This article refers to the article and paper below:
On August 13, 2012, ScienceDaily.com published an article entitled, “Eating Egg Yolks as Bad as Smoking?” ScienceDaily.com concludes “eating egg yolks accelerates atherosclerosis in a manner similar to smoking cigarettes.”
Unfortunately, ScienceDaily.com and many other news networks failed to accurately describe the details and outcomes of the study. Here, I carefully examine the study and suggest an alternative conclusion from the data.
First, it is important to look at the participants of the study. The data was collected from individuals soon after they had a stroke or transient ischeamic attack (known as a “mini stroke”). This study is not examining healthy individuals or comparing the number of strokes in people who ate lots of eggs vs. those who ate few eggs. All participants in the study already had a stroke regardless of their egg consumption.
Next, the means of data collection is important to consider. Participants were given questionnaires and asked to recall the number of eggs and packs of cigarettes they had smoked during their lifetime. Questions regarding exercise, stress levels, and other aspects of the diet were not asked. The researchers relied on the participants to be both truthful and accurate in their memory of egg consumption and smoking history during their lifetime.
There are important differences in the makeup of each group in the study. The group that ate the most eggs had an average age of 69.77 years compared to only 55.70 years for the group who ate the least eggs. The group who ate the most eggs also smoked the most and had the highest rate of diabetes. Surprisingly, the group that ate the most eggs had the lowest total cholesterol, lowest LDL cholesterol, highest HDL cholesterol, and lowest body mass index.
The difference in age between the groups eating the most and least eggs is important, as the authors themselves admit that plaque area increases with age. Although raw data is not presented in the paper, based on figure 1A, it appears that individuals with an age of 69.77, solely based on age, would have an average cartoid plaque area of 170 mm2. The group that ate the most eggs had an average carotid plaque area of about 175 mm2, while the group that smoked the most cigarettes had an average carotid area of about 240 mm2. This indicates that the group that ate the most eggs had an average carotid plaque area that was 2.94% greater than expected, while the group that smoked the most cigarettes had an average carotid plaque area 40.00% greater than expected. Unfortunately, figure 1C, comparing eggs eaten and plaque area, does not correct for age so the effect of egg consumption appears to have much more of an effect than it would if age was eliminated as a variable.
The authors promote the idea that egg yolks are bad because they are high in cholesterol and they argue eating foods high in cholesterol increases serum cholesterol in the blood. However, as stated earlier, the group that ate the most eggs actually had the lowest total cholesterol, lowest LDL cholesterol, and highest HDL cholesterol. According to their data, it seems that eating lots of eggs actually promotes a healthier cholesterol profile and lower body mass index. Amazingly, the authors do not address this in their paper nor do they hypothesize on what mechanism is causing high egg consumption to increase plaque buildup.
Egg consumption is likely not the cause of increased plaque. Too many other variables are at play (exercise, stress, dietary factors). Interestingly, the authors note that these patients had been advised to lower egg consumption and had not complied prior to their stroke. Perhaps they were less concerned with their health than the group that had complied and lowered egg consumption, causing them to make a variety of poor health choices unrelated to egg consumption.
Alternatively, this data could be interpreted completely differently. The data shows the individuals who ate the most eggs were the oldest and had the most plaque after their stroke. Perhaps the eggs actually had a protective effect allowing those who ate the most eggs to withstand more plaque buildup and live the longer before having a stroke. Those individuals who ate the fewest eggs had a stroke an average of 14 years earlier than those who ate the most eggs. Perhaps if they would have been eating more eggs, they would have lived longer without a stroke.
It is important to remember that these epidemiological studies do not show cause and effect. They merely show correlation. They serve as a point of reference to form a hypothesis to be tested in prospective studies. Unfortunately, the authors say, “Our findings suggest that regular consumption of egg yolk should be avoided by persons at risk of cardiovascular disease.” This is not true. That statement is merely their hypothesis that needs to be tested in prospective studies. Based on my logic in the previous paragraph, with the same data I could have concluded, “Our findings suggest that regular consumption of egg yolk should be encouraged for persons at risk of cardiovascular disease.”