The egg is one of the most valuable and ancient nutritional resources. It has been in the human diet for hundreds of thousands of years. Modern times, however, have caused its use, presence, and derivatives to change a lot and for the better.
Now we understand why it has always been so interesting for our diet; we know its ins and outs, its secrets, and its tricks. So much so that we can even make “synthetic eggs” (if I may use the crude comparison). In this article, we are going to dissect the egg as a concept, as a food, and as a consumer product.
What is the egg
The egg is the matured ovum with a protective layer. In the case of birds, this layer is calcified, forming the shell. Many animals lay eggs as part of their sexual reproduction. As a curiosity, in the case of fertilization, this occurs before the egg white is added and the shell is formed through the oviduct.
The idea of the egg is to allow the embryo that emerges from the union of the sperm and the egg to grow in a protected environment until the time comes to emerge. In the culinary case, this will never happen because the egg is not fertilized, basically, and what is eaten are, normally, sterile eggs.
Parts of the egg
The egg is made up of several parts, each with a specific function but with a single objective: to carry the chick to term safely and efficiently.
- The shell is the hard, protective layer that surrounds the egg. It is composed primarily of calcium carbonate and has microscopic pores that allow gas exchange.
- The egg has two testaceous membranes, the inner and outer, which are located under the shell and surround the egg. These help protect the embryo from external substances and keep the contents of the egg in place.
- The egg white is the transparent, viscous substance that surrounds the yolk. It makes up 60% of the egg’s weight and is composed mainly of water and proteins. Its function is to provide additional protection to the embryo and act as a nutritional source during development.
- Chalazae consist of two cord-like gelatinous structures. These are found in the egg white and keep the yolk centered and in place. Have you noticed when separating the egg white from the yolk that there are some parts that resist coming loose? These are called chalazae.
- The air chamber of the egg is located at its base and acts as a shock absorber. It can take up a significant section of the egg and affect the quality gof rading. The air chamber gets larger as the days go by, so it is a good indicator of its freshness.
- The yolk is the egg cell and accounts for 30% of the weight of the egg. Here we find the yolk (a part that provides nutrients for the development of the embryo) and the germinal disc (the base of the embryo), among other parts. This yellow part of the egg contains a high concentration of nutrients, including proteins, fats, vitamins, and minerals. The yolk is the main food for the developing embryo.
- The germinal disc, germ, or embryo, is, as we said, the part of the egg that has the potential to develop into a bird. It is found in the yolk and contains cells that can lead to the development of the chick if the egg is fertilized. Sometimes we can see it as a dark dot.
Egg categories and types
There are several ways to classify eggs. Three are the most common and useful for the consumer. The first is by freshness and “quality.” The second classifies them by size. The third, and most interesting, is a classification by origin, also called category.
Eggs classified by their class (freshness)
There are three classes, A, B, and Extra:
- Class A eggs: These are the ones that normally arrive at the store. They are not damaged and have not been washed or treated in any way. They are sold as they have been collected and cannot be refrigerated at less than five degrees in the establishments where they are displayed and sold. On the other hand, the air chamber of type A eggs must be less than 6 mm.
- Class B eggs: these are eggs that, although of normal quality, have small defects or an air chamber larger than 6 mm (therefore, they are not fresh), and are not suitable for sale in stores. They are subjected to cleaning, disinfection by immersion, refrigeration or preservation treatments and are not usually sold to the public, but are instead used for processing or industrial egg by-products.
- Extra class eggs: also known as “extra fresh”, these eggs have been collected less than nine days ago, after which the extra label must be removed. They also tend to have a noticeably smaller air chamber as they have been collected very recently.
Eggs classified by size
There are four classifications, S, M, L and XL:
- Size S eggs are the smallest, weighing 45 to 53 grams.
- Size M eggs are medium-sized, weighing 53 to 63 grams.
- Size L eggs are large, weighing 63 to 73 grams.
- XL-size eggs are extra large, weighing over 73 grams.
Eggs classified by their category
There are 4 categories, from 0 to 3. A little further on we explain how to identify them properly:
- Category 0 eggs are organically produced. The hens are raised free-range and fed with corn, cereals, field vegetables, and organic feed.
- Category 1 eggs are from free-range hens that are raised freely, under the same conditions as organic hens, but without consuming organic feed.
- Category 2 eggs come from hens raised on the ground, with limited freedom in sheds or chicken coops, without access to the outdoors, and fed conventional feed.
- Category 3 eggs are those from hens raised in cages, with no access to the outdoors and artificial lighting. Although they meet specific EU requirements for minimum space per hen and availability of nests and perches, there are well-founded concerns about the treatment provided on some farms, where space is maximised at the expense of their welfare.
Nutritional composition of the egg
Because of its purpose (forming a new chick), the egg’s content is highly nutritious and it is considered one of the most complete foods. This is why it is the nutritional basis of so many cultures. While the white contains mainly water and proteins, the yolk contains water, proteins, and lipids. The egg is rich in high-quality proteins with a good balance of amino acids of high biological value, which means that they are easily used by the body.
For a medium-sized egg (weighing 53 to 63 grams), its composition in macronutrients (nutrients present in greater quantities) and micronutrients (present in minuscule, but very important, quantities) is generally as described below.
Macronutrients of eggs
They have a high water content, about 40 g per egg, and a minimal proportion of carbohydrates (0.34 g). Like meat and fish, they have a high amount of protein (6.4 g) of high biological value. On the other hand, the proteins in the egg white are only partially digested if consumed raw, and cooking helps digestion to be complete. The egg has about 4.8 g of lipids, all in the yolk in the form of complex lipoproteins. In addition, it has a particularly interesting balance in terms of saturated and unsaturated fatty acids. Of the total lipids, about 4 g are fatty acids, 35% saturated (SFA), and 65% unsaturated. Of these, most are monounsaturated (MUFA) 1.8 g and the rest, polyunsaturated (PUFA) 0.8 g.
- Energy value: 593 kJ-141 kcal (7% Nutrient Reference Value or NRV, which indicates the percentage that the quantity represents in relation to the established reference intakes)
- Protein: 12.7 g (25.4% NRV)
- Carbohydrates (Sugars): 0.68 g (0.75% NRV)
Fats (9.7 g, 14% NRV), of which:
- Saturated fatty acids: 2.8 g (49% NRV)
- Monounsaturated fatty acids: 3.6 g (3.6 g % NRV)
- Polyunsaturated fatty acids: 1.6 g (1.6 g % NRV)
- Dietary fiber : 0 g (0 g% NRV)
- Salt : 0.36 g (6% NRV)
Micronutrients in eggs
Eggs are a complete source of vitamins, except for vitamin C, which is distributed unevenly between the yolk and the egg white. The yolk contains fat-soluble vitamins (A, D, E, and K), choline, folic acid, and vitamin B12, as well as most of the biotin, pantothenic acid and vitamins B1 and B6. However, the biotin in raw egg white cannot be used by our body due to its bond with the protein avidin. It is necessary to cook it to break this bond so that it can be metabolized.
The albumen or egg white contains approximately 50% of vitamin B2 (riboflavin) and niacin. Eggs are an important source of vitamin D, which is often deficient in the population. Eggs also contain minerals of great importance for health, such as phosphorus, zinc, iron, and iodine. Iron is found in the yolk and is an essential nutrient for our body. Iron absorption is improved by consuming the whole egg since the white contains amino acids and polypeptides that promote its absorption in the small intestine. In addition, consuming foods rich in vitamin C, such as citrus fruits, potatoes, peppers, or broccoli, also improves iron absorption.
It is rich in selenium, an important trace element. Egg yolk also contains other nutrients, such as carotenoid pigments (orange, yellow and red) that give it its characteristic colour and have antioxidant properties. The concentration of lutein, zeaxanthin, and red xanthophylls determines the pigmentation of the yolk.
It is important to note that the nutritional composition of eggs can vary depending on the diet and age of the birds. The diet of hens primarily affects the lipid composition (type of fats and fat-soluble vitamins), trace elements, and yolk pigments.
The following values correspond to 2 M-size eggs (about 100 g) and include the percentage of the Nutrient Reference Value (NRV):
- Vitamin A (µg) : 227 (% NRV: 28.4)
- Vitamin D (µg) : 1.8 (% NRV: 36)
- Vitamin E (mg) : 1.9 (% NRV: 15.8)
- Riboflavin (mg): 0.37 (% NRV: 26.4)
- Niacin (mg) : 3.3 (% NRV: 20.6)
- Folic Acid (µg) : 51.2 (% NRV: 25.6)
- Vitamin B12 (µg) : 2.1 (% NRV: 84)
- Biotin (µg): 20 (% NRV: 40)
- Pantothenic acid (mg): 1.8 (% NRV: 30)
- Phosphorus (mg): 216 (% NRV: 30.8)
- Iron (mg) : 2.2 (% NRV: 15.7)
- Zinc (mg): 2 (% NRV: 20)
- Selenium (µg) : 10 (% NRV: 18.2)
- Choline (mg) : 250 (% NRV: 63)
Benefits of eggs
As we have seen, eggs are an excellent source of essential nutrients, such as high-quality proteins, vitamins, and trace elements, among others.
They have very bioavailable proteins
One of the benefits of eating eggs is their high-quality, or bioavailable, protein content, which is important for building and repairing tissue, as well as maintaining a healthy immune system. While it is true that they need to be cooked, once cooked, virtually any nutrient from the egg can be used, making it a nutritional resource like no other.
They can help control weight
Although this claim should be taken with a grain of salt, there are researchers who claim that eggs can help control weight. This is because they are satiating foods, with a relatively high lipid content, but with a very good profile, and almost no free sugar content. In addition, being so complete on a nutritional level, they can help reduce excessive consumption of other foods. In any case, as always happens with these issues, everything will depend on intake and eating habits.
They contain choline, an essential component for the brain
This nutrient plays a crucial role in brain development and function. Choline is involved in the production of neurotransmitters and can have positive effects on memory and cognitive function. The high availability of this nutrient makes it especially interesting for any stage of development.
It can help maintain vision
As for eye health, eggs contain lutein and zeaxanthin, antioxidants linked to protecting the eyes against diseases such as age-related macular degeneration. They also contain vitamin A (retinol), another key component in maintaining our visual capacity.
Contraindications of eggs
While eggs are a nutritious and safe food for most people, some people may have certain contraindications or restrictions on their consumption due to medical conditions or allergies. Among the most common ones we find:
Egg allergy
Egg allergy is an adverse immune reaction to the proteins present in eggs. People who are allergic to eggs should avoid eating them altogether, as it can trigger severe symptoms such as skin rashes, difficulty breathing or even anaphylaxis (which can be fatal). For this reason, eggs are always listed as a possible allergen.
Egg intolerance
Some people may have difficulty digesting or tolerating certain components of eggs, such as the proteins or yolk. This is not the same as an allergy, as there is no severe immune process, although the immune system may be involved. It usually manifests itself with gastrointestinal discomfort, nausea, diarrhea or abdominal swelling. In these cases, it is recommended to limit or avoid eating eggs.
High cholesterol levels
Eggs are rich in cholesterol, so people with high blood cholesterol levels or cardiovascular diseases are advised to restrict their consumption. However, this is under review because the presence of cholesterol, according to the latest evidence, is not always related to an increase due to its consumption. In any case, prevention always comes first.
Loss of control of diabetes and other metabolic diseases
Although it is not common, sometimes people with diabetes can see their blood sugar spikes out of control. This is because eggs contain protein and fat, which can affect blood glucose levels. It is important to control egg consumption within a balanced and personalized diet plan in case of a metabolic disease such as dyslipidemia, obesity, or another.
Liver diseases
Due to their cholesterol and fat content, many health professionals advise people with severe liver disease to restrict or completely eliminate egg consumption. These are, as in the previous case, specific situations that should be supervised by a doctor or nutritionist.
Be careful if the egg has been washed at home
The eggshell is not watertight, but has small holes that allow the egg to “breathe”. These pores can be enough for bacteria to pass through and take advantage of the rich environment that the egg represents. For this reason, for example, it is advisable to cook it properly, never pass the expiration date or wash it, to prevent bacteria from passing inside. Otherwise, we could face food poisoning.
How many eggs can you eat per week?
As we explained in this article, at a clinical level, doctors usually recommend reducing intake and not exceeding between 3 and 5 per week. However, scientific evidence does not fully support this decision, which seems somewhat obsolete.
Eating eggs does not necessarily lead to a direct increase in cholesterol simply because they contain too much cholesterol. There are even studies that show that eating them can help regulate excessive levels of this substance. However, other factors, nutritional, genetic, physiological or behavioural, can link diet, and therefore eggs, with a problem with this fat.
In conclusion, given how complicated it is to determine something as concrete as the number of eggs per week, the best thing to do is to apply prevention. And, of course, all of this is subordinated to the most important thing: listening to your doctor or specialist.
How to read egg codes
Commercial eggs have an 11-digit code on their shell that provides various indications about their origin and category. For example: 1ES64010496.
The most relevant part for the consumer is the first three digits, as it tells us how the chickens have been raised and their nationality (which helps us determine freshness). In this example, and as we have seen above, the first one indicates that they are category 1 and, therefore, from free-range chickens that are raised in freedom, in the same conditions as organic chickens, but without consuming organic feed.
The “ES” refers to its origin in Spain. The other 6 digits are used to indicate the province and municipality where the egg was collected. This can be useful for evaluating freshness or consuming local products, although we should remember that freshness is indicated by the type of egg.
What is an egg?
Egg white, also known as dehydrated egg white or dehydrated egg protein, is a product obtained from fresh eggs (usually those of class B). It consists of separating the egg white from the yolk and then dehydrating it, resulting in a fine, easy-to-store powder.
Egg white is used in various industries, such as food and pharmaceuticals, due to its functional and nutritional properties. It is an excellent source of high-quality protein, as it contains all the essential amino acids necessary for the proper functioning of the body. It is used as an ingredient in processed foods, dietary supplements, bakery, and confectionery products, among others. Egg white can also be reconstituted with water to obtain liquid egg white, making it convenient for use in cooking and the food industry.
Among its advantages, we find its sterility, in principle, since its processing eliminates harmful microorganisms, so it can be used with a fair amount of food safety.