Introduction
Eggs are a major part of people’s diet. Also, in many cultures, eggs are considered a traditional breakfast meal. So clearly, people seem to love eating eggs. But how good are eggs actually? And what does an egg actually contain? Is it healthy? And for those that love to exercise: will eggs be a good protein source for muscle recovery?
These are several questions that people have around eggs and there is a lot of misconception about eating eggs. So, lets clear things up here.
Nutritional value of eggs
First of all, eggs have a great culinary potential together with low economic cost, making it a very popular food product. Also, when cooked, eggs are generally highly digestible, with only small amounts of protein that are not taken up in the human body (more on this later) (3). Eggs contain many great nutrients, including proteins, essential lipids, vitamins, minerals, and trace elements (1) and offer a moderate calorie source, making it a well-balanced nutrient source for humans together with a myriad of biologically active compounds (1, 2). All sounds good so far, but what exactly does an egg contain then? Let’s have a look into this.
Macronutrients in eggs
Water
Water is the most abundant ‘nutrient’ in an egg and about 75% of the egg is water (1). If the egg white would be separated from the yolk, about 88% of water can be found in the egg white, whereas this would be 55% in the yolk.
Proteins
Eggs are considered a good protein source, given that protein is the second most abundant nutrient (after water) in an egg (about 12.5% of the egg is protein). Both egg white and egg yolk contain many proteins (yes there are indeed many different proteins in eggs of which almost 1000 different types have been identified so far). If we separate the egg white from the yolk we see that egg white contains about 11% of protein, whereas the yolk in fact contains about 16% of protein. So, first take-home message: don’t ditch the egg yolk to easily!
What is also interesting to know about the proteins within eggs, is that egg white contains some protease inhibitors. This essentially means that these proteins can delay digestion of egg components, especially when ingesting eggs in their raw form (more on this later).
Fat
Fat contains for about ~10% of the nutrients in eggs and is only found in the egg yolk. One type of fat that is abundant in eggs is cholesterol and because of this many years ago people were eating less eggs because it was suggested that this would be detrimental for health (see below for more information; spoiler: it’s not as bad as people thought it was).
Carbohydrates
Carbohydrates contain for about ~1% of the nutrients in eggs, which are distributed between the egg white and yolk. From all carbohydrates in an egg it contains mostly (albeit, again, in very minor amounts!) glucose. Eggs do not contain any fibers.
Micronutrients in eggs
Vitamins
Eggs, and in particular the yolk, are a good source of vitamins. Vitamins that can be found in egg yolk are vitamin A, D, E, K, B1, B2, B4 (choline), B5, B6, B9, and B12. Vitamins that can be found in the egg white are vitamin B1, B2, B3, B5, B6, B8, B9, and B12. Eggs do not contain vitamin C, so that’s a micronutrient that needs to be taken from other food sources (such as fruits and vegetables).
Minerals and trace elements
Eggs contain many important minerals. These include phosphorus, calcium, potassium, and sodium. In addition, eggs also contain essential trace elements such as copper, iron, magnesium, manganese, selenium, and zinc. These minerals and trace elements can be found in both egg white and yolk.
So, now we have a good idea of what is in an egg, let’s further have a look why this would make it a great food product to help us for muscle recovery and growth.
Eggs as a protein source to support your workout recovery and growth
For those with some nutrition background, the information above already shows that eggs can be a good source of protein to ingest around your workouts. Indeed, scientific studies have also shown that egg (protein) intake after exercise strongly stimulates muscle growth (5, 6) (if you want to know all about muscle growth, see our guide here). More specifically, it seems that whole egg ingestion is even better to stimulate muscle growth compared to only ingesting the egg whites (6). So, another reason not to ditch the yolk.
Interestingly, Rocky already showed us that he was aware of the great benefits of eggs around his workouts by ingesting 5 raw eggs in the 1976 Movie ‘Rocky I’. However, many people don’t eat raw eggs and actually prefer to eat the eggs ‘processed’ (by boiling or cooking them). So, we were wondering whether Rocky was actually right by ingesting his eggs in a raw form. Would it not be better for Rocky to have boiled his eggs before eating them? Are there actually differences between raw and boiled eggs?
Let’s see what science tells us about this…
Processing of eggs
Previous work has tried to answer the question of what happens when eggs are eaten in their raw form or when they are processed (e.g. cooked/boiled) before consumption. These studies have shown that when eggs are eaten in their raw form, that substantially less of the egg protein will be digested compared to when the eggs are cooked (3, 4). This means that less of the egg protein-derived amino acids (which are necessary for muscle growth, see our guide to building muscle mass here) will become available in our body.
Now you likely wonder why raw eggs are actually less well digested compared to processed (e.g. cooked/boiled) eggs?
This can be explained by 2 reasons:
- First of all, eggs contain several proteins that are known to inhibit protein breakdown by inhibiting digestive enzymes (such as pepsin, trypsin, and chymotrypsin) in our stomach and small intestine. These proteins (so called ‘protease inhibitors’), include ovostatin, ovomucoid, ovoinhibitor, and cystatin (7). Some of these proteins may be (partly) denaturated by heating such as cooking/boiling (which means that the structures of these proteins are broken down and thereby they lose their function). So, by boiling or cooking, you can increase the digestibility of the eggs, as you will ‘destroy’ the function of proteins within eggs that are inhibiting your digestion. As a result, we can say that cooking eggs will increase the digestibility.
- The second reason by which processing eggs can help us to digest them better, is because of denaturation of all other proteins. This will also make it in general easier for the digestive enzymes to break down these proteins into amino acids which can then subsequently be taken up into the systemic circulation.
So, processing eggs seems to be beneficial for digestibility. But what does this mean for muscle recovery and growth?
Boiling eggs for muscle recovery/growth
In order to answer the question whether boiled eggs would indeed better stimulate muscle recovery and growth compared to raw eggs, we performed a research study to specifically answer this question.
We asked healthy recreationally active men, familiar to resistance exercise, to ingest either 5 raw eggs or boiled eggs after a whole-body resistance exercise session. We observed that after ingesting boiled eggs more of the amino acids became available in the body (which makes sense, as more can be digested what I just mentioned). We also observed that both the ingestion of boiled and raw eggs stimulated muscle protein synthesis, which is an essential aspect of muscle recovery and growth. However, we did not observe any differences between raw or boiled egg ingestion on stimulating muscle protein synthesis (12).
Therefore, if the goal is muscle growth, you can simply choose between ingesting raw or boiled eggs as it doesn’t seem to matter much. So, whilst Rocky was not aware of the benefits of boiling his eggs before consumption, he did not hamper his muscle growth by not boiling his eggs.
You may wonder now how it is possible that there are no differences for muscle growth, given the differences in digestibility between raw and boiled eggs. This is likely explained by the fact that giving 5 eggs (which equals ~30 grams of protein) provides sufficient protein to the body to help its recovery and adaptation from a workout. Therefore, the lower digestibility after ingesting raw eggs becomes less relevant. It is absolutely possible that when you would ingest lower amounts of eggs, that there will be differences. However, Rocky seemed to have chosen his egg amount wisely, by taking sufficient eggs around his workouts to overcome the digestibility limitations of raw eggs.
What would the advice of Strictly Science then be?
Some people (including me) would probably prefer to eat processed eggs over raw eggs because of the texture and taste preferences. Also, with raw eggs there is a (very!) small risk of salmonella infection. So, if you want to fully prevent that, it is better to process the eggs before consuming them. But overall, you may benefit from both processed and raw eggs if you want to help your body to recovery and grow after a workout. In that case do ensure you eat sufficient eggs.
Cholesterol in eggs
In 1968, the American Heart Association recommended people to reduce their egg intake because they claimed that high dietary cholesterol equals high blood cholesterol and, as a result, higher cardiovascular disease risks. Despite these early concerns, scientists later actually discovered that egg intake is not associated with increased health risks (8). In fact, egg cholesterol does not appear to be well absorbed and, thus, consumption of eggs does not substantially impact blood cholesterol concentrations (9, 10).
Taken together, it has becoming clear that eggs are a great source of high-quality nutrients that may actually be beneficial for human health.
Of note: people that suffer from metabolic disorders such as diabetes, hypercholesterolemia, and hypertension need to be cautious with their dietary cholesterol intake (11). In addition, people suffering from egg allergies also better avoid eating eggs. Egg allergy is most prevalent in young children (prevalent in ~2% of children younger than 5 years) and, fortunately, many children outgrow egg allergy when they get older.
Conclusion
Eggs are a great food source of protein.
Eating whole-eggs are better for the acute muscle growth response compared to eating only raw eggs. Ingesting processed eggs will improve the digestibility compared to eating raw eggs, but does not lead to differences in muscle growth (at least when ingesting sufficient amounts: 5 eggs). People do not need to worry about health effects of eggs when they eat some eggs per day/week.
So, feel free to put eggs back on the menu! If you didn’t do this already…
Some references
1. Rehault-Godbert S, Guyot N, and Nys Y. The Golden Egg: Nutritional Value, Bioactivities, and Emerging Benefits for Human Health. Nutrients. 2019;11(3).
2. Kovacs-Nolan J, Phillips M, and Mine Y. Advances in the value of eggs and egg components for human health. J Agric Food Chem. 2005;53(22):8421-31.
3. Evenepoel P, Claus D, Geypens B, Hiele M, Geboes K, Rutgeerts P, et al. Amount and fate of egg protein escaping assimilation in the small intestine of humans. Am J Physiol. 1999;277(5):G935-43.
4. Evenepoel P, Geypens B, Luypaerts A, Hiele M, Ghoos Y, and Rutgeerts P. Digestibility of cooked and raw egg protein in humans as assessed by stable isotope techniques. J Nutr. 1998;128(10):1716-22.
5. Moore DR, Robinson MJ, Fry JL, Tang JE, Glover EI, Wilkinson SB, et al. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr. 2009;89(1):161-8.
6. van Vliet S, Shy EL, Abou Sawan S, Beals JW, West DW, Skinner SK, et al. Consumption of whole eggs promotes greater stimulation of postexercise muscle protein synthesis than consumption of isonitrogenous amounts of egg whites in young men. Am J Clin Nutr. 2017;106(6):1401-12.
7. Saxena I, and Tayyab S. Protein proteinase inhibitors from avian egg whites. Cell Mol Life Sci. 1997;53(1):13-23.
8. Pelletier X, Thouvenot P, Belbraouet S, Chayvialle JA, Hanesse B, Mayeux D, et al. Effect of egg consumption in healthy volunteers: influence of yolk, white or whole-egg on gastric emptying and on glycemic and hormonal responses. Ann Nutr Metab. 1996;40(2):109-15.
9. Kim JE, and Campbell WW. Dietary Cholesterol Contained in Whole Eggs Is Not Well Absorbed and Does Not Acutely Affect Plasma Total Cholesterol Concentration in Men and Women: Results from 2 Randomized Controlled Crossover Studies. Nutrients. 2018;10(9).
10. Lopez Sobaler AM, Aparicio Vizuete A, and Ortega RM. Role of the egg in the diet of athletes and physically active people. Nutr Hosp. 2017;34(Suppl 4):31-5.
11. Kuang H, Yang F, Zhang Y, Wang T, and Chen G. The Impact of Egg Nutrient Composition and Its Consumption on Cholesterol Homeostasis. Cholesterol. 2018;2018:6303810.
12. Cas J Fuchs, Wesley J H Hermans, Joey S J Smeets, Joan M Senden, Janneau van Kranenburg, Stefan H M Gorissen, Nicholas A Burd, Lex B Verdijk, Luc J C van Loon, Raw Eggs to Support Post-Exercise Recovery in Healthy Young Men: Did Rocky Get It Right or Wrong?, The Journal of Nutrition, 2022. https://academic.oup.com/jn/advance-article/doi/10.1093/jn/nxac174/6659196?login=false
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