When you cook an egg, the texture and flavor of the yolk changes, so sometimes preparation choices come down to personal preferences. But there are some health benefits to consider. One important benefit of thoroughly cooking the yolk is that the heat kills any bacteria. Eating uncooked yolks is not recommended, but if they're lightly cooked, yolks retain more nutrients and you'll lower the risk of unhealthy changes to cholesterol.
Eliminate Bacterial Contamination
Eggs are sanitized at processing facilities, yet it's still estimated that 1 in every 20,000 eggs may contain salmonella, according to the University of Minnesota. Even if the egg looks normal and has a clean, uncracked shell, bacteria can still be present outside and inside the egg. Heat kills the bacteria, but the amount destroyed depends on how you cook the egg. If your egg has a runny white or yolk, it can still retain bacteria. Lightly cooked eggs have caused outbreaks of salmonella infections, reports the Centers for Disease Control and Prevention.
Boost Nutrient Retention
The egg yolk supplies almost all of the whole egg’s iron, calcium, zinc, vitamin B-6, folate and vitamin B-12. It also contains 100 percent of the egg’s vitamin A, which includes two antioxidant carotenoids -- lutein and zeaxanthin -- that help keep your eyes healthy. Lutein and zeaxanthin are susceptible to heat, so you’ll get more from your eggs if you eat them with the yolks lightly cooked. When eggs are boiled, you’ll lose about 23 percent of the lutein, while microwaving and frying result in losses of 17 and 19 percent respectively, according to a report in the “Journal of Agricultural and Food Chemistry” in December 2012.
Avoid Oxidized Cholesterol
All of the egg’s cholesterol is found in the yolk. When cholesterol is exposed to heat during cooking, some of it oxidizes, or combines with oxygen, and forms new substances called oxysterols. Once in your system, oxysterols are active compounds that help regulate fat metabolism and may contribute to hardening of the arteries, reports a review in the “Circulation Journal” in October 2010. More research is needed to determine the role of dietary oxysterols and whether they increase the risk of cardiovascular disease. Meanwhile, you'll get fewer oxysterols by eating lightly cooked yolks.
Safe Handling Tips
If you keep eggs refrigerated and cook them thoroughly, you'll reduce the risk of getting sick from bacteria. Take a look at the eggs before you buy them and don't get any that are cracked or look dirty. Refrigerate them as soon as possible because that stops bacteria from growing. If you don’t hard boil your eggs, the University of Minnesota recommends frying eggs two to three minutes on each side and poaching eggs for five minutes in boiling water. Soft-cooked eggs should be boiled in the shell for seven minutes. Don’t keep cooked eggs at room temperature for more than two hours before putting them back in the refrigerator.
- USDA National Nutrient Database: Egg, Yolk, Raw, Fresh
- USDA National Nutrient Database: Egg, White, Raw, Fresh
- Linus Pauling Institute: Carotenoids
- Journal of Agricultural and Food Chemistry: Effect of Domestic Cooking Methods on Egg Yolk Xanthophylls
- Circulation Journal: Macrophages, Oxysterols and Atherosclerosis
- Centers for Disease Control and Prevention: Tips to Reduce Your Risk of Salmonella From Eggs
- University of Minnesota: Handle Eggs Properly to Prevent Salmonella
- Asian Pacific Journal of Clinical Nutrition: Cholesterol Oxides: Their Occurrence and Methods to Prevent Their Generation in Foods