We unscramble recent findings to crack a new controversy over eggs 05/22/2019
Humans likely began eating birds’ eggs long before they migrated out of Africa.
People in South and East Asia domesticated chickens as far back as 3,200 BC, while Egyptian and Chinese cultures were raising fowl for their eggs as early as 1,400 B.C.
And many Americans ate eggs at almost every breakfast — until the 1970s, when dietary cholesterol and saturated fat were mistakenly decried as drivers of cardiovascular disease.
Reversing decades of demonization, credible evidence has exonerated saturated fat and cholesterol as primary promoters of cardiovascular disease — except among a small minority who carry certain genetic traits.
Indeed, there’s no consistent evidence that averaging one egg a day promotes cardiovascular risk factors or raises the risk of a heart attack or stroke.
And, although some health authorities assert that frequent egg consumption promotes type II diabetes, the evidence for that is equivocal.
In fact, a recent epidemiological study from Finland linked diets higher in eggs to a reduced risk for diabetes in middle-aged men: findings echoed by the reassuring results reported by a Harvard team (Virtanen JK et al. 2015; Djoussé L et al. 2010).
But the concerning, headline-making results of a recent evidence review revived fears that frequent consumption of eggs can promote cardiovascular disease.
Those findings conflict with a great deal of evidence to the contrary — so let’s unscramble this apparent conflict.
First, let's recall why eggs are so nutritious.
The cholesterol and nutritional profile of eggs
These are the key — and generally attractive — nutritional attributes of eggs:
Cholesterol, only in the yolk
The yolk of one large egg averages 186 mg of cholesterol, versus the 100 to 300 mg daily limit suggested in the current U.S. Dietary Guidelines.
Cholesterol is a major component of all cell membranes and is used to make hormones, fat-soluble vitamins — including vitamin D — and the bile acids to help digest food. The body makes all the cholesterol it needs, and does not need to get more from your diet.
Protein, only in the white
Egg whites contain all the essential amino acids and are therefore a source of complete protein.
Bodybuilders have long touted eggs — especially egg whites — as aids to muscle-building, and University of Illinois researchers recently confirmed that eating whole eggs after resistance/strength exercise helped build muscle.
However, in a refutation of bodybuilding folklore, the Illinois team found that eating only the protein-rich egg whites — without the yolk — didn’t have the same benefit.
Fat, only in the yolk
Egg yolks consist almost entirely of fat — mostly unsaturated kinds.
A large egg has 4.5 grams of fat, or 7 percent of the recommended daily value. Only one-third (1.5 grams) of its fat is saturated, while nearly half (2 grams) is of the monounsaturated type that predominates in avocados and olive oil.
Essential and beneficial nutrients in egg yolk
The fat in an egg yolk aids the absorption of its fat-soluble nutrients: vitamins D, E and A, the brain-nerve nutrient choline, and the colorful, beneficial antioxidants lutein and zeaxanthin, which support eye health and help prevent macular degeneration.
Despite the benefits, have eggs gone “bad” again?
Recent, negative headlines about eggs were triggered by a large evidence review from Northwestern University’s Feinberg School of Medicine.
The Northwestern team analyzed data from six studies involving 29,615 American adults, some of which followed their participants for 31 years (Zhong VW et al. 2019).
The authors linked eating two eggs a day — or an equivalent amount of cholesterol from any source — to a significantly higher risk for heart disease and risk of death from any cause.
“The take-home message is really about cholesterol, which happens to be high in eggs and specifically yolks,” said study co-author Norrina Allen, PhD. “People who consume less cholesterol have a lower risk of heart disease.”
The authors of the evidence review linked consuming 300 mg of dietary cholesterol daily — from any sources, not necessarily eggs — to a 17 percent higher risk of cardiovascular disease and an 18 percent higher risk of death from all causes.
Further, the Northwestern team linked eating three or four eggs a week to a 6% increase in the risk for developing heart disease and an 8% higher risk of death from any cause.
Experts and other studies don’t support the renewed worries
The Northwestern study hasn’t convinced other medical and diet experts that it’s time for everyone to banish scrambled eggs or omelets from the breakfast table.
In an interview with National Public Radio (NPR), Thomas Sherman, PhD, of Georgetown University’s School of Medicine, said he tells his students to eat a protein-rich breakfast — and that eggs fill the bill in healthful fashion.
As Sherman said, if you typically fill your plate with fiber-rich plant foods — fruits, vegetables, beans, nuts, seeds and whole grains — then "eggs are a welcome part of the diet,” as long as you don’t overdo it.
And in an article about the Northwestern study, Frank Hu, PhD, of the Harvard School of Public Health stressed that most of the available evidence does not link low-to-moderate egg consumption with a higher risk for developing cardiovascular disease.
Dr. Hu said that the Northwestern University evidence review suffered from a major weakness: linking a single aspect of diet — egg consumption — to cardiovascular health outcomes up to 30 years later.
As he wrote, many of the participants in the six studies selected for the evidence review might have changed their diets during studies that lasted up to three decades — a confounding factor that seriously undermines the conclusions offered by the authors of the review.
And recent studies that looked for links between higher egg consumption and higher risk for cardiovascular disease couldn’t find any.
For example, a large, 13-year-long Swedish epidemiological study — involving 37,766 men and 32,805 women — found no links between higher egg consumption and the risk for cardiovascular disease, heart attack, heart failure, or stroke (Larsson S et al. 2015).
And a smaller but longer Finnish study published a year — which followed 1,032 middle-aged men for 20 years — later found no links between higher egg or cholesterol consumption and higher risks for coronary artery disease (CAD).
To understand their findings, it helps to understand the effects of the Apoe protein and its various "genotypes" on blood levels of cholesterol and fats, and the consequent risks for coronary artery disease.
There are three variants of the ApoE protein: e2, e3 and e4. Everyone has two copies of the ApoE gene, so there are six possible ApoE "genotypes": e2/e2, e2/e3, e2/e4, e3/e3, e3/e4, and e4/e4:
- People who have the e3/e3 or e2/e4 genotype have normal LDL cholesterol and triglyceride levels and are at normal risk for heart disease.
- People who have the e3/e4 or e4/e4 genotype have high LDL cholesterol and triglyceride levels and are at greatest risk of heart disease.
- People who have the e2/e2 or e2/e3 genotype have higher levels of triglycerides but lower LDL cholesterol levels, and are at intermediate risk.
Importantly, the no-risk finding of the Finnish held true even among study participants with ApoE genotypes that raise the risk for developing CAD (Virtanen JK et al. 2016).
Likewise, two comparably small (1,950 to 2,497 participants respectively) but lengthy (22 year) studies from the same Finnish team found no links between higher egg consumption and a higher risk for developing stroke or dementia (Ylilauri MP et al. 2017; Abdollahi AM et al. 2019).
So, the takeaway seems clear.
Eggs are healthful when consumed in moderation — unless you have a gene variant (ApoE2) that makes dietary cholesterol raise blood cholesterol levels and the risk for cardiovascular disease.
- Abdollahi AM, Virtanen HEK, Voutilainen S, Kurl S, Tuomainen TP, Salonen JT, Virtanen JK. Egg consumption, cholesterol intake, and risk of incident stroke in men: the Kuopio Ischaemic Heart Disease Risk Factor Study. Am J Clin Nutr. 2019 May 16. pii: nqz066. doi: 10.1093/ajcn/nqz066. [Epub ahead of print]
- Cleveland Heart Lab. Apolipoprotein E: Know your risk for lipid abnormalities. Accessed at http://www.clevelandheartlab.com/wp-content/uploads/2017/03/ApoE-Patient-OnePager-CHL-P020.pdf
- Djoussé L, Kamineni A, Nelson TL, Carnethon M, Mozaffarian D, Siscovick D, Mukamal KJ. Egg consumption and risk of type 2 diabetes in older adults. Am J Clin Nutr. 2010 Aug;92(2):422-7. doi: 10.3945/ajcn.2010.29406. Epub 2010 Jun 9.
- Egg Nutrition Center. Eggs 101 – Egg FAQs. Accessed at https://www.eggnutritioncenter.org/egg-facts/
- Harvard T.H. Chan School of Public Health. Eggs and cholesterol back in the spotlight in new JAMA study. Harvard University: The Nutrition Source. Accessed at https://www.hsph.harvard.edu/nutritionsource/2019/03/18/eggs-and-cholesterol-back-in-the-spotlight-in-new-jama-study/
- Larsson SC, Åkesson A, Wolk A. Egg consumption and risk of heart failure, myocardial infarction, and stroke: results from 2 prospective cohorts. Am J Clin Nutr. 2015 Nov;102(5):1007-13. doi: 10.3945/ajcn.115.119263. Epub 2015 Sep 23.
- Northwestern Now. Bad news for egg lovers: Higher egg and cholesterol consumption hikes heart disease and death risk. March 15, 2019. Accessed at https://news.northwestern.edu/stories/2019/03/eggs-cholesterol/
- NPR. Cholesterol Redux: As Eggs Make a Comeback, New Questions About Health Risks. Accessed at https://www.npr.org/sections/thesalt/2019/03/16/703804493/egg-lovers-new-study-finds-eating-too-many-can-increase-risk-of-heart-disease 1/10
- US Department of Health and Human Services. Dietary Guidelines for Americans 2015-2020. 8th Edition. December 2015. Accessed at https://health.gov/dietaryguidelines/2015/guidelines/
- van Vliet S 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. The American Journal of Clinical Nutrition. Volume 106, Issue 6, December 2017: 1401–1412. Accessed at https://doi.org/10.3945/ajcn.117.159855
- Virtanen JK, Mursu J, Tuomainen TP, Virtanen HE, Voutilainen S. Egg consumption and risk of incident type 2 diabetes in men: the Kuopio Ischaemic Heart Disease Risk Factor Study. Am J Clin Nutr. 2015 May;101(5):1088-96. doi: 10.3945/ajcn.114.104109. Epub 2015 Apr 1.
- Virtanen JK et al. Associations of egg and cholesterol intakes with carotid intima-media thickness and risk of incident coronary artery disease according to apolipoprotein E phenotype in men: the Kuopio Ischaemic Heart Disease Risk Factor Study. Am J Clin Nutr. 2016 Mar;103(3):895-901. doi: 10.3945/ajcn.115.122317. Epub 2016 Feb 10.
- Ylilauri MP, Voutilainen S, Lönnroos E, Mursu J, Virtanen HE, Koskinen TT, Salonen JT, Tuomainen TP, Virtanen JK. Association of dietary cholesterol and egg intakes with the risk of incident dementia or Alzheimer disease: the Kuopio Ischaemic Heart Disease Risk Factor Study. Am J Clin Nutr. 2017 Feb;105(2):476-484. doi: 10.3945/ajcn.116.146753. Epub 2017 Jan 4.
- Zhong VW et al. Associations of Dietary Cholesterol or Egg Consumption with Incident Cardiovascular Disease and Mortality. JAMA. 2019;321(11):1081-1095. doi:10.1001/jama.2019.1572. Accessed at https://jamanetwork.com/journals/jama/article-abstract/2728487