What eggs-actly does this mean? A study just published in JAMA seemed to give eggs a bit of a beating after they’ve been on a roll since 2015. After all, that year the Dietary Guidelines of America no longer included a recommended limit on the number of eggs that you should eat a week. But does this new study scramble this situation and raise the possibility of such limits returning? Well, here’s a closer egg-amination, which may be a bit punny.
The study laid together data from six different cohorts in the U.S. that had a combined total of 29,615 people who were followed for an average of 17.5 years between March 25, 1985, and August 31, 2016. During this eggs-tensive time period, these people had a total of 5400 cardiovascular events, which included 2088 coronary artery problems (like a heart attack), 1302 strokes, 1897 heart failure events, and 113 deaths from cardiovascular disease. There were also 6,132 deaths in general.
Additionally, the researchers had information the participants’ diets based on questionnaires that participants’ had completed when they had entered the cohorts. Therefore, they did not track the diets of the participants throughout the course of the studies. Keep in mind that this would eggs-clude any changes in diet during the course of the cohort. Moreover, this relies on the participants to accurately recall what they usually ate and sometimes trying to get very accurate recall can be a bit eggs-asperating.
The research team then tried to determine if there was an association between the amount of cholesterol and eggs that these people had consumed each day (again at the beginning of their participation in the cohorts) and the likelihood of suffering cardiovascular events or dying during that time period. In their statistical analysis, the team tried to account for factors such as people’s ages, sexes, races, ethnicity, education levels, smoking habits, alcohol intake, physical activity levels, body mass indices (BMIs), blood pressures, lipid levels, use of particular medications, and medical conditions.
The analysis found a correlation between the amount of cholesterol consumed each day and the likelihood of suffering a cardiovascular event and dying. Every 300 mg increase in cholesterol intake each day was associated with a 3.24% higher likelihood of having a cardiovascular event and a 4.43% higher likelihood of dying during that time period.
The analysis also found correlations with the number of eggs consumed each day. For each additional half an egg eaten per day, the likelihood of a cardiovascular event went up by 1.93% and the likelihood of death increased by 0.71%. It’s not nit-pecking to re-emphasize that this was based on the number of eggs consumed per day at the beginning of the cohort and not throughout the cohort.
So, should this study re-hatch recommended limits on the number of eggs that your should eat a week due to their cholesterol content (186 mg on average in a large egg)? What about the fact that eggs are eggs-ellent sources of protein, vitamin D, choline, lutein, and zeaxanthin without an eggs-essive amount of calories (just 78 an egg)? What about studies that have suggested more sunny-sides of eggs such as the cohort study published in the journal Heart and covering over a half a million people in China? In that study, those who ate a moderate amount of eggs (less than one a day) had a lower risk of cardiovascular disease than those who ate no eggs.
This video from last year summarized some of the American Heart Association’s thoughts about eggs:
While the JAMA and Heart studies may have been relatively well-done population cohort studies, there are numerous cracks in such study approaches in general. These types of studies can never really show or determine cause-and-effect. They tend to take large pots of data and try to boil them down to relatively simple correlations or associations.
But life is a lot more complex than that. The relationships between a food item and cardiovascular disease involve complex systems, many of which were not really considered or represented in such analyses. For example, how about things such as job stress, social situations, or the environment? Such things can affect both a person’s diet as well as his or her cardiovascular risk. Then, there are the other components of a person’s diet. A person typically doesn’t just eat eggs or nothing, at least he or she shouldn’t. Do people who tend to eat more eggs tend then concurrently eat more or less of other things? For example, could a heavy egg eater also be a heavy bacon eater? Moreover, eggs can be prepared in many, many different ways, some healthier (e.g., less salt, less sauce, less yolk, and less oil) than others (e.g., a deep fried, heavily-salted egg smothered in ketchup).
There are other limitations of the JAMA study. It relies on a single self-assessment at the beginning to determine a person’s diet. Remembering what you eat over time can be challenging. Heck you may not even remember what you just ate for lunch or what was in that spoon that just went into your mouth. Furthermore, your diet can be quite complex and change over time.
It would be the wrong ap-poach to depend too heavily on such large population cohort studies to develop nutrition recommendations. Notice how popular viewpoints about eggs have seemed to run back and forth over the years. That’s because these large cohort studies only provide indirect evidence, no more than shells of what may really be occurring. Nevertheless, every time one of these studies comes out, headlines fry around saying either “eggs are bad” or “eggs are good.” The same has happened to other food and beverage items such as coffee.
In 2017, the National Academies of Science, Medicine, and Engineering convened a committee (of which I was a member) to review the process by which the Dietary Guidelines of America are determined. One of our committee’s recommendations was to use more systems approaches and methods. There are a number of emerging methods such as systems mapping and computational modeling that can help better account for and delineate the systems that govern the relationships between diet and various health outcomes such as cardiovascular diseases. Such methods can bring together data and information from laboratory studies, animal studies, clinical trials, cohort studies, and other sources and determine how they fit together and try to reconstruct the systems involved.
When determining what will happen to the weather or a rocket launch, you don’t just focus on one or two factors and show how these correlate with what may happen. Instead, meteorologists and aerospace engineers build sophisticated computer models and try to simulate what may occur. The same needs to be done more extensively in nutrition research. If you want to determine how many eggs you should eat, you need to dive eggs-tra deeper and better understand these complex systems involved. After all, again your choice is not simply between eating only eggs versus eating no eggs at all.
So, for now, omletting go of trying to make any broad recommendations about how many eggs you can and should eat each day or each week. The recommended limit depends on a lot of different factors and probably varies from person to person. In general, moderation and balance are key (or quiche) for a healthy diet. You don’t want to eat an egg-cessive number of eggs but you also don’t have to completely eggs-lude eggs from your diet, unless of course you are vegetarian or vegan. Keep in mind that eggs can offer important nutrients but also have cholesterol. Your decision about how many eggs to eat should depend on a number of factors such as your other possible sources of protein, vitamin D, other nutrients, and cholesterol as well as the way you are preparing the eggs. While setting recommended daily intake limits for nutrients such as sugar and salt may be easier (but by no means over easy), doing so with whole food items such as eggs is more challenging. There is still much to be learned about the complex systems connecting the different aspects of a food item with various health outcomes. Hopefully all of this will egg on changes in how nutrition research is conducted.