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Nutritional value of eggs

Energy value of eggs

An average medium egg has an energy value of 66 kilocalories (277 kilojoules) and the consumption of one egg daily would contribute only around 3% of the average energy requirement of an adult.

With their significant protein, vitamin and mineral content and relatively low saturated fat content, eggs have a low energy density and are a valuable component in a healthy diet. Read more about eggs and energy density.

Protein

Eggs are an important source of high quality protein. On the evaluation scale most commonly used for assessing protein, egg protein is at the highest point, 100, and is used as the reference standard against which all other foods are assessed. This is because of the essential amino acid profile and the high digestibility of egg protein. When assessed against a range of different measures of protein quality (protein digestibility corrected amino acid score; biological value; net protein utilisation; protein efficiency ratio; protein digestibilty) eggs rank consistently high, even against other high quality sources of protein such as beef and cows’ milk [1].

12.6% of the weight of the edible portion of the egg is protein and it is found in both the yolk and the albumen. Although protein is more concentrated around the yolk, there is in fact more protein in the albumen.

As people age, the loss in muscle mass and strength (sarcopenia), increases in parallel to the rise in body fat. It had been argued that these changes in body composition are related to a decline in physical activity [2], but this view has been challenged by research suggesting that poor protein intake and changes in the body’s ability to utilize amino acids with age may also contribute to sarcopenia [3, 4]. Therefore it is possible that an adequate intake of high quality protein from sources such as eggs could help to prevent the degeneration of skeletal muscle in older people.

Egg protein is a rich source of the essential amino acid leucine, which is important in modulating the use of glucose by skeletal muscle and in facilitating muscle recovery after exercise. It has therefore been postulated that this would be advantageous to people undergoing endurance training [1].

In comparison with other high protein foods, eggs are a relatively inexpensive source of protein [5].

Vitamins

Eggs contain most of the recognised vitamins with the exception of vitamin C. The egg is a source of all the B vitamins. It is a particularly rich source of vitamins B12 and riboflavin (vitamin B2) and a useful source of folate. The egg is also a good source of the fat-soluble vitamins A and D and provides some vitamin E. Find out more about vitamins in an egg.

Minerals

Eggs contain many of the minerals that the human body requires for health. In particular eggs are an excellent source of iodine, required to make the thyroid hormone, and selenium, an important antioxidant. The egg is a significant source of phosphorus, required for bone health, and provides some zinc, important for wound healing, growth and fighting infection. Eggs also contain iron, the vital ingredient of red blood cells, although the availability of this iron to the body is still being investigated. Find out more about minerals in an egg.

Fat

9.0% of the egg content is fat. The fat of an egg is found almost entirely in the yolk; there is less than 0.5% in the albumen.

Most of an egg’s total fatty acid composition is monounsaturated (approximately 38%). About a further 16% is polyunsaturated and only 28% is saturated. 

Eggs are also rich in long chain omega-3 fatty acids, mainly in the form of DHA (docosahexaenoic acid). They therefore provide a useful alternative source of these important essential fatty acids, especially for people who do not consume oily fish. DHA contributes to normal brain function and normal vision. These beneficial effects are obtained with a daily intake of 250mg of DHA and of another fatty acid (EPA) from various dietary sources. An average medium egg provides about 70mg of omega-3 fatty acids.

An average medium size egg contains 177mg cholesterol, about 12% less than eggs contained twenty years ago.

Cholesterol

Eggs also contain cholesterol and lecithin, which are fat-like substances that are essential to the structure and function of all cells in the body. However these substances are not dietary essentials, as our bodies are able to synthesise them. Cholesterol helps to maintain the flexibility and permeability of cell membranes and is also a raw material for the fatty lubricants that help to keep the skin supple. Cholesterol is essential for the production of sex hormones, cortisol, vitamin D and bile salts. Find out more about cholesterol in eggs.

References

  1. Layman KL, Rodriguez NR. Egg protein as a source of power, strength and energy, Nutrition Today, 44, 1, 2009

  2. Joint WHO/FAO/UNU Expert Consultation Protein and amino acid requirements in Human Nutrition,WHO Technical Report Series 935, Geneva, 2002

  3. Wolfe RR. The underappreciated role of muscle in health and disease, American Journal of Clinical Nutrition 84,475-82 2006

  4. Thalacker-Mercer A E, Fleet J C, Craig B A, Carnell N S, Campbell W W. Inadequate protein intake affects skeletal muscle transcript profiles in older humans, American Journal of Clinical Nutrition, 85, 1344-1352, 2007

  5. Ruxton C. New evidence and recommendations for the use of eggs in the diet, Nursing Standard, 19 May 2010.

 

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