Health Concerns about Eggs
I’ve been intrigued with eggs lately, and thought I would compile all the research I’ve been reading into one place, as a blog. Please keep in mind I was only looking at the negative risk factors associated with eggs, rather than the benefits. From a health perspective, it makes sense to avoid eggs altogether if you have diabetes or a cardiovascular disease, or you want to avoid certain cancers that might run in your family such as colon cancer and prostate cancer.
The main dietary source of environmental contaminants for humans, comes from animal body parts and secretions. One study compared the concentrations of 7 contaminants in the breast milk of 12 vegans with that of the general population and found that for all contaminants except PCBs, the highest vegan value was lower than the lowest value in the general population. This does varies depending on the vegans studied however, but what does seem to be consistent across the board is the very low levels of organochlorine pesticides in vegans. (2) From what I have read though, it seems as though meat and dairy are a higher risk source of environmental contaminants than eggs are.
Porous and fragile shells and crowded egg farms allow eggs to become the perfect host for salmonella (15). Salmonella is the main micro-organism of concern for egg eaters, but this risk is mainly linked to undercooked, raw or cracked eggs. And while Australian authorities consider our ‘salmonella risk from eggs’ is small (16), I found this interesting link from the American Food and Drug Administration saying that each year there are approximately 79,000 cases of food-borne illness and 30 deaths caused by consumption of eggs contaminated with the bacterium Salmonella Enteritis. I’m uncertain how up to date these figures are, with most of the associated pages and links dating 2009, and they are certainly attempting to put measures into place to reduce this, so perhaps this has improved. Here is a good link from them regarding safe consumption if you are an egg eater. And a fact sheet from Animals Australia here, about the ethical considerations.
Cholesterol is a wonderful building block for the structure of every living cell in the human body. We don’t need to consume any from our food, because we create it naturally within our body. While trace amounts are found in plants, most dietary cholesterol comes from the consumption of animal body parts and secretions, especially their organs and eggs. “High intakes are associated with an increase in chronic diseases, especially those of the heart and blood vessels.” (2)
It has been estimated that for every 1% decrease in cholesterol levels, there’s a 2-4% decrease in heart attack risk. Dietary cholesterol appears to increase the susceptibility of LDL (lower density lipoproteins) to oxidation by nearly 40%, leading to hardening of the arteries. (2) This physicians’ health study found that 1 or more eggs per day was associated with an increased risk of heart failure.
In a study published in Atherosclerosis, researchers monitored the diets of 23,417 South Korean participants and found that those who ate the most eggs, compared with those who ate the least, had 80 percent higher coronary artery calcium scores, a measure of heart disease risk. Eggs also appeared to increase the risk for obesity, diabetes, and hypertension. (4)
Researchers found that those who consumed the most eggs increased their risk for cardiovascular disease by 19 percent, and for those who already had diabetes, their risk for develop- ing heart disease spiked to 83 percent. (5) Dr Greger does an interesting video called Eggs vs Cigarettes in Artherosclerosis, based on research done by this same team, and Kimberly Snyder mentions it in one of her blogs. This research suggests that people with a high egg consumption have a significant increase in artery-clogging plaque buildup in the carotid arteries going to their brain, a strong predictor of stroke, heart attack, and death. (5a)
A large chicken’s egg contain 33% calories from protein and 64% calories from fat. (2)
Foods rich in fat can increase insulin resistance (14)
Eggs are one of the highest dietary sources of choline. It has been suggested that choline, though important in cellular signaling, may increase the risk of cancer emergence, spread, and lethality (see the cancer section below).
New research suggests that there may be a byproduct of choline, a component found at a high concentration in eggs, that increases one’s risk for a heart attack or stroke. (6)
TMAO (trimethylamine N-oxide) is a toxic substance produced in the body when people consume choline or carnitine from certain foods and supplements (e.g. eggs, organ meats, red meat etc). TMAO may increase the risk of build up of cholesterol and inflammatory cells and atherolseclerotic plaques in our arteries, leading to heart attack, stroke and death.
In the New England Journal of Medicine, a Cleveland Clinic research team fed people hard-boiled eggs and the egg-eaters experienced a spike of the same TMAO compound associated with red meat consumption (6a)
In a study published in the Journal of the American College of Cardiology, researchers followed 720 patients for 5 years. These patients had previously been treated for heart failure. Those with the highest levels of (TMAO) in their blood had a 3.4-fold increase risk of dying, compared with those with the lowest levels. (6b)
Heterocyclic amines are carcinogens definitely found in cooked meat, but also possibly in eggs, depending on the way they are cooked. From what I can tell, it’s frying eggs to the extent that the white crisps and goes brown, that results in heterocyclic amines. In a video blog on this topic, Dr Greger points out that if you have a ‘meatless monday’ by tuesday morning, two of the worst heterocyclic amines are all but non-detectable in your bloodstream by tuesday morning. And these are two of the most potent carcinogens known!
For those who already have diabetes, high egg consumption increased the risk for developing heart disease spiked to 83 percent. (5)
A review of 14 studies published in the journal Atherosclero- sis showed that those who consumed the most eggs increased their risk for diabetes by 68 percent. (7)
Egg consumption also increases the risk of gestational diabe- tes, according to two studies referenced in the American Journal of Epidemiology. Women who consumed the most eggs had a 77 percent increased risk of diabetes in one study and a 165 percent increased risk in the other, compared with those who consumed the fewest. (8)
People who consume just 1.5 eggs per week have nearly five times the risk for colon cancer, compared with those who consume less than 11 eggs per year, according to a study published in the International Journal of Cancer. (9)
In analyzing data from 34 countries, the World Health Organization found evidence that eating eggs is associated with death from colon and rectal cancers. (10)
A 2011 Harvard study funded by the National Institutes of Health found that eating eggs is linked to developing prostate cancer. By consuming 2.5 eggs per week, men increased their risk for a lethal form of prostate cancer by 81 percent, compared with men who consumed less than half an egg per week. (12) The researchers suggested this might be due to the choline in the eggs (see the section above on choline).
Research published in International Urology and Nephrology suggests that even moderate egg consumption can triple the risk of developing bladder cancer. (13)
Common triggers for rheumatoid arthritis include eggs, dairy products and fish. Wheat, gluten-containing grains, nightshades and citrus can also be triggers, but it seems as though many individuals on a plant-based diet find RA symptoms resolving completely even with nightshades and gluten-containing foods still being included. (2)
This one is more indirect, but it’s still relevant for people who are already consuming a high protein diet, because eggs are such a high source of protein. I read somewhere that egg whites are %100 protein! Too much protein damages the kidneys, increasing the risk for kidney disease, kidney stones and some kinds of cancer. (11)
East Asian perspectives:
While eastern medicine recognises chicken eggs as a potential blood and yin tonic, they suggest they be used in small amounts, if at all, and avoided altogether by sluggish, overweight people. Chicken eggs are said to create a thick, extremely sticky type of mucous in the body, which can “eventually obstruct the gallbladder, slow the functioning of the liver, and leave deposits throughout the body.” (3)
Research notes and resources:
(1) My main source, and where a lot of the following references come from, was a fact sheet on eggs written by PCRM, the Practitioners Committee for Responsible Medicine. This facts sheet also contains a really good ‘egg replacement’ list for use in the kitchen! Definitely a blog theme for another day. Another great resource for egg replacement ideas is this one.
(2) Book: Becoming Vegan, Comprehensive Edition, by Brenda Davis RD and Vesanto Melina MS RD
(3) Book: Healing with Whole Foods : Asian traditions and modern medicine, by Paul Pritchford
(4) Choi Y, Chang , Lee JE, et al. Egg consumption and coronary artery calcification in asymptomatic men and women. Atherosclerosis. 2015;241:305-312.
(5) Spence JD, Jenkins DJ, Davignon J. Dietary cholesterol and egg yolks: not for patients at risk of vascular disease. Can J Cardiol. 2010;26:336-339.
(6) Tang WHW, Wang Z, Levison BS, et al. Intestinal microbial metabolism of phosphatidylcholine and cardiovascular risk. N Engl J Med. 2013;368:1575- 1584.
(6b) Tang WH, Wang Z, Fan Y, et al. Prognostic value of elevated levels of intestinal microbe-generated metabolite trimethylamine-n-oxide in patients with heart failure: refining the gut hypothesis. J Am Coll Cardiol. 2014;64:1908-1914.
(7) Li Y, Zhou C, Zhou X, Li L. Egg consumption and risk of cardiovascular diseases and diabetes: a meta-analysis. Atherosclerosis. 2013;229:524-530.
(8) Qiu C, Frederick IO, Zhang C, et al. Risk of gestational diabetes mellitus in relation to maternal egg and cholesterol intake. Am J Epidemiol. 2011;173:649-658.
(9) Iscovich JM, L’Abbe KA, Castelleto R, et al. Colon cancer in Argentina. I: risk from intake of dietary items. Int J Cancer. 1992;51:851-857.
(10) Zhang J, Zhao Z, Berkel HJ. Egg consumption and mortality from colon and rectal cancers: an ecological study. Nutr Cancer. 2003;46:158-165.
(11) Fontana L, Klein S, Holloszy JO. Long-term low-protein, low-calorie diet and endurance exercise modulate metabolic factors associated with cancer risk. Am J Clin Nutr. 2006;84:1456-1462.
(12) Richman EL, Kenfield SA, Stampfer MJ, et al. Egg, red meat, and poultry intake and risk of lethal prostate cancer in the prostate specific antigen-era: incidence and survival. Cancer Prev Res. 2011;4:2110-2121.
(13) Radosavljevic V, Jankovic S, Marinkovic J, Dokic M. Diet and bladder cancer: a case-control study. Int Urol Nephrol. 2005;37:283-289.
(14) Schrauwen P. High-fat diet, muscular lipotoxicity and insulin resistance. Proc Nutr Soc. 2007;66:33-41.
(15) De Reu K, Grijspeerdt K, Messens W, et al. Eggshell factors influencing eggshell penetration and whole egg contamination by different bacteria, including salmonella enteritidis. Int J Food Microbiol. 2006;112:253-260.