Eggs of birds are a common food source. The most commonly used bird eggs are those from the hen, duck and goose. Most commercially produced chicken eggs intended for human consumption are unfertilized, since the laying hens are kept without any roosters. Fertile eggs can be purchased and eaten as well, with little nutritional difference. They will not contain a developed embryo, as refrigeration prohibits cellular growth.

Chicken eggs are widely used in many types of cooking. Dishes that use eggs range from both sweet to savory dishes. Eggs may be boiled or fried or eaten raw, though the latter is not recommended. Eating raw eggs can be hazardous, with the most obvious problem being the risk of salmonella. In addition, the protein in raw eggs are only 51% bio-available, whereas a cooked egg is nearer 91% bio-available, meaning the protein of cooked eggs is nearly twice as absorbable as the protein from raw eggs.

Egg yolks are used to make dishes high in fat. Egg yolks are important as binding agents in many preparations in cooking due to the emulsifying action of lecithin. This property is crucial for sauces, custards and meat dishes. The albumen or egg white contains protein but little or no fat. It is used in cooking separately from the yolk, and can be aerated or whipped to a light, fluffy consistency known as soft peaks and stiff peaks. Beaten egg whites are used in desserts.

Eggs provide a significant amount of protein and various nutrients to our diet. Chicken eggs are the most commonly eaten eggs, and are highly nutritious. They supply a large amount of complete, high-quality protein which contains all essential amino acids, and provide significant amounts of several vitamins and minerals, such as iron, calcium, phosphorous and potassium. They are also one of the least expensive single-food sources of complete protein. One large chicken egg contains approximately 7 grams of protein.

Egg is one of the few foods which naturally contain Vitamin D. A large yolk contains more than100 mg of cholesterol but the human body does not absorb much cholesterol from eggs). The yolk makes up about 33% of the liquid weight of the egg. It contains all of the fat in the egg and slightly less than half of the protein and much of the nutrients. It also contains all of the chlorine, which is an important nutrient for development of the brain, and is important for pregnant and nursing women to ensure healthy fetal brain development.

Recently, chicken eggs that are especially high in Omega 3 fatty acids have come on the market. These eggs are made by feeding laying hens a diet containing polyunsaturated fats. Eggs may have different nutritional content depending on the feed and living conditions of the chickens who lay them. About 60% of the calories in an egg come from fat; Chicken egg yolks contain about 10 grams of fat. People on a low-cholesterol diet may need to cut down on egg consumption, although most of the fat in egg is unsaturated fat and may not be harmful. The egg white consists primarily of water (87%) and protein (13%) and contains no cholesterol and little fat.

Some people try to avoid eggs in their diet because they are high in cholesterol, which is concentrated in the yolk. This issue is sometimes addressed by eating only some or none of the yolk. People sometimes remove the yolk themselves, or may use prepared egg substitutes such as Egg Beaters. There is debate over whether egg yolk presents a health risk. Some research suggests it may lower total LDL/ bad cholesterol, while raising HDL/good cholesterol. Some advocate the eating of raw eggs and egg yolks for this reason, as cholesterol in the yolk is healthier when uncooked.

Most health experts advise people to cook their eggs thoroughly before eating them, as heat is necessary to kill any infectious micro organisms that may be present. Raw and undercooked eggs have been associated with salmonella infection. The risk of infection from raw or undercooked eggs is dependent partly on the sanitary conditions under which the hens are grown and kept. Some smaller egg producers make it a point to keep the hens in cleaner conditions, and observe few or no cases of salmonella.