Boiling eggs may seem simple, but it's difficult to get the timing right. Too short a time leaves the yolk undercooked, while too long makes the egg tough and unpalatable. In this regard, Dr. Chang Cuiqing from the Institute of Sports Medicine at Peking University Third Hospital explains that the optimal time for boiling an egg is actually quite easy to grasp. Place the eggs in cold water, and once the water boils, let them cook for exactly 5 minutes. This method kills harmful pathogens while preserving the nutrients in the egg relatively intact.
If an egg is boiled in water for more than 10 minutes, a series of chemical changes occur inside. The protein structure becomes more compact, making it less accessible to digestive enzymes in the stomach, and therefore harder to digest. Egg protein contains a significant amount of methionine, which, after prolonged heating, breaks down into sulfides. These sulfides react with the iron in the yolk to form iron sulfide, a compound that is not easily absorbed by the human body, resulting in significant nutrient loss.
Undercooked eggs pose even greater risks. Raw eggs not only carry the risk of Salmonella contamination but also contain two harmful substances: avidin and antitrypsin. The former affects the digestion and absorption of protein, while the latter binds to biotin in food, leading to biotin deficiency in the body, which can cause symptoms like mental fatigue and muscle soreness. However, these two substances are rendered inactive once the egg is cooked.
Furthermore, you can use the following techniques to prevent nutrient loss when boiling eggs: The water must completely cover the eggs; otherwise, the protein in the parts not submerged will not coagulate properly, affecting digestion. Before boiling, soak the eggs in cold water for a while to reduce the internal pressure. Then, bring the water to a boil over medium heat. This will prevent the eggshells from cracking and avoid nutrient loss.