Egg whites are about 90% water and 10% protein. The white of one large egg has only 17 calories.
The egg white, or albumen, is nutritionally distinct from the yolk in almost every respect. Where the yolk is dense with fat, cholesterol, and fat-soluble vitamins, the white is a lean, nearly pure protein matrix suspended in water. A large egg white contains approximately 17 calories, 3.6 grams of protein, less than 0.1 grams of fat, negligible carbohydrates, and roughly 55 milligrams of sodium. It is about 90% water by weight. This composition makes egg whites one of the most calorie-efficient protein sources in the standard diet, which explains their prominence in high-protein, calorie-restricted eating plans.
## The Protein Composition of Egg White
Egg white is not a simple protein solution. It contains at least 40 distinct proteins, each with different functional and nutritional properties. The most abundant is ovalbumin, which constitutes about 54% of total white protein. Ovalbumin is a phosphoglycoprotein that is partially denatured during storage and more completely denatured by heat, which is why cooking changes the texture of egg whites from translucent and viscous to opaque and firm.
Ovotransferrin (formerly called conalbumin) makes up about 12% of egg white protein and has antimicrobial properties due to its iron-binding capacity. Ovomucoid (11%) is a trypsin inhibitor, meaning it can reduce the digestibility of the egg white protein when raw. Lysozyme (3.5%) is an enzyme that disrupts bacterial cell walls and has been used as a natural preservative. These functional proteins contribute to the egg's defense against microbial contamination during incubation and have applications in food science and biotechnology beyond their nutritional role.
## Why Cooking Matters for Egg White Protein Absorption
The protein inhibitors in raw egg white are a meaningful nutritional factor. Ovomucoid inhibits trypsin, a protease secreted by the pancreas that is essential for digesting proteins in the small intestine. When egg whites are consumed raw, ovomucoid's trypsin-inhibitory activity is intact, and protein digestion is partially impaired. Heat denaturation inactivates ovomucoid and the other antinutritional proteins, restoring full digestibility.
Research by Evenepoel et al., published in the *American Journal of Clinical Nutrition* in 1998, quantified this effect using isotopically labeled egg protein. They found that the digestibility of cooked egg protein was 91%, compared to 51% for raw egg protein. This is not a small difference. Consuming raw egg whites as a protein strategy, as has been done in athletic subcultures, is substantially less effective than consuming cooked whites.
The folk image of the athlete cracking raw eggs into a glass for protein gain is, nutritionally speaking, counterproductive. The cooked version delivers nearly double the bioavailable protein per gram consumed.
## Egg White as a Functional Food Ingredient
Beyond direct consumption, egg white proteins have distinct functional properties that make them valuable in food manufacturing and culinary applications. Ovalbumin and other globular proteins form foams when whipped: the mechanical agitation partially denatures the proteins, which then aggregate at air-water interfaces to stabilize bubbles. This foaming capacity is the basis for meringues, soufflés, and angel food cake. Ovomucin, a glycoprotein complex, contributes to the viscosity of fresh egg white and helps maintain foam stability.
The water-binding capacity of egg white proteins is used in meat processing to improve yield and texture. Lysozyme extracted from egg white is used as a preservative in some cheeses and wines.
For people managing caloric intake while maintaining protein targets, egg whites are among the most efficient options available. At approximately 4.7 calories per gram of protein, they compare favorably to skinless chicken breast (approximately 4.5 calories per gram) and beat most other commonly consumed protein foods. The sodium content of about 55 mg per white is moderate and generally not a concern in the context of a varied diet.
The practical takeaway: egg whites are an efficient, low-calorie protein source, but their protein is most bioavailable when cooked. Raw egg white consumption reduces protein utilization by roughly 40% compared to cooked egg white.