Eggs, KFC Double Downs, and Heart Disease

Last week, my husband sent me a link to a press release. (He loves sending me press releases that he thinks will incense me.) This one was a doozy: “One Egg Yolk Worse than a KFC Double Down When it Comes to Cholesterol,” the headline read. Um. Wow.

Intrigued (and, I’ll admit, a little incensed), I looked up the study—which actually turned out to be a review article—published in the Canadian Journal of Cardiology. I also looked up what I could find in the scientific literature about the risks associated with eating too many eggs. The general idea is that egg yolks contain upwards of 200mg of cholesterol, and dietary cholesterol is thought to increase blood cholesterol levels and therefore heart disease risk. But dietary cholesterol only contributes a tiny amount to your blood cholesterol—about 70 percent of your cholesterol is actually made by your liver. And I won’t go into this right now, but earlier this year in Slate, I discussed some of the reasons we should question the link between blood cholesterol levels and heart disease risk.

Here’s what I found: according to a handful of epidemiological studies, eggs aren’t so bad (and may even be good) for the heart.  A study based on the famous Framingham Heart Study, which investigated the effects of host and environmental factors on the development of coronary heart disease, concluded that there is “no relationship between egg intake and coronary heart disease incidence.” A 1999 study published in the Journal of the American Medical Association drew on data from the Nurses’ Health Study and the Health Professionals Follow-Up Study and reported “no evidence of an overall significant association between egg consumption and risk of CHD or stroke in either men or women,” though the study did find that diabetic subjects had an increased risk of developing heart disease if they ate more than one egg per day. A 2008 study published in the American Journal of Clinical Nutrition analyzed data from 21,327 subjects who participated in the Physicians’ Health Study and concluded that egg consumption was not associated with heart attack or stroke. And finally, an analysis from the National Health and Nutritional Examination Survey (NHANES) III found that people who reported eating more than 4 eggs per week had significantly lower mean serum cholesterol levels that than those who reported eating less than 1 egg per week.

The epidemiological data seem pretty convincing to me, so I wondered how the authors of the review paper were going to address the findings. Interestingly, I found, they chose not to delve immediately into the science—instead, they began by attacking two studies published earlier this year that reported that eating eggs had health benefits, pointing out that the studies were funded by egg marketing agencies. There’s nothing wrong with questioning conflicts of interest in research, of course, but something about the vigor with which they made the point felt funny to me. I glanced to the end of the paper to see whether the authors had any conflicts of interests themselves. Here’s what I found:

None of the authors receives funding from purveyors of margarine or eggs. Dr Spence and Dr Davignon have received honoraria and speaker’s fees from several pharmaceutical companies manufacturing lipid-lowering drugs, and Dr. Davignon has received support from Pfizer Canada for an annual atherosclerosis symposium; his research has been funded in part by Pfizer Canada, AstraZeneca Canada and Merck Frosst Canada Ltd.

Okay, so it seems that Dr. Spence and Dr. Davignon have their own potential biases to contend with. Maybe they’re motivated by more than just concern for the health of their fellow Canadians? But back to the science: what do the authors say? “Concern about dietary cholesterol has been developing over the past 40 years,” they write. “This concern is based on the careful and independent conclusions of Ancel Keys and Mike Hegsted, who formulated our two most commonly used equations relating dietary saturated and polyunsaturated fat and cholesterol to serum cholesterol.” Now, I can’t say that I myself have closely looked at Keys’ and Hegsted’s work, but I know that science writer Gary Taubes has. His famous 2001 piece in Science, for instance, suggests that these “careful conclusions” aren’t actually based on sound data. I’m not going to go into all that here, but suffice it to say, I don’t think an equation that two scientists came up with 40 years ago trumps recent epidemiological data.

Thankfully, towards the end of the article, the authors do address the epidemiological findings. They mention the findings from the Physician’s Health Study suggesting that diabetics may for some reason be adversely affected by high egg consumption. Fine. But what about the risks posed to people without diabetes? “Failure to show harm from eggs in healthy people is likely an issue of statistical power,” they write. “In healthy people, a larger study with longer follow-up would be required.”

In other words, maybe all those studies just aren’t big enough to find evidence that eggs are harmful. Really, guys? The Health Professionals Follow-up Study included 37,851 people. The Nurses’ Health Study had 80,082. NHANES had 27,378. Surely if eggs were deadly, these studies would have found a signal amongst the noise. And as for your implication that people might be better off starting the morning with a KFC Double Down than a single egg yolk, well, that I can’t even dignify with a response.

Citations:

JD Spence, DJ Jenkins, J Davignon (2010). Dietary cholesterol and egg yolks: Not for patients at risk of vascular disease The Canadian Journal of Cardiology, 26 (9)

Dawber TR, Nickerson RJ, Brand FN, & Pool J (1982). Eggs, serum cholesterol, and coronary heart disease. The American journal of clinical nutrition, 36 (4), 617-25 PMID: 7124663

Hu, F. (1999). A Prospective Study of Egg Consumption and Risk of Cardiovascular Disease in Men and Women JAMA: The Journal of the American Medical Association, 281 (15), 1387-1394 DOI: 10.1001/jama.281.15.1387

Djoussé L, & Gaziano JM (2008). Egg consumption in relation to cardiovascular disease and mortality: the Physicians’ Health Study. The American journal of clinical nutrition, 87 (4), 964-9 PMID: 18400720

Song WO, & Kerver JM (2000). Nutritional contribution of eggs to American diets. Journal of the American College of Nutrition, 19 (5 Suppl) PMID: 11023007

Taubes, G. (2001). NUTRITION: The Soft Science of Dietary Fat Science, 291 (5513), 2536-2545 DOI: 10.1126/science.291.5513.2536

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10 Responses to Eggs, KFC Double Downs, and Heart Disease

  1. BenSix says:

    This piece calmed an egg-eater’s heart…

  2. Keep fighting the good fight, Melinda. Americans, and most nutritionists, need a remedial course in how to eat.

  3. Adam says:

    I’d like to see Gary Taubes destroy them in a debate.

    Thanks for the thoughtful article.

  4. darwinsdog says:

    The problem isn’t with dietary cholesterol, it’s with saturated fatty acid consumption. Saturated fatty acids are preferentially shunted to the cholesterol synthesis pathway in the liver. Foods such as red meat, that are high in saturated fat are also high in cholesterol. This is not the case with eggs. So even though the amount of cholesterol in egg yolks is relatively high, egg consumption contributes negligibly to serum cholesterol titers, as the studies cited above indicate.

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  7. RockyBob says:

    All of this “cholesterol and saturated fat is bad” seems so surreal. Admittedly my own sample of one doesn’t “prove” anything, but then again experts don’t seem to even acknowledge that numerous cases like mine exist. Specifically, I’m familial hypercholesterolemic (FH). Even with maximum drug treatment (80mg of Lipitor) I was never below 250 total cholesterol. Now off all drugs for years I’m almost 600! I eat butter, eggs, cheese, steaks with fat, and very few carbs. Oh yeah, I’m a 65 year old male, and every test run, including direct imaging of heart arteries, shows I have ZERO plaque buildup. I don’t exercise and I pour salt on everything. Two university cardiologists have said “enigma” and “somebody should study you”, but nobody considers that the fat-cholesterol hypothesis might be wrong.

  8. Paul says:

    I can see why you’re incensed. How is it the slightest bit responsible to suggest that KFC’s double down is a preferrable alternative to an egg in any way, shape, or form? We’re talking about what? 75 calories for an egg – 7 grams of protein and 6 grams of fat? And the double down weighs in at 540 calories, 32 grams of fat, and almost 1400 mg of sodium? Pardon my French, but WTF?

    What drives me crazy about articles like the one you reference is not only the lack of factual accuracy, but the complete absense of any context.

    BTW, I too have elevated cholesterol levels – I take Crestor daily. My doctor and pharmachist have told me the same thing; it makes almost no difference what you eat. This isn’t a license to eat anything, as there as a million other reasons why you must eat sensibly to stay healthy.

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