Do eggs harm or benefit health? How many can we safely eat?
In general, there is confusion as to whether eggs can be considered part of a healthy diet or whether they can actually be bad for our health.
This comes mainly from the fact that until a few years ago the recommendations were negative, as the egg is a source of cholesterol. Over the years, however, it has been found that not all sources of cholesterol have the same effect on cholesterol levels.
It seems that finally the cholesterol has a relatively modest effect on total and LDL cholesterol, while egg phospholipids have the ability to increase HDL-c and may have positive effects on total cholesterol, things we will deal with later.
However, a recent survey found that eating even half an egg a day can increase the chances of mortality.
So who is right? Most people who have neither the time, nor access to scientific articles, nor the necessary foundation to understand who is right and who is wrong are understandably unable to attend this debate.
So, we will try to list the results of major studies to clarify whether or not eggs are ultimately a risk to our health.
So let's start with one relatively old meta-analysis which used 8 articles.
Here, no significant association was found between egg consumption and the risk of coronary heart disease or stroke, but data on more than one egg per day were limited.
Also of note, among diabetic participants, higher consumption was associated with an increased risk of coronary heart disease but a lower risk of bleeding stroke.
Go ahead in an investigation which was done by studying and comparing food groups.
Again, no association was found between egg intake and risk of coronary heart disease or stroke (with an intake of 75g/day considered high), but an association was found between egg intake and risk of heart failure (with an intake of 140g/day considered high).
So what we have here is a limit of just under 2 eggs per day.
This survey used data from 3 large international studies from 50 countries with a total of about 177000 people.
As you can deduce from the graph, this study found no significant associations between egg intake and blood lipids, mortality or major cardiovascular events, when it comes to eating one egg a day.
We go to this meta-analysis, which used 7 studies for stroke and 7 for coronary heart disease.
Here we found that high egg intake versus low egg intake (less than 2 eggs per week) was not associated with coronary heart disease risk, but instead was associated with a reduction in stroke risk.
Again, however, the high egg intake threshold was judged to be about 1 egg per day.
Go ahead in this 2019 study which included a total of 21 articles.
Here there was no meaningful association between egg consumption and a wide range of health outcomes, including cancer, cardiovascular and metabolic disorders. In contrast, evidence was found for possible beneficial effects of egg consumption on the risk of stroke.
Unfortunately, the recruitment limits are not mentioned here.
But let's move on to this investigation which included data from 39 studies and about 2 million people.
Here we start to see contradictory results.
On the one hand, it was found that there were consistent results on the association between moderate egg consumption (four eggs per week compared to no consumption) and lower risk of cardiovascular disease.
On the other hand, while overall there were no strong associations with increased or decreased risk of cardiovascular outcomes after moderate egg consumption (i.e. one egg per day compared to no intake), there was an association with the risk of heart failure.
This was found to be higher especially from studies from the US and the male population.
Which makes things even more complicated, as we understand that there are health outcomes in this particular survey that vary by region.
As we can see in the table above, in the case of four eggs per week, egg consumption may be associated with favourable outcomes in the US but unfavourable in Europe (or with unfavourable outcomes in both regions as in the case of heart failure and consumption of one egg per day), while in Asia it seems that egg consumption is always associated with favourable outcomes.
And anyway, again we see that we are talking about relatively moderate egg consumption (up to 1 egg per day) and not excessive.
So let's focus our attention on China by going to another huge survey that lasted 4 years and included almost half a million people there.
Here, more frequent consumption of eggs was associated with a lower risk of cardiovascular disease, ischaemic heart disease, major coronary events, haemorrhagic stroke and ischaemic stroke in non-diabetics.
But again, frequent consumption of eggs was considered something less than 6 eggs per week.
And finally we will refer to in a 2018 survey which was done again in China. Something less than 30,000 people took part and were followed for just under a decade, on average.
Here, no association was found between egg consumption and the risk of cardiovascular disease, ischaemic heart disease, stroke or all-cause mortality.
The comparison was between eating less than 1 egg with 7 or more per week.
To draw more definitive conclusions, however, let's move on to meta-analyses that analyse lipids.
This meta-analysis of 2017 found that egg consumption increases total cholesterol, "bad cholesterol" (LDL-C) and "good cholesterol" (HDL-C) by 5.32, 5.28 and 2.08 mg/dL, respectively, but does not significantly change total cholesterol:HDL-C ratio, LDL-C:HDL-C ratio and triglycerides.
This 2019 meta-analysis found that the consumption of more than four eggs a week instead of equivalent amounts of egg substitutes resulted in greater increases in total cholesterol, LDL-C and HDL-C, not triglycerides.
And finally this 2020 meta-analysis comes to much the same conclusions as the previous ones, but notes that this increase is greater in healthy populations and in people who consume more than one egg per day.
So we can draw some conclusions.
- There are differences in the health effects of egg consumption depending on the region.
- This is probably due to the fact that in the West we often eat eggs with processed meats (such as bacon and sausage), fried with butter, as well as in pastries and cakes containing trans fats.
- Finally, we have to take into account the fact that eggs are a cheap source of protein, which can have health benefits in poor and/or older populations vulnerable to sarcopenia and malnutrition, which in itself is a confounding factor in terms of positive health effects.
- The majority of meta-analyses suggest that one egg a day seems to be safe. However, this number is not a rule of thumb, as it is possible that one can consume more by keeping the second point in mind and having frequent blood tests. This does mean, however, that there are cases where either they will need to change their diet to control their cholesterol, and/or they will need to eat fewer eggs.
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