What are the health benefits of eggs?

Eggs are a common food source and have been eaten by humans across the world for thousands of years. 

Eggs are produced by the female animals of many different species, but by far and away the most common choice for consumption is the egg of the chicken.

The USA is regarded as the world's largest exporter of eggs and it is estimated that in 2014, 256 eggs will be produced for each member of the population - the highest rate of production in the past 8 years.

This article provides a nutritional breakdown for eggs, an in-depth look at their possible health benefits, tips on how to incorporate more eggs into your diet and any potential health risks of consuming eggs.

Contents of this article:

• Nutritional breakdown
• Possible health benefits
• Incorporating eggs into your diet
• Potential health risks

Nutritional breakdown

Eggs contain many vitamins and minerals that are essential parts of a healthy and balanced diet. Below is a list of nutrients that can be found in eggs, along with a brief summary of what they are useful for:

• Vitamin A: maintains the skin, immune system and normal vision.
• Vitamin B2 (riboflavin): aids energy metabolism, red blood cells, vision and the nervous system.
• Vitamin B12: aids energy metabolism, red blood cells, the immune system and the nervous system.
• Vitamin B5 (pantothenic acid): aids energy metabolism and mental functioning.
• Vitamin D: keeps bones and teeth healthy and aids absorption of calcium.
• Vitamin E: keeps the reproductive system, nervous system and muscles healthy.
• Biotin: aids energy metabolism, maintains skin, hair and the immune system.
• Choline: aids fat metabolism and liver function.
• Folic Acid: aids blood formation and tissue growth during pregnancy.
• Iodine: aids thyroid gland function, maintains the skin and nervous system.
• Iron: assists red blood production and the transportation of oxygen throughout the body.
• Lutein and zeaxanthin: maintain normal vision and protect from age-related eye disease.
• Phosphorus: maintains bones and teeth and aids energy metabolism.
• Protein: needed for building and maintaining muscle, organs, skin and tissue, and producing antibodies, enzymes and hormones.
• Selenium: protects cells from oxidative damage, maintains the immune system and aids thyroid gland function.

Eggs are considered to be one of the best sources of protein available. One medium-sized egg weighing 44 g typically contains 5.53 g of protein. 

Nutritionists often use eggs as a point of comparison when assessing whether another food is a good source of protein or not. Around 12.6% of the edible portion of an egg is protein.

A medium-sized egg typically contains 5.53 g of protein and only 63 Calories.

Around 9% of an egg's content is fat, found almost exclusively in the egg's yolk.

The majority of fat in an egg is that which is generally regarded to be the most healthy; approximately 38% is monounsaturated and 16% is polyunsaturated, with only 28% being saturated.

Eggs are also a rich supply of long-chain omega-3 fatty acids. These are predominantly in the form of docosahexaenoic acid (DHA) which helps with the maintenance of brain function and normal vision.

These fatty acids are most commonly found in oily fish and so eggs provide an alternative source for people that are unable to eat fish.

Cholesterol

Eggs are also known for containing cholesterol. One medium-sized egg weighing 44 g typically contains 164 mg of cholesterol.

In the past, dietary cholesterol was considered to be something that could increase the risk of conditions such as coronary heart disease. Experts believed that high levels of dietary cholesterol significantly affected the levels of LDL cholesterol (also known as "bad" cholesterol) in the body.

The problem was that dietary cholesterol is, more often than not, found in foods that contain high levels of saturated fats. 

Further research has managed to separate the effects of dietary cholesterol and saturated fat and found that dietary cholesterol increases the levels of both LDL cholesterol and HDL cholesterol (also known as "good" cholesterol).

The changes were also small in comparison with those instigated by saturated fat. Aside from this, the increase made to good cholesterol levels balances out the increasing levels of bad cholesterol. As eggs are low in saturated fats, the effect that they have on blood cholesterol is deemed to be clinically insignificant.

Possible health benefits

As suggested by their wide nutritional content, there are several health benefits that can be derived from eggs:

• Strong muscles: the protein within eggs helps keep muscles working well while slowing the rate at which they are lost.
• A healthy brain: eggs contain vitamins and minerals that are needed for the regular functioning of cells, including the brain, nervous system, memory and the metabolism.
• Good energy production: eggs contain all the daily vitamins and minerals that are needed to produce energy in all the cells of the body.
• A healthy immune system: likewise, vitamin A, vitamin B12 and selenium are all key to keeping the immune system healthy.
• Lower risk of heart disease: having a healthy immune system helps. Choline plays an important part in breaking down the amino acid called homocysteine, which is associated with the development of heart disease.
• Healthy baby development during pregnancy: nutrients within eggs help to prevent birth defects such as spina bifida.
• Healthy eyesight: lutein and zeaxanthin help to prevent macular degeneration, an eye condition which is the leading cause of age-related blindness. Other vitamins also promote healthy vision.
• Weight loss and maintenance: the high quality of protein within eggs has been found by researchers to keep people energized and feeling fuller for longer. Feeling full prevents unhealthy snacking and reduces overall calorie intake.
• A healthy appearance: some vitamins and minerals within eggs help promote healthy skin and work to prevent the breakdown of body tissues. A strong immune system also contributes to a healthy look overall.

Incorporating eggs into your diet

In many parts of the world, eggs are a readily available and inexpensive source of food. They are very easy to add into quick and healthy meals such as sandwiches and salads, but can also be used to make meals of themselves.

Kedgeree is a dish made from eggs, fish, rice, parsley and curry powder.

Eggs are a versatile food that can be prepared in many different ways, such as frying, hard cooking, poaching, scrambling and baking.

Here are a few examples of meals that can be made using eggs. Some of these are naturally healthier than others:

• Omelet
• Huevos rancheros
• Pancakes
• Kedgeree
• Quiche.

Potential health risks

Bacteria

People are advised to avoid eating raw or undercooked eggs. Bacteria can enter the egg through pores in the shells.

Eggs exit the bird's body via the same passageway that feces are excreted from and so there is a risk that bacteria such as Salmonella could enter the egg at this stage. Bacteria can also enter the egg if they are present in the bird's reproductive tract before the shell has formed around the egg's contents.

In the US, all eggs graded by the United States Department of Agriculture (USDA) are washed with a sanitizing rinse during the screening stage at a processing plant.

Pasteurization

In the USA, egg products - eggs removed from their shells for factory processing - distributed for consumption are required by law to undergo a process called pasteurization. During this process, eggs are rapidly heated and kept at a specific temperature for a certain amount of time in order to kill off any Salmonella bacteria.

Pasteurization does not cook the eggs or alter their flavor or nutritional value. Eggs can be pasteurized while still in their shells - indeed, some grocery stores sell them - but it is very difficult to carry this out without specific equipment and not end up cooking the egg. As a result, pasteurizing shell eggs is best left to food processing factories.

Storage and cooking

Eggs should be avoided if their shells are cracked or if they are out-of-date. Most advisory bodies recommend that eggs are stored in the refrigerator. The USDA state that if eggs are left out at room temperature they can sweat, making it easier for bacteria to move into the egg and grow.

Eggs with cracked shells should not be consumed, unless the cracking occurs during the process of cooking.

Washing eggs is not recommended as this can not only lead to water getting into the egg through the pores of the shell but also remove the protective coating that is put on the outside of the shell by the bird that lays it. 

USDA-graded eggs will have been sanitized using materials that do not compromise the shell.

When cooking eggs properly, they must be cooked thoroughly until the yolks are firm. Scrambled eggs, for example, should not be runny.

If an egg floats in water, it will have enough air within it to keep it buoyant. Although this indicates that the egg is old, it does not necessarily mean that the egg cannot be used. 

The best way to check whether the egg is safe to be consumed is to crack open the shell; if the contents smell unpleasant or the coloration is unusual then it may not be safe.

It is also possible to tell whether an egg is raw or hard-cooked by spinning it on a flat surface. If the insides are not cooked then they will cause the egg to wobble, while a hard-cooked egg will spin easily.

It is best not to put all your eggs in one basket; it is the total diet or overall eating pattern that is most important in disease prevention and achieving good health. It is better to eat a varied diet than to concentrate on individual foods as the key to good health.

References:

1. International Egg Commission (IEC) The World Egg Industry - a few facts and figures, accessed 3 October 2014.
2. American Egg Board (AEB) About The U.S. Egg Industry, accessed 3 October 2014.
3. IEC Nutrition, accessed 6 October 2014.
4. Egginfo Vitamins and minerals in an egg, accessed 6 October 2014.
5. Egginfo Nutritional value of eggs, accessed 6 October 2014.
6. USDA National Nutrient Database for Standard Reference, accessed 7 October 2014.
7. Egginfo Cholesterol in eggs, accessed 6 October 2014.
8. Egginfo Eggs and dietary cholesterol - dispelling the myth, accessed 6 October 2014.
9. American Heart Association Good vs. Bad Cholesterol, accessed 6 October 2014.
10. IEC Eggs Can, accessed 6 October 2014.
11. USDA Shell Eggs from Farm to Table, accessed 7 October 2014.
12. IEC Fascinating Facts, accessed 7 October 2014.