Eggs: A Controversial Topic in Nutrition
Eggs are a staple in many diets, but the debate about their health benefits has been ongoing for decades. Some people see eggs as a nutritious and affordable source of protein, while others believe they are unhealthy due to their high cholesterol content.
The truth is that the health effects of eggs are somewhere in between and this is a conversation that deserves a little deeper look in order to make an informed decision. We explain the latest research on the health effects of eggs, and dispel some of the myths and misconceptions surrounding this versatile food.
Eggs are Nutrient-Dense
One of the biggest advantages of eggs is their high nutrient density. A single large egg contains about 6-7 grams of protein, 5 grams of fats, and 23% of our daily needs for selenium, 14% of our needs for riboflavin, 11% of our B12 needs, 10% of daily needs for phosphorous, and 5-10% of needs for Vitamin A, Folate, B5, and iron (1).
Eggs are one of the highest-quality protein sources due to their high amounts of essential amino acids (2). They also contain carotenoids lutein and zeaxanthin, which are dietary nutrients that have antioxidant and anti-inflammatory effects (3), Carotenoids from eggs are also highly bioavailable due to the fat and phospholipid content and eggs can also improve the absorption of carotenoids from foods consumed with eggs such as greens, carrots, and sweet potatoes (3).
Eggs are also a rich source of choline providing ~150 mg of this nutrient per large egg. Choline has important and diverse functions in both cellular maintenance and growth across all life stages, particularly in pregnant mothers (4). It also plays some roles in neurotransmission, brain development, and bone integrity.
On the surface, eggs seem like a nutritional no-brainer. However, the health effect of a food is based on what happens to our health when we eat that food, not the individual nutritional components of that food. So, let’s look at what the existing research shows regarding egg consumption and health.
Eggs and Cholesterol
One of the biggest concerns about eggs is their cholesterol content. It's true that eggs are a very rich source of cholesterol, providing about 200 mg of cholesterol per serving, but research has shown that dietary cholesterol does not have a significant impact on blood cholesterol levels for most people (5). This is because eating dietary cholesterol sends a signal to our liver to produce less cholesterol to meet our body’s needs.
However, eggs also provide 1.5 grams of saturated fat per egg and saturated fat consumption can upregulate cholesterol synthesis and increase LDL levels. A recent meta-analysis of randomized controlled trials (studies where they feed people eggs) found that egg consumption of at least 1 egg per day or more increased LDL cholesterol on average – with higher doses leading to greater increases (6).
It's important to note that cholesterol responses to saturated fat consumption are highly variable and are driven by a combination of genetics and health status. Therefore, some people will experience an increase in LDL with regular egg consumption while others won’t.
If you are someone who has a high LDL cholesterol you might want to be more mindful of your egg consumption as opposed to someone whose LDL levels are in the normal range.
Eggs and Health Outcomes
Next, we take a look at the research regarding egg consumption and long-term health outcomes including the risk of death, heart disease, and cancer. We will do this by covering some recently published meta-analyses of prospective cohort studies. A meta-analysis is a compilation of studies and prospective cohort means that these studies These studies compile ask people about their egg consumption and follow them up over time. Then they take that data and compare individuals who consume higher amounts of eggs to those who consume fewer eggs and determine if those who consume fewer eggs tend to have more favorable health outcomes after adjusting for other variables that may influence this relationship (e.g. income, BMI, exercise habits, etc.)
These studies aren’t perfect, but they are the best way to gain long-term data regarding dietary patterns and health outcomes since it is nearly impossible to feed people eggs for these long periods of time and track changes.
The first study that we are going to cover is a study that was published by Mousavi et al., in 2022 (7). This study included 32 prospective cohort studies with a total of 2.2 million participants and found that people who reported the highest level of egg consumption did not demonstrate an increased risk of death from any cause, death from heart disease, or death from respiratory disease.
However, there was a 20% higher risk of death from any cancer among the high egg consumption group, and a 19% lower risk of death from stroke. These combined effects, seem to mostly cancel each other out when it comes to overall risk.
Even though this study was a compilation of studies, we still want to look at other studies to help paint the full picture. For example, another study published by Zhao and colleagues that included 40 cohort studies with 3.6 million participants found that 50 grams of eggs per day (~1 large egg) was associated with a 4% higher risk of death from heart disease (8).
Interestingly, this effect was 8% among studies that were done in the US and there was no increased risk among studies that came from Asia or Europe. This might be one of the reasons that the meta-analysis published by Mousavi et al. (7) found no effect of egg consumption on the risk of death from heart disease. Asian and European cohorts made up most of the studies included in that meta-analysis.
Another reason is the way the statistical analysis was conducted. In the previous study, they were comparing the highest vs. lowest consuming groups, whereas in this study a risk estimate was calculated based on the consumption of about 1 egg per day. In many Asian countries, the highest egg consumption groups will fall far short of the 1 egg per day cut-off.
The last study that I want to cover to help paint the full picture is a study published by Mofrad and colleagues, also in 2022 (9). This analysis included 55 studies and 2.7 million total participants and they found that each additional egg per day was associated with a 7% higher risk of death from any cause and a 13% higher risk of death from cancer.
For death from any cause this effect didn’t seem to show up until participants were consuming more than 1 egg per day, but for cancer more eggs even at lower levels of consumption were associated with slightly higher risk. These effects were mainly isolated to US studies and they didn’t approach significance in non-US studies.
This could be because in the US, baseline saturated fat consumption tends to be higher than in other regions and the prevalence of obesity and metabolic syndrome is higher as well. These two factors could influence someone’s response to the dietary cholesterol and saturated fat contained within eggs. It could also be the fact that eggs are often consumed with processed meat sources (bacon, sausage, etc.) and these foods are known to increase cancer risk (10) and this isn’t always accounted for in the analysis.
Regardless, there does seem to be a small positive association between egg consumption and cancer outcomes. This was also reported in a study that was published in 2015 which showed intakes of 5 eggs/week was associated with a 4% increased risk of breast cancer, a 9% increased risk of ovarian cancer, and a 47% increased risk of fatal prostate cancer (11).
Now, I know this last statistic sounds scary, but keep in mind that 1 in 41 men will die from prostate cancer and an increase of 47% changes this value to 1.47 in 41. Not to downplay the increase, but this is why we try to focus on death from any cause, heart disease, and total cancer. These are the most common causes of death, so a 4% increase in something that occurs in everyone (in the case of death) can be more meaningful than the 47% increase in something that is very rare and helps us understand the bigger picture better.
Eggs have also been associated with higher rates of cancers of the GI tract (12). However, most of the studies included in this paper are what are called case-control studies where we take individuals who already have cancer and compare them to those without cancer and examine dietary differences. These are not as strong as prospective cohort studies and, in this paper, when the prospective studies were examined on their own no increase in risk was found.
Since Eggs Are So Nutritious Why Are They Increasing the Risk for Some Cancers?
There are several possible explanations for this phenomenon that we are seeing. First, as mentioned above eggs can increase LDL cholesterol levels and higher LDL cholesterol levels are associated with higher rates of various cancers (13). Second, these effects could be driven by choline as choline plays an essential role in the synthesis of new cells and may contribute to the growth and replication of cancer cells (14).
Choline can also get converted into a compound called TMAO, which can damage our blood vessels and is associated with a higher risk of cardiovascular disease (15). However, the conversion of eggs to TMAO occurs in the gut microbiota and the influence of choline consumption on TMAO levels varies dramatically from person to person.
The last thing that we can’t rule out is that eggs are simply an innocent bystander that happens to be consumed with foods that can increase the risk of various cancers (e.g. bacon, sausage, etc.). This would explain why the risks described are mainly limited to US studies where these foods generally tend to be paired alongside eggs.
So What Does This Mean For You?
As discussed above, eggs are a nutritious food that can help meet our needs for several important vitamins and minerals and they also contain some antioxidant nutrients as well. I don’t want to discourage their consumption, but I also don’t want to skip over the fact that eating more than 1 egg per day may increase cancer risk.
My recommendation would be to consume eggs in moderation (up to ~1 egg per day on average) to take advantage of their nutrition while minimizing risk. If you are currently consuming within those ranges for egg consumption, there’s likely no need to change your current consumption habits.
If you are consuming more than this because you enjoy eggs as a part of your diet and you are a healthy non-diabetic person with LDL cholesterol levels that are within range, the increased risk is likely low, but you may want to weight the benefits of including this number of eggs in your diet vs. the small increased you may be exposing yourself to in terms of cancer risk.
If you are consuming more than 1 egg per day are diabetic, or you have elevated LDL cholesterol, this level of egg consumption probably carries some risk in terms of heart disease and cancer. It may be wise to consume fewer eggs or replace some whole eggs with egg whites which will reduce exposure to the components that are likely responsible for the increased risk (saturated fat, cholesterol, and choline) while still allowing you to take advantage of the high-quality protein found in the whites.
If you are currently not consuming eggs at all and they are not part of your current dietary pattern, I wouldn’t recommend adding them in simply for their nutrients as you can get enough of the nutrients found in eggs from other food sources. One exception might be pregnant women for whom meeting choline needs is twice as important and adding eggs to the diet regularly can help to meet those needs.
Free Range vs. Cage Free vs. Caged Eggs
The last point is that there aren’t obvious differences in the nutritional value of different eggs based on farming practices(16-18). So choose what makes the most sense for you based on your own budget.
Citations
Sources:
- https://nutritiondata.self.com/facts/dairy-and-egg-products/111/2
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9316657/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4480671/
- https://ods.od.nih.gov/factsheets/Choline-HealthProfessional/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9143438/
- https://pubmed.ncbi.nlm.nih.gov/32524644/
- https://pubmed.ncbi.nlm.nih.gov/35396834/
- https://pubmed.ncbi.nlm.nih.gov/35360933/
- https://pubmed.ncbi.nlm.nih.gov/35711545/
- https://pubmed.ncbi.nlm.nih.gov/34455534/
- https://pubmed.ncbi.nlm.nih.gov/26293984/
- https://pubmed.ncbi.nlm.nih.gov/24500371/
- https://pubmed.ncbi.nlm.nih.gov/33751965/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3441112/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4135488/
- https://pubmed.ncbi.nlm.nih.gov/28339969/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6853034/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8103914/
