06-05-2014, 02:20 PM
EGGS
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INTRODUCTION
Eggs are laid by females of many different species, including birds, reptiles, amphibians, and fish, and have been eaten by mankind for thousands of years.[1] Bird and reptile eggs consist of a protective eggshell, albumen (egg white), and vitellus (egg yolk), contained within various thin membranes. Popular choices for egg consumption are chicken, duck, quail, roe, and caviar, but the egg most often consumed by humans is the chicken egg, by a wide margin.
Egg yolks and whole eggs store significant amounts of protein and choline,[2][3] and are widely used in cookery. Due to their protein content, the United States Department of Agriculture (USDA) categorizes eggs as Meats within the Food Guide Pyramid.[2] Despite the nutritional value of eggs, there are some potential health issues arising from egg quality, storage, and individual allergies.
Chickens and other egg-laying creatures are widely kept throughout the world, and mass production of chicken eggs is a global industry. In 2009, an estimated 62.1 million metric tons of eggs were produced worldwide from a total laying flock of approximately 6.4 billion hens.[4] There are issues of regional variation in demand and expectation, as well as current debates concerning methods of mass production, with the European Union's ban on battery farming of chickens.
Cooking substitutes
For those who do not consume eggs, alternatives used in baking include other rising agents or binding materials, such as ground flax seeds or potato starch flour. Tofu can also act as a partial binding agent, since it is high in lecithin due to its soy content. Applesauce can be used, as well as arrowroot and banana. Extracted soybean lecithin, in turn, is often used in packaged foods as an inexpensive substitute for egg-derived lecithin.
Cholesterol and fat
More than half the calories found in eggs come from the fat in the yolk; a large (50 gram) chicken egg contains approximately 5 grams of fat. People on a low-cholesterol diet may need to reduce egg consumption; however, only 27% of the fat in egg is saturated fat (palmitic, stearic and myristic acids[36]) that contains LDL cholesterol. The egg white consists primarily of water (87%) and protein (13%) and contains no cholesterol and little, if any, fat.
Type 2 diabetes
Studies have shown conflicting results about a possible connection between egg consumption and type two diabetes. A 1999 prospective study of over 117,000 people by the Harvard School of Public Health concluded, in part, that "The apparent increased risk of CHD associated with higher egg consumption among diabetic participants warrants further research."[44] A 2008 study by the Physicians' Health Study I (1982–2007) and the Women's Health Study (1992–2007) determined the “data suggest that high levels of egg consumption (daily) are associated with an increased risk of type 2 diabetes.”[45] However, a study published in 2010 found no link between egg consumption and type 2 diabetes.[46]
Heart disease
Eggs are one of the largest sources of phosphatidylcholine (lecithin) in the human diet.[47] A study published in the scientific journal Nature showed that dietary phosphatidylcholine is digested by bacteria in the gut and eventually converted into the compound TMAO, a compound linked with increased heart disease.[48][49] The 1999 Harvard School of Public Health study of 37,851 men and 80,082 women concluded that its "findings suggest that consumption of up to 1 egg per day is unlikely to have substantial overall impact on the risk of CHD or stroke among healthy men and women."[44] However, in a study of 4,000 people published in the New England Journal of Medicine, scientists found that eating eggs lead to significantly increased levels of TMAO in the blood of study participants and that this in turn led to significantly higher risk of heart attack and stroke after three years of follow-up.