Mariusz Rajczakowski
Nutritionist
8 min read | 2 years ago

9 things you didn't know about eggs

Bird eggs are very common food’s used in cooking. The most popular ones, are those from the chicken. Other ones like goose or quail are eaten less often [1].

Chicken eggs are widely used in many different dishes, both sweet and savory, including baked products.

The preparation techiques include: scrabled, fried, soft-boiled, hard-boiled, omelettes, poached and pickled eggs.

hardboiled

Eggs are amazing food, but how much do you know about them? Let's get to know some more (bear in mind: whenever we use word „eggs” within this article we mean chicken eggs as the most popular around the world).

1.Eggs contain almost every nutrient

Eggs contains almost all required essential nutrients for human beings, with exceptionof a few (such as vitamin C, carbohydrates [arguably essential], dietary fibre).

The prominent egg specialist – prof. Tadeusz Trziszka said: „There is no other raw food found in nature, which would be equally valuable.

Fertilized chicken egg, when heated to 40°C for 21 days transforms into chick, which has brain, nervous system, blood, bones, immune system and everything that dermine life.

All the essential biological components the allow the creation of life only by adding an extra thermal energy” (translated from the original) [3].

Eggs can be the part of a vegetarian diet, and people who don't eat meat but eat eggs are called ovo-vegetarians (or lacto-ovo-vegetarians, when they also eat dairy).

Various vegetarian diet are enchanced with eggs, it can easily provide all essential nutrients and can be used by children and adults to cover dietary requirements [4].

2.Eggs will help you reduce weight

Chicken eggs are extremely nutritional-dense food, which is also low in calories (100g provides only 155 kcal).

Ratlif et al have undertaken a study which showed that consuming eggs for breakfast can significantly reduce appetite and reduce energy intake throughtout day in comparison to a carb-like breakfast (bagel).

This finding suggested that consumption of eggs breakfast results in less variation of plasma glucose and insulin (better satiety), and suppressed ghrelin (hunger hormone) response, and reduced energy intake [5].

Another study showed eggs, when combined with low-calorie diet enhances weight loss, but not induce weight loss in a free-living condition.

According to the researchers, eggs inclusion in weight management program may offer a nutritious supplement to engance weight loss [6].

eggs

3. Gold-standard proteins

Eggs (in this case: a hard-boiled one) contains 12.6g complete proteins per 100g serving.

Complete proteins means, that it provides all essentail amino acids that our body needs to maintain the nitrogen balance, build and sustain muscle and other tissue turnover.

In fact, the BV (biological value) and protein efficiency ration of proteins is so high that scientists use eggs as the standard for evaluating the protein quality of other foods. The biological value of certain protein sources has been presented in a table 1 [7].

The eggs position in quality rankings, can explain why eggs are essential part of sports nutrition as the extensive physical exercises increase requirements for proteins and higher proteins intake helps with muscle recovery.

Table 1. Protein quality rankings

Protein Type Protein Efficiency Type Biological Value Net Protein Utilisation Protein Digestibility Amino Acid Score
Beef 2.9 80 73 0.92
Black beans 0   0 0.75
Casein 2.5 77 76 1.0
Egg 3.9 100 94 1.0
Milk 2.5 91 82 1.0
Peanuts 1.8     0.52
Soy protein 2.2 74 61 1.0
Wheat gluten 0.8 64 67 0.25
Whey protein 3.2 104 92 1.0

Adapted from: U.S. Dairy Council, Reference Manual for U.S Whey Products 2nd Edition, 1999 and Sawar, 1997

4. Cholesterol myth?

yolk

Eggs receive a lot of bad press because of the cholesterol present in yolks. However, the data coming from studies of healthy people, who consumed 1-6 eggs a day, usually did not change blood lipids [12].

The findings from meta-analysis (2013) say that higher consumption of eggs (up to one egg per day) is not associated with increased risk of coronary heart disease or stroke [10].

Dietary recommendation aimed at restricting egg consumption should not be generalized to all individuals.

It is advised to acknowledge that diverse healthy populations, experience no risk in developing coronary heart disease by increasing intake of cholesterol, but in contrast they may have multiple beneficial effects from the inclusion of the eggs in their regular diet [11].

When it comes to the studies, targeting unhealthy populations, people with higher LDL (colloquially „bad cholesterol”) or diabetic patients should restrict they eggs consumptions as they increase the serum LDL levels [8,9].

5. Why you should avoid raw eggs?

The study on digestibility of cooked and raw egg protein in humans has shown that raw eggs is bioavailable in 51% in comparison to cooked eggs 91%. Study has shown that after ingestion of 25g of raw egg protein, almost 50% is malabsorbed over 24h [11].

The higher digestibility of cooked egg protein presumably results from structural changes in protein molecule induced by heating, therefore digestive enzymes have better access to peptide bonds.

It has also been suggested that impaired protein digestion from the raw eggs might be partially caused by trypsin (proteinase – enzyme which digests proteins in human body) inhibitors which may decrease their activity once egg is cooked [11].

Second reason against raw eggs is still the risk of salmonellosis, especially in the elderly, the infirm, or pregnant women [1].

The results from meta-analysis performed by Dominiques et al suggested that factors such travel, predisposing factors, eating raw eggs and eating in restaurants are the most important risk for salmonellosis (Salmonella infection) [14].

The third reason is avidin present in raw egg whites. This compound binds the biotin (vitamin B7) and make it unavailable.

When cooked, avidin is partially reduced, but still 30-40% activity of avidin in fried or boiled egg can create concerns, especially when you eat a lot of eggs.

However having the whole eggs (as yolk contains a lot biotine) and not eating raw eggs can mitigate the problem [1,15].

6. Do not waste the yolks!

More that half the calories found in eggs come from the fat in the yolk. 50g of chicken eggs contains approximately 5g of fat. Is this something that should worry you?

If your on low-cholesterol diet, you might reduce eggs consumption, however if your afraid about gaining extra pounds of body fat, you might be suprised with the nutritional information about the yolk.

Yolk actually provides 43% all proteins of the whole egg, contains the fat soluble vitamins (A, D, E, K), has a good fat profile (where only 27% of the fat in egg comes from saturated fatty acids), phospholipids (lecithin, kefalin), carotenoids (beta-carotene, lutein and zeaxanthin), plenty of B vitamins and minerals [1].

Generally egg whites contains not much more than just proteins, but the heart of the egg is yolk. Takeaway note: do not skip yolks!

7. Free-range vs cage eggs

Cconsumers perceive that the nutritional quality of eggs produced as free range is superior to that of eggs produced in cages.

There is no doubt the hens living conditions are different and the quality of life is better, however when we separate the emotional part and analyze the raw data, there is not much difference in terms of nutritional value.

Anderson's study failed to show nutritional advantage of eggs produced by range chickens over eggs produced by chickens mainained in cages [16].

Another study, which measured the quality characteristics of eggs demonstrated the same results (free-range eggs are not better than cage one) [17].

Takeaway notes: if you can afford it - buy free-range/organic eggs, the animals environmental conditions are better in the above breeds, but regardless which one you buy (even the cage one), you won't be dissapointed with the most nutritional food in the world

8. To worry or not to worry - a few words about salmonella

A health problem associated with eggs is contamination by pathogenic bacteria, such as Salonella enteridis.

Contamination of eggs existing in a female bird via the cloaca may also occur with other members of Salmonella genus [1].

As mentioned above some people are more susceptible to the infection (elderly, pregnant women), so extra caution should be required.

Extra procedures such as egg refigeration, using them within expiry date, and never consuming raw eggs can minimize the risk dramatically.

In United Stanes the prevalence of the problem is not that high as thought (only 1 in every 30,000 eggs is contaminated with salmonella), but data from other countries, suggest that Salmonella infections are mainly because of egg consumption [1].

Normally egg shells act as hermetic seals that guard agains bacteria entering, but this seal can be broken though improper handling or if laid by unhealthy chickens.

Most forms of contamination enter through weaknesses of the shell.

Salmonella can be killed at 71°C, but when held of sufficient time in 57°C for and hour and 15 minutes becomes harmless [18]. Conclusions? Do not eat raw eggs, as an extra precaution!

egg_heart

9. Future of the eggs

The future of the eggs is promising, as not all health properties of eggs are yet known.

The lastest studies suggest that egg can be source of many nutrients which possibly can help in prevention and treatment of diseases.

The researches from the University of Environmental and Life Sciences and Medical University in Wroclaw recently discovered and examined the properties of immunoglobulin Y („Yolkin”) and cystatine found in eggs [19].

The experimental research on mice has shown that polypeptide Y complex (Yolkin), isolated from chicken egg yolk has strong procognitive capabilities, improve spatial and episodic memory, due to the neuroprotective and immunomodulatory properties and may in the future help with finding the treatment for a dementia and Alzheimer disesase [19,20].

Another powerful egg derived compound – cystatine has shown at the in-vitro studies to have anti-tumor properties, hence may in future become a component of new generation drugs in the so-called inhibitor theraphy [21].

References
  1. https://en.wikipedia.org/wiki/Egg_as_food as seen on 17.07.2016
  2. Zdrojewicz Z., Herman M., Starostecka E., Hen's egg as a source of valuable biologically active substances. Postepy Hig Med Dosw 2016 Jul 6, 70(0): 751-9
  3. http://www.naturaity.pl/artykul/446,jaja-na-zdrowie.html#ad-image-0 as seen on 17.07.2016
  4. M Amit, Vegetarian diets in children and adolescents. Paediatr Child Health 2010 May-jun; 15(5):303-308
  5. Ratliff, J., Leite, J.O., de Ogburn, R., Puglisi, M.J., VanHeest, J., Fernandez, M.L. (2010) Consuming eggs for breakfast influences plasma glucose and ghrelin, while reducing energy intake during the next 24 hours in adult men. Nutrition Research, 30, 96-103
  6. Vander Wal, J.S., Gupta, A., Khosla, P., Dhurandhar. (2008). Egg breakfast enhances weight loss. International Journal of Obesity, 32, 1545-1551
  7. Hoffman J.R., Falvo M.J., Protein – which is the best? Journal of Sports Science and Medicine (2004) 3, 118-130
  8. Romano G., Tilly-Kiesi M.K., Patti L., Taskinen M.R., Pacioni D., Cassader M., Riccardi G., Rivellese A.A., Effects of dietary cholesterol on plasma lipoproteins and their subclassess in IDDM patients. Diabetologia 1998 Feb, 41(2):193-200
  9. Knopp R.H., Retzlaff B.M., Walden C.E., Dowdy A.A., Tsunehara C.H., Austin M.A., Nguyen T., A double-blind, randomized, controlled trial of the effects of two eggs per day in moderately hypercholesterolemic and combined hyperlipidemic subjects taught the NCEP step I diet. J Am Coll Nutr. 1997 Dec; 16(6): 551-61
  10. Rong Y., Chen L., Zhu T., Song Y., Yu M., Shan Z., Sands A., Hu F.B., Liu L., Egg consumption and risk of coronary heart disease and stroke: dose-response meta-analysis of prospective cohort studies. BMJ 2013, 346
  11. Fernandez M.L., Effects of eggs on plasma lipoproteins in healthy populations. Food Funct. 2010 Nov; 1(2): 156-60
  12. https://examine.com/faq/will-eating-eggs-increase-my-cholesterol as seen on 17.07.2016
  13. Evenepoel P., Geypens B., Luypaerts A., Hiele M., Ghoos Y., Ruthgeerts P., Digestibility of Cooked and Raw Egg Protein in Humans as Assessed by Stable Isotope Techniques 1,2,3. J Nutr. October 1, 1998 vol. 128, no 10, 1716-1722
  14. Domingues A.R., Pires S.M., Halasa T., Hald T., Source attribution of human salmonellosis using a meta-analysis of case-control studies of sporadic infections. Epidemiol Infect 2012 Jun; 140(6): 959-69
  15. Durance T.D., Residual Avid in Activity in Cooked Egg White Assayed with Improved Sensitivity. Journal of Food Science 2006, vol 56, issue 3
  16. Anderson K.E., Comparison of fatty acid, cholesterol, and vitamin A and E composition in eggs from hens housed in conventiona cage and range production facilities. Poultry Science 2011 Jul, 90(7) 1600-8
  17. Hidalgo A., Rossi M., Clerici F., Ratti S., A market study on the quality characteristics of eggs from different housing systems. Food Chem 2008, 106, 1031-1038
  18. http://www.edinformatics.com/math_science/science_of_cooking/cooking_temperatures.htm as seen on 17.07.2016
  19. Zabłocka A., Sosnowska A., Urbaniak A., Janusz M., Polanowski A., Peptides accompanying egg yolk IgY – alternative methods of isolation and immunoregulatory activity. Food Funct. 2014 Apr; 5(4): 724-33
  20. Lemieszewska M., Jakubik-Witkowska M., Stańczykiewicz B., Zambrowicz A., Zabłocka A., Polanowski A., Trziszka T., Rymaszewska J., Pro-Cognitive Properties of the Immunomodulatory Polypetide Complex, Yolkin, from Chicken Egg Yolk and Colostrum-Derived Substances: Analyses Based on Animal Model of Age-Related Cognitive Deficits. Arch Immunol. Thera. Exp. 2016
  21. http://naukawpolsce.pap.pl/aktualnosci/news,404464,prof-tadeusz-trziszka-jajo-to-doskonaly-surowiec-z-natury.html as seen on 18.07.2016
  22. Hap A., Kielan W., Grzebieniak Z., Siewiński M., Rudnicki J., Tarnawa R., Rudno-Rudzińska J., Agrawal A.K., Control of active B and L cathepsins in tissues of colorectal cancer using cystatins isolated from chickenegg proteins: in vitro studies. Filia Histochem Cytobiol 2011; 49(4): 670-6

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