Australasian Science: Australia's authority on science since 1938

What The Egg Industry Doesn’t Want You To Know

Credit: nito

Credit: nito

The health claims of the egg industry rely on a red herring and a half-truth.

The egg industry has fostered widespread belief that dietary cholesterol in egg yolks is harmless. Its proposition rests on a red herring and a half-truth. The red herring is a misplaced focus on elevated fasting levels of low density lipoprotein (LDL) cholesterol as the main harmful effect of dietary cholesterol. The half-truth is the slogan: “Eggs can be part of a healthy diet for healthy people”. Those at risk of heart attack or stroke should understand the issues.

The Red Herring

Dietary cholesterol and egg yolks do raise fasting levels of LDL cholesterol, but more important are the effects after meals. For several hours after a high-cholesterol, high-fat meal there are increased levels of oxidised LDL (the most harmful form of cholesterol), impaired function of the artery lining, making arteries sticky and twitchy, and inflammation of the arteries.

Longstanding recommendations that patients at risk of vascular disease should reduce dietary cholesterol below 200 mg/day are based on strong evidence that dietary cholesterol increases cardiovascular risk. A yolk of a single jumbo (65 gram) egg contains 237 mg of cholesterol, which is more than the recommended daily intake of cholesterol for those at risk of heart attack or stroke.

The Half-Truth

Egg marketers maintain that studies have not shown harm from egg yolk consumption among healthy people. This is based on two US studies that did not find such harm among those who remained healthy. However, both of those studies also showed that an egg a day doubled coronary risk among people who became diabetic during follow-up. Since the US diet is generally poor, it is difficult to show harm from egg consumption in Americans. In Greek diabetics, an egg a day increased coronary risk fivefold, and each 10 grams of egg per day (about one-sixth of a large egg) doubled cardiovascular risk. Egg consumption also increases the risk of diabetes and congestive heart failure.

Among participants in the Racial Ethnic and Geographic Differences in Stroke study, dietary cholesterol and egg consumption significantly predicted the risk of atherosclerotic events such as myocardial infarction, stroke and revascularisation.

Beyond Cholesterol

Lecithin is another important ingredient in egg yolks (~250 mg in a large egg) that causes vascular harm. Intestinal bacteria convert dietary lecithin to trimethylamine. This is oxidised in the liver to trimethylamine n-oxide (TMAO), which causes atherosclerosis in animals. In patients referred for coronary artery imaging, high TMAO levels after a test dose of two hard-boiled eggs increased major cardiovascular events 2.5-fold in 3 years. These revolutionary findings suggest new approaches to cardiovascular prevention by manipulating gut flora with macrobiotics, or targeted replacement of harmful intestinal flora with beneficial flora.

The combination of high cholesterol and lecithin levels in egg yolks may also explain why egg yolk consumption accelerates hardening of the arteries by about 60% as much as smoking, and these effects are additive. A young man might think he can smoke and eat eggs with impunity because his heart attack is decades in the future, but why would he want to bring it on sooner?

Is It Safe to Eat Two Eggs Per Week?

One large egg yolk contains 237 mg of cholesterol, which is as much cholesterol as a 12-ounce (340 gram) burger. That’s more than 4 days worth of meat in the Mediterranean diet, which is the best diet for diabetes and the prevention of vascular disease. Two eggs per week (100 per year) amounts to 400 extra days worth of cholesterol in a year.

Regular consumption of egg yolks should be avoided by people at risk of cardiovascular disease – those who expect to live past middle age. Stopping the consumption of egg yolks after a stroke or myocardial infarction would be like quitting smoking after a diagnosis of lung cancer.

Only people who know they will die of another cause can eat egg yolks with impunity. I advise my vascular patients to use egg whites, or egg white-based products to make tasty omelettes, frittatas and egg salad sandwiches.

Dr J. David Spence is a Professor of Neurology and Clinical Pharmacology, and Director of the Stroke Prevention & Atherosclerosis Research Centre at the Robarts Research Institute, Western University, Ontario, Canada.