The dietary role of eggs has always been a rather controversial topic. For their very high nourishing capacity, on the one hand they are considered an irreplaceable resource, and on the other, a food "to be treated with pliers".
However, birds' eggs (the most consumed ones) are actually a complex of two distinct factors, egg white and egg yolk (contained in equal measure), which have very different biological roles and nutritional properties. The yolk is a concentrate of proteins, fats, vitamins and minerals; egg white, on the other hand, is mainly composed of water and proteins. It goes without saying that feeding on whole eggs, only egg white or exclusively yolk can have a completely different impact on health.
We will begin our study by trying to understand what eggs are, what are their nutritional properties and their impact on health.
female sexual gametics, are deposited by many different animal species, including birds, reptiles, amphibians, mammals and fish, and have been part of the human diet for thousands of years.
Those of birds and reptiles consist of: an external shell, albumen (egg white) and yolk (more properly called vitellus, which would be the red egg, enclosed within various thin membranes).
The eggs most consumed for food by humans are chicken eggs. However, many others also have a relevant market such as: quail eggs, duck eggs, goose eggs, ostrich eggs etc. Fish roe and their derivatives are also widespread in the human diet: bottarga, caviar, lumpfish roe, flying fish roe, salmon roe, etc.
Hens and other oviparous avian creatures are raised all over the world and egg production can be called global. In 2009, around 62.1 million tons of eggs were produced from a set of around 6.4 billion hens. In 2012, the European Union (EU) banned battery-operated chicken rearing.
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Whole egg yolks and eggs are famous above all for their high protein content; in fact, the excellent profile of essential amino acids makes these foods the best source of high biological value (BV) protein ever. On the other hand, egg proteins are also among those statistically endowed with the greatest allergenic power.
However, it should be emphasized that a single yolk contains more than 2/3 of the recommended daily intake (300 mg) of cholesterol for a healthy person. At the same time, the yolk also contains very high levels of phosphatidylcholine (lecithin), an emulsifying molecule that reduces absorption. cholesterol in the intestine and lowers its metabolic synthesis. At the moment it has not been demonstrated a real direct correlation between the intake of cholesterol with eggs and a possible increase in total or LDL cholesterol (bad cholesterol); it is however reasonable to think that all the nutrients contained in them have a certain nutritional impact (positive or negative), even if it is probable that subjectivity plays a decisive role in the ultimate result.
Even cooked, eggs contain very high levels of vitamins and minerals, which cover most of the Daily Value (DV); the most significant are: retinol and retinol equivalent or vitamin and provitamin A (19% DV), riboflavin or vit B2 (42% DV), pantothenic acid or vit B5 (28% DV), cyanocobalamin or vitamin B12 (46% DV) , choline (60% DV, commonly called vitamin J, complexed in phosphatidylcholine), phosphorus (25% DV), zinc (11% DV) and active vitamin D (15% DV).
Note: while phosphatidylcholine could reduce the absorption of cholesterol on the one hand, it could also inhibit the uptake of fatty acids and fat-soluble vitamins on the other.
However, cooking significantly affects the nutritional values of eggs. Raw, they preserve most of the molecules contained in them, but an anti-nutritional agent called avidin remains, which hinders the absorption of biotin (vitamin H). Cooked, however, are easier to digest and have a lower risk of salmonellosis.
The diet of laying hens significantly affects the nutritional quality of eggs produced, although a 2010 United States Department of Agriculture (USDA) study found that there were no significant differences in macronutrients observed in various eggs. of commercial hen. However, it is undeniable that hens fed rocket or with a diet rich in fish oil, chia seeds or flax seeds, produce eggs with a higher content of essential fatty acids and essential omega 3 seeds (alpha linolenic acid ALA, eicosapentaenoic acid EPA and docosahexaenoic DHA).
essential it is possible to increase the phenomenon of musculation due to hypertrophy. Obviously this is an "inaccuracy or a half truth, however very difficult to deny, since there are many successful body builders who make a massive consumption to say the least (strange that no one wonders why, of the hundreds of thousands of people who exaggerate with eggs, only a very small percentage have achieved these results).
In any case, the protein excess, regardless of the food that determines it, is generally unhealthy for the organism and in particular for the liver and kidneys (without excluding the stomach, responsible for the acid denaturation of the proteins in digestion). Amino acids. of proteins, if not used for plastic purposes, must undergo a neoglucogenesis or a conversion into fatty acids, two processes that only the liver can carry out. Furthermore, part of the amino acids, once converted, leave many nitrogenous groups in turn to be transformed into urea (this process is also carried out by the liver), to be expelled with the urine by the kidneys, so it is logical that by subjecting the liver and kidneys to daily overwork they can also get tired.
What is the "protein excess" proper "? Good question. The topic is actually quite difficult and long to deal with, so we will limit ourselves to saying that 0.8 g / kg of physiological weight may be sufficient for a sedentary person. , while for strength athletes some sources define a coefficient that reaches 1.8 g / kg as safe.
Secondly, the egg yolk is rich in lipids, including triglycerides, lecithins and cholesterol. The fatty acids, if in excess, can favor their deposition in the adipose tissue (actually, the excess protein also contributes to the same process. and carbohydrate). In predisposed subjects, especially obese, diabetic and sedentary - but, taking the concept to the extreme, probably in anyone - the deposit can also affect the liver itself, giving rise to the so-called non-alcoholic fatty hepatic steatosis.
This last correlation between eggs and alimentary steatohepatitis, in particular, is demonstrated on a scientific level. However, it must be specified that the investigation, purely statistical, involved people already suffering from the discomfort. It is therefore difficult to understand to what extent individual predisposition or other risk factors participated in the onset.
Let us now pass, more generally, to the impact of eggs on human health.
of the eggs comes from only the fatty acids present in the yolk; 50 g of whole shelled chicken egg contain about 5 g of lipids (among which, although marginal in reference to absolute weight, also cholesterol, lecithins, etc.).
Due to the high content of cholesterol in the yolk, those who need to reduce total and / or LDL cholesterolemia may have to moderate the consumption of eggs. However, only 27% of all the lipid fraction of the egg is made up of saturated fatty acids (palmitic, stearic and myristic acid), which, as we know, are responsible (more than cholesterol itself) for the increase in blood cholesterol. . The egg white is mainly made up of water (87%) and proteins (13%) and, in addition to not containing cholesterol, it is practically devoid of other lipids.
Whether or not the yolk can harm your health is still a matter of debate. Some research suggests that, more generally, dietary cholesterol increases the ratio of total cholesterol to HDL cholesterol, negatively affecting the cholesterol profile. Other studies show that moderate consumption of eggs, up to 1 per day (which would be 7 per week), does not seem to increase the risk of heart disease in healthy individuals. Harold McGee argues that egg yolk cholesterol is not a real problem, because it is mainly saturated fats that are responsible for the worsening of cholesterolemia - of which the yolk is all in all poor.
