It is well known that eggs are one of the most nutritious foods. However, many people may not know that although they are in the same eggshell, egg white and egg yolk are two completely different foods, and their nutritional value is also very different.

　　The composition of egg white contains 84.4% of water, 11.6% of protein, 0.1% of lipids, 3.1% of carbohydrates, and 0.8% of minerals (the total of the aforementioned values is 100%). Egg yolk contains 51.5% water, 15.2% protein, 28.2% lipid, 3.4% carbohydrate, and 1.7% minerals (the total of the aforementioned values is 100%).

The biggest difference between 　　 egg white and egg yolk is in terms of lipids. The content of egg yolk lipids is 280 times that of egg white. In fact, 98% of the lipids in the whole egg are concentrated in the yolk, and the lipids in the egg white are very few. Among the yolk lipids, triglycerides accounted for 62%, phospholipids accounted for 33%, and cholesterol accounted for 5% (the aforementioned values totaled 100%). In other words, in 100g of egg yolk, the total amount of lipids is about 28g, of which triglyceride (ie fat) is 17.5g, phospholipid is 9g, and cholesterol is 1.5g. In addition, there are small amounts of cerebrosides. These ingredients are almost absent in egg whites.

Among the fatty acids of egg yolk fat, the highest content is oleic acid (that is, the monounsaturated fatty acid sold in olive oil), accounting for 36.7%, followed by linoleic acid (which is a polyunsaturated fatty acid, also soybean oil or The main component of peanut oil is 26.1%, followed by palmitic acid 20.9% and stearic acid 8.4% (both are saturated fatty acids, usually the highest in animal fat), then palmitoleic acid 3.2% and linolenic acid 3.0% , The remaining 1.7% is other types of fatty acids. The fat in the egg yolk is in an emulsified state, which is very easy to digest and absorb.

　　The egg phospholipids are mainly lecithin and brain phospholipids, and a small amount of sphingomyelin. Phospholipids help improve liver fat and cholesterol metabolism and are good for health.

Cholesterol in egg yolk is a tangled ingredient. It can be said that if there is no cholesterol in the egg yolk, then the egg yolk is perfect. Egg yolk contains a large amount of cholesterol, accounting for about 1.5% of the total weight of egg yolk, and it definitely belongs to the "leader". The cholesterol content of an egg yolk is about 290mg, which is close to the accepted limit of 300mg/day for a healthy diet. Therefore, the "Chinese Dietary Guidelines 2007" formulated by the Chinese Nutrition Society recommends that no more than one egg be eaten per day.

　　 egg white contains about 40 kinds of protein, such as ovalbumin, ovalbumin, ovomucin, ovalbumin, ovalbumin and so on. The proteins in egg yolk are mainly yolk phosphoprotein and yolk globulin. The nutritional value of these proteins is similar. The carbohydrates in egg white are mainly mannose and galactose, while the egg yolk is mainly glucose. The nutritional value of these sugars is not much different.

In terms of minerals, egg white and egg yolk are quite different. Not only is the total amount of minerals in egg yolk twice that of egg white, but also trace elements such as iron, zinc, and selenium are much higher than egg white. 100g egg yolk contains 112mg calcium, 240mg phosphorus, 41mg magnesium, 6.5mg iron, 3.79mg zinc, 27.01mg selenium, 0.28mg copper. 100g of egg white contains 9mg of calcium, 18mg of phosphorus, 15mg of magnesium, 1.6mg of iron, 0.02mg of zinc, 6.97mg of selenium, and 0.0.05mg of copper, which are far less than egg yolk. But the content of sodium and potassium in egg white is much higher than that of egg yolk. It is worth noting that although the iron in the egg yolk is non-heme iron and is interfered by the yolk phosphoprotein, its absorption rate is not high, only 3%, far lower than lean meat (20%), but for those who cannot eat meat For babies, it still has important value.

In terms of vitamins, the difference between egg white and egg yolk is much greater than the difference in fat between the two. Almost all fat-soluble vitamins in eggs, such as vitamin A, vitamin E, vitamin D, and vitamin K, are concentrated in the egg yolk, and the egg white is basically free. Among water-soluble vitamins, vitamin B1 is mainly in egg yolk, and egg white is basically free; vitamin B2 egg yolk is similar to egg white; vitamin C is not in egg yolk and egg white.

　　 Egg yolk contains phytochemicals such as lutein and zeaxanthin, which has a certain health care effect. These substances are not found in egg whites.

　　All in all, egg yolk and egg white have huge differences in nutritional composition, and the nutritional value of egg yolk is higher and stronger. Although the high cholesterol content is a nutritional defect of egg yolk, but the defect does not cover the jade, egg yolk is still a rare nutritional good. The act of eating egg whites and throwing away the yolks is not only violent, it is also serious ignorance.

　　 (Note, the data used in this article mainly refers to the "Chinese Food Composition Table 2002". Eggs from different sources have slightly different ingredients, and the data provided by different testing agencies are also different, but the overall trend is consistent. ).