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 eggs.

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: