The Wonderful Egg and Your Heart
I think eggs are wonderful. They are little balls of nutrition that can be prepared in numerous fascinating ways to make breakfast interesting and delicious. I particularly like omelets. Alas, when I was training as a medical student the medical establishment had embraced the diet-heart hypothesis. It was felt that dietary cholesterol and fat (subsequently modified to saturated fat) by increasing levels of cholesterol in the blood (subsequently modified to raising levels of bad or LDL cholesterol) were responsible for the increasing rate of coronary heart disease that was being observed.
This certainly made sense at the time: If you eat too much cholesterol, of course it’s going to raise your blood cholesterol levels and contribute to the buildup of those nasty cholesterol plaques that would clog your arteries and give you heart attacks and strokes.
Since egg yolks contain 210 mg of cholesterol on average (more recent data suggest they only contain 184 mg/egg), eggs became a target of the dietary police.
The American Heart Association (AHA, the same organization that until recently endorsed sugar-laden cereals like Cocoa Puffs as “heart healthy”) had decided decades ago to recommend restricting egg consumption. In 2010, AHA guidelines restricted everybody’s total cholesterol to <300 mg per day on the flimsiest of evidence. From the AHA guidelines:
“Although there is no precise basis for selecting a target level for dietary cholesterol intake for all individuals, the AHA recommends <300 mg/d on average. By limiting cholesterol intake from foods with a high content of animal fats, individuals can also meet the dietary guidelines for saturated fat intake. This target can be readily achieved, even with periodic consumption of eggs and shellfish. As is the case with saturated fat intake, reduction in cholesterol intake to much lower levels (<200 mg/d, requiring restriction of all dietary sources of cholesterol) is advised for individuals with elevated LDL cholesterol levels, diabetes, and/or cardiovascular disease.”
The official US dietary guidelines on the topic of dietary cholesterol read as follows
“the body uses cholesterol for physiological and structural functions, but it makes more than enough for these purposes. Therefore, people do not need to eat sources of dietary cholesterol. Cholesterol is found only in animal foods. The major sources of cholesterol in the American diet include eggs and egg mixed dishes (25% of total cholesterol intake), chicken and chicken mixed dishes (12%), beef and beef mixed dishes (6%), and all types of beef burgers (5%). Cholesterol intake can be reduced by limiting the consumption of the specific foods that are high in cholesterol. Many of these major sources include foods that can be purchased or prepared in ways that limit the intake of cholesterol (e.g., using egg substitutes). Cholesterol intake by men averages about 350 mg per day, which exceeds the recommended level of less than 300 mg per day. Average cholesterol intake by women is 240 mg per day.
Dietary cholesterol has been shown to raise blood LDL cholesterol levels in some individuals. However, this effect is reduced when saturated fatty acid intake is low, and the potential negative effects of dietary cho- lesterol are relatively small compared to those of saturated and trans fatty acids. Moderate evidence shows a relationship between higher intake of cholesterol and higher risk of cardiovascular disease. Independent of other dietary factors, evidence suggests that one egg (i.e., egg yolk) per day does not result in increased blood cholesterol levels, nor does it increase the risk of cardiovascular disease in healthy people. Consuming less than 300 mg per day of cholesterol can help maintain normal blood cholesterol levels. Consuming less than 200 mg per day can further help individuals at high risk of cardiovascular disease.”
Americans were being told to severely restrict their egg consumption, especially if they had high cholesterol levels, diabetes, or heart disease. Even one egg a day seemed too much. As a cardiologist in training I dutifully took these recommendations to heart. I can’t tell you how many egg beater or egg white omelets I cooked over the next 25 years.
As more evidence accumulated, however, the bulk of the scientific evidence was coming down clearly on the side of eggs and the lack of effect of dietary cholesterol on blood cholesterol levels. As The Skeptical Cardiologist I began embracing the heresy of eating eggs, yolk and all, about two years ago.
Several large epidemiological studies have examined the association of egg consumption and serum cholesterol. The Framingham Heart Study examined the serum cholesterol in high versus low egg consumption and found no significant difference in either men or women. The association between self-reported dietary intake of eggs and serum cholesterol was examined in a population of 12,000 men in the Multiple Risk Factor Intervention Trial. Paradoxically, the men who consumed more eggs had lower serum cholesterol than those who consumed fewer eggs.In the Third National Health and Nutrition Examination Survey (NHANES III), the diets of 20,000 participants were evaluated.
“Compared to egg consumers, nonconsumers had higher rates of inadequate intake (defined by Estimated Average Requirements (EAR) or < 70% Recommended Dietary Allowance (RDA)) for vitamin B12 (10% vs. 21%), vitamin A (16% vs. 21%), vitamin E (14% vs. 22%) and vitamin C (15% vs. 20%). After adjusting for demographic (age, gender and ethnicity) and lifestyle variables (smoking and physical activity), dietary cholesterol was not related to serum cholesterol concentration. People who reported eating > or = 4 eggs/wk had a significantly lower mean serum cholesterol concentration than those who reported eating < or = 1 egg/wk (193 mg/dL vs. 197 mg/dL, p < 0.01”
Study after study in the next 20 years showed that egg consumption was not associated with coronary heart disease and strokes. A more recent study from Spain shows no association of egg consumption on cardiovascular disease. A meta-analysis of all prospective cohort studies published in 2013 concluded that there was no association between higher egg consumption and coronary heart disease or stroke. Studies (randomized controlled trials) that actually prove that egg consumption causes cardiovascular disease are totally lacking. Nutritional guidelines should have concluded that there was no reason to restrict egg consumption in the vast majority of Americans.
Unfortunately, the AHA guidelines (and mainstream nutritional advisors) to this day continue to embrace the 300 mg/ day limit on cholesterol (although most other countries have dropped it). Most of my patients, having heard that eggs are bad for the heart, mistakenly try to restrict the amount they eat or eat egg whites. I see my fellow doctors in the doctors’ lounge taking boiled eggs out of the refrigerator, scooping the yolk out and eating only the egg white.
Why doesn’t more cholesterol in the diet lead to higher blood cholesterol level and subsequently to heart attacks? The answer is complicated, beyond the scope of this blog, but it illustrates how amazingly complex the body’s regulation of lipids and lipoproteins is, as well as how complicated the process of atherosclerosis is.
There are at a very basic level 3 main types of fat that doctors measure in the blood to help us gauge heart disease risk: the low density lipoprotein (LDL) cholesterol portion or “bad”, the high-density lipoprotein (HDL) cholesterol or “good,” and the triglycerides (esterified fatty acids). On a very simplistic level, we tell patients that higher LDL levels tend to build up fatty plaques, whereas higher HDL levels can be thought of as reducing fatty plaques. When we eat an egg there is a complex reaction to the fats, proteins, sugar, and cholesterol absorbed into the blood stream. Although the LDL rises (which might increase coronary artery disease (CAD) risk), the HDL also rises (which might lower CAD risk) and there is a variable response of triglycerides. To further complicate things, each of the cholesterol fractions has good forms and bad forms. LDL can be in a large, “fluffy” state that is not prone to promoting plaque formation or a small, dense form that does promote plaque formation. Eggs seem to promote the less atherogenic forms of both LDL and HDL. In addition, inflammation plays an important role in the process of atherosclerosis. Certain components of egg yolks may actually reduce inflammation, making plaque formation less likely.
Certain components of eggs may be beneficial and outweigh any theoretical concern about cholesterol consumption.. Eggs are the major sources of lutein and zeaxanthin, two potent anti-oxidants, which in addition to their recognized protective effects against macular degeneration and cataract formation, may also reduce LDL oxidation.
Eggs also contain choline, a nutrient that is needed for membrane formation, methylation and acetylcholine biosynthesis, which plays a major role in normal fetal development. Some studies suggest a role of choline in protecting against Alzheimer’s disease
Eating eggs may contribute to weight loss compared to eating carbohydrates. A recent study compared two different breakfasts, a bagel-based and an egg-based breakfast. During the egg period, men had a significantly lower caloric intake not only in the next meal, but also in the following 24 hours.
To make things more complicated, all eggs are not created equal. Hens that are allowed to range freely on a farm and eat grass, bugs and what might be considered their normal diet, have a different amount of omega-3 fatty acids than those that are fed grain. Given America’s current obsession with fish oil supplements (see my prior post), this makes these eggs perceived as healthier. By manipulating the diet of hens, even those stuck in cages, the omega-3 content of eggs can be increased. Is this healthier?
The limit on dietary cholesterol of 300 mg imposed by the AHA and the USDA in their guidelines, unnecessarily has my patients worrying about cholesterol in all the things that they eat. For example, there is a lot of cholesterol in shellfish. There is no evidence that eating shellfish is bad for the heart or your cholesterol profile. For example, this recent study showed no effect of eating cold water prawns on plasma cholesterol or lipoproteins.
The Bottom Line:
Eggs are an affordable (15 cents/egg) source of high quality protein and fat. Although they contain a lot of cholesterol, there is no evidence (with the possible exception of diabetics) that egg consumption is related to risk of coronary heart disease; they may in fact reduce the risk of stroke.
Since this new evidence has emerged, I regularly enjoy the deliciousness of a three egg omelet with cheese and other ingredients without guilt and I encourage my patients to do the same. Personally, especially in my home kitchen, I try to eat eggs that come from hens that are raised under more natural and humane circumstances as I view them as healthier than eggs from factory farms.
Not everyone is an egg lover and I’m fine with that. There is no evidence that you have to eat them. You could feel towards them as did Alfred Hitchcock :
“I’m frightened of eggs, worse than frightened, they revolt me. That white round thing without any holes … have you ever seen anything more revolting than an egg yolk breaking and spilling its yellow liquid? Blood is jolly, red. But egg yolk is yellow, revolting. I’ve never tasted it.”