Proteins are the main constituents of all organisms, both animal and vegetable. These very important molecules are made up of smaller units called amino acids. There are 20 different kinds of amino acids that participate in the production of proteins, and their combination, in number and pattern, determines the formation of proteins with different functions.
We consume lots of different types of protein through what we eat. We mustn’t believe that proteins are only found in animal source foods; plant based foods have them too. The amount and quality of proteins varies from food to food.
In our stomach and intestines, proteins are digested and broken down into amino acids, which are then absorbed and “enter” into our body and into our cells. Inside the cells, the amino acids will be used to produce new proteins, which will have a different composition from those coming directly from the food, because these proteins are made by our bodies, but the amino acids that form them are also the same as the ones we consumed through the food. So, in simpler but accurate terms, the amino acids that made up the protein found in the bread I ate, will become the proteins in my muscles.
Some of the 20 amino acids that make up proteins are more important than others: 8 of them (9 in children) are called “essential” because it is essential that they be introduced with food because the human body is not able to produce them itself, and if they are not present in the diet we can become deficient, and therefore lose the ability to synthesize proteins.
So the protein requirement is not only quantitative but also qualitative, and the dietary proteins that contain all the essential amino acids in the correct quantity for correct formation of our proteins are said to have a high biological value. The foods that contain these are of animal source foods (meat, fish, eggs, milk and derivatives). Vegetable proteins have medium (legumes) or low biological value, because they contain scarce amounts of some essential amino acids. Following a vegan diet, however, does not necessarily mean being short of essential amino acids: the important thing is to combine vegetable foods correctly, and consume good quantities of legumes.
In adults, both men and women, it is recommended to consume 0.90 g of protein per kg of body weight each day (Italian Recommended Nutrients Levels*). In children and adolescents, this amount is a little higher and ranges from 1 g / kg in 1-3 years to 0.97 g / kg in 11-14 years (0.95 g / kg in females).
Alessandra Bordoni
Department of Agricultural and Food Sciences
University of Bologna
*Italian Society of Human Nutrition (SINU): LARN – Reference Intake Levels for Nutrients and Energy for the Italian population – 4th edition. SICS ed.