Egg research clarifies cholesterol confusion

A recent Yale-Griffin Prevention Research Center study indicates that breakfast gourmands who fear ill effects of eggs can cast off their yolks of burden.

A research group has concluded that eggs can be part of a heart-healthy diet for individuals without heart problems, said Dr. David Katz, professor of epidemiology and public health. The group is currently in the middle of a follow-up study that will test whether eggs are problematic for people with high blood cholesterol.

Katz said he chose to study eggs because of their real-world relevance. Eggs are a good source of protein, but he said more people have recently cut eggs out of their diets because they believe the food’s high cholesterol content will raise blood cholesterol. Katz said a growing body of evidence suggests that eggs may have no negative effect on blood cholesterol.

“The value [of the study] lies in assessing whether a very commonly used food item should be used or not,” said Zubaida Faridi, the center’s clinical research associate who ran the study. “It’s challenging established normative beliefs.”

The researchers assigned subjects randomly to eat a breakfast of either two eggs or a bowl of oatmeal, which has a beneficial effect on blood vessels, for six weeks, Katz said. The subjects’ calorie intakes and levels of physical activity stayed fairly constant before and during the study. The scientists then tested the health of the subjects’ blood vessels.

The subjects went off the diet for a four-week washout period and then followed the other diet — those who first ate eggs for breakfast ate oatmeal in the second round.

Faridi said the washout allowed any effects of the first diet to dissipate before the subjects began the second diet.

“Instead of having an intervention group of 40 people and a control group of 40 people, the 40 people serve as a control for themselves,” she said. “It allows us to work with smaller sample sizes.”

The study tests function of blood vessels’ inner lining, or endothelium, to determine cardiac health, Faridi said.

Katz said endothelial function was tested by cutting off blood flow to the brachial artery in the arm for five minutes, then releasing the pressure and observing the change in the artery’s diameter. The blood vessel should dilate 10 percent, Katz said. A lesser dilation after the pressure is released shows poor endothelial function.

“[Endothelial function] is a measure of how effectively blood vessels dilate when they should dilate,” he said. “You’re in essence asking the blood vessels, ‘how’s it going?'”

Cardiac disease first manifests itself in endothelial function, Faridi said

The test is not yet ready to be used as a clinical measure, Katz said. Michelle LaRovera, a research assistant managing several parts of the study, said she believes the test is a promising, noninvasive means to test cardiac risk.

The study found that eggs had no negative effect on endothelial function, Katz said.

“Our hypothesis was the effects on endothelial function would be neutral,” he said. “The oatmeal did lower cholesterol significantly while the eggs did not. Our primary measure [of cardiac health] was the blood vessel behavior, and the two were the same there.”

Katz said he believes information about what constitutes a healthy diet can be obtained from analyzing our natural environment.

“It’s useful to invoke some model of what our species eats in our native habitat,” he said. “Our ancestors ate virtually no saturated fat … but they ate a lot of cholesterol.”

Since cholesterol has long been a part of the human diet, our bodies have probably adapted to tolerate it well, Katz said. Many common foods that have been shown to lead to heart problems are sources of both saturated fat and cholesterol, he said, but it may be only the saturated fat, not the cholesterol, in these foods that leads to heart disease.

While Katz said he would not recommend eating more than six eggs per week, he believes eggs can be part of a heart-healthy diet. He said that both this study and much of the recent literature point to this conclusion.

The group is currently conducting a study of people with high cardiac risk factors, but they give subjects either eggs or egg beaters instead of oatmeal, Faridi said.

LaRovera said the study, which will focus on subjects with cholesterol levels over 200, began in January, and the subjects are just now entering the phase after the washout period.

Faridi said she predicts this study will have the same result as the earlier version.

“Our hypothesis is that there should be no difference between the intervention and control group,” she said.

The group will continue to study the effects of different foods on endothelial function. Faridi said she will soon be conducting a study of the effects of antioxidants in fruits and vegetables. Katz said he is planning to study dark chocolate, which he expects will better heart health.

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