Animal proteins, as the name suggests, are contained in foods and food products of animal origin (meat, fish, eggs, milk, cheese and dairy products).
Like all proteins, even animal proteins are made up of the concatenation of about twenty amino acids, 8-9 of which are essential; the body, in fact, is unable to synthesize these amino acids in sufficient quantities for its needs; consequently, they must be introduced regularly with food.
Animal proteins are considered of high nutritional value, as they contain all the essential amino acids in the right proportions; vegetable protein sources, on the other hand, are considered incomplete, because they lack one or more of these amino acids. Fortunately, there is a different deficiency for each source of vegetable proteins (cereals, legumes, dried fruit, etc.), which as such can be filled by combining two complementary protein sources. Let's see some examples:
These associations are especially indicated for vegetarians, while the problem does not arise for those who follow a normal balanced diet; there is no problem, for example, in consuming a meal based only on animal proteins and the next one based only on vegetable proteins. In fact, a pool of free amino acids circulates in the blood in constant equilibrium with the body's demands in anabolic processes (in which amino acids are needed for the construction of tissues) and catabolic (in which the amino acids deriving from the breakdown of aged "proteins are recovered. "or malfunctioning).
Skinny and Fat
Lean protein and fat protein
Lean and fat are adjectives that refer to food sources, i.e. foods, not proteins themselves - which by definition do not contain lipids.
From the health point of view, the animal or vegetable origin of the proteins does not make a huge difference; what matters, apart from the aforementioned differences in the amino acid composition, is the presence of other nutrients, such as fats, cholesterol, carbohydrates and fiber.
The animal proteins contained in pork or beef are, for example, rich in cholesterol and saturated fats, with significant differences based on the cut considered. Those of poultry, on the other hand, despite having similar concentrations of cholesterol, are less rich in saturated fats; for this reason, doctors recommend preferring them to red ones.
In fish the saturated fat content is reduced, while omega three fats abound, which have an anti-inflammatory and balancing action on plasma cholesterol and triglyceride levels.
Fish is also poor in connective tissue and this makes it an easier digestive food than meat; this is an important feature, so much so that the digestibility of proteins has been taken into consideration in the new quality index developed by the WHO: the PDCAAS (Protein Digestibility Corrected Amino Acid Score or amino acid value corrected for the digestibility of proteins).
Crustaceans are particularly rich in cholesterol; however, as they contain very few saturated fats, they can be consumed with some freedom, but without exaggerating. It is somewhat the same concept seen for white meats compared to red ones: the interaction between cholesterol and saturated fatty acids is in fact potentially more dangerous than cholesterol alone. Even more important is the overall amount of calories in the diet, since one thing is excess saturated fat in the context of a high calorie diet, and another is the high intake of saturated fat in a low calorie diet. (the Fulani, a nomadic ethnic group from West Africa, derive about 25% of their daily calories from saturated fat (therefore 2,5 times more than the recommended levels); nevertheless their lipid profile indicates a low cardiovascular risk) .
Animal egg proteins are also associated with large amounts of cholesterol; in this case "the hostile presence" (remember that cholesterol is essential to life) is compensated by the high content of lecithins, which favors the reverse transport of cholesterol (from the arteries to the liver) by enhancing the activity of HDL (the so-called good cholesterol). Lecithins also promote the digestive processes of food.
In cheeses we find important quantities of cholesterol and saturated fats, which are not balanced by adequate quantities of omega-three fats, lecithins, antioxidant vitamins or fibers; they must therefore be consumed with a certain moderation and never in addition, but as a substitute, to other animal proteins.
Too many are bad?
To promote digestive processes, it is important to avoid mixing proteins of different origins in the same meal, both animal-animal (for example eggs and fish, milk and meat), and animal-vegetable (meat-legumes). These associations, in fact, like an excessive ingestion of proteins (regardless of their origin), reduce their digestion and absorption capacities; the unrecovered amino acids favor the growth of a putrefactive flora in the colon, which can be accompanied by constipation or the emission of poorly formed and oily stools, with the expulsion of intestinal gas with a particularly bad smell and a possible increase in the risk of colon cancer. In addition, high-protein diets promote the loss of important minerals such as calcium, predisposing to the development of osteoporosis. However, not all authors agree that the high-protein diet is a risk factor for osteoporosis, given the positive effect on intestinal calcium absorption and on the secretion of osteo-anabolic hormones, such as IGF-1. Furthermore, the hypercalciuria associated with high-protein diets could be compensated by the simultaneous and generous intake of alkalizing foods (fresh fruit and vegetables).
If animal proteins, as we have seen, are burdened by the simultaneous presence of cholesterol and saturated fats, vegetable ones are generally associated with some antinutrients, including trypsin inhibitors) that block the digestion of proteins), and significant quantities of phytates (which by binding to some calcium, magnesium, manganese, zinc, copper and iron, they reduce its absorption). The phytoestrogens of soy, if taken in excess, can subvert the normal endocrine balance of the body, in a positive sense according to some studies, but also in a negative sense according to many others.
All these examples have been set out to clarify that there are no optimal or better protein sources than the others; Not surprisingly, nutrition must first of all be varied. In this way, in fact, it is likely that all the nutrients the body needs are taken in the right quantities. Furthermore, the negative consequences deriving from the ingestion of potentially harmful substances, which may be present from the origin or formed following the food processing, storage and cooking processes, are minimized. It is therefore no coincidence that the guidelines for a healthy diet of the country recommend the dietary introduction of both types of proteins, animal and vegetable, in the ratio 1: 1 in the developmental age and 1: 3 - 1: 2 in the adult.