Regulators fault for not picking up on it. Also the peoples fault for voting these kinda regulators into their position. Happened decades ago with all the teflon thats now in all of our bloodstreams and will continue in the future.

Depends on how much information the people have. If they are aware this chemical is present and its effects, the consumers. If they are not, the criminals who poisoned the food secretly.

Although I think that if people notice themselves getting fat they should probably take action for their own sakes anyway, it falls down a bit here with this idea no one has agency..