14th July, 2019
First, it’s not good, then it’s Ok and now we are not sure. Maybe it is, maybe it isn’t. We are talking about eggs and the association with cardiovascular disease and mortality. It’s stuck in many of our and our patients’ minds that eggs are no good. It doesn’t help when the 2015-2020 Dietary Guidelines for Americans came out with somewhat contradictory recommendations: “ (1) Cholesterol is not a nutrient of concern for overconsumption” and (2) “Individuals should eat as little dietary cholesterol as possible while consuming a healthy eating pattern” (1). So, are eggs associated with an increase in cardiovascular disease and mortality or not?
Let’s not get confused about the message like many of my patients who came running in to see me when they heard it on current affairs somewhere. High blood cholesterol has been proven to be strongly associated with cardiovascular disease and mortality. Further, reducing cholesterol levels in these patients have been proven to reduce those numbers. What the American guidelines conclude is that the evidence linking dietary cholesterol with cardiovascular disease (CVD) is tenuous and therefore, they cannot draw meaningful conclusions linking dietary cholesterol and CVD.
Overall, there were 29,615 participants with 524,376 person years of follow-up data. The median follow-up was 17.5 years. The 6 cohorts differed considerably in terms of sample size, age, sex, race/ethnicity, education level, BMI, and behavioural and clinical CVD risk factors, as well as incident CVD and all-cause mortality rates. Various modelling was used to identify any associations between dietary cholesterol or egg consumption and CVD and CV mortality adjusting for various confounding factors (e.g. BMI, diabetes, blood pressure, and serum lipids, dietary fats, animal protein, fibre, sodium, cholesterol-containing foods, or dietary patterns).
So, what did they find?
When they analysed the subgroups of participants, association between dietary cholesterol consumption and heart disease was stronger in participants who were more overweight (i.e. BMI lower than 25). The association was also stronger in participants high lipid levels, women and participants who consumed a high saturated fat diet.
This is one of many studies (again) looking at the association between dietary cholesterol and egg consumption and CVD and all cause mortality. Trying to answer this simple question is going to be difficult. Cholesterol, saturated fat, and animal protein often coexist in foods. The interaction and independence between dietary cholesterol and these nutrients in relation to CVD and mortality remain uncertain. Data linking dietary cholesterol or eggs are sparse. Pretty much all the studies are observational studies. The study methodology and study population are heterogeneous and therefore difficult to analyse.
Egg consumption was commonly correlated with unhealthy behaviours such as low physical activity, current smoking, and unhealthy dietary patterns. Eggs and processed or unprocessed red meat are rich in other nutrients such as choline, iron, carnitine, and added sodium (for processed meat) that have been implicated in CVD risk via different pathways.
The effect of dietary cholesterol or egg consumption appears to be different in men and women, different depending on the lipid levels and whether there is consumption of other saturated fats.
As you can see, the effects if they are correct, are only very small.