This questions has been around for many years and even made it to the movie Rocky. No studies were available to confirm or dismiss this practice. Until now! Cas Fuchs from Maastricht University will discuss the results of his recent study in this blog and investigates whether Rocky was right or wrong!
Did Rocky get it right by ingesting them raw?
It is well-known that egg (protein) ingestion after exercise strongly stimulates muscle growth (1, 2). Recent work has even shown that the ingestion of whole eggs stimulates muscle growth to a greater extent compared to only ingesting the egg whites (2). So, the intake of whole eggs appears to benefit your muscle growth. Rocky already showed us several decades ago that he was well aware of the great benefits of whole eggs around his workouts, as he ingested 5 raw eggs in the 1976 Movie ‘Rocky’.
However, the question remains whether Rocky should have boiled his eggs before ingestion or whether he was indeed fine by simply ingesting them in a raw form. Before giving an answer to that question, let’s first look at what the scientific literature tells us about differences between raw and boiled eggs.
Processing of eggs
Previous research in humans investigated the differences between ingesting raw and cooked eggs on its digestibility. These studies have clearly shown that substantially less of the egg protein will be digested after eating eggs in their raw (vs cooked) form (3, 4). So, it appears that less of the amino acids from an egg will become available in the systemic circulation when eggs are eaten raw vs cooked.
The reason why this happens, can be explained by two factors.
First of all, eggs contain several proteins that are known to inhibit protein breakdown. They do this by inhibiting digestive enzymes such as pepsin, trypsin, and chymotrypsin in our stomach and small intestine. These so called ‘protease inhibitors’, include ovostatin, ovomucoid, ovoinhibitor, and cystatin (5). Some of these proteins may be (partly) denaturated by heating such as cooking/boiling (which means that the structure of these proteins are broken down and thereby they lose their function). So, by boiling/cooking, you can increase the digestibility of the eggs, as you will ‘destroy’ the function of proteins within eggs that are in fact inhibiting the digestion process.
Another reason by which processing eggs can help us improve its digestibility, is because of denaturation of other proteins, which will make it in general easier for the digestive enzymes to break down these proteins into amino acids which can subsequently be taken up into the systemic circulation. As a result, we can say that cooking eggs will increase its digestibility and as a result also increase the amino acid uptake into our systemic circulation. So, did Rocky make a mistake by not boiling his eggs before he ate them? And would this have negatively influenced his muscle recovery and growth?
Boiling eggs for muscle recovery/growth
It is well-known that the amino acids coming from protein-rich food products are necessary to stimulate muscle recovery and growth. However, until now it still remained speculative whether boiled eggs would indeed better stimulate muscle recovery and growth compared to raw eggs. Therefore, we decided to perform a research study to investigate this. 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 subsequently took multiple blood samples and muscle biopsies over a 5-hour postexercise and postprandial period to assess the amino acids that became available into the systemic circulation as well as the acute muscle growth response.
In line with previous findings, we indeed observed that more of the amino acids became available in the body after ingesting boiled (vs raw) eggs. However, for the muscle growth response (i.e. muscle protein synthesis), we did not observe any differences between raw or boiled egg ingestion (6). Therefore, if the goal is muscle growth, you may as well ingest 5 raw or boiled eggs as it doesn’t seem to matter.
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. It would be unclear if lower amounts could in fact show differences, but when ingesting 5 eggs (~30 grams of protein) you can choose yourself.
Photo by Klaus Nielsen: https://www.pexels.com/photo/raw-eggs-placed-in-carton-box-on-marble-table-6294438/
Conclusion
The ingestion of boiled eggs will improve egg digestibility compared to ingesting raw eggs. As a result, boiled egg ingestion will lead to more amino acids becoming available in the systemic circulation. However, at least when ingesting 5 eggs, there is no difference in stimulating muscle protein synthesis between boiled vs raw eggs. So, purely from a recovery and muscle growth perspective you seem to equally benefit from both. Still, most people would probably prefer to eat cooked/boiled 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, you may decide to process your eggs before consuming them. Given that Rocky was more concerned with muscle recovery and growth, he was fine by ingesting his eggs in a raw form.
References
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.
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.
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.
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.
Saxena I, and Tayyab S. Protein proteinase inhibitors from avian egg whites. Cell Mol Life Sci.1997;53(1):13-23.
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
