Also published in The Atlantic

What is the most heart-healthy diet? The answer to this much-debated question just became more controversial after a study in the forthcoming issue of Atherosclerosis reported that egg yolks are nearly as bad for your arteries as cigarette smoke. After years relegated to the do-not-eat list for fear of cholesterol-raising effects, the humble egg was finally making its way back into mainstream acceptance as a heart-healthy food full of healthy fats and protein. But it appears this latest study may indeed send us back to the days of egg-white omelets and Egg Beaters.

The study's authors surveyed more than 1,200 men and women, with an average age of 61.5, who were attending vascular prevention clinics. The author's claim that regular consumption of egg yolks is about two-thirds as bad as smoking when it comes to increased build-up of carotid plaque, a risk factor for stroke and heart attack.

But many believe there are issues with this study's methodology as well as the way the authors drew their conclusion. First, the study was based on recall questionnaires, which are notoriously unreliable. More importantly, the authors singled out one food from the patients' diets and determined this caused the trend towards atherosclerosis. They could have picked another food at random -- say the toast eaten with the eggs -- and drawn an associative relationship between toast and atherosclerosis.

"I think it's dangerous to look at just one food and deduce that the trend you see is caused by that food," MIT researcher and senior scientist Stephanie Seneff wrote to me in an email regarding the study.

Dr. Frank Hu, professor of nutrition and epidemiology at the Harvard School of Public Health, also wrote to me in an email, "[The study] did not measure or control other aspects of diet such as intakes of meats, fruits, or vegetables and did not control for lifestyle factors such as physical inactivity. The data could be useful for generating some hypotheses, but it is difficult to draw any causal conclusions."

Despite these flaws, the damage to the reputation of egg yolks may already be done. "It's very worrisome that these authors of the egg-yolk-is-bad article have managed to come up with a fairly simple and relatively compelling story which will scare a lot of people away from eating egg yolks," Seneff said.

The study has potentially serious consequences for people trying to improve their health and reduce their risk of stroke and heart disease -- and that's because most people should be eating more eggs, and particularly the yolks, not fewer. That's what Seneff told me in a recent phone interview. She and her team at MIT are working on some compelling new research about the role of dietary fat and cholesterol and our health. Her research is so counter to the current dietary dogma that it sounds shocking at first: Seneff believes that Americans are actually suffering from a cholesterol deficiency rather than excess. She's concerned that studies like these only serve to confuse the public more about the role of dietary cholesterol. Seneff believes that cholesterol has been wrongly vilified and in fact, foods that contain high amounts of cholesterol -- like egg yolks and other animal proteins -- are key to improving heart health, maintaining a healthy weight, and staving off many diet-related diseases.

Of course, not everyone agrees. There are conflicting studies to show that dietary cholesterol both does and does not affect our blood levels of cholesterol. "Much of the cholesterol in the blood is produced endogenously," Hu wrote. "However, dietary factors (fats and cholesterol) can influence serum cholesterol levels." An article about eggs on the Harvard School of Public Health's website reads, "While it's true that egg yolks have a lot of cholesterol -- and so may weakly affect blood cholesterol levels -- eggs also contain nutrients that may help lower the risk for heart disease, including protein, vitamins B12 and D, riboflavin, and folate."

The picture becomes even more complicated because elevated cholesterol levels do not necessarily mean one is at greater risk for a heart attack. More than 60 percent of all heart attacks occur in people with normal cholesterol levels and the majority of people with high cholesterol never suffer heart attacks. Many studies now show that high LDL (the so-called "bad cholesterol") and heart disease are not linked. In 2005, the Journal of American Physicians and Surgeons reported that as many as half of the people who have heart disease have normal or desirable levels of LDL. Also in 2005, researchers found that older men and women with high LDL live longer.

Dr. J. David Spence, the first author of the egg yolk study and professor of neurology and clinical pharmacology at Western University, told me in an interview that serum cholesterol is "not the be all, end all of vascular risk." He's more concerned about what happens to our cholesterol levels after we consume cholesterol-containing foods, rather than our fasting cholesterol levels, which is what's checked at the doctor's office. "Egg yolks only raise fasting cholesterol by about ten percent," he said. "But four hours after you eat a high cholesterol meal you get inflammation in the arteries, there's increased oxidative stress, the increase in oxidized LDL cholesterol--which is the most harmful form or cholesterol -- is almost 40 percent, and you have impairment of the function of the artery lining."

Spence is concerned that people do not know just how much cholesterol is in one egg yolk. "For people who are at high risk for heart attacks and strokes the recommended amount of cholesterol is below 200 mg a day and one large egg yolk has 210 mg of cholesterol--there is more cholesterol in one egg yolk than the total recommended daily intake of cholesterol," he said. "To put that in perspective, one egg yolk has more cholesterol than a Hardee's Monster Thickburger which contains 12 ounces of beef, three slices of cheese, and four slices of bacon. I know the burger is worse than the egg because it also has saturated fat but the cholesterol per se is harmful and in fact, cholesterol is permissive of the harmful effects of saturated fats."

As such, Spence recommends switching to egg whites or to egg-substitutes and eating a diet that is low in animal fats and low in cholesterol. "I tell my patients to learn how to make a nice tasty omelet or frittata with egg whites, or--what I like even better--is a carton of scrambled eggs with no cholesterol. They're called Egg Beaters, or Better-n-Eggs," Spence said.

Better-n-Eggs is an egg substitute product that contains 98 percent egg whites and includes these additional ingredients: corn oil, water, natural flavors, sodium hexametaphosphate, guar gum, xanthan gum, color (includes beta carotene).

Is Spence concerned about the various additives and the processing that goes into these types of products? "No. I'm more concerned about the cholesterol in eggs."

It's worth pointing out that many of the nutrients found in eggs are found in the yolk. Among many other nutrients, egg yolk contains lecithin, which helps the body digest fat and metabolize cholesterol; betaine and choline which lower homocysteine levels; glutathione, which helps fight cancer and prevents oxidation of LDL; lutein and zeaxanthin, which have been shown to prevent colon cancer; and biotin, a B vitamin crucial for healthy hair, skin, and nerves.

I asked Spence what he thought about the various nutrients found in egg yolks -- if we eliminate eggs from our diets won't we be missing out on these nutrients? "Oh come on," he said. "You can get those nutrients a lot safer if you eat them in other foods that aren't loaded with cholesterol. There are no nutrients in the egg yolk that you need."

The MIT researcher Stephanie Seneff would beg to differ. In fact, research she is currently working on shows that one crucial nutrient -- sulfur, which egg yolks contain in very high amounts -- may be the underlying deficiency to our collective problems with cholesterol and heart disease. "The key to everything may just be sulfur," Seneff says.

Sulfur is a mineral found in several foods, including vegetables like broccoli, cauliflower, Brussels sprouts, garlic, and kale. It is also found in very large amounts in animal proteins -- one of the best-known sources is egg yolk. When sulfur combines with four oxygen molecules, it becomes sulfate. Sulfate is combined with cholesterol to produce cholesterol sulfate in large amounts when our skin is exposed to sunlight as well. Sulfation is important to enable cholesterol transport to all the tissues.

The research Seneff and her team are working on is a complete reevaluation of our understanding of cholesterol and its role. It's a fairly complex biological process but put simply, Seneff believes that the build up doctors find in arteries is "cholesterol trapped in the wrong place," or cholesterol trapped in the plaque. The reason it's trapped in the plaque is because the LDL is damaged from excess sugar in the blood. As a result of our highly processed, starchy, sugary diets, many Americans have excess blood sugar. Once the sugar has damaged the LDL it cannot go back to the liver where the cholesterol would be processed and recycled back into the body. The plaque then builds up in the arteries, where it "waits for the opportunity to become cholesterol sulfate, which all of the body's systems need," Seneff says. "The bottleneck is the sulfate. Cholesterol needs sulfate to be mobile. The damage then is a consequence of lack of cholesterol and lack of sulfate."

This may be why a much larger study in The Journal of the American Medical Association found "no overall significant association between egg consumption and heart disease." In fact, the study of 118,000 people found that those who ate five or six eggs per week had significantly lower mean serum cholesterol levels than those who ate one egg per week. Plus, the daily nutrient intake of people who ate eggs was much higher than the non-egg eaters.

In the public imagination, cholesterol is the villain whose only function is to clog up arteries. "This is the complete wrong picture," Seneff says. "It's very easy to imagine plaque build up -- but it's not the correct picture. Cholesterol is vital -- it is a precious substance in our bodies. Cholesterol is to animals what chlorophyll is to plants."

Are we to increase our consumption of egg yolks as Seneff suggests or completely eliminate them as Spence advises? What we need are clear guidelines, not influenced by industry, that present a straightforward approach to weight loss and a healthy body. The simplest answer currently available is to eliminate processed foods from our diets -- the saturation of processed foods into our diets tracks most closely with the rise in obesity and diet-related disease in this country. So when presented with confusing dietary advice or questions while food shopping ask yourself this simple question: What's my least processed option? Take that one.