Although they have been controversial for years, today we know that eggs are a nearly perfect food. They are rich in complete proteins, essential fats, vitamins and minerals. It must be taken into account that inside an egg there are all the elements necessary for a chick to hatch. For years, moderation has been recommended when consuming eggs due to an unwarranted fear of dietary cholesterol and disease. Today we know that this has no scientific basis and that you can eat several eggs per day not only safely, but it can also reduce inflammation and improve tissue turnover.
However, the way eggs are cooked can influence the absorption of these nutrients. To understand how nutrient bioavailability varies depending on whether eggs are eaten boiled, fried, or as an omelet, it is important to explore what happens during cooking and how each method affects key components of the egg.
Proteins and their digestibility
Eggs are a complete source of high-quality protein, containing all the essential amino acids that our bodies cannot produce. Cooking eggs does not cause loss of protein, but it changes the degree of absorption in the body. When eaten raw, the protein in eggs is not fully absorbed. Indeed, egg proteins have a structure that makes it difficult for them to be broken down by digestive enzymes.
A study published in the Journal of Nutrition found that the human body can only absorb 51% of the protein from a raw egg, compared to 91% from a cooked egg. This is because heat denatures egg proteins, making them easier to digest.
Proteins are very large molecules in which the atoms are arranged in a three-dimensional structure similar to a tangled thread. With heat, certain bonds break and proteins “unravel” or denature. Additionally, this process causes the egg to solidify. The bonds are exposed and cause the proteins to stick together, forming a rubbery substance instead of a liquid substance.
When fried or made into a tortilla, the proteins are also denatured. When frying, for example, high temperatures can cause greater denaturation than if the egg is cooked at lower temperatures, such as when boiling.
Some experiments have shown that maximum protein absorption occurs in poached eggs, which have a solid white and a liquid yolk. The solid yolk is harder to digest, so hard-boiled eggs use less protein.
Fats and fat-soluble vitamins
Eggs are a good source of healthy fats, especially the yolk, which contains monounsaturated and polyunsaturated fats. These fats are not significantly affected by cooking, although additional fats may be added when cooking fried eggs, depending on the oil used.
More relevant for nutrient absorption are the fat-soluble vitamins contained in eggs: vitamins A, D, E and K, present in the yolk. These vitamins depend on the fats absorbed by the body. In this case, the absorption of vitamin A is higher in omelets than in hard-boiled or poached eggs. However, when the yolk solidifies, it affects the absorption of vitamin D3, which is more digestible in the liquid yolk of poached eggs.
Water-soluble vitamins and cooking
B vitamins, especially B12, are essential for the nutrition provided by eggs. However, water-soluble vitamins can be partially lost during cooking due to the action of heat and their dissolution in water. In poached eggs, the losses of B vitamins may be greater, since they are immersed in water, which facilitates the dissolution of these vitamins. In the case of fried or omelet eggs, the losses of group B vitamins are lower, since they are not in contact with water. Although these losses are not significant, they are enough to make fried or omelet eggs preferable if one seeks to maximize the retention of water-soluble vitamins.
Avidin and biotin
Avidin is a protein found in raw egg whites that may interfere with the absorption of biotin (vitamin B7). However, heat inactivates avidin, meaning that cooking eggs, whether boiled, fried or in an omelette, eliminates this problem. This ensures that the body can fully absorb biotin, regardless of the cooking method chosen.
Antioxidants and cooking
Eggs also contain antioxidants such as lutein and zeaxanthin, which are essential for eye health. Cooking can reduce the levels of these antioxidants, but not uniformly. One study showed that boiled eggs reduce lutein and zeaxanthin levels by 20%, while in fried eggs the reduction can be greater, around 40%. Despite this loss, eggs remain an important source of these compounds, and their regular consumption, regardless of the cooking method, can provide health benefits.
Ultimately, cooking eggs, regardless of the method, will facilitate the absorption of their nutrients, including protein. However, it should also be taken into account that in highly cooked hard-boiled eggs, prolonged heat and a solid yolk can interfere with the absorption of certain vitamins. The most important thing is that eggs, in all their forms, deserve to be part of our diet.
