I'm often saddened to see how even on this kind of community where the level of discussion is relatively high given the openness of the platform, this kind of cross-country comparison is almost completely forgotten when it debunks so many, possibly even the majority, of arguments made on a host of topics including this one. It isn't helped by the fact that HN, given its roots and SV focus, is very Ameri-centric - ime e.g. Europeans are at least somewhat more likely to consider regional comparisons, though they're still underutilized.

A 20-second search for "obesity rates by country" will show that plastics or other chemicals are very unlikely to play more than a minor role. It's so straightforward, yet there are dozens and dozens of comments above this one with not a single one bringing it up.

In the end, CICO is correct. The question then becomes "why do certain countries have a higher CI" to which the answer is "culture", as with anything to do with human behaviour. But most are very unwilling to point at things about certain cultures that are very clearly negative, something that both mainstream Western political leanings have in common. One of them because they believe their culture is inherently Great (Again?) even if it's sending them to an early deathbed, the other because they believe (or at least outwardly adhere to the dogma) that cultures should not be compared in any kind of positive vs negative way unless it's one they see as a political opponent on the national scale.