Eggs, are you eating them right?

Author: Ye Linfang The First Affiliated Hospital of Anhui Medical University

Reviewer: Xia Tongjia, deputy chief physician, the First Affiliated Hospital of Anhui Medical University

Pan Jianyuan, deputy chief physician, First Affiliated Hospital, University of Science and Technology of China

Many patients with high blood lipid levels often control their blood lipids by improving their eating habits, but a large number of them believe that eating eggs will increase their blood lipid levels, so they stay away from eggs. Even if they eat them occasionally, they only eat egg whites. This practice is not only a waste of food, but also has no scientific basis. The "Dietary Guidelines for Chinese Residents 2022" points out that Chinese residents should consume 300-350g of eggs per week. Eggs are rich in nutrients, and the yolk should not be discarded when eating eggs.

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1. The "charm" of egg yolk is far greater than that of egg white

1. The cholesterol content in 1 egg can reach 200 mg, and all of it is concentrated in the yolk. There are two sources of cholesterol in the human body: one is through food intake, that is, exogenous cholesterol; the other is synthesized by the human body itself, that is, endogenous cholesterol. The cholesterol homeostasis in the human body mainly depends on the intestinal absorption of cholesterol, the synthesis of endogenous cholesterol, and the excretion of bile acids and steroids. Intake of an appropriate amount of cholesterol through food can inhibit the production of endogenous cholesterol to a certain extent, so that the cholesterol level in the body is in a dynamic equilibrium state.

2. Eggs are an excellent source of high-quality protein, providing the human body with essential amino acids, helping muscle repair and growth, and enhancing immunity.

3. Although the fat content in egg yolk is high, it is mainly unsaturated fatty acids, which account for nearly 2/3 of the total lipids. It plays a positive role in regulating blood lipids and immunity, and nourishing the brain [1].

4. All B vitamins and fat-soluble vitamins (vitamin A, vitamin D, vitamin E, vitamin K) are almost all concentrated in egg yolks. Among them, vitamin A has a regulatory effect on vision, skin and mucous membranes, bone growth, immune function, etc.; vitamin D can regulate calcium and phosphorus metabolism, maintain bone health, and prevent rickets, osteomalacia, and osteoporosis; vitamin E is an antioxidant and has an anti-aging effect; vitamin B6 can reduce uric acid by inhibiting homocysteine ​​levels [2-3].

5. Egg yolks are rich in phosphatidylcholine, which is the main component of lecithin, accounting for about 70%. Studies have found that lecithin has many functions, including regulating blood lipids, improving memory and anti-oxidation [4].

6. One egg yolk contains nearly 331 μg of carotene, lutein and zeaxanthin. Studies have found that lutein has a protective effect on the retinal structure and can also reduce the risk of heart disease [1].

2. How to enjoy eggs reasonably?

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Common ways to cook eggs include boiled eggs, egg custard, fried eggs, and stewed eggs. It is recommended to choose boiled eggs and egg custard, and avoid frying, long-term stewing, deep-frying hairy eggs, etc. Although boiling eggs is simple, people often ignore the boiling time when boiling eggs, which greatly reduces the nutritional value of eggs. On the one hand, boiling eggs for too long will not only destroy the vitamins and other nutrients in the eggs, but also cause the unsaturated fatty acids and cholesterol in them to oxidize. The unsaturated fatty acids contained in eggs, such as linoleic acid, arachidonic acid and DHA (docosahexaenoic acid), are easy to oxidize. During the heating process, the rate of their oxidation reaction will accelerate as the temperature rises. Oxidized unsaturated fatty acids are like a "good citizen" turned into a "demon". When they enter the human body, they will increase the production of free radicals and even destroy DHA and cell structures, causing harm to the human body. On the other hand, boiling eggs for too short a time also poses a safety hazard. If the heating is not sufficient, not only can harmful bacteria such as salmonella not be effectively killed, but also anti-nutrients such as biotin-binding proteins in eggs cannot be destroyed, thus affecting absorption. So, how long should eggs be boiled? Generally speaking, the ideal state of boiled eggs is: the egg white has solidified, and the yolk has just solidified, and the texture is soft and tender, and the color is golden. The solidification of egg white and yolk indicates that the center temperature of the egg can reach about 70°C at this time, the salmonella has been killed, and the anti-nutrients can also be removed; the just solidification of the yolk indicates that the cooking time will not be too long, and the oxidation degree of nutrients is relatively low at this time, which is more conducive to human absorption. To achieve this effect, you can use a special egg cooker when boiling eggs; you can also boil eggs in cold water and boil them for about 3 to 5 minutes after the water boils. If it is summer and the eggs are stored in the refrigerator, take them out half an hour in advance and put them at room temperature before boiling. It is recommended to rinse the eggs with cold water after the fire is stopped, because the residual heat may continue to heat the eggs, causing the nutrients in the eggs to be destroyed.

3. Eggs are not a “sweet burden”

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When choosing food, diabetic patients should choose foods with a low glycemic index (<55%), and the glycemic index of eggs is generally around 30%. Patients with diabetes and hypercholesterolemia do not need to abstain from egg yolks, but should consume them in moderation. It is recommended to eat 3 to 4 eggs per week, which can ensure nutrition without causing an increase in cholesterol levels. Studies have shown that certain components in eggs can regulate the absorption, transport and metabolism of cholesterol [1]. Therefore, patients with diabetes and hypercholesterolemia can eat eggs with confidence on the premise of a balanced diet, and do not need to discard the egg yolks.

In addition, eggs are high-protein, low-purine foods (low-purine foods refer to foods with a purine content of less than 25 mg per 100 g) [5], so consuming eggs will not lead to increased uric acid.

【References】

[1] Xu Yichi, Peng Shiyi, Yang Fang. Research progress on the correlation between egg consumption and cholesterol homeostasis[J]. Food Science, 2020, 41(7): 245-254.

[2] Health Management Branch of Chinese Nutrition Society. Expert consensus on evaluation and improvement of vitamin D nutritional status[J]. Chinese Journal of Health Management, 2023, 17(4): 245-252.

[3] Yu Yang, Wei Jinfeng, Deng Shijie, et al. Research progress on types of vitamins and their mechanisms of lowering uric acid[J]. China Medical Herald, 2024, 21(15): 190-193.

[4] Zhu Shuai, Huang Mengling, Fan Li, et al. Extraction and molecular structure analysis of phosphatidylcholine from egg yolk rich in unsaturated fatty acids [J]. Journal of Cereals, Oils and Food Science and Technology, 2020, 28(3): 10-17.

[5] Du Yunxuan. Methods for reducing purine in food and analysis of low-purine products[J]. Food Safety Guide, 2021, (24): 49-50.