According to Türkiye Beslenme Rehberi (TÜBER), Türkiye's national dietary guideline, the food with the highest protein quality is the egg, because its proteins are known to be converted into body proteins at a rate of 100 percent. For this reason the egg's protein is judged to be the reference protein; that is, it is what other proteins are compared against when their quality is measured.
What does reference protein mean?
The definition of the measure and its score bands are in the protein quality article; what matters here is where the egg falls on that scale. The guideline counts 100 percent and above as high protein quality and shows the egg and milk as the examples of that band.
This score is not a production claim but a measurement scale: it shows how fully a protein meets the essential amino acid pattern. Looking at dried legumes is enough for the comparison. In them the protein value is high and the quality low; the reason is that they are limited in the essential sulfur-containing amino acids, that their fiber content is high, and that they are hard to digest.
The fat side of the egg
Of the egg's fat 33 percent is saturated, 16 percent polyunsaturated, and the rest is made up of monounsaturated fatty acids. The fat is concentrated in the egg yolk, and the cholesterol and unsaturated fatty acid content of the yolk is high.
Here the guideline makes a distinction. Because the egg contains lecithin, which is a phospholipid, its effect in raising blood cholesterol is less than that of fatty meat and milk products. The yolk is also rich in iron and in the A and B group vitamins. The fat gathering in the yolk also lets the protein side and the fat side of the egg be managed separately within the same food. The protein comparison of one standard portion of the same egg against the other foods in its group stands in the portion equivalence article.
How many a day?
The measure the guideline gives for healthy individuals is one a day; it is stated that, especially in cases where red meat and its products are not consumed, this amount does not raise the risk of cardiovascular disease. The measure given for people who have cardiovascular disease is one to two times a week.
In children, because the protein quality is high, eating one egg every day is stated to be useful. The portion measure is defined in the table: one egg is one small egg, that is 50 grams. In situations where the amount of protein in the diet is restricted, such as kidney and liver failure, the egg is also shown as an important source because it contains the reference protein; in such a situation the plan is made under the supervision of a doctor and a dietitian.
Why does it come forward at older age?
The guideline states that older people should take in enough protein at every meal in order to make muscle synthesis as good as it can be, and brings the egg forward in this context: compared with other animal protein sources it is cheaper, easy to digest, and contains a high amount of leucine, an amino acid that matters for muscle synthesis.
What it carries alongside is counted as well: essential fatty acids, choline, vitamin A, vitamin B12 and selenium. In situations where the amount of protein in the diet is restricted it is also shown as an important source because it contains the reference protein.
Where does it turn into a mistake?
The first mistake is eating the egg raw. In terms of food safety the guideline does not recommend eating raw egg; it is hard to digest and biotin, one of the B group vitamins, cannot show its useful effect. What these two mistakes share is taking the egg's protein quality to be independent of cooking and freshness; but food safety and digestibility are a part of that quality. The second mistake is long cooking: if the egg is stale and is cooked for a long time, a green iron sulfide ring forms around its yolk, which is why in a hard-boiled egg the boiling time is limited to 5-8 minutes after the water boils.
Choosing and storing
The guideline gives a criterion on the buying side as well: eggs that are clean on the outside and have no cracks or breaks should be chosen, and they should be stored in the refrigerator without being washed. Washing not entering the recommendation has to do with the shell's own protective function.
Freshness is a separate item. When a stale egg is cooked for a long time a green iron sulfide ring forms around its yolk; that is why eating fresh eggs is recommended. The same reason is why the boiling time is limited.
Its place within the meal is defined too. The guideline states that eating the egg together with vegetables and grains brings its negative effect on blood cholesterol down further; and the lecithin it contains is counted as helpful in keeping brain functions regular and in protecting the liver.
This content has been prepared to support general nutrition literacy; it does not take the place of medical diagnosis or treatment and does not carry the character of personal nutrition advice. A personalized plan is prepared only by a qualified dietitian; if there is pregnancy, chronic illness, regular medication use, child nutrition or a clinical condition, supervision by a doctor and a dietitian is required before starting a plan.