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WUHAN, CHINA. Shortly after the birth of the hypothesis that dietary
fat and dietary cholesterol were bad, eggs were demonized, characterized
as a toxic food, and true believers took to eating only the egg white.
The reason - an egg contains about 200 mg of cholesterol. This was a disaster
for the egg industry since egg whites were not that popular, and also
unfortunate for the general public since eggs are an inexpensive and
low calorie source of important nutrients, including proteins, unsaturated
fatty acids and minerals. As most readers know, it turned out that fat
was not bad in the context of cardiovascular disease according to many
studies up to the present, all of which seem to be ignored, and most humans
can eat quit a lot of cholesterol without any impact on their blood levels.
The latest study just-published employed a meta-analysis (study of pooled,
weighted studies) in order to address the association between egg
consumption and the risk of coronary heart disease and stroke. The studies
involved were prospective, i.e. cohort follow-up studies, and dose response
was an issue. The meta-analysis included eight published studies with 17
reports (nine for heart disease and eight for stroke). They involved over
3 million person years follow-up for heart disease and 4 million person-years
for stroke.
The results are simple to relate. Higher consumption of eggs (up to one per
day) was not associated with increased risk of coronary heart disease or
stroke. Dose response showed no increase in risk with increased consumption,
although there was no data for greater than 10 eggs/week for heart disease
and 7 eggs per week for stroke.
Those who hold fast to the cholesterol fat is bad hypothesis will no doubt
now want studies covering wider range of egg consumption, and might even point
out that one egg a day meets the Americans Heart Association guidelines for
cholesterol consumption. However, it must also be pointed out that many
individuals can eat two or more eggs a day with no impact on their blood
cholesterol levels, and the ideal study would include both 2-3 eggs per
day and serum monitoring. The endpoints would have to be clinical and large
cohorts needed to obtain meaningful results. It is clear that this will
probably never happen.
Uffe Ravnskov, MD, PhD, describes an experiment he conducted on a sceptical
Danish doctor (himself), where he measured blood cholesterol levels after
eating from zero to 8 eggs per day. There was no trend at all. There are a
number of similar studies which reveal that responders represent only a
small percentage of random populations and that for most, the level of
blood cholesterol is independent of the dietary consumption over a
significant range. Therefore the results of the meta-analysis should
not come as a surprise. For the small minority who experience significant
cholesterol elevation with dietary consumption, we are back to the problem
that serum cholesterol is a very weak risk factor in CVD evens and LDL is
not involved in coronary atherosclerosis.
Rong Y, Chen L, Zhu T et al. Egg consumption and risk of coronary heart
disease and stroke: dose-response meta-analysis of prospective cohort
studies. BMJ 2013;346:e8539
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