No, Eating Eggs Will NOT Protect You From Cardiovascular Death

No, Eating Eggs Will NOT Protect You From Cardiovascular Death


All those egg-bashing scientists are going
to have egg on their face when this study, which is no yolk, cracks the case on the dietary
benefits of those calcium-carbonate covered comestibles. This ends the egg humor part of the presentation. I need to joke a bit though, because honestly,
it sort of pains me to talk about studies like this. But I need to talk about them, because other
people talk about them, and I feel like as a physician part of my job is to say no, don’t
take these studies seriously. But before I rant, here’s what you need
to know: a huge study of 500,000 Chinese people found that those who ate more eggs had less
cardiovascular death. So, are eggs back on the menu? I don’t know – these studies really don’t
tell us whether adding eggs or removing eggs from your diet will make any difference. I’ll put it really plainly: Studies that
use responses to a food-frequency questionnaire to link to some health outcome are not worth
the paper they are printed on. And so let me use this recent egg study as
an object lesson in the problems with dietary epidemiology research. First – no one eats randomly. Except my two year old who asked for pasta
this morning. The rest of the world chooses what they eat
based on a variety of social, economic, practical, and gustatory factors. These confounders can not be controlled for
with simple statistical adjustment. If I told you that American eaters of foie
gras live longer than those who don’t, would you attribute that to the foie gras, or to
the fact that these 1 percenters have access to quality healthcare and other good things? And, as I’ve discussed before, adjustment
for things like “income range” does not fully account for the complex socioeconomic
web we weave. Second – Eggs, like coffee, marijuana, wine,
chocolate, and many other exposures are not really one thing. While the macronutrient composition of eggs
is somewhat stable, the micronutrient composition is all over the map. When researchers say coffee protects against
colon cancer, are they referring to black coffee or a double-tall mocha Frappuccino? When the exposure is muddy in this way, inferences
about effects become much less reliable. Third – multiple comparisons. There are over 130 food items on the dietary
health questionnaire. The chance that one of those 130 items will
appear to be statistically linked to any health outcome is near 100% – I just have to try
them all. In fact, given no true relationship, there
will be, on average, 6 or 7 items on the questionnaire that nevertheless fall below our conventional
statistical significance threshold of 0.05. Fourth – I told you there are 130 items
on the food frequency questionnaire. But I can make even more. I can combine items to calculate your total
calorie intake, or fat intake, or magnesium intake, or even your pesticide intake. More potential exposures! Fifth – many of these dietary studies use
huge datasets, like the China Kadoorie biobank with its 500,000 participants in the egg study. This means it is trivially easy to find statistically
significant effects that are not remotely clinically interesting. Even if you believe the primary findings of
this study – that consuming an egg per day reduces your risk of cardiovascular death
by 18% compared to rarely eating eggs, the absolute effect is tiny. You’d need to treat nearly 800 people with
daily eggs to prevent one cardiovascular death per year. That’s a lot of umm… The bottom line: what you put into your body
matters, but you put a lot of stuff into your body. No one thing is going to keep you alive, and
conversely, no one thing is going to kill you. So when your friend tells you that you should
eat more eggs based on this study, remember how Homer Simpson handled it:
So the next time you see a study that uses a food frequency questionnaire to make some
inference about something you eat, remember: it’s all a shell game.

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