Chopped boiled eggs are favorite of chickens from chicks to adult.
Boiled egg whites are favorite of persons with high protein diet.
– Gameness til the End
Common misconceptions keep many people, especially those worried about heart disease, from eating eggs. The July issue of the Harvard Heart Letter unscrambles the dietary facts and myths about the egg.
Fact: Eggs are a good source of nutrients. One egg contains 6 grams of protein and some healthful unsaturated fats. Eggs are also a good source of choline, which has been linked with preserving memory, and lutein and zeaxanthin, which may protect against vision loss.
Fact: Eggs have a lot of cholesterol. The average large egg contains 212 milligrams of cholesterol. As foods go, that’s quite a bit, rivaled only by single servings of liver, shrimp, and duck meat.
Myth: All that cholesterol goes straight to your bloodstream and then into your arteries. Not so. For most people, only a small amount of the cholesterol in food passes into the blood. Saturated and trans fats have much bigger effects on blood cholesterol levels.
Myth: Eating eggs is bad for your heart. The only large study to look at the impact of egg consumption on heart disease—not on cholesterol levels or other intermediaries—found no connection between the two. In people with diabetes, though, egg-a-day eaters were a bit more likely to have developed heart disease than those who rarely ate eggs.
If you like eggs, eating one a day should be okay, especially if you cut back on saturated and trans fats. Other ways to enjoy eggs without worrying about cholesterol include not eating the yolk, which contains all the cholesterol, or using pourable egg whites or yolk-free egg substitutes.
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. 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, 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. 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. 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.
|Nutritional value per 100 g (3.5 oz)|
|Energy||647 kJ (155 kcal)|
|– Tryptophan||0.153 g|
|– Threonine||0.604 g|
|– Isoleucine||0.686 g|
|– Leucine||1.075 g|
|– Lysine||0.904 g|
|– Methionine||0.392 g|
|– Cystine||0.292 g|
|– Phenylalanine||0.668 g|
|– Tyrosine||0.513 g|
|– Valine||0.767 g|
|– Arginine||0.755 g|
|– Histidine||0.298 g|
|– Alanine||0.700 g|
|– Aspartic acid||1.264 g|
|– Glutamic acid||1.644 g|
|– Glycine||0.423 g|
|– Proline||0.501 g|
|– Serine||0.936 g|
|Vitamin A equiv.||149 μg (19%)|
|Thiamine (vit. B1)||0.066 mg (6%)|
|Riboflavin (vit. B2)||0.5 mg (42%)|
|Pantothenic acid (B5)||1.4 mg (28%)|
|Folate (vit. B9)||44 μg (11%)|
|Vitamin B12||1.11 μg (46%)|
|Choline||294 mg (60%)|
|Vitamin D||87 IU (15%)|
|Vitamin E||1.03 mg (7%)|
|Calcium||50 mg (5%)|
|Iron||1.2 mg (9%)|
|Magnesium||10 mg (3%)|
|Phosphorus||172 mg (25%)|
|Potassium||126 mg (3%)|
|Zinc||1.0 mg (11%)|
|For edible portion only.
Refuse: 12% (shell).
One large egg is 50 grams.
Percentages are roughly approximated
using US recommendations for adults.
Source: USDA Nutrient Database
Eggs add protein to a person’s diet, as well as various other nutrients.
Chicken eggs are the most commonly eaten eggs. They supply all essential amino acids for humans (a source of ‘complete protein’), and provide several vitamins and minerals, including retinol (vitamin A), riboflavin (vitamin B2), folic acid (vitamin B9), vitamin B6, vitamin B12, choline, iron, calcium, phosphorus and potassium. Although not as abundant as red meats, eggs are a source of CoQ10 depending on how they are prepared.
All of the egg’s vitamins A, D, and E are in the egg yolk. The egg is one of the few foods to naturally contain vitamin D. A large egg yolk contains approximately 60 Calories (250 kilojoules); the egg white contains about 15 Calories (60 kilojoules). A large yolk contains more than two-thirds of the recommended daily intake of 300 mg of cholesterol (although one study indicates the human body may 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, slightly less than half of the protein, and most of the other nutrients. It also contains all of the choline, and one yolk contains approximately half of the recommended daily intake. Choline is an important nutrient for development of the brain, and is said to be important for pregnant and nursing women to ensure healthy fetal brain development.
The diet of the laying hens can greatly affect the nutritional quality of the eggs. For instance, chicken eggs that are especially high in omega 3 fatty acids are produced by feeding laying hens a diet containing polyunsaturated fats and kelp meal. Pasture-raised free-range hens which forage largely for their own food also tend to produce eggs with higher nutritional quality in having less cholesterol and fats while being several times higher in vitamins and omega 3 fatty acids than standard factory eggs. Focusing on the protein and crude fat content, a 2010 USDA study determined there were no significant differences of these two macronutrients in consumer chicken eggs.
Cooked eggs are easier to digest, as well as having a lower risk of salmonellosis.
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) that contains LDL cholesterol. The egg white consists primarily of water (87%) and protein (13%) and contains no cholesterol and little, if any, fat.
There is debate over whether egg yolk presents a health risk. Some research suggests dietary cholesterol increases the ratio of total to HDL cholesterol and, therefore, adversely affects the body’s cholesterol profile; whereas other studies show that moderate consumption of eggs, up to one a day, does not appear to increase heart disease risk in healthy individuals. Harold McGee argues that the cholesterol in the yolk is not what causes a problem, because fat (in particular, saturated) is much more likely to raise cholesterol levels than the actual consumption of cholesterol. In a randomized trial, Sacks et al. found that adding one egg per day to the usual diet of 17 lactovegetarians whose habitual cholesterol intake was very low (97 mg/day) significantly increased LDL cholesterol level by 12%.
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.” 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.” However, a study published in 2010 found no link between egg consumption and type 2 diabetes.
Eggs are one of the largest sources of phosphatidylcholine (lecithin) in the human diet. 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.
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.” 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.
A 2007 study of nearly 10,000 adults demonstrated no correlation between moderate (six per week) egg consumption and cardiovascular disease or strokes, except in the subpopulation of diabetic patients who presented an increased risk of coronary heart disease. One potential alternative explanation for the null finding is that background dietary cholesterol may be so high in the usual Western diet that adding somewhat more has little further effect on blood cholesterol. Other research supports the idea that a high egg intake increases cardiovascular risk in diabetic patients. A 2009 prospective cohort study of over 21,000 individuals suggests that “egg consumption up to 6/week has no major effect on the risk of CVD and mortality and that consumption of 7+/week is associated with a modest increased risk of total mortality” in males, whereas among males with diabetes, “any egg consumption is associated with an increased risk of all-cause mortality and there was suggestive evidence for an increased risk of MI and stroke”. A meta-analysis published in the British Medical Journal in 2013 found no association between egg consumption and heart disease or stroke.
A health issue associated with eggs is contamination by pathogenic bacteria, such as Salmonella enteritidis. Contamination of eggs exiting a female bird via the cloaca may also occur with other members of the Salmonella genus, so care must be taken to prevent the egg shell from becoming contaminated with fecal matter. In commercial practice in the US, eggs are quickly washed with a sanitizing solution within minutes of being laid. The risk of infection from raw or undercooked eggs is dependent in part upon the sanitary conditions under which the hens are kept.
Health experts advise people to refrigerate washed eggs, use them within two weeks, cook them thoroughly, and never consume raw eggs. As with meat, containers and surfaces that have been used to process raw eggs should not come in contact with ready-to-eat food.
A study by the U.S. Department of Agriculture in 2002 (Risk Analysis April 2002 22(2):203-18) suggests the problem is not as prevalent as once thought. It showed that of the 69 billion eggs produced annually, only 2.3 million are contaminated with Salmonella—equivalent to just one in every 30,000 eggs—thus showing Salmonella infection is quite rarely induced by eggs. However, this has not been the case in other countries, where Salmonella enteritidis and Salmonella typhimurium infections due to egg consumptions are major concerns. Egg shells act as hermetic seals that guard against bacteria entering, but this seal can be broken through improper handling or if laid by unhealthy chickens. Most forms of contamination enter through such weaknesses in the shell. In the UK, the British Egg Industry Council award the lions stamp to eggs that, among other things, come from hens that have been vaccinated against Salmonella.
One of the most common food allergies in infants is eggs. Infants usually have the opportunity to grow out of this allergy during childhood, if exposure is minimized. Allergic reactions against egg white are more common than reactions against egg yolks.
Food labeling practices in most developed countries now include eggs, egg products and the processing of foods on equipment that also process foods containing eggs in a special allergen alert section of the ingredients on the labels.