Egg whites are. Egg yolks are not. Though eggs are packed with protein and nutrients, egg yolks are also packed with cholesterol, which can harm our hearts.
To help unscramble the truth, let’s talk a bit more about cholesterol.
When we hear the word "cholesterol," it usually refers to one of two things. There is dietary cholesterol, which is the cholesterol we eat. Egg yolks have the most dietary cholesterol of any food. With just one yolk, we’re swallowing about 200 milligrams of dietary cholesterol. That’s the amount the American Heart Association recommends most of us not exceed for the entire day. For optimal prevention against heart disease, the Pritikin Eating Plan recommends no more than 100 milligrams of dietary cholesterol a day.
Counsels Dr. Kenney: "If you eliminate three egg yolks a day, you will likely lower your blood cholesterol at least 15%, on average, and improve the overall health of your arteries."
Blood, or serum, cholesterol is the amount of cholesterol in our blood. About 85% of the cholesterol in our blood comes from our liver. And here’s a really important point: Our liver manufactures all the cholesterol our bodies need.
About 15% of the cholesterol in our blood comes from the food we eat – yes, dietary cholesterol. Consistently, research has found that the more dietary cholesterol we eat, the higher our blood cholesterol levels rise, and the greater our risk of heart disease. That’s why it’s so important to keep a lid on the amount of cholesterol we eat.
Saturated and Trans Fats
Now, it’s certainly true that dietary cholesterol is not the only thing that raises blood cholesterol. Saturated and trans fats are spectacularly good at ratcheting up blood cholesterol levels. We get saturated and trans fat from foods like red meat, cheese, and butter, as well as from processed foods, everything from margarine to frozen entrees, that contain ingredients like coconut oil, palm oil, and partially hydrogenated oils.
Let’s get back to dietary cholesterol. For decades, scientific research has demonstrated that rising intake of egg yolks, rich in dietary cholesterol, contributes to rising blood cholesterol levels.
Here is just a sampling of that research…
Just One Extra Egg a Day
As early as 1984, in a well-designed clinical study published in the leading medical journal The Lancet1, researchers from Harvard Medical School studied the effects of adding just one extra-large egg a day to the regular diets of young, healthy men and women. All of them were lacto-vegetarians (vegetarians who also ate dairy products).
That one daily jumbo egg increased the subjects’ dietary cholesterol intake on average from 97 to 418 milligrams per day. After three weeks – just three weeks – blood cholesterol levels among the men and women had also shot up. Levels of LDL (bad) cholesterol rose on average 12%. "Ingestion of egg seems selectively to raise cholesterol and protein in LDL particles in the plasma of free-living normal people," lead author Frank M. Sacks, MD, and colleagues concluded.
Egg Whites vs Whole Eggs
In another study2, a carefully controlled clinical trial published in 2006, researchers at the University of Sao Paulo in Brazil fed three egg whites daily to one group of healthy young men, and three whole eggs daily to another group of men, also young and healthy. The study lasted 15 days. Except for the egg variations, all the men were eating the exact same thing. Their meals, prepared daily by the university, were heart-healthy-style – fairly low in fat and high in a variety of whole foods like fruits, green vegetables, beans, chicken, and fish.
Among the men in the group eating three egg whites daily, total intake of dietary cholesterol averaged only 174 milligrams per day. Among the men eating three whole eggs a day (egg whites plus egg yolks) daily dietary cholesterol intake averaged a whopping 804 milligrams.
More Eggs, Higher LDL
Along with increased dietary cholesterol, the egg yolk eaters ended up with increased blood cholesterol. Their LDL bad cholesterol, after 15 days of eating whole eggs, was about 30% higher compared to the egg white eaters. "A high-cholesterol diet clearly enhances LDL levels," wrote the authors. At the end of the study, the egg white eaters had average LDL levels of 86. The LDL levels of the whole egg eaters was 120.
There was more troubling news. The scientists found that in addition to raising LDL cholesterol, the three-whole-eggs-a-day diet hindered the body’s ability to clear out artery-clogging chylomicron remnants. Chylomicrons are particles, like LDL, that transport triglycerides and other fats to various cells throughout the body. Chylomicrons also absorb the dietary cholesterol we eat. Once chylomicrons start "unloading" their cargo, they become chylomicron remnants, which are taken up by the liver and discarded from the body. But if these chylomicrons remnants are stuffed with dietary cholesterol and fats, they tend to "hang around" in our bodies longer, taking up residence in our artery walls, just as LDL cholesterol does, where they can wreak havoc.
And sure enough, the Brazilian study found that eating three egg yolks daily "increased the residence time of chylomicron remnants, which may have undesirable effects related to the development of coronary artery disease," the scientists wrote.
Fouling Up HDL
"The cholesterol from these chylomicron remnants can also be passed to HDL particles, and that’s potentially a big problem," points out Dr. Jay Kenney, Nutrition Research Specialist at the Pritikin Longevity Center. "It can contribute to the conversion of HDL from ‘good’ to ‘bad’ cholesterol, from being anti-inflammatory to pro-inflammatory. And no longer is HDL doing its job of transporting cholesterol out of the artery walls and back to the liver for disposal."
"Unfortunately," continues Dr. Kenney, "many physicians don’t pay attention to chylomicrons, and ignore their role in promoting coronary artery disease, or atherosclerosis. That’s troubling, especially since doctors’ key strategy for fighting heart disease – prescribing statins – does little to reduce the formation of chylomicrons or the amount of chylomicron remnants burrowing into the artery wall and damaging arteries."
The good news is that an optimal heart-health food and fitness plan like the Pritikin Program does appear to reduce chylomicron activity, "which may help explain why lifestyle programs like Pritikin can reverse atherosclerosis better than statins," notes Dr. Kenney.
The most recent study3 documenting the dangers of egg yolks was published this month by scientists at the Stroke Prevention & Atherosclerosis Research Centre in Ontario, Canada. The researchers looked at more than 1,200 people, average age 61, who already had artery disease, asking them about their daily diets and any other cardiovascular risk factors they might have, including smoking. Then, using carotid ultrasound imaging, the researchers found that those people who ate the most whole eggs had the most plaque-ridden arteries.
The scientists also noted that the people who had eaten the most eggs over the years had even more plaque build-up than those with the highest cholesterol levels or body weights.
The egg industry must have been concerned about consumer reaction to this new study because immediately after its online publication, doctors affiliated with the industry shot out press statements criticizing the study, pointing out, for example, that the subjects with the higher egg intakes also tended to be heavy smokers.
"Nice spin," smiles Dr. Kenney, "but these press statements failed to mention that the Canadian scientists had in fact looked for a statistically significant correlation between egg yolk consumption and smoking history. They found none."
Counsels Dr. Kenney: "If you eliminate three egg yolks a day, which is about 600 milligrams of dietary cholesterol, you will likely lower your blood cholesterol at least 15%, on average, and improve the overall health of your arteries. That’s very good news for your heart."
Do enjoy egg whites. Breakfast at the Pritikin Longevity Center includes a big, beautiful egg-white-omelet bar full of fresh, colorful additions like salsa, green onions, nonfat ricotta cheese, and roasted red peppers.
But steer clear of egg yolks most of the time, if not all. What the egg industry describes as "nature’s perfect food" is not perfect for your arteries.
What is perfect is a lifestyle program like Pritikin that substantially limits saturated and trans fats as well as dietary cholesterol, and promotes an eating plan full of whole, fiber-rich foods, plus daily exercise.