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.


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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If BPA exposure is so low, why should we be worried?

In response to my earlier post about bisphenol A in soda and beer, reader Skeptic had an insightful comment:

As someone involved in environmental health myself, I have been following the BPA controversy from north of the 49th parallel with some interest. I have often wondered whether the actual data supports regulation of BPA. The first study you cite, for example, hides this line in its discussion: “Thus, median and 95th percentile intake estimates were approximately two to three orders of magnitude below the current health-based guidance value. This result is similar to that given by Ye et al. (2009) for a cohort of Norwegian women, with the estimated average daily intakes of BPA reported to be about three orders of magnitude lower than the RfD and TDI.”

What is your take?
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Soda, beer, and BPA (and hey, congrats to Canada!)

Canada deserves a big pat on the back: On Wednesday, our northerly neighbor added bisphenol A (BPA) to its list of known toxic substances. Canada still has to iron out how it will regulate the chemical, but this is definitely a step in the right direction. (Bryan Walsh over at Time just posted a great piece about this, too—among other things he explains why BPA is “a litmus test for environmental health and for risk tolerance.”)

Let me use this news as an excuse to talk some more about my (least) favorite chemical. (You knew it would happen.) We’ve known for a while where BPA hides—canned goods, polycarbonate bottles, and receipts, among other things. But how do these each contribute to our overall body BPA burden?

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How not to fight colds: is it really that clear cut?

The most popular piece in the New York Times today is an Op-Ed published on Monday by Jennifer Ackerman, “How Not to Fight Colds.” It’s an interesting piece and points out something that a lot of people probably don’t know—it’s the immune system, not the virus itself, that causes the cold’s nasty symptoms. But in my opinion, Ackerman takes her assertions a little too far, in the process confusing multiple aspects of the immune response. While it’s probably true that certain immune responses worsen symptoms once a cold infection has been established, Ackerman also implies that a strong immune system does not help the body stave off infections in the first place.  And based on the scientific evidence I’ve been able to find, I don’t think that’s a fair conclusion.
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Cell phones, cancer, and scientific oversimplification

I’ve always been a big fan of Michael Shermer’s Skeptic column in Scientific American, but this month I have to say I’m disappointed. In his piece*, titled “Can You Hear Me Now? Physics shows that cell phones cannot cause cancer,” Shermer argues that it is “virtually impossible” for cell phones to cause cancer because they “do not emit enough energy to break the molecular bonds inside cells.” While this latter statement may be true—the radiation that cell phones emit is not thought to be energetic enough to directly break DNA molecules—it is not fair (or scientific, for that matter) to use this as proof that cell phones do not cause cancer. The issue is far more complex than that.

*Update, 10/4/2010: Shermer’s piece was just posted online.

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Goodbye, milk—hello, added sugar!

As usual, my readers are raising interesting questions in the comments section (thanks, guys! You’re awesome). In response to my post yesterday highlighting how our food portions have changed (as in, exploded) over the past 20 years, commenter AEK said, “It would be interesting to note how much added sugar was in the foods at both measurement periods.” It’s a point I’ve frequently considered myself, so I decided to do some digging.
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America’s ever-expanding meal portions

It’s not too surprising to learn that U.S. meal sizes have ballooned in the past several decades—anyone who has attempted to finish a meal recently at TGI Friday’s knows that. But have you ever actually seen the differences laid out in front of you? Yesterday, while reading a paper about gender differences in heart disease, I stumbled across a table derived from National Heart Lung and Blood Institute data that compared, side-by-side, just how much more calorie-laden a variety of common American meals are today compared to 20 years ago. Here is the table, which comes from Cheryl Hermann’s paper, “Raising Awareness of Women and Heart Disease—Women’s Hearts are Different,” published in 2008 in Critical Care Nursing Clinics of North America. Amazing (and disturbing), right?
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Misleading food labels—are you eating what you think you are?

As someone with both personal and career interest in food safety and nutrition, I’m frequently shocked by how little I know. The other day I was leafing through The New American Diet, a book that includes a guide to foods low in endocrine-disrupting chemicals, and I was surprised to read that the “hormone-free” poultry label is basically just a marketing gimmick: the USDA does not allow poultry manufacturers to feed their chickens hormones, so every chicken on the market is hormone-free. While I’m pleased to hear about the USDA’s policy, I’ll admit I’ve been a sucker for years, shelling out way more cash for the “hormone-free” chicken I find at my local grocery store. Wow do I feel like a jerk.

Of course, this is just one example of the many ways in which food manufacturers mislead the American public with their labels. After a little digging—the Center for Science in the Public Interest has done a lot of work in this area—here are four of the craziest examples I have found.
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Breastfeeding may prevent disease by changing gene expression in the gut flora

Let’s face it: breast milk is pretty amazing. It contains antibodies that help wee ones establish strong immune systems, and some studies suggest the act of breastfeeding even lowers mom’s breast cancer risk. Now researchers at the Universities of Chicago, Maryland, and Illinois have another potential bonus to add to the mix: according to a study they conducted in pigs, breast milk shapes the expression of bacterial genes in the infant gut, potentially boosting antioxidant activity and protecting against at least one rare debilitating disease.
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Could dieting pollute us?

I just stumbled across a thought-provoking study that I have to share. Korean researchers publishing in the International Journal of Obesity have found that weight loss is associated with higher blood levels of persistent organic pollutants (POPs)—chemicals used to make pesticides and solvents that are notorious for accumulating in our bodies and in the environment. The researchers believe that POPs, which typically build up in fat, get released into the bloodstream when fat is burned. There, they could potentially cause health problems, increasing the risk for cancer, nervous system and reproductive damage (in part because many are considered endocrine disruptors).
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