What are they
Proteins are a very important class of nutrients for human nutrition because they represent the only source of assimilable nitrogen for the body.
Although they exist in tens of thousands of variations that are extremely different from each other in terms of specific composition, structure and function, all proteins are made up of the combination of only 21 amino acids, similar to what happens in the case of words and letters of the alphabet.
The proteins taken from food can be used for structural purposes (building and renewing muscles, skin and mucous membranes, hair, nails and other tissues of the body), to control certain metabolic processes (neurotransmitters and hormones) or to produce energy (if carbohydrates are not enough) or reserve fats (when the amount of protein introduced is higher than the need).
Food sources
Since all living organisms contain protein, no food is completely devoid of protein, except for oil (of any kind) and starch.
The percentage and nutritional quality of proteins present in different foods can vary greatly.
Meat (red and white), cured meats (especially the “leanest”), fish, shellfish, eggs and dairy products (especially aged cheeses) are the main sources of proteins so-called “of high biological value” as they are composed of an ideal combination of the most important amino acids for the body.
Legumes such as peas, soybeans, chickpeas, lentils and beans also ensure a good supply of protein, but of lower biological value, since they are less similar in composition to human proteins.
To perfect the amino acid intake of legumes, however, it is sufficient to combine them with cereals, characterized by proteins that are also “incomplete” from a nutritional point of view, but complementary to the former.
The protein quotas present in fruit and vegetables tend to be negligible for nutritional purposes.
Absorption
The proteins taken from food are roughly broken down by pepsin and gastric acids as they pass through the stomach, but the actual digestion takes place in the duodenum thanks to the action of pancreatic juices and, in particular, to enzymes called proteases.
The amino acids released in this way are absorbed by the intestinal epithelium, pass into the blood and arrive at the liver where they can be used as such to produce new proteins (muscles, tissues, hormones, enzymes, etc.) or demolished to obtain glucose, to be used immediately for energy purposes or to be converted into storage fats.
In these last two cases, since glucose and triglycerides do not contain nitrogen, that present in the starting amino acids is eliminated with the urine in the form of urea and ammonia.
In some cases, amino acids taken with food undergo a slight chemical transformation and are used to regulate specific functions of the body, especially in the brain.
This is the case, for example, of neurotransmitters such as dopamine, derived from the amino acid tyrosine and essential for the control of muscle tone and movements (when it is missing, Parkinson’s disease occurs), and serotonin, produced from tryptophan and involved in the modulation of mood (when it is scarce, depression can develop).
Other times, amino acids can have an “intrinsic” regulatory role as happens with glutamate, a compound that exerts a direct excitatory action in particular regions of the brain.
Deficiency
If you do not take every day a certain amount of amino acids, especially essential ones (phenylalanine, isoleucine, leucine, lysine, methionine, threonine, tryptophan, valine) that the body is not able to produce from other substances, you will encounter situations of deficiency that determine a general deterioration in the state of the tissues and an overall physical deterioration.
The skin and mucous membranes become less toned and elastic, muscles lose mass and functionality, glands work inefficiently, hormone production is compromised and endocrinological imbalances are established more or less important, blood proteins decrease, hair and nails become brittle and opaque, you are more prone to infectious diseases, There is a reduction in fertility.
Recommended doses
Protein should account for about 15% of the daily caloric intake, but never fall below a certain amount even when following low-calorie diets.
A simple formula to know your minimum daily requirement is to calculate 1 g of protein per kg of body weight: in practice, a person of 60 kg should eat at least 60 g of protein per day (equal to about 240 Kcal).
To get an idea of how to reach this quota, the table shows the protein content per 100 grams of some foods.
Food | Grams of protein/100 grams |
---|---|
Parmigiano Reggiano | 33,5 |
Bresaola – Italy | 32 |
Turkey breast | 24 |
Chicken | 23,3 |
Lentils | 22,7 |
Steak of beef | 21,3 |
Cod | 20,9 |
Borlotti beans | 20,2 |
Precautions
Just like deficiencies, protein excesses must also be avoided: they impose considerable effort on the liver, which must transform the amino acids derived from them and convert unnecessary nitrogen into ammonia and urea, and damage the kidneys since the excess of ammonia and urea exerts a toxic action on the renal tubules and excretory ducts.
In addition, foods rich in protein (in particular, red meats, cured meats and aged cheeses), in general, also contain a lot of salt, which favors the development of hypertension and cardiovascular diseases.
Long-term high-protein diets also facilitate the onset of hormonal alterations and can promote the development of certain cancers.
Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.
The blog covers a wide range of topics related to health and wellness, with articles organized into several categories.