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The Definitive Egg Story: Why That Study Was Flawed & What's Actually True

Stephanie Eckelkamp
Author: Expert reviewer:
Updated on October 7, 2019
Stephanie Eckelkamp
Contributing Health & Nutrition Editor
By Stephanie Eckelkamp
Contributing Health & Nutrition Editor
Stephanie Eckelkamp is a writer and editor who has been working for leading health publications for the past 10 years. She received her B.S. in journalism from Syracuse University with a minor in nutrition.
Abby Cannon, J.D., R.D., CDN
Expert review by
Abby Cannon, J.D., R.D., CDN
Registered Dietitian
Abby K. Cannon, JD, RD is an attorney turned dietitian who lives a very low waste lifestyle. She graduated from the University of Pennsylvania with a degree in psychology and received her law degree from Brooklyn Law School cum laude. She graduated from Queens College and became a registered dietitian in 2016.
Image by Claudia Totir / Getty
October 7, 2019

For a while, it felt as if we'd gotten over our paranoia about eggs. Studies emerged showing that dietary intake of cholesterol from eggs was not as closely tied to high blood cholesterol (a risk factor for heart disease) as once thought, and a good number of doctors and nutritionists stopped preaching egg-white omelets and started embracing whole eggs—yolks and all—citing their beneficial levels of vitamin D, choline, vitamin K2, and other nutrients that are often hard to find elsewhere.

So then, what are we supposed to make of the JAMA1 study1 published in March 2019 concluding that the dietary cholesterol in eggs is associated with a higher risk of heart disease and early death? The study, which analyzed data from six different observational studies involving 30,000 U.S. adults, found that for each extra half-egg eaten per day, the risk of cardiovascular disease (CVD) increased 6 percent, and risk of early death went up 8 percent—which sounds frightening at first glance.

Countless news outlets published articles stating the egg debate was once again open and questioning what this research meant for the future of our nation's dietary guidelines, which were recently updated to remove the recommended cholesterol cap of 300 mg per day. (For context, one egg contains about 200 mg of cholesterol.) But soon after the initial "eggs are bad again" news frenzy, the counter-opinions began trickling in, with a number of respected health experts and journalists calling the study and its findings into question. Longtime New York Times health and nutrition reporter Anahad O’Connor referred to it as "bad science," and nutritional researcher Zoe Harcombe, Ph.D., posted a 10-point Twitter rant about "things wrong with the egg study," highlighting that the truly concerning thing here was not eggs and their cholesterol content, but rather, how findings of nutritional epidemiological studies are often taken as gospel when, in reality, they're highly flawed. 

The result of all this, of course, is a confused population that has no idea what the hell to believe anymore. While nobody needs eggs to survive—as countless people following a balanced plant-based diet know firsthand—should everyone be swapping them out in favor of green smoothies now? Should the focus of this type of research even be on a single whole food like eggs? For some much-needed perspective, I spoke with several heart health and nutrition experts. (Spoiler: One registered dietitian interviewed for this piece personally eats 12 eggs per week.)

Why this study (and much nutritional research) is flawed.

When I asked Ethan Weiss, M.D., cardiologist and associate professor at U.C. San Francisco's Cardiovascular Research Institute, if this study's findings were enough to consider revising our dietary guidelines to reinstate a cholesterol cap, his response was an emphatic no. In fact, when he first heard about this new study, he recalls that his response was "some sort of expletive-laced rant about how I can't believe we're having this conversation again."

The first problem with this study, says Dr. Weiss, is that it's an observational study. Nutritional epidemiology2, in which researchers observe and examine the eating habits and health outcomes of a population over time, has long been criticized for its inability to measure diet accurately, and for the tendency of these studies to yield conflicting results.

"Plenty of people much smarter than me have written eloquently about the idea that nutritional epidemiology is just kind of garbage," he says. "It's basically a tarot card reading; you can see whatever you want in these results. But it gets a lot of attention, and as long as people keep reacting to it the way they have been, we're going to keep seeing it." 

The core problem with nutritional epidemiology, Dr. Weiss says, is that we are very bad at measuring what people are actually eating. In fact, people tend to only accurately recall about 50 percent of what they eat. The other problem with nutritional epidemiology? Even if the data compiled is good (which it probably isn't), there are so many confounding factors that it's difficult to identify how one component of a person's diet is truly affecting their health. "What goes along with eggs? Well, maybe people who eat eggs are also eating lots of bread or potatoes or bacon. It's really hard to untangle what the actual problem is," says Dr. Weiss. Meaning, it's possible that other dietary or lifestyle factors are responsible for the increased risk.

John Ioannidis, M.D., DSc, professor of medicine and health research and policy at Stanford University School of Medicine, has spoken and written extensively3 on the flaws of observational nutrition studies, suggesting that funds be redirected to fewer better-designed, randomized trials. "These studies need to be largely abandoned," he said in a recent Stanford Medicine interview. "Recall biases, in which study participants remember something incorrectly, can be addition, dietary intake of a single nutrient probably has small or even tiny effects on major health outcomes."

A huge shortcoming of this particular study: The dietary questionnaire was completed at only one point in time over the course of the 17-year study—and this limited data was the basis of their conclusions. "To draw any firm causative conclusions from this type of data is impossible," says Laura Schoenfeld, R.D., a registered dietitian trained in functional nutrition.

It's also important to note that even if the data compiled for this study was completely accurate, the increased health risk of eating eggs was actually pretty damn slim when you break it down. "The risk increase was only 6 to 8 percent, which is still such an insignificant increase compared to the true risk factors for heart disease," says Schoenfeld. "Compare that to smoking, which increases your CVD risk by 200 to 400 percent, or taking the birth control pill, which increases your risk of a heart attack by 50 to 80 percent in some cases. We need to be focused on the true heart disease risk factors and not be splitting hairs about the pros and cons of consuming nutritious real foods like eggs."

And other experts agree: "These findings shouldn't necessarily scare anyone away from eggs, given that the increase in risk associated with eating eggs was really minimal," says neuroscientist and integrative nutritionist Lisa Mosconi, Ph.D.

When I reached out to O'Connor, he told me that he tends not to write about single-nutrient observational studies for many of the reasons above. "I think that as health reporters, we have to be careful about giving the public whiplash by sensationalizing every single contradictory finding," he says. "[These] studies certainly have their place. But they have to be put in proper context."

A brief history of our love-hate relationship with eggs.

When did this whole egg-cholesterol controversy start in the first place? It dates back to 19684, the year the American Heart Association (AHA) issued a recommendation that people consume no more than 300 mg of cholesterol per day, and no more than three whole eggs per week (how they got to this number still remains a mystery4, which is kind of crazy). After that, cholesterol-containing foods were widely considered the biggest dietary villain implicated in heart disease. "My dad's a cardiologist too, and when I was a kid, there was this rule in our house that we'd never eat eggs," says Dr. Weiss. "We'd have Egg Beaters, and we didn't eat shrimp or any foods rich in cholesterol."

This fear of cholesterol was reflected in our dietary guidelines for quite some time, with the recommendation for limiting cholesterol to 300 mg per day remaining intact until recently. But in 2015, the Dietary Guidelines Advisory Committee issued a report5 stating that "available evidence shows no appreciable relationship between consumption of dietary cholesterol and serum cholesterol." Shortly after, when the official U.S. Dietary Guidelines for Americans 2015-2020 were issued, they still emphasized minimizing cholesterol in the diet, but they did not include a recommended cholesterol cap. "It became clear that the intake of dietary cholesterol was not as tightly related to levels of blood cholesterol as people thought," says Dr. Weiss.

The amount of high-quality data needed to truly implicate dietary cholesterol (and, by default, eggs) in the development of heart disease simply wasn't there. And, most people agree, it still isn't. "I've covered nutrition for a long time and have noticed that the large number of studies looking at the link between dietary cholesterol and heart disease appears to be contradictory or at best mixed," says O'Connor. 

Here are a few studies to illustrate the murkiness of it all:

  • On the somewhat negative side: This 2015 study6 found that eating one or more eggs per day was associated with heart failure in men (but not women); this 2012 study7 found that egg yolk consumption was associated with increased amounts of carotid artery plaque among patients at risk for heart disease; and this 2013 meta-analysis8 found that eating one or more eggs per day was associated with increased risk of CVD among patients with type 2 diabetes but not the general population.
  • On the somewhat positive side: This large 2015 systematic review and meta-analysis9 found no clear link between dietary cholesterol and heart disease; this 2016 meta-analysis10 actually found a reduced risk of stroke with the consumption of one egg per day; this 2017 systematic review11 of randomized controlled trials found that eating six to 12 eggs per week (in the context of a heart-healthy diet) had no adverse effect on CVD risk factors; and this 2018 research review12 found that up to seven eggs per week could safely be consumed without increasing the risk for heart disease or type 2 diabetes.

So, can we say eating an egg or two a day won't up your risk for heart disease? Absolutely not. But we can't say it will either. "This response is very variable and probably genetically driven," says Dr. Mosconi. "But only about 20 percent of the cholesterol we measure in blood comes from cholesterol in the diet. There is some evidence that other fats, especially trans-fat and saturated fat, raise cholesterol levels more than actual cholesterol does."

So, we may be overly fixated on the wrong things.

You probably don't need to cut out all eggs, but how many can you safely eat?

First, let's get this out of the way: Nobody needs eggs in their diet to survive—and we're not telling you to eat them. "Eggs definitely include many beneficial nutrients, but they contain nothing that cannot be obtained in many other foods," says Thomas Sherman, Ph.D., professor of endocrinology and metabolism at Georgetown University. A well-rounded plant-based diet, plus a good vitamin B12 supplement, will cover your bases. But, are the effects of eggs as worrisome as this new study makes them out to be? Probably not.

Many experts I spoke with agreed that, for most people, there's no reason to eliminate eggs from your diet or to let this study negatively color your opinion about them. "I really believe you need to look at the big picture of someone's health," says Jess Cording, R.D., registered dietitian and mbg Collective member. "Eggs definitely have a place in an overall nutrient-rich whole-foods-based diet. All of the foods we eat contribute all kinds of nutrients and compounds that can support overall health. Even if someone was eating the exact 'perfect' amount of eggs, that won't matter much if the rest of their diet is total crap."

Meaning, if you have pretty good dietary and lifestyle habits, eggs probably aren't something to worry about; and if you don't, well, it's probably not the eggs' fault that you're unhealthy.

The fact is, eggs are an incredibly potent source of nutrients. In addition to being packed with protein, which can keep blood sugar levels stable throughout the day, egg yolks (where all the cholesterol is found), are truly a superfood and contain most of the vitamins and minerals our bodies need for good health, says Schoenfeld. A few standout nutrients: choline, which is critical for cognitive function and liver health (and fetal brain development); vitamin K2, an underappreciated vitamin that's actually protective against heart disease by preventing arterial calcification; and biotin, a nutrient well-known for supporting hair, nail, and skin health. All that said, the types of eggs you choose are also very important, so consider opting for pasture-raised varieties, which tend to be higher in omega-3 fatty acids and vitamins K2, E, and A.

But still, in light of all the contradictory research on eggs, wondering how many you can safely consume per week isn't an unreasonable question—especially since experts think the answer depends on a variety of genetic and lifestyle factors. To help you come to your own conclusion, we asked our experts about their personal egg-eating habits, or what they recommend to patients. As you'll notice, their responses ran the gamut, but there are some useful take-aways.

"I probably eat seven eggs a week without even thinking about it," says Dr. Weiss. "I don't think that remotely sets off anything; and for me, because I'm lean and in tune with my health, I could probably double that. If somebody wants to have an egg every day, go for it." For reference, the AHA says an egg a day13 can be part of a heart-healthy diet.

As for Schoenfeld: "My typical recommendations for general health is that people can consume an average of two to three eggs per day without any concern of excessive intake. I'm not really concerned about someone developing heart disease strictly from eating too many eggs, especially if the rest of their diet and lifestyle is generally heart-healthy." Integrative dietitian Ali Miller, R.D., agrees: "I personally consume 12 to 16 eggs per week for nutrient support and hormonal balance, as cholesterol is a precursor or building block of hormones."

Other experts, however, take a much more cautious approach, particularly with higher risk groups. "I would strongly urge patients with pre-diabetes, diabetes, and heart disease to avoid all egg yolks," says cardiologist and mbg Collective member Joel Kahn, M.D., who also suggested in a recent article that most people would benefit from swapping out eggs for plant-based options. His recommendations reflect some of the studies mentioned above, which have found an increased risk of heart disease with egg consumption, particularly among diabetic patients.

Dr. Mosconi also errs somewhat on the side of caution, saying that while she considers eggs a great brain food, she wouldn't recommend more than three to four per week. "A couple of eggs here and there can't possibly harm you, whereas eating several eggs every single day might, depending on your genetics, your medical status, and your lifestyle, among other factors."

Clearly, there are a lot of opinions. And while every body is unique, a good common-sense approach might be this: "If your cholesterol levels are good and you eat eggs, then keep eating eggs," says Dr. Weiss. "But if your cholesterol levels aren't great and you want to avoid taking medicine, you can play around with reducing your consumption of eggs to see if it helps."

A better way to keep cholesterol and heart health in check.

"The biggest risk factors for heart disease are smoking, uncontrolled high blood pressure, physical inactivity, obesity, uncontrolled diabetes, and uncontrolled stress and anger," says Schoenfeld. So making a point to eat a nutrient-dense, whole-foods-based diet (fiber-rich foods are especially good at lowering "bad" LDL cholesterol), manage your stress, and get plenty of physical activity can go a long way in cutting your risk. 

As mentioned above, trans fats and saturated fats are probably much more likely to raise cholesterol levels in the body than are sources of dietary cholesterol. Research14 also links added sugars to an increase in "bad" LDL cholesterol and reduction in "good" HDL cholesterol. So putting your energy toward reducing your intake of these, especially in the form of highly processed foods (which often contain all three), is probably the smarter route. 

You should also take a closer look at the numbers on your blood lipid panel test. "Arguably, the best blood-lipid-related marker of heart disease risk is the total-to-HDL cholesterol ratio, which ideally should be below 4 (3 to 4 is optimal)," says Schoenfeld. "Simply zeroing in on total cholesterol levels is not helpful when it comes to predicting a person's heart disease risk."

But even then, experts are beginning to question whether cholesterol is really the gold-standard predictor of cardiovascular risk in the first place—at least for certain people. Turns out, you can be the picture of health (with perfect cholesterol scores to prove it) and still be at triple the risk of having a heart attack or stroke at an early age if you have high blood levels of a fatty particle called lipoprotein(a).

According to a New York Times article, doctors rarely test for lp(a), but up to one in five Americans have high levels of it, including trainer Bob Harper of The Biggest Loser, who, to the surprise of many, suffered a massive heart attack in 2017. Because genetics determine your levels, and not even the perfect diet and exercise regimen can lower them, some doctors recommend that people with a strong family history of early-onset cardiovascular disease consider testing. 

Who (if anyone) should definitely avoid eggs?

Most experts I spoke with said there are only a few reasons (beyond the obvious food allergies or sensitivities) that someone may need to eliminate all eggs from their diet. "The only clients I suggest to try eliminating eggs are those who are dealing with an active autoimmune disease," says Schoenfeld. "Occasionally eggs can be a trigger for autoimmunity. But we always try reintroducing them later to see how they are tolerated. Otherwise, I don't know of any client I would ever tell to stop eating eggs." Miller's main concern is for patients with dermatological issues such as eczema, as eggs can be a common irritant, but "I do not see value in limiting egg consumption for metabolic conditions or heart health," she says.

The bottom line?

When you consider the entire body of research on eggs and heart health, and the fact that they contain many beneficial nutrients, most of our experts agree that high-quality eggs can be a good addition to an overall healthy diet—and that our fears are probably being unreasonably stoked by this latest study.

However, exactly how many eggs you can eat per day is highly variable and there is no one-size-fits-all answer. While some people may not tolerate eggs, other people may benefit greatly from their nutrients. So you should always consider your personal health history and habits before ramping up your intake of any food, and pay attention to how they react in your individual body.

But also, let's be reasonable: Considering all the overly processed junk that's out there, it's probably a bit unfair to put so much focus on the egg, a whole food that's been part of the human diet for thousands of years.

Confused about the endless stream of conflicting nutrition advice? Check out mbg's Functional Nutrition Program for lessons from leading experts in the field.

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