But when we think about the structure of proteins outside food it gets a little more complex. This is because they are not meat, milk or eggs, but are present in them, as well as in many other foods – but with generally smaller amounts.
Proteins are made up of carbon, hydrogen, oxygen and nitrogen, which make up a large molecule. You can think that amino acids are small pieces, or bricks, that have specific functions in the body.
Like loose bricks, they can be stacked, forming more complex structures (almost like a wall), which are proteins.
In the body, they participate in several functions, being essential for the maintenance of organic systems and tissues.
Transport of substances, support of the skin, digestion, circulation, breathing are systems that directly or indirectly depend on an adequate protein intake.
To understand how proteins act in the body, it is necessary to know a little more about their forms and mechanisms.
What are amino acids and what are they for?
Amino acids are micronutrients that are joined by peptide chains to form a protein, forming different types of the macromolecule (the blocks of a large piece). The human organism is able to harness only 20 of the approximately 300 existing amino acids.
Each type performs structural (form tissues) and functional (form hormones and antibodies) functions. As proteins are the result of the union and chaining of amino acids, there are several possible formations.
Despite appearing to be a limited number (only 20 types), when they come together, these micronutrients form different structures, combining each other in formations (peptide bonds) and varying amounts, which result in up to 100 thousand types of proteins.
The variety of formation is so great that the organism can present chains of up to 3 thousand amino acids.
Chemically, amino acids are formed by a carbon (C), a carboxyl group (-COOH), an amine group (H2N) interconnected – but each molecule is different due to the side chain (R), a bond that characterizes the structure and amino acid functions.
To maintain a good diet, it must be ensured that amino acids are being properly ingested, as soon as the body synthesizes (produces) some, while others need to be obtained through food. Understand each type:
- Essential: they are those that need to come from food, being fundamental to the organism. They are phenylalanine, valine, tryptophan, threonine, lysine, leucine, isoleucine and methionine;
- Partially essential : they are even produced by the body, but in insufficient quantities, requiring that the food reinforces the micronutrient levels. They are arginine and histidine;
- Non-essential : the body is able to produce the amino acids, which are glycine, alanine, serine, cysteine, tyrosine, aspartic acid, glutamic acid, asparagine, glutamine, taurine and proline.
What do proteins do?
Proteins participate in some processes in the body, performing functions such as:
Growth and maintenance
Proteins are part of the composition of nails, hair, skin, teeth, being fundamental for the protection of internal organs, resistance and support.
Perform biochemical reactions
Macromolecules are essential for the body to be able to perform essential functions, such as cell renewal, digestion and maintaining the body’s health.
Without the action of proteins, movements would be impossible. Myosin and actin are responsible for muscle contraction, making it possible to move a finger or run a marathon.
In addition, proteins form the joints and ligaments, which give the members relative flexibility.
Defend the body from invaders
Antibodies are proteins that act in defense of the organism and fight infectious agents, preventing diseases and infections from occurring constantly.
Regulate organic actions
After eating food, practicing physical activities, cutting your finger or being infected by the flu virus : proteins are involved in the regulation of different organic actions to resolve each condition by means of digestive, energetic and immunological actions, respectively.
Transport nutrients and oxygen
In order for the body’s systems to function properly, carrier proteins need to deliver oxygen and nutrients to cells, keeping systems throughout the body in harmony.
They are sources of energy
In some situations, the body can deplete the stores of carbohydrates and fats, making it necessary to use proteins as an energy source. Thus, macromolecules are an emergency resource for maintaining the functioning of the body.
Types of protein
There are some types of proteins in the body and they perform very specific and different functions. Among the most abundant are:
Some proteins participate in the formation and maintenance of tissues, supporting the body, protecting organs and promoting more resistance to structures. Between them:
- Collagen : has high resistance and is present in the skin, nails, hair, cartilage and tendons;
- Actin and myosin : participate in muscle contraction and relaxation (body movement), so they are abundant in the muscles;
- Keratin : present in the skin, hair and nails, the protein has a waterproofing function.
The proteins that are arranged on the cell membrane are called receptors. They act by triggering chemical reactions within cells from external stimuli and messages.
For example, after meals, blood sugar rises and receptor proteins stimulate the production of insulin (regulatory hormone).
Antibodies are proteins produced by lymphocytes (white blood cells), responsible for the body’s defense and immunity. These antibodies are produced when a foreign element (antigen) invades the body.
Proteins are a source of amino acids needed by the body, such as casein (milk protein), ovoalbumin (egg protein) and gliadin (wheat protein).
In addition to nourishing the body, they can be used as a source of energy.
Under normal conditions, carbohydrates are the first option for gaining energy and maintaining organic functions – if there are no more carbohydrates available, fats are the nutrients used.
Only after these two resources are exhausted or rendered impossible does the body use proteins.
Among the functions of proteins is the transport of substances throughout the body. Hemoglobin is one of the most famous examples, because the protein that circulates in the blood is responsible for the conduction of oxygen – essential to the cells and tissues of the whole organism.
Enzymes are highly specialized proteins that have a catalytic function, that is, they accelerate reactions in the body through the breakdown of molecules.
There are about 2,000 different enzymes in the body, such as lipases, which break down fats in digestion, amylases, which break down starches (carbohydrates) and polymerases, which act in the duplication of DNA.
Many hormones are proteins, such as insulin and glucagon – responsible for regulating blood sugar -, growth hormone and peptide hormones.
For example, after eating and sugar levels rise, the hormone insulin is released and works by lowering blood glucose again.
How is protein digested?
Essential proteins are acquired through food. After eating a piece of meat or an egg, for example, the food goes through a series of processes that break it down, transforming it into smaller and smaller parts, until they can be absorbed by the body.
But this degradation and absorption is divided into a few stages:
- Protein digestion begins in the stomach. There, hydrochloric acid, or stomach acid, acts on food by destroying peptide bonds (denaturing proteins).
- An enzyme present in stomach acid, called pepsin, initiates the hydrolysis (breaking of molecules by the action of water) of peptide bonds, transforming proteins into even smaller molecules.
- From that moment, the food mass is sent to the duodenum, the initial part of the intestine, responsible for most of the protein digestion.
- In the duodenum, the pancreatic enzymes trypsin, chymotrypsin, carboxypolipeptidase and proelastase attack the food mass, acting in specific ways and reducing proteins in molecules. The process rarely occurs until the protein reaches the fundamental unit (that is, the smallest and simplest structure of the amino acid). Proteins are usually degraded until they become chains with 2 or 3 peptides.
- Hydrolysis occurs in the intestinal lumen and amino acids and proteins are absorbed by the intestine, that is, they penetrate the walls of the organs (through villi) and fall into blood vessels, being directed to their organic functions, such as tissue composition and production of enzymes.
- A small percentage of all the food product that has reached the intestine is not absorbed, being sent to the large intestine and eliminated (evacuation).
Protein synthesis (biochemistry)
Proteins are synthesized (or created) from information contained in the gene – which is a piece of DNA. Protein synthesis basically consists of the construction or production of the peptide chains.
For this, the participation of some elements is necessary, such as the gene (DNA), messenger RNA, ribosomes and RNA-transporter. The synthesis is also called gene translation, as soon as it is the information contained in the gene that is transcribed.
The synthesis is divided into two phases: the one that occurs in the DNA nucleus (transcription) and the one that occurs in the cytoplasm (translation).
Therefore, the DNA gene is read and forms the messenger RNA, which sets out to meet the transporter RNA and finally forms the protein.
At this stage, the chain will still mature freely. That is, after being released, the amino acid sequence may twist and form more complex bonds.
Protein synthesis in bodybuilding
Anyone who goes to the gym or is more interested in food also hears a lot about protein synthesis, but that is actually another process like the one described above – while the one referring to protein transcription, the most popular protein synthesis for athletes is the one that refers to the increase in lean mass .
Despite occurring all the time, the entry and exit of proteins in muscle tissue is intensified after physical exercises, especially those of strength.
Weightlifters generally want to increase lean mass and reduce fat. Although the goal is only to make the arms and legs stiffer, it is through muscle work that this occurs.
When activities are started, a series of organic reactions occur so that it is possible to carry them out and still maintain the other normal functions.
All the activity generates a lot of wear and tear to the muscle tissue, increasing catabolic reactions (that is, releasing some amino acids that are in the muscles) to ensure that the body is able to supply all functions (such as breathing, keeping the heart beating, blinking).
To optimize this process of taking advantage of the stock of amino acids, the entry of amino acids in the muscles is temporarily suspended as well. This great wear and tear on the fabric is repaired after a few hours.
As there were microlesions to the muscle fibers (which are normal reactions and do not cause damage to the body) after the exercises, the body itself increases the entry of amino acids, making the synthesis to be optimized. The result is that damaged fibers are recovered and become stronger.
In other words, this protein synthesis generates muscle hypertrophy.
Whoever chooses to eat partially or totally free of animal products, often ends up being questioned about how to meet protein demands.
The truth is that there are a lot of myths and misinformation about plant proteins.
Macronutrients are found in several cereals, legumes and oilseeds, making it not difficult to find an adequate protein source.
Although they are less concentrated (that is, they have less grams of protein per serving), vegetable sources are excellent options to compose meals, sometimes even healthier, as soon as they have less calories and more fiber.
In general, there is the idea that only animal sources have complete proteins, that is, that they contain all the essential amino acids. But in fact, this is one of the myths, according to studies by the American Institute NutritionFacts , which specializes in plant nutrition.
It turns out that many plant foods have very low amounts of specific amino acids, while meat and milk, for example, have higher concentrations of all.
But there is a simple way to circumvent this: with a varied and balanced menu, this imbalance is compensated and all amino acids can be supplied. For example, just combine rice and lentils – that is, cereals and vegetables.
For those who want to supplement with vegetable proteins, there are products available as well. Among the most popular are:
- Vegetable protein from rice;
- Pea vegetable protein;
- Soy protein.
Animal proteins are those that come from meat, milk and dairy products, and eggs. Because they have good concentrations of all essential amino acids, these foods are considered to be good protein sources.
Regardless of the choice – eat meat and animal products or not – one thing is a consensus: variety and moderation.
People who consume proteins of animal origin must diversify their choices, always paying attention to other nutrients, such as fats and sodium (in the case of industrialized products, such as ham).
Although they are not good sources of fiber, meats have good amounts of iron and vitamin B12, so the ideal is to always keep the rule of combined meals, balancing all the necessary nutrients.
In addition to food, animal proteins can also be found in supplements, such as:
- Whey protein (whey protein);
- Albumin (egg protein);
- Casein (based on milk);
- Beef protein.
Each 1g of protein has 4 calories and, therefore, between 15% and 20% of the food must be composed of the macronutrient, being the general recommendations of the World Health Organization (WHO).
Remember that amino acids are divided into essential, partially essential and non-essential? If the body cannot produce or does not produce enough, the amino acids must be ingested from food.
That is, those essential amino acids need to be properly balanced in meals.
Animal foods – such as meat, milk and eggs – are great sources of protein and vitamins . In general, they have higher concentrations of these nutrients compared to plant products. But that does not necessarily mean that they are better.
Poor in fiber and generally more caloric, products of animal origin, when consumed without moderation, do not favor intestinal transit and may increase the risks to heart health (due to saturated fats).
On the other hand, although vegetables, fruits and vegetables are generally associated only with fibers and vitamins, when well varied and balanced, they can supply protein needs as well.
Among the fruits with the most protein per 100g serving are:
- Tamarind : 3.2g;
- Raw Tucumã : 2.1g;
- Passion fruit : 2g;
- Banana apple : 1.75g;
- Kiwi : 1.3g.
The vegetables that provide the body with the most protein, in 100g, are:
- Coriander : 20.1g;
- Sunflower seed : 20g;
- Garlic : 7g;
- Bean sprouts : 4.1g;
- Broccoli : 3.6g.
Protein-rich cereals and grains
good protein options for cereals and grains include:
- Soy beans : 37g;
- Peanut : 30g;
- Lentil : 28g;
- Black beans : 21g;
- Rolled oats : 14g.
Among the options of protein-rich meats, per 100g serving, are:
- Duckling beef : 36g;
- Painted fish : 36g;
- Pork loin : 35.7g;
- Chicken breast: 33.4g;
- Sardine : 33.1g.
Other protein products rich in protein
To vary the intake of animal proteins or for vegetarian people, other protein products include:
- Parmesan cheese : 35g (100g portion);
- Cottage cheese : 11g (100g portion);
- Eggs : 6g (unit);
- Milk : 4g (200mL).
What can excess protein cause?
By eating a lot of protein-rich foods your body can feel the effects in an undesirable way. One of the results, although the least dangerous of them, is the increase in fat. This is because the excess is metabolized and ends up being stored as adipose tissue.
But the danger lies in kidney damage, especially if there is a predisposition to kidney disease or changes.
As the body is forced to work harder to eliminate excess, there may be overload and, even in healthy people, it is possible that the risks are increased.
High concentrations of protein can also affect the proper maintenance of some nutrients, such as calcium, which can be eliminated in greater quantities.
What happens to the lack of protein in the body?
Low protein intake can cause atrophy of parts of the sympathetic nervous system (responsible for sending and maintaining commands to the body). As it is responsible for communication with the small intestine, protein insufficiency directly affects the digestion and absorption of other nutrients.
In addition, the absence of proteins can cause damage to muscle nutrition, resulting in loss of lean mass, weakening of other tissues, such as hair and skin, and impaired immunity.
How much protein to consume per day?
In general, the ideal amount of protein intake is 0.8g per kilogram of body per day. That is, if you weigh 60kg, you should consume something close to 48g (about 120g of lean beef or 240g of sunflower seeds), dividing throughout the meals and avoiding concentrating everything in a single intake.
For athletes or people with high sporting performance, this value is usually higher, since the muscular demand is high. On average, you need at least 1.2g, reaching 1.8g per day.
Food or supplementation?
Everything that our body needs, in nutritional matters, can be obtained through food. A healthy organism manages, through a balanced diet, to supply the needs of all vitamins and minerals, keeping the organic functions regulated.
Sometimes, digestive changes, disease or poor diet can impair the balance of nutrients, making it necessary to supplement or replace certain substances.
But, it is worth remembering, that the use of dietary or vitamin supplements should always be indicated by the doctor or nutritionist, because – even if necessary to the body -, the unnecessary use can have a reverse effect and cause harm.
This also occurs with proteins.
Therefore, supplementation is indicated only when the recommended daily values are not reached or when there is a need to increase the average daily intake.
Those who work out in the gym probably take, or at least know, protein supplements, like Whey Protein and albumin (egg protein), the most famous.
Supplementation, in itself, is not the problem. In fact, if it is duly recommended by health and food professionals, whey is an ally to gains in the gym.
But excessive protein consumption can overwhelm the kidneys, making it possible for the person who is predisposed to liver dysfunction to suffer future damage.
This is because, when metabolizing the macronutrients consumed in excess, the body releases the substance ammonia (which is toxic to the body) and then transforms it into urea, which is thrown into the bloodstream.
The kidneys, which filter the blood, cannot always handle so much urea and end up accumulating the substance that can be harmful.
Therefore, before any supplementation, it is necessary to talk to a professional .
A number of diets highlight proteins. Although the macronutrient is quickly associated with fitness, weight training and hypertrophy, there are protein diets that aim to lose weight or just maintain health.
In general, menus consist of choosing good sources of protein – leaner, low in sodium and preferably non-industrialized – including them in a balanced way in meals.
However, it is worth remembering that every dietary change must be indicated and monitored by a nutritionist, who will help in calculating the daily intake of each nutrient, avoiding deficiencies or overloads.
A good way to increase your protein intake, if necessary, or to make healthier choices, is to choose foods like:
- Boiled eggs instead of fried;
- Skimmed milk instead of whole milk;
- White cheeses (ricotta, mines, cottage) instead of cheddar or plate;
- Lean meats (chicken breast, pork loin, fish) instead of steak or sausage;
- Natural yogurts instead of flavored.
In addition, including plant foods is a great alternative to boost your protein intake along with fiber, vitamins and minerals.