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What's the Difference Between Egg Whites and Egg Yolks?
The yolk is the first part that forms when a hen’s egg cells reach maturity. It’s made primarily of fats and proteins and gets its yellow color from plant pigments in the hen’s food. The white (aka albumen) forms around the yolk later in the game, providing cushioning between the embryo and the shell. The yolk provides most of the nutrition for the embryo, while the white supplies the embryo with water and protects it from viruses, bacteria, and even predators (proteins found in the white block the digestion of nutrients).
The different properties of the white and the yolk reflect how chickens feed and protect their embryos, but we can take advantage of them in the kitchen by using egg yolks to emulsify rich sauces like mayonnaise and hollandaise, and egg whites to stabilize foams such as meringue. Together, the white and the yolk make beautiful sunny side-up and poached eggs.
Nutritional Value of an Egg White
Although the egg white makes up most of the egg’s volume, it only accounts for about a quarter of its calories. A large egg white contains almost zero fat, a good source of protein, and most of the egg’s sodium (but not that much—only around 2 percent of they recommended daily value). Egg whites are generally not a good source of vitamins, but one large white does contain about 0.145 milligrams of riboflavin (aka vitamin B2), an important vitamin for energy production and cell growth that’s not as prevalent in the yolk. Egg white alone is a high-quality, complete protein, meaning that it contains all nine of the essential amino acids.
Nutritional Value of an Egg Yolk
The yolk is the source of the most of an egg’s vitamins, including iron, thiamin (vitamin B1), vitamins A and D. It also contains all of the egg’s fat (about 4.5–6 grams in one egg yolk, less than 10 percent of the daily recommended value, and 1.6 grams of saturated fat). Yolks are notorious for having one of the highest levels of dietary cholesterol of any food that we eat (about 213 milligrams per yolk), a quality once believed to increase risk of cardiovascular disease. More recent studies show that high levels of cholesterol in food do not necessarily correspond to high blood cholesterol levels or heart disease risk.
Are Egg Whites Healthier Than Egg Yolks?
Egg whites were long thought to be healthier than yolks because they do not contain cholesterol, but while they’re fat free and have a few more grams of protein, the whites’ lack of vitamins and minerals means they’re not necessarily healthier than the yolks. If you need to minimize your fat intake for health reasons, egg whites are a safer bet. But if you’re looking to increase your vitamin consumption, the yolk’s where it’s at.
Are Egg Yolks Bad for Your Health?
A good source of linoleic acid, some minerals, most vitamins, and the antioxidants lutein and zeaxanthin, eggs yolks are one of the most nutritious foods humans eat. Fattier and higher in calories than egg whites, yolks have long been demonized for their high cholesterol content, but a new study published in the American Journal of Clinical Nutrition found that eating a dozen or more eggs a week did not increase the cardiometabolic risk of adults with type-2 diabetes.
Should You Eat the Whole Egg for the Most Nutrition?
Egg whites have less than half the amount of calories as egg yolks, so they’ve long been recommended for weight loss, but if you eat egg whites alone you’ll miss out on most of the egg’s vitamins. The yolk and the white each contain about half of the egg’s amount of protein, and the yolk contains over 90 percent of its calcium, iron, phosphorus, zinc, thiamin (vitamin B1), vitamin A, vitamin E, vitamin D, and vitamin K. The white contains most of its magnesium, potassium, riboflavin (vitamin B2), and niacin (vitamin B3).
How to Cook Eggs to Maximize Nutrition Intake
Cooking eggs neutralizes protective proteins present in the white that attach to vitamins, a defense mechanism that makes the whites inedible to other animals, but cooking will also cause eggs to lose some of their nutrients. It turns out the tastiest way to cook an entire egg is also the most nutritious: fully cook whites, to destroy the egg proteins that interfere with our absorption of nutrients, but keep yolks mostly raw, to preserve their vitamins. That means to maximize nutrition, you’ll want to eat a sunny side-up, soft-boiled, or poached egg—not just an egg white omelet. Just be aware that the FDA recommends cooking whites and yolks thoroughly to avoid Salmonella, which is especially important for people with compromised immune systems.