|See Also||Clinical Nutrition|
An egg consists of a protective outer shell made of calcite, layers of the water soluble proteins albumin, mucoproteins and globulins (egg white), vitellus (egg yolk) and structural fibers called chalazae that anchor each end of the yolk in the egg white. Each of these structures lies within a number of thin membranes.
The development of an egg begins as a yolk inside a hen. A yolk (which is an oocyte at this point) is produced by the hen's ovary during ovulation, however, it is important to note that eggs sold for human consumption have not been fertilized. Blood spots are occasionally found on an egg yolk and do not indicate a fertilized egg. They are caused by a rupture of a blood vessel on the yolk surface during the formation of the egg and are safe to eat.
There are a number of different types of eggs commonly consumed by humans including: duck, quail, turkey, goose and chicken, with the latter being the most popular.
As a result of changing dietary habits, annual total chicken egg consumption in Canada dropped from 23 dozen per person per year in 1960 to 14.4 dozen in 1995. Since 1995, egg consumption has increased slightly, and in 2009 16.1 dozen eggs were consumed per person..
|See Also||Egg Alternatives|
- Eggs are one of the few food sources that are considered to be a complete protein because they provide all nine essential amino acids and are easily absorbed by the body. It is estimated that one large egg contains approximately 6 grams of protein, a macromolecule which is essential for building and repairing muscles, organs, skin, hair and other body tissues, and producing hormones, enzymes and antibodies.
- In addition to high-quality protein, eggs also contain valuable vitamins and minerals, such as choline, folate, riboflavin, biotin, vitamin B12, zinc, vitamins A, D, E, iron and phosphorus.
- The yolk contains the majority of the nutrients, including biotin, omega 3 and omega 6 fatty acids, and antioxidants such as lutein and zeaxanthin which are important for eye health. Egg yolks also contain the richest known source of choline which is an essential nutrient needed for the normal functioning of all cells. Choline is especially important for proper liver, brain and nerve function, and transporting nutrients throughout the body, and is necessary to emulsify the cholesterol in the egg and keep it moving within the bloodstream once consumed. Two eggs provide about 250 milligrams of choline or roughly half the recommended daily intake for men and women (550 mg and 425 mg respectively). One egg contains twice the choline found in a three-ounce (85 gram) beef steak.
- In addition to the vitamins and nutrients, one chicken yolk also contains approximately 201 grams of cholesterol, 65 grams of sodium, 5 grams of fat (1.6 of which are saturated), 1 gram of carbohydrates and 75 calories.
- In contrast, egg whites consist primarily of 90% water and 10% proteins such as albumin, mucoproteins and globulins. Egg whites contain close to zero fat or cholesterol, less than 1% carbohydrate content and are a good source of vitamin B12 and riboflavin.
- There is no nutritional difference between brown eggs and white eggs.
- Following is a list of the most common types of eggs and their respective quantity of cholesterol and saturated fat. Amounts reflect the content found in one egg:
- Chicken egg (55 gm egg): 201mg cholesterol, 1.6 gm saturated fat
- Duck egg (70 gm egg): 621mg cholesterol, 2.6 gm saturated fat
- Quail egg (9 gm egg): 76mg cholesterol, 0.3 gm saturated fat
- Turkey egg (80 gm egg): 747mg cholesterol, 2.9 gm saturated fat
- Goose egg (145 gm egg): 1226mg cholesterol, 5.3 gm saturated fat
- When determining whether to include eggs in your diet it is advisable to consider the recommended daily limits on cholesterol derived from food sources.
- Eggs are one of the most common food related allergens. In fact, the allergenic potential of eggs is among the highest of any food source due to their protein content.
- An egg allergy usually occurs during the first year of life when eggs are first introduced to a baby's diet. Children typically outgrow the allergy around five to seven years of age, however the same does not hold true for adults who usually have the egg allergy for life.
- People suffering from severe egg allergies should note that eggs are sometimes present in the bodies of slaughtered mature female chickens, and despite manufacturing processes some traces of egg can remain. It is best to review labels of poultry products to determine if trace amounts of egg exists prior to consumption.
- Nutrient Deficiencies
- Consumption of large quantities of raw eggs (15 or more a day) is not advised as egg whites contain Avidin, a protein which in its raw state prevents the absorption of Biotin (vitamin B7). Biotin is necessary for cell growth and the production of fatty acids, is a coeznyme in the synthesis of fats and amino acids, plays a role in gluconeogenesis, and also helps to strengthen hair and nails.
- There has been an increase in eggs containing the Salmonella Eneritidis bacterium over the past several years according to the Centers for Disease Control. Symptoms of infection in humans include: vomiting, fever, diarrhea, and abdominal cramps.
- To mitigate the risk of infection it is important to wash and thoroughly cook eggs prior to eating, refrigerate them at all times and avoid consuming eggs that are dirty or cracked.
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- Agriculture and Agri-Food Canada, Canada’s Egg Industry, 
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