Eggs are an amazing food for many reasons.
But, perhaps the most fascinating thing about them is their reputation.
Eggs are known for being a nutritional powerhouse and even a superfood.
Yet at the same time, eggs have a reputation for raising cholesterol and increasing the risk of heart disease.
So, which of the two is true?
And more importantly, how many eggs can I eat?
In a previous post, I took an in-depth look at the relationship between cholesterol and heart disease, so this post isn’t specifically focusing on that relationship.
Likewise, I’ve talked about some of the health benefits of eggs previously.
In this post, I’m specifically focusing on some recent research that adds important information to this discussion on eggs, cholesterol and heart disease.
This research is very recent and it’s fascinating because it provides support for the idea that eggs really aren’t as bad as many people think.
The Study Itself
This particular study was published just this year (Virtanen et al., 2016).
In this study, the authors were particularly interested in the connection between cholesterol intake and coronary artery disease.
The study involved 1,032 men, who ranged from 42 to 60 years old at the beginning of data collection (which was 1984 to 1989). Data collection occurred as part of the Kuopio Ischaemic Heart Disease Risk Factor Study.
For 846 of those men, information on carotenoid artery intima-media thickness (a measure for coronary heart disease) was available.
So, those 846 men became the sample group.
The participants were then followed for an average of just over 20 years.
During this time, 230 incidents of coronary artery disease occurred.
Across the study, the average egg intake was around 4 medium-sized eggs per week.
This accounted for 27.7% of the total intake of cholesterol for participants.
Out of the study population, 15% of individuals ate at least 1 egg per day.
Participants with higher levels of egg intake were more likely to be physically active and less likely to have diabetes or to smoke.
The ApoE4 Phenotype
As part of this study, the authors were interested in the ApoE4 phenotype of the APOE gene.
People with this particular phenotype are particularly interesting.
The APOE gene plays a role in how people respond to dietary cholesterol. Specifically, people with the ApoE4 phenotype show the strongest response to dietary cholesterol.
In theory, this means that people with the ApoE4 phenotype are most likely to experience negative outcomes as the result of cholesterol in the diet. The gene is also linked to Alzheimer's disease risk, as the site Mayo Clinic explains.
The authors found that approximately one-third of their sample population (32.5%) had this phenotype.
The authors did note that people with the ApoE4 phenotype had worse lipid profiles than those without the phenotype. However, this did not translate into a greater risk of coronary artery disease.
The authors also found that egg consumption was associated with a better lipid profile in people without the ApoE4 phenotype, while there was no association for those who had the phenotype.
Overall, the authors did not find any association between egg consumption or cholesterol intake in general, and coronary artery disease.
This was true in the study population in general and also in the people who had the ApoE4 phenotype.
So, even in the most susceptible individuals, there was no relationship between egg consumption and the risk of coronary artery disease.
This strongly reinforces the concept that dietary cholesterol doesn’t have much impact on heart disease at all.
The authors did also find that each additional egg was associated with a hazard ratio of 1.17 for people without ApoE4 and a hazard ratio of 0.93 for those with the ApoE4 genotype.
In both cases, this is a very low hazard ratio, which reinforces the idea that eggs and cholesterol have very little impact on coronary artery disease.
Strengths and Limitations of the Study
Every study has strengths and limitations – that’s the nature of research.
In this particular study, key strengths included the significant sample size and the way that the population was followed for an extended period of time.
Following a population for this length of time allows researchers to see the long-term effects of dietary practices.
This is very relevant in the case of cholesterol, because issues like heart disease can show up at any point during a person’s lifetime.
As a consequence, experimental research would not be a viable way to find out whether or not an association between cholesterol and heart disease exists. Besides which, an experimental study like that would be unethical.
That brings me to the key limitation of this study.
Like many similar studies, this research is completely observational.
This means that the researchers didn’t try to alter the behavior of participants in any way.
Instead, the research involved measuring variables and looking at how outcomes changed over time.
As I mentioned above, this approach really is necessary for the topic at hand, as an experimental study would not have been viable or ethical.
Nevertheless, the observational nature of the study does limit the strength of the research.
The biggest issue with observational studies is cause and effect.
Specifically, observational studies can find associations between two factors, but they can’t find whether one caused the other.
This is a major problem, because things can be associated without one causing the other.
In fact, associations can happen for a number of reasons.
- Both factors being influenced by something external (for example, red meat is associated with heart disease risk because, on average, people who consume high amounts of red meat also have unhealthy lifestyles)
- Reverse causation
So, we have to be very careful when looking at correlations.
If you want an illustration of this, there is a fun site called Tyler Vigen that actually focuses on correlations where the two factors are unlikely to be related (you can see it here).
Here’s one example:
As you can imagine, the odds of those two variables actually being related are pretty slim.
So, we do need to be careful with any observation-based study for this reason.
Nevertheless, I will note that the authors did focus on statistical analysis and tried to account for any possible confounding factors.
As such, the results of the study are still strong, even though it was observational in nature.
This study failed to find any association between eggs (or cholesterol) and coronary artery disease.
Even with the observational design of the study, this is an encouraging outcome.
More importantly though, other research shows that egg consumption is safe and may even promote health in some areas.
For example, one study showed that consuming more than 3 eggs per week was associated with a decreased risk of metabolic syndrome (1).
Another study showed that consuming 2 eggs per day didn’t have a negative effect on lipid profiles for people who were overweight or obese and had either type 2 diabetes or prediabetes (2).
So, what about the original question, how many eggs can I eat?
For the main study we looked at, the authors found no significant association between egg consumption and coronary artery disease for people eating an average of 4 eggs per week.
In general, this suggests that even a fairly high amount of eggs isn’t going to have any negative effect.
In fact, eggs are a pretty good choice for food, especially in the morning.
After all, they tend to be filling and can be a good way of giving you long-lasting energy. Besides, there is no shortage of amazing ways to prepare them - like this list of egg breakfast recipes from Serious Eats.
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