Egg whites are the clear, viscous liquid inside an egg that surrounds the yolk. They’re composed of about 88% water and just over 10% protein, with trace amounts of carbohydrates and minerals. In nature, they cushion and nourish a developing bird embryo while fighting off bacteria. In your kitchen, they’re one of the leanest protein sources available, packing 4 grams of protein into just 20 calories.
What Egg Whites Actually Contain
A single large egg white has zero fat, zero cholesterol, less than 1 gram of carbohydrates, and about 4 grams of protein. That 20-calorie count makes it one of the most protein-dense foods relative to its calories. For comparison, the yolk of the same egg carries about 55 calories, 4.5 grams of fat, and all 186 milligrams of the egg’s cholesterol.
The protein in egg whites isn’t a single substance. It’s a mix of several distinct proteins, each with different properties. Ovalbumin makes up about 54% of the total protein, followed by ovotransferrin at 12%, ovomucoid at 11%, and smaller amounts of ovomucin and lysozyme. These proteins are what give egg whites their unique ability to foam when whipped, set firm when heated, and bind ingredients together in cooking.
Vitamins and Minerals in the White vs. the Yolk
Egg whites contain meaningful amounts of a few B vitamins, particularly riboflavin (B2), niacin (B3), and pantothenic acid (B5). In fact, an egg white has nearly as much riboflavin as the yolk itself. They also carry small amounts of biotin, thiamin, and B12.
What egg whites lack is just as notable. They contain zero vitamin A, zero vitamin D, zero vitamin E, and zero vitamin K. All of these fat-soluble vitamins live exclusively in the yolk, along with most of the egg’s iron, zinc, calcium, and phosphorus. Egg whites do contribute some potassium (163 mg per 100g, actually more than the yolk) and magnesium, but overall, the yolk is far more nutrient-dense.
This is the core tradeoff when you choose egg whites over whole eggs: you get a very lean, high-protein food, but you lose most of the micronutrients.
Their Biological Role Inside the Egg
Before egg whites became a staple of omelets and protein shakes, they evolved to serve a developing chick. The albumen (the scientific name for egg white) has two jobs: feeding the embryo and protecting it from bacteria. As the embryo grows, proteins in the white gradually break down into nutrients the chick can absorb. Ovalbumin, the most abundant protein, degrades steadily during incubation to fuel early development.
The antimicrobial role is equally important. Lysozyme, one of the egg white proteins, directly attacks bacterial cell walls. Another protein called avidin binds tightly to biotin, a vitamin that bacteria need to grow. By locking up biotin, avidin essentially starves any microbes that penetrate the shell. This defense system is one reason eggs can remain viable for weeks before incubation begins.
Why Raw Egg Whites Can Cause Problems
That same avidin protein is relevant if you eat egg whites raw. Because avidin binds biotin so effectively, regularly consuming raw egg whites can lead to biotin deficiency over time. Symptoms include brittle nails, hair thinning, and skin rashes. Cooking solves this: heat changes avidin’s structure so it can no longer grab onto biotin. This is one of the practical reasons to cook egg whites rather than adding them raw to smoothies.
There’s also the standard food safety concern. Raw egg whites can harbor Salmonella bacteria. Pasteurized liquid egg whites, sold in cartons, have been heat-treated just enough to kill bacteria without cooking the protein, making them safe for recipes that call for uncooked whites.
Egg White Allergies
Egg allergy is the second most common food allergy in the United States, after milk allergy, and most of the allergenic proteins sit in the white rather than the yolk. Five proteins trigger the majority of reactions: ovomucoid, ovalbumin, ovotransferrin, lysozyme, and ovomucin. Despite ovalbumin being the most abundant protein overall, ovomucoid is considered the dominant allergen because it resists heat and digestive enzymes, meaning it can still trigger reactions even in thoroughly cooked eggs.
Most egg allergies appear in early childhood, and many children outgrow them by adolescence. Children who react only to lightly cooked egg but tolerate baked egg (in muffins or cakes, for example) tend to outgrow the allergy faster. If you can eat baked goods containing egg without symptoms, that’s generally a positive sign, though the specific proteins you react to matter.
How Egg Whites Work in Cooking
Egg whites are unusually versatile in the kitchen because of their protein structure. When you whip them, the proteins unfold and trap air bubbles, creating a stable foam. This is the foundation of meringues, soufflés, and angel food cake. A single egg white can expand to six or eight times its original volume when beaten to stiff peaks.
Fat interferes with this foaming process, which is why even a small trace of yolk (which is about one-third fat) can prevent egg whites from whipping properly. It’s also why recipes insist on spotlessly clean bowls. When heated, egg white proteins bond together and solidify, which is why a fried egg white turns from translucent to opaque at around 144 to 149°F (62 to 65°C). This setting ability makes egg whites useful as a binder in meatballs, a clarifying agent in broths, and a coating for baked goods.
For people focused on protein intake, egg whites offer a simple math: about 4 grams of protein per white with almost no calories from fat or carbs. Three egg whites give you 12 grams of protein for just 60 calories. Liquid egg whites from a carton make this even more convenient, since you skip the separating step entirely.