From Heartwire
Debate Over Dangers of Egg-Yolk Consumption Continues With New Study
|
August 20, 2012 (London, Ontario) — Researchers who have long argued that egg-yolk consumption contributes to cardiovascular disease have now published a study showing that lifelong consumption of egg yolks is correlated to development of carotid artery plaques and therefore should be avoided by anyone at risk for cardiovascular disease.
Dr J David Spence (Robarts Research Institute, London, ON) publish the results of a study of 1262 consecutive patients attending vascular prevention clinics in Canada online August 1, 2012 in Atherosclerosis. All of the subjects had baseline measurement of total carotid plaque area by ultrasound and filled out questionnaires about their diet and lifestyle, including medications they take, smoking, and the number of egg yolks they've eaten per week times the number of years they've kept that dietary pattern (egg-yolk years).
The results show that carotid plaque area increased linearly with age after age 40 and increased exponentially with both pack-years of smoking and egg-yolk years. The average plaque area in subjects claiming to consume fewer than two eggs a week (n=388) was 125 mm2 vs 132 mm2 in subjects eating three or more egg yolks per week (n=603) (p<0.0001 after adjustment for age).
Multiple regression analysis found that egg-yolk years were a significant predictor of disease after adjustment for other coronary risk factors.
Spence is a long-time critic of the egg industry and believes the industry's lobbyists have confused the public by convincing government dietary guideline writers to downplay the dangers of dietary cholesterol. He often points out that a single egg yolk contains approximately 215 mg to 275 mg of cholesterol, more than the 200-mg daily limit recommended by the American Heart Association (AHA) and National Cholesterol Education Program.
"We've known that [dietary cholesterol is a cardiovascular risk factor] for 50 years, but the egg marketing people have been so successful with their propaganda that in Canada there are no longer recommendations against consuming dietary cholesterol," he told heartwire .
He argues that the defense of eggs as part of a healthy diet depends largely on a study in the 1990s based on the Health Professionals Follow-up Study and Nurse's Health Study [2]. Together, these studies found that consumption of up to one egg per day had little or no impact on cardiovascular risk. But Spence maintains that "the reason they failed to show harm in the people who remained healthy was that they were too young and they weren't followed long enough."
That study found a link between cardiovascular risk and egg consumption in diabetics, and a 2006 study in Greece found that increased consumption of eggs and saturated fat was associated with a significant increase in mortality among diabetics [3], Spence stresses. Also, a 2009 study of data the Women's Health Study andPhysicians' Health Study showed that high levels of egg consumption are associated with an increased risk of type 2 diabetes [4].
Bad Diet vs Bad Foods
In an interview with heartwire , nutritionist Dr Susan Racette (Washington University School of Medicine, St Louis) pointed out that cholesterol is certainly not the only dietary factor that can contribute to the development of cardiovascular disease, yet the study by Spence et al provides no other dietary information. "Cholesterol itself may not be the biggest player, but cholesterol is included in foods with saturated fats," she said.
"If people are consuming more eggs, then people might be consuming more saturated fat from other sources as well," she suggested. She pointed out that the preparation of eggs--fried vs boiled--makes a difference, but that wasn't specifically addressed in the study. Also, the subjects in the study were consuming a lot of eggs despite the professional recommendations to cut back because of their disease risk. "That implies that perhaps they weren't following other dietary recommendations, either. It might not just be the cholesterol, but part of a whole dietary pattern that may not be optimal, although that doesn't mean the cholesterol doesn't have potentially an important role."
Racette says she supports the AHA's recommendation that individuals concerned about their cardiovascular risk limit their egg-yolk intake "within the constellation of limiting saturated fats, trans fats, and cholesterol." She also pointed out that some dietary choices can offset the consumption of cholesterol. Plant sterols (phytosterols)have been shown to reduce the body's absorption of cholesterol. "But people who eat a lot of cholesterol are probably consuming fewer plant products," she said.
Egg Industry Is Not Impressed
Researchers aligned with egg producers are not persuaded by the study by Spence et al. Dr Mitch Kanter, executive director of the Egg Nutrition Center (ENC), in Park Ridge, IL told heartwire that the study "is just not that well done." He pointed out that the study included mostly older at-risk patients and relied entirely on their self-reports of egg consumption. "There are so many confounders just in a question like that," he said. "The people who were oldest were the people in the highest quintile, and that makes sense because if a guy is 75, even if he ate only one and half eggs per week, 75 times one-and-a-half per week is going to give you a high number. If these are the premises upon which these data were collected, then how do you put a lot of faith in the results that you get?"
The Egg Nutrition Center is funded by the American Egg Board, which is supported by egg farmers as a so-called "check-off" program overseen by the US Department of Agriculture.
As further evidence that eggs can be part of a heart-healthy diet, the ENC cites a study published in Risk Analysis that found that modifiable lifestyle risk factors account for less than 40% of coronary heart disease mortality and that for most adults, consuming one egg a day accounts for less than 1% of coronary disease risk [5]. The group also highlights a small randomized study in England that found that increased intake of dietary cholesterol from two eggs a day did not increase total plasma or LDL cholesterol when accompanied by moderate weight loss [6].
Dr Maria Luz-Fernandez (University of Connecticut, Storrs), who has received research funding from the ENC and has criticized Spence's position on eggs in the past, told heartwire in an email that the conclusions of Spence et al are "really overstated based on the data."
She points out that "the subjects under study were already sick and came to the clinic with high blood pressure, hyperlipidemia, and excess body weight, [and because] this is a cross-sectional study it is not possible to reach a causal conclusion."
She also questions the usefulness of measuring consumption in egg-years. "It is not surprising that the individuals with more egg-years (older) had higher plaque area. So a big problem is that they did not control their data with age, which as we all know is highly associated with heart disease and high lipid levels." Also, she argues that the questionnaire used in the study was biased because it only asked about egg intake and smoking and not other potentially relevant dietary factors such as saturated fat and high sugar intake.
Spence, however, anticipated this reaction in his interview with heartwire . "Every time a paper like this comes out the media come and . . . they ask what my study shows, and then they go ask what the egg marketers think and give equal weight to three of Canada's leading experts on stroke prevention nutrition and cholesterol and to the egg marketers," Spence said. "No wonder the public is confused."
This research was supported by the Stroke Prevention & Atherosclerosis Research Centre and the Heart & Stroke Foundation of Ontario. Disclosures for the authors were not provided. Luz-Fernandez has received research funding from the American Egg Board, the Egg Nutrition Center, and the National Dairy Council. Racette reports no potential conflicts.
No comments:
Post a Comment