All About Proteins

Find out all about proteins and their function in the human body in this fascinating article.
All About Proteins
Saúl Sánchez

Written and verified by el nutricionista Saúl Sánchez.

Last update: 23 June, 2023

Proteins are essential macronutrients for the body. They can be produced endogenously, that is, in the body itself, although it is necessary to include them in the diet. They’re composed of elements called amino acids, which, in turn, are subdivided into two types according to the ability of the human body to synthesize them: essential and non-essential.

It’s essential to ensure that the diet provides the necessary proteins to develop vital physiological functions, which we’ll describe below. Both the origin of the protein and its content in essential amino acids and their digestibility are important.

Not all proteins are the same

Before commenting on the functions of proteins, it’s worth noting the differences that exist between them. We can talk about two fundamental types of these nutrients, depending on their origin. Proteins are found in foods from the animal kingdom and the vegetable kingdom, although depending on where they’re obtained, their biological value is different.

Biological value is the quality of the protein, understanding the highest quality to be that of a high biological value. This parameter depends on two factors: the essential amino acids that are part of the nutrient and their digestibility. It must be borne in mind that the greatest biological value is always found in animal products.

As we discussed, amino acids are the units that make up proteins. The essential ones are those that the human body isn’t capable of synthesizing on its own, so it’s necessary to ingest them through the diet. They’re as follows: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Each of them carries out different functions separately. Some, like leucine, are closely linked to the ability of lean tissue to regenerate and hypertrophy, as confirmed by a study published in The Journal of Nutrition .

In turn, protein digestibility refers to the body’s ability to metabolize the nutrient and use the amino acids that make it up to produce new proteins.

Protein of animal origin.
Proteins of animal origin have a higher biological value than vegetable proteins.

The quality of vegetable proteins

As we said, proteins of animal origin are the ones with the highest quality. Those found in plant foods are deficient in at least one essential amino acid, which limits their functions. In addition, they have a lower digestibility, so they aren’t as useful.

This means that when considering a vegan diet or one low in foods of animal origin, you need to be careful in how you combine food, and increase the total protein intake. In this way, the amounts of nutrients that can’t be absorbed at the intestinal level can be saved.

Function of proteins in the human body

Proteins, along with fats, are the nutrients that perform the most functions within the human body. They have an enormous weight in the development and maintenance of muscle mass, as evidenced in research published in the journal Nutrients.

Proteins are essential to ensure hormonal balance. The amino acids that compose them are involved in many of the physiological reactions that are responsible for synthesizing hormones or neurotransmitters, one of the most characteristic being the relationship between the intake of tryptophan and the secretion of serotonin.

At the same time, they also have an enzymatic function, catalyzing many reactions that occur daily within the human body. This increases the efficiency of said processes of cell metabolism.

Neither can we forget its regulatory role when it comes to mediating gene expression and cell division. A failure in the protein supply can increase the number of inefficiencies in the replication of cells or the components that make up the organs, which could be the cause of the development of complex pathologies.

How much protein should be consumed?

There has been much controversy around this point. Traditionally it was advised not to consume more than 0.8 grams of protein/kilogram of weight/day in sedentary individuals. It was stated that a higher intake could be harmful to the liver and kidneys, as it increased the work of these organs.

However, this association has now been ruled out. It has been possible to demonstrate that higher protein intakes are related to greater muscular health, which in the long run translates into a more efficient functioning of the organism. At the same time, it’s good t o increase the daily protein dose up to 2 grams/kilogram of weight/day, as this doesn’t produce any negative impacts on any organ.

More recently, the effects of hyperproteic diets on renal function have begun to be investigated, with doses greater than 3 grams/kilogram of weight/day. Such a significant increase hasn’t been shown to impair kidney function, at least for a period of 20 weeks.

It should be noted that, within the framework of vegan diets, protein needs are increased. This occurs, as we already mentioned, to save their low biological value. In this way, it would be necessary to increase the total contribution of these nutrients, in addition to monitoring the foods they come from, in order to overcome deficits in essential amino acids.

Protein supplements

Another of the questions that arise when talking about proteins is the need to take protein supplements or shakes. These types of products are able to offer high-quality nutrients, generally from whey. However, it’s also possible to find protein supplements obtained from eggs or beef on the market.

In principle, these supplements have been designed for athletes or for people who have difficulty meeting the daily requirements of the nutrient. For sedentary people without illnesses they wouldn’t be advisable at first.

It’s important to obtain the necessary proteins from food, as, in this way, you also obtain other essential nutrients for the body, such as vitamins or minerals. However, in the case of people who practice sports, the question changes.

Protein supplements are an excellent option to increase protein intake and to administer these nutrients at any time of the day, thus favoring the recovery of lean tissue and stimulating muscle hypertrophy processes.

In this way, performance can be increased in the medium term. In addition to that, combining protein with carbohydrates will result in more efficient muscle glycogen restoration, according to research published in Nutrients.

Going back to protein shakes and supplements, there’s a special application framework here. One of the nutrients found in milk, casein, has been shown to be able to increase endogenous protein synthesis when administered just before bedtime, which can improve muscle function in athletes and sedentary people.

Protein shakes for athletes.
In sports, protein can be obtained from protein shakes designed for this purpose.

Food with the highest protein content

Meat, eggs, fish and dairy products stand out above the rest of the products. These foods don’t only contain a high percentage of protein, but they also have a high biological value, which ensures their quality.

Within the foods of plant origin with the most protein we find legumes, nuts and seeds. Despite this, many of them are deficient in essential amino acids, such as leucine or methionine. For this reason, it’s best to combine them with each other when consuming them.

These are foods that can easily be eaten as morning or afternoon snacks. For example, peanut butter is an excellent way to provide high-quality fat and protein, helping to meet daily needs for the nutrient; seeds also contain significant amounts of protein.

Proteins: essential nutrients

It’s clear that proteins are essential nutrients in our diet. Reducing their intake is frowned upon, as it could impair muscle health and the functioning of many determining physiological reactions for the human body, such as the production of hormones or neurotransmitters.

It’s important not only to ensure we get an adequate amount of them, but also to ensure that there are no deficits in essential amino acids, as the body isn’t able to synthesize them on its own and they have important functions. To ensure this, there’s nothing better than a varied, flexible and balanced diet from a caloric point of view.

Finally, if you practice sports regularly, it may become necessary to include a protein supplement in your diet routine. In this way, the recovery of lean tissue can be improved, conditioning performance in training and subsequent events.

However, before opting for this option, it’s always advisable to consult with a nutrition professional to choose the right product for each specific situation.

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