The cholesterol present in eggs has given rise to quite different dietary positions, which have evolved from rigorous restrictions in the past to more lax and tolerant current recommendations with the intake of up to one egg a day in healthy people. The surprising thing is that all these recommendations did not have much evidence behind them, since intervention trials on the topic were scarce and their results were quite heterogeneous. he Latest meta-analysis on the relationship between egg intake and blood cholesterol., was published in 2017 and was a work that did not reach very conclusive results either, as explained in this post. Therefore, he was also not able to definitively settle the debate on this controversial relationship.
Fortunately, we have news. Just a few weeks ago a new meta-analysis was published, «Association between egg consumption and cholesterol concentration: a systematic review and meta-analysis of randomized controlled trials» (2020). This research, although it also focuses on intervention trials, has some differences with the previous one. In this case, only trials carried out with healthy people (without hypercholesterolemia or any other known pathology) have been taken into account and includes some additional trials, one recent and four before the year 2000 (in the previous meta-analysis only works after the year 2000 are selected).
After the appropriate searches and filters, the authors selected 17 trials, in which the changes produced in LDL and HDL cholesterol were compared after eating one, two and up to three eggs a day with respect to the usual diet or with respect to not eating any. The following table summarizes the characteristics of each of them, as well as their main results (click to enlarge):
At the end of the document we can find the authors’ final conclusions:
«(…) this is the largest meta-analysis analyzing the impact of egg consumption on the LDL-c/HDL-c ratio among healthy subjects and reveals that a greater number of eggs consumed per day may influence disease risks cardiovascular by increasing LDL-c and the LDL-c/HDL-c ratio. In particular, long-term high egg consumption can lead to a higher LDL-c/HDL-c ratio and LDL-c. However, «Randomized trials with long-term follow-up are needed to ensure the association between egg consumption and human health.»
This does not seem like good news, since a higher intake is associated with higher LDL values.
But let’s get to know the details and conclusions of the review better, because there are some quite interesting aspects.
Firstly, with regard to LDL cholesterol (known as «bad»), the review concludes that daily egg intake leads to an average increase of about 8 mg/dL, as seen in the following figure:
If we look at the results of each of the trials, we can see that in some studies there is a lot of interpersonal variability in the results; in some groups of people the changes were even negative (and were classified as «hyperresponders» and identified with the letter «a» in the figure) and in other cases cholesterol clearly increased (classified as «hyperresponders» and identified with the letter » b»). In any case, an increase was mostly seen, so the final average value was positive, remaining at those modest 8 mg/dL.
Regarding HDL (or «good») cholesterol, the calculations show a small increase in its value (1.27 mg/dL), which was not statistically significant.
On the other hand, the variation of the LDL/HDL coefficient was analyzed, since as the relationship with cardiovascular disease for one is direct and that for the other is inverse, this figure helps to know the variation in the global effect. The result of the meta-analysis showed that by eating eggs daily this coefficient increases on average by 0.14:
Again we find broad interpersonal differences, «hyporresponders» (a) and hyperresponders (b).
If we continue reading the meta-analysis, we find more interesting aspects. The authors have segmented the results based on the number of eggs ingested daily, one, two or three units. And they present them in the following table:
If we analyze the figures, we see that in any of the three cases the LDL and LDL/HDL figures are positive, that is, they increase compared to not eating eggs, but there does not seem to be a «dose response», something that was also detected . in the 2017 meta-analysis. That is, eating more eggs does not increase cholesterol concentration to a greater extent: when comparing LDL values with one egg a day, two or three (red box) the values practically do not change nor do they present any trend. However, in the case of HDL (blue box) the values do seem to change, especially if 3 or more eggs are ingested daily; In this case, HDL increases clearly. And let us remember that in principle HDL is associated with lower risk (although it is also true that these changes will not be considered statistically significant).
Therefore, paradoxically, the LDL/HDL ratio eating three eggs a day is somewhat lower than with one egg a day, which «formally» could translate as a small reduction in risk (although it is still greater than without eating eggs).
Interesting, right?
In any case, since cholesterol is not a»hard-point» (a direct indicator of disease or mortality), but rather an intermediate indicator, it is best to stick to the data: this meta-analysis indicates that in the case of healthy people and Without hypercholesterolemia (personally I think the group of people with high cholesterol would be more interesting), eating one or more eggs a day compared to not eating any increases LDL by an average value of 8.18 mg/dL. And by eating three eggs a day or more, the LDL/HDL ratio slightly improves compared to eating one or two.
Interpretation of the conclusions
When interpreting all these data and using them as a reference for clinical application, the ranges recommended in the official recommendations: For LDL, normal concentrations are considered below 100 mg/dL, normal-high concentrations of 100-160 mg/dL and high concentrations above 160 mg/dL. Regarding HDL, it is recommended that it be above 35-40 mg/dL. And regarding the LDL/HDL coefficient, a value less than 3 in men and less than 2.5 in women is usually recommended. Considering all this, we will be able to make the appropriate decisions with the help of our healthcare professional. And if you want to delve deeper into the topic of cholesterol and health, you can consult this series of posts that I published on the subject.
But we should not take these results as absolute and definitive either. If you read the results of the meta-analysis above, you will see that the conclusions are quite different. This is what can happen when the trial selection criteria are not the same, as has been the case. «We must also take into account the aforementioned interpersonal variability, which has been known for some time and has been reconfirmed in a subsequent trial (not included in the meta-analysis),»Differences in response to egg-derived dietary cholesterol result in distinct lipoprotein profiles, while plasma concentrations of carotenoids and choline are not affected in a young, healthy population.» (2019). In this recent research, only a third of the subjects suffered an increase in their LDL cholesterol values after eating three eggs a day, while two thirds had no changes or these were reduced. In addition, the increase in LDL in This third of people was mainly due to the greater number of larger lipoprotein particles, which are associated with lower risk. And on the other hand, they did not suffer changes in the LDL/HDL ratio and improved in other interesting health indicators.
In any case, it is worth keeping a couple of things in mind, which I have already mentioned on several occasions.
The first, that the concentration of cholesterol in the blood is especially affected by the intake of saturated fats (1, 2), rather than dietary cholesterol. And, as explained in detail in this previous post, a good part of the saturated fat we eat comes from ultra-processed foods. Therefore, in order to change something in the diet with the aim of reducing cholesterol, I think it would be a good idea to start by reducing these types of products. It is very likely that it will improve significantly in a short time and almost certainly other parameters will also improve, as explained in this previous post, or as can be deduced from the recent review.Ultra-processed foods and health outcomes: a narrative review» (2020).
And second, we must always keep in mind that cardiovascular risk not only depends on LDL and HDL cholesterol, but also on other indicators and habits. That is why it is important to evaluate the risk taking into account all the factors, not just that related to an isolated indicator, to ensure that what we can improve on one hand we do not ruin on the other.
Eggs, cardiovascular diseases and diabetes, plus meta-analysis
The authors detected that a certain reduction in the risk of coronary heart disease could be deduced from eating up to about 4 eggs per week, and a certain increase in the risk of heart failure from said value, but given the diversity of results and their lack of solidity, they concluded Que ««There is no conclusive evidence on the role of eggs in the risk of cardiovascular disease.»
The meta-analysis included the calculation of the following curves, showing the dose response in the relationship of four cardiovascular diseases (coronary heart disease, stroke, cardiovascular disease and heart failure) and egg intake:
«The results of this updated meta-analysis do not show an overall association between moderate egg consumption and the risk of type 2 diabetes.»
The most curious thing about the study is that it once again brought to light the difference in the relationship between eggs and type 2 diabetes depending on the geographical origin of the studies. North Americans find a positive relationship, Europeans find it neutral, and Asians find it negative, as seen in the image below:
