[scythe]

>Correlation does not imply causation

Correlation does not guarantee causation. But the stronger the correlation, the more you suspect that two phenomena are causally linked somehow. In this case, three pounds over half a year is a surprisingly large effect. If it were to continue, even if it slowly approaches an equilibrium, it could be responsible for a substantial increase in total body weight in millions of people. It's very possible that PFAS is just acting as a proxy for exposure to packaged foods, but that would be interesting in itself.

In this case, the best course of action is to study the phenomenon more closely, mostly because it is large.

[twawaaay]

Causal link requires an investigation to understand what is the nature of the link.

Is it possible that people who are likely to be more obese are also likely to eat garbage food delivered in low quality plastic packaging? And more healthy people are more likely to cook their food from higher quality ingredients like fresh produce that is not delivered in plastic?

See, the above explanation, I think very reasonable (though requiring a proof), could explain why obese people could have higher PFAS?

Another possible explanation (again, I am just sayin', no proof for it): imagine all food is contaminated with PFAS, but obese people have different chemistry that is worse at removing PFAS from their bodies.

This is why we say "correlation does not imply causation". Yes, highly correlated things are interesting and require further investigation. Even if PFAS is not causing obesity we still might learn something interesting about either PFAS or obesity or something else that is connected to both.