten, reacting as if the gluten molecules were an invading microorganism.
Hordein – prolamin glycoprotein in barley

Fish: Rich source of protein

Fish and seafood products, have a high nutritional value regarding beneficial amounts of protein, lipids as well as essential micronutrients.

Aquatic animal foods are a rich source of protein and currently supplies 17% of all the protein consumed in the world. Fish is also a good source of easily digestible protein, and its amino acid profile usually contains most of the essential amino acids which is required to humans for balanced diet.

A 100 g cooked serving of most types of fish and shellfish provides approximately 18–20 g of protein, or about a third of the average daily recommended protein intake.

The amount of protein in fish muscle is usually between 16 and 21 %, but values lower than 16 % or as high as 28 % are occasionally found in some species. Proteins are important for growth and development of the body, maintenance and repairing of worn out tissues. Fish is known to be a source of protein rich in essential amino acids (lysine, methionine, cystine, threonine, and tryptophan). Eighteen amino acids were identified in tuna species, and glutamic acid was the most predominant.

Aquatic animal foods have a higher protein content than most terrestrial meats. In addition, aquatic protein is highly digestible and rich in several peptides and essential amino acids that are limited in terrestrial meat proteins, as for example methionine and lysine.

In addition to the high nutritional value, fish proteins also have good functional properties such as water-holding capacity, gelling, emulsification, and textural properties for the products such as fish mince and surimi, the water-holding capacity and the gelling properties which determine the textural attributes of the products are important quality parameters.
Fish: Rich source of protein

Amino acids – fundamental units of protein

Amino acids, peptides and proteins are important constituents of food. They supply the required building blocks for protein biosynthesis.

 The amino acids are the fundamentals units of protein structure. All amino acids contain at least one amino group (-NH2) in the alpha position and one carboxyl, and all (except Glycine) contain an asymmetric carbon atom. For this reason, they may exist as isomers.

The term amino acid might mean any molecule containing both an amino group and any type of acid group; however, the term is almost always used to refer to an carboxylic acid. The simplest acid is aminoacetic acid, called glycine.

Amino acids play major role in regulating multiple processes related to gene expression, including modulation of the function of the proteins that mediate messenger RNA (mRNA) translation.

Most naturally occurring amino acids are of the L-configurations, although D-amino acids are not uncommon in some microorganisms. The presence of a D-amino acid oxidase in mammalian tissue, however, suggests that the D-forms may play some yet unrecognized role in mammalian protein metabolism.

Based on their nutritional/physiological roles, amino acids can be differentiated as:
• Essential amino acids: Valine, leucine, isoleucine, phenylalanine, tryptophan, methionine, threonine, histidine (essential for infants), lysine and arginine (“semi-essential”).
• Nonessential amino acids: Glycine, alanine, proline, serine, cysteine, tyrosine, asparagine, glutamine, aspartic acid and glutamic acid.

Amino acids are utilized in formation of protein. If amino acids are deficient, then protein synthesis does not occur. As a result protein deficiency disease may occur. It is necessary to take balanced diet containing all essential amino acids.
Amino acids – fundamental units of protein

Peptide bonds of protein

All proteins yield amino acids when hydrolyzed and all but two of these are α-amino carboxylic acids. Proline and hyroxyproline are α-imino acids.

In proteins, amino acids are united through amide linkages between the α-carboxyl and α-amino functional groups of adjacent amino acid residues. Such bonds are called peptide bonds. Linkage of many amino acids through peptide bonds results in an unbranched chain called a polypeptide. Each component amino acid in a polypeptide is called a “residue” or “moiety”.

Proteins thus have a repeating backbone from which 20 different possible kinds of side chains protrude.

Chemically, the peptide bond is a covalent bond that is formed between a carboxylic acid and an amino group by the loss of a water molecule. In the cell, the synthesis of peptide bonds is an enzymatically controlled process that occurs on the ribosome and is directed by the mRNA template.

The peptide bond has a partial double-bond character, that is, it is shorter than a single bond and is rigid and planar. The bonds between the α-carbons and the α-amino or α-carboxyl groups can be freely rotated and this allows the polypeptide chain to assume a variety of possible configuration.

A peptide chain has directionality because its two ends are different. There is an N-terminal end and a C-terminal end. By convention, the direction of the peptide chain is always

N-terminal end S C-terminal end 

The N-terminal end is always on the left, and the C-terminal end is always on the right.
Peptide bonds of protein

Common properties of protein

Proteins play a fundamental role not only in sustaining life, but also foods derived from plants and animals. Proteins exhibit a number of common properties that just be accounted for in any definition of these compounds:

*There are polymeric of high molecular weight, which are built up by the linking together of a large number of small molecules.

*They are amphoteric, i.e., they being able to act as an acid or a base. This enables them to resist small changes in pH. 

Structure of protein

*Following complete hydrolysis of a protein, the hydrolysate consists entirely of amino acids (except that additional groups, such as heme, iron, copper, may also be found in the case of a conjugate protein). It is commonly recognized that amino acids being linked by peptide bonds formed between α-amino and α-carboxylic acid groups of neighboring amino acids in the polypeptide sequence.

*In their polymeric structures, the amino acid units of proteins are joined together in definite sequences and exist in definite three-dimensional conformations. This sequence built from a limited number of well-defined building blocks, the 20 genetically determined amino acids and a smaller number of posttranslational modifications of them.
Common properties of protein

Plant protein

Food proteins have an important nutritional role and are primarily used by the body to supply nitrogen and amino acids. Although complex proteins come from animal products many consumers get their proteins from plant sources,

Plants are able to synthesize proteins from inorganic sources of nitrogen, water and carbon dioxide assimilated by their roots and leaves.

In contrast animals and man are dependent on plant and animal proteins in the diet provide the necessary constituent for protein synthesis.

Corn plants

Plant proteins can be modified by chemical, enzymatic, or physical processes to meet the ingredient’s functional requirements. Source of plant proteins include grains such as corn and oats and oil-rich seeds such as soybeans and peanuts.

In grain crops, seeds are normally high in protein relative to other parts of the plants as harvested although on a global basis the latter may synthesize a greater total quantity of protein.

The properties of seed proteins may change during storage or with the method of seed drying.
Plant protein

Marasmus - Protein energy malnutrition

Appropriately named form the Greek word meaning ‘dying away’, marasmus reflects a severe deprivation of food over a long time.

Marasmus is the state which virtually all available body fat stores have been exhausted because of starvation. It results in a reduction in body weight adjusted for age and size.

It is the commonest severe form of PEM (protein energy malnutrition) and tends to occur earlier in life than kwashiorkor, usually within the first year. It is common in all overpopulated and impoverished areas of the world.

Children living in poverty simply do not have enough to eat. They subsist on diluted cereal drinks that supply scant energy and protein of low quality; such food can barely sustain life, much less support growth.

Illnesses that produce marasmus is developed countries are chronic and indolent, such as cancer, acquired immunodeficiency syndrome and chronic pulmonary disease.

Marasmus is easy to detect because of the patient’s emaciated appearance: marasmic children look like little old people – just ‘skin and bones’.
Marasmus - Protein energy malnutrition

Anemia due to protein deficiency

Anemia is a reduction of hemoglobin in red blood cells below normal levels.

Patients with protein deficiency anemia also show signs of multiple nutritional deficiencies, especially of folic acid, vitamin B12, and iron.

Protein is essential for the proper production of hemoglobin and red blood cells. Due to deficiency of proteins, the synthesis of hemoglobin is reduced. The RBCs are macrocytic and hypochromic.

The deficiency protein results in decreased formation of all hematopoietic cells. Hematopoietic cells are lodged within the bone marrow that give rise to all the other blood cells and are derived from mesoderm.

A mild normocytic anemia develops after 6 months of semi-starvation and after 3 months of complete starvation.

In chronic protein deficiency, the decreased RBC production is proportionate to the reduced by decreased secretion of erythroproietin.
Anemia due to protein deficiency

Protein content in corn

The protein content of corn is inversely related to starch content and grain yields. Bulk density is related to increased starch content when other factors are constant.

Corn proteins are classified into four classes: albumins, globulins, prolamine and glutenin.

Protein content in corn kernel is about 10% and protein content in corn germ is about 20%m but the germ is only 10% of the kernel.

Zein protein form corn has some unique characteristics compared to most other agricultural proteins used for edible films and coatings. Zein is a class of prolamine protein in maize.

The development of hybrid strains has improved the yield of field corn, which is lower in protein than wheat and like all vegetable protein, including wheat, corn is deficient in some amino acids and so does not provide a complete protein for humans. This contributes to the low protein quality of this grain.

Corn is especially deficient in the amino acid, lysine, but a variety of high-lysine corn has been developed that may eventually have a great impact in human nutrition in some parts of the world.
Protein content in corn

Meat protein

Proteins are the basic functional components of various high protein processed food products and thus determine textural, sensory and nutritional properties.

Protein is the dominant component in meat. Meat is rich in the essential amino acids – lysine, leucine, isoleucine and sulfur containing amino acids and in this sense meat is a high quality protein.

Meat is composed of three tissue: muscle tissue, connective tissue and adipose tissue. Inside the muscle tissue cell membrane, there are myofibrils containing alternating thin and thick protein filaments, namely the actin and myosin, which contract and relax in the living animal.

Myofibrils are the main component of meat structures which occupy about 70% of the volume of meat. 

Connective tissue is made up of protein and mucopolysaccharides. It is located throughout the muscle and determines the degree of meat tenderness.

Collagen is the most abundant protein found in mammals – in bone, cartilage, tendons, and ligament, enveloping muscle groups and separating muscle layers. The collagen content of meat and meat products is often of particular interest to food processors because it alters batter gelation properties.

The meat proteins, especially myosin, actin and to some extend tropomyosin, are the main water binding components in muscular tissue.

Interactions between meat proteins and water significantly affect the textural properties of meat. Approximately 97% of the water holding capacity of meat is related to the myofibrillar protein fraction. 

Protein meats contain small quantities of carbohydrates. When protein are heated to about 154 °C the amino acids in the proteins chains react with carbohydrate molecules and undergo a complex chemical reaction which resulted they turn brown and develop richer flavors. This reactions is called Maillard reaction.
Meat protein

Protein compositions in cereal grains

Since the beginning of agricultural production in the prehistoric time, cereals have been the main agricultural products in most parts of the world playing important role in nutrition generally, and in the protein supply. 

Cereals are quite similar in gross composition being low in protein and high in carbohydrate.

Protein composes 7-14% of the grain, depending on the grain. The nutritional quality of cereal proteins is not as high as that of most animal proteins. Cereals grains are also low in total protein compared to legumes and oil seeds.

Lysine is the first limiting essential amino acid for man, although rice, oats, and barley contain more lysine than other cereals. Corn proteins is also limiting in the essential amino acids tryptophan, while other cereals are often limiting in threonine.

The protein is low of biological value and therefore, less efficient in supporting body needs. Combining food sources of protein is common in cultures throughout the world.

Cereals together with oil seeds and legumes, supply a majority of the dietary proteins to the bulk of populations in developing nations.

Of all the cereal grains, oats ranks highest in protein and runs neck to neck with wheat as the all-round most nutritive cereal grain.
Protein compositions in cereal grains

Proteins and Amino Acid

Protein was the first substance to be recognized as an essential part of health. Major structural parts of the body’s cells that are made of nitrogen-containing amino acids assembled in chains. About 20% of human body mass is protein.

The word protein was coined by the Dutch chemist Gerardus Mulder in 1838 and comes from the Greek word protos, meaning ‘of first importance’.

Structural components of the cell, antibodies, and many of the hormones are proteins but as much as 90% of cellular proteins are the enzymes upon which fundamental cellular function depends. They may be as many as 1000 different enzymes in a single cell.

The function of a dietary protein is to supply the nitrogen for the synthesis of a a variety of nitrogen-containing compounds such as heme, creatine, hexosamine, dispensable amino acids and to provide those amino acids that cannot be synthesized in adequate amounts.

Proteins catalyze virtually all chemical reactions in the body, regulate gene expression, comprise the major structural elements of all cells, regulate the immune system and form the major constituents of muscle. 

Proteins are considered to be organic matter because they are made up of carbon, oxygen and hydrogen molecules. Proteins are unique that they are also made of up of a nitrogen molecules. The protein molecule is a polymer of amino acids joined in peptide linkages. Although the molecular weight is usually high, there is a vast range in both structure and complexity of protein molecules.

A peptide is a strand of amino acids. A strand of between 4 to 10 amino acids is called an oligopeptide. 

When a person eats food proteins, whether from cereal, vegetables, beef, fish, or cheese. The body must first alter them by breaking them down into amino acids; only the can it rearrange them into specific human body proteins.

Hemoglobin for example is one of the proteins with quaternary structure, It consist of four globulin molecules held together by hydrogen bonds. It has a molecular weight of about 64,500; myosin, a muscle protein is estimated to have a molecular weight of about 489,000.
 Proteins and Amino Acid

Amino acid: the basic structure of proteins

Amino acid is the name given to the basic structural unit of proteins. Nitrogen molecules are combined with hydrogen molecules to make what is called an amino group.

All amino acids contain at least one amino group (-NH2) in the alpha position and one carboxyl, and all (except Glycine) contain an asymmetric carbon atom. For this reason, they may exist as isomers.

Amino acids have what is called an R group, which is a side group that distinguishes one amino acid from another.

Most naturally occurring amino acids are of the L-configurations, although D-amino acids are not uncommon in some microorganisms.

The presence of a D-amino acid oxidase in mammalian tissue, however, suggests that the D-forms may play some yet unrecognized role in mammalian protein metabolism.

Amino acids enter into the general metabolic path ways which have been called anabolism and catabolism. Every aspects of physiology involves proteins. Individual amino acids serve as neurotransmitters, hormones, and modulator of various physiological processes.

Nine of amino acids are called essential amino acids, because human body cannot make them and must get them though diet. The body can manufacture the remaining 11 amino acids, called nonessential amino acids. 

Consuming the essential amino acids presents no problem to people who regularly eat proteins containing ample amounts of al the essential amino acids such as those of meat, fish, poultry, cheese, eggs, milk and most soybean products.

When amino acid backbones joined end to end, a protein forms. The bonds that from between adjoining amino acids are called peptide bonds. Proteins often contain from 35 to several hundred or more amino acids.
Amino acid: the basic structure of proteins

Anabolism of protein

Protein synthesis or anabolism is important functions of cell. Small molecules are used as the starting points of a variety of reactions to produce larger and more complex molecules, including proteins and nucleic acids; this process is called anabolism.

Protein synthesis is stimulate by growth hormone, thyroxin and insulin. Among the anabolic hormones, the pituitary makes available one of the most potent anabolic agents.

During digestion, food protein is broken down to amino acids. Once absorbed, the amino acids circulate in the blood to build new proteins. Protein anabolism is highly dependent on dietary nutrient intake. Adequate supply of nutrient material is necessary for protein synthesis.

The new protein perform numerous function including growth and maintenance, creation of essential substances, structure components of cells, primary constituents of antibodies, fluid regulation, acid-base balance, and transportation of nutrients in the body.

Anabolism is a reductive process that requires energy. One of liver function is protein anabolism. For examples, the liver produce albumin, a protein that circulates in the blood and helps to transport nutrients to tissues.

Apart from this, liver also uses amnion acids to manufacture compounds such as creatine.

Anabolism of protein

Proteins in Human Body

Protein are the main building blocks of the tissues of the body. The proteins are made up of smaller molecules called amino acids.

Once consumed (eaten) a protein is digested into the smaller amino acids and transported to the all the cells of the body where the amino acids can be put back together to make the proteins the body needs.

The human body contains thousands of different proteins, each with a specific function determined by this unique shape.

Most proteins the body makes function as structural proteins. Muscle tissues and connective tissues are mainly composed of proteins.

Collagen, which appears microscopically as a densely packed long rod, is the most abundant protein in mammals and gives skin and bone their elastic strength.

Hair and nails are made of keratin, which is another dense protein made of coiled helices.

Some proteins have an extremely important function by serving as enzymes.

Enzymes make biological chemistry efficient and less wasteful of energy.

The digestive system produces digestive enzymes whose function is to break down food into its chemical constituents.

Amylase is an enzymes that is involved in the breakdown of the polysaccharide starch into the monosaccharide glucose.

Protein can be involved in the Immune Response Mechanism and serve as carrier or transport molecules and also participate in the translation of DNA.

About half the dietary protein that consume each day goes into making enzymes, the specialized worker proteins that do specific jobs such as digesting food and assembling or dividing molecules to make new cells and chemicals substances.

To perform these functions, enzymes often need specific vitamins and minerals.

Obviously, the new born animal needs lots of proteins for growth and maturation.

The genes of DNA decide which amino acids (obtained from digestion) will go on to make a protein the cell needs for whatever structure or function requirement.

Dietary protein is one of three sources that contributes amino acids to the amino acid pool. The other two are protein turnover and biosynthesis of amino acids in the liver.
Proteins in Human Body

Protein in Human Nutrition

Muscles are built from protein. We need to consume enough protein to allow our muscles to be healthy and perform work.

Generally, to survive we consume only several types of biological molecules: carbohydrates, lipids, and proteins (plus vitamins and the "non-biological" molecules: minerals and water)

The proteins are made up of smaller molecules called amino acids.

Biologically active proteins are polymers of consisting of amino linked by covalent peptide bonds.

Once consumed, a protein is digested into the smaller amino acids and transported to the all the cells of the body where the amino acids can be put back together to make the proteins the body needs.

Amino acids enter onto the general metabolic pathways which have been called anabolism and catabolism.

Most proteins the body makes function as structural proteins. Muscle tissues and connective tissues are mainly composed of proteins.

Some proteins have an extremely important function by serving as enzymes. Enzymes make biological chemistry efficient and less wasteful of energy. Still there are other "jobs" for proteins.

They can be involved in the immune response. Mechanism and serve as carrier or transport molecules and also participate in the translation of DNA.

A specific group of body’s proteins specializes in moving nutrients and other molecules into and out of cells. Some of these transport proteins act as pumps, picking up compounds on one side of the membrane and depositing them on the other.

Obviously, the new born animal needs lots of proteins for growth and maturation. The genes of DNA decide which amino acids (obtained from digestion) will go on to make a protein the cell needs for whatever structure or function requirement.

Some twenty two or more different amino acids are needed for the growth of new tissues, for the maintenance of established cellular constituents and for other metabolic requirements.

So it is remarkable that some proteins work together (with DNA/RNA) to make more proteins. Proteins, it might be said, more than any other molecule, are good at "re-booting" themselves.

Regarding the other nutrients taken with protein, apart from fat and carbohydrate it must also be accompanied by the full array of vitamins and minerals.

Other factor, protein quality, helps determine how well a diet supports the growth of children and the health of adults. Two factors influence protein quality; a protein’s digestibility and its amino composition.
Protein in Human Nutrition

Food sources of protein

During digestion, large molecules of proteins are broken down into simpler units called amino acids.

Amino acids are necessary for the synthesis of complete body proteins and many others tissue constituent.

Proteins are described as essential and nonessential proteins or amino acids. The human body requires approximately 22 amino acids in specific patterns for the synthesis of its proteins.

All the essential amino acids must be present simultaneously in the diet in order for the other amino acids to be utilized – otherwise, the body remains in negative nitrogen balance.

A lack of vital proteins in the body can cause problems ranging from indigestion to depression to stunted growth.

The body can make only 13 of the amino acids -- these are known as the nonessential amino acids.

They are called non-essential because the body can make them and does not need to get them from the diet.

The nine of these amino acids can be produced are called essential amino acids, and they must be supplied in the diet.

They are methionine, threonine, tryptophan, leucine, isoleucine, lysine, valine, phenylalanine and histidine.

If the protein in a food supplies enough of the essential amino acids, it is called a complete protein.

If the protein of a food does not supply all the essential amino acids, it is called an incomplete protein.

All meat and other animal products are sources of complete proteins. Spirulina contains all the essential amino acids. Soy comes close to being a complete plant protein.

These include beef, lamb, pork, poultry, fish, shellfish, eggs, milk, and milk products.

Protein in foods (such as grains, fruits, and vegetables) are either low, incomplete protein or lack one of the essential amino acids. These food sources are considered incomplete proteins.

To obtain a complete protein form incomplete protein foods, one must combine them carefully so that those foods that are low or missing an essential amino acid will be balanced by another food that supplies that amino acid.
Food sources of protein

Protein consumption

Protein consumption
Protein seems to have more positive image than the other macronutrients. Unlike carbohydrates and fats, protein is usually associated with promoting good health and increasing one’s strength and vitality.

Athletes often choose high protein foods or take protein supplements with the promise of increasing muscle mass, strength and endurance.

But does dietary protein deserve such a positive reputation? Does it really increase a person’s strength and vitality? Should we be concerned about eating to much protein?

First, as an essential nutrient, protein is required in the diet to replace body proteins that degraded as part of normal metabolism.

Most people in developed countries consume about twice as much protein as the body needs.

Second, the body uses only what it needs, so excess dietary protein in mostly “burned” for energy. Consuming excess protein doest not automatically make muscles larger or become stronger – only exercise will do that.

Finally, consuming high protein diets does have some risks. The processing of protein in the body requires lots of water.

Consequently, dehydration is a common problem, particularly for people who exercise and lose even more water through sweat and evaporation.

Also, the kidneys arte the only organs that can process the waste products metabolism for elimination in the urine.

An excess of dietary protein over time can overwhelm the kidneys and cause permanent damage.

Like all nutrients, protein should be consumed as part of an overall balanced diet that contains adequate - but not excessive - amounts of protein.

Overconsumption of protein can easily occur in economically developed countries where both animal and plant foods containing protein are readily available.
Protein consumption

Transport Proteins

One of protein function is transporting of other substances. It is specific group of the body’s proteins specialize in moving nutrients and other molecules.

Transport protein regulate the flow of substance (including nutrients) into and out of the cell.

For example, hemoglobin, the iron-containing protein of blood, transport oxygen from the lungs to other parts of the body. Other proteins transport molecules across cell membranes.

Transport proteins may function by acting as carriers or they may provide protein-lined passages (pores) through which water-soluble materials of small molecular weight may diffuse.

There are two different types of transport proteins: those that carry molecules to “distant” locations (within a cell or an organism), and those that serve as gateways carrying molecules across otherwise impermeable membranes.

In order for vast numbers of multicellular to exist, they must have a system for delivering oxygen to all their cells, especially those cells that are not in direct contact with the organisms external; environment.

Hemoglobin is an example of an oxygen transport protein and is part of these oxygen delivery systems.

Other transport proteins move about in the body fluids, carrying nutrients and other molecules from one organ to another. Those that carry lipids in the lipoproteins are examples.

Special proteins also ca carry fat-soluble vitamins, water-soluble vitamins, and minerals.

Therefore, a protein deficiency can cause a vitamin A deficiency or a deficiency of whatever other nutrient needs a transport protein to reach its destination in the body.
Transport Proteins