When fish fails to protect: interrogating the South Asian cardiometabolic paradox in the era of aquaculture transition.

South Asia presents a striking nutritional paradox: populations among the world's highest fish consumers carry disproportionate cardiometabolic risk at BMI levels well below disease thresholds for European populations. Marine fish is established as cardioprotective in fatty-fish-consuming coastal populations, yet this benefit appears to break down in South Asian contexts. This commentary interrogates four interlocking mechanisms. First, aquaculture-driven species substitution has replaced n-3-rich species such as hilsa and coastal sardines with leaner farmed varieties offering only a fraction of the cardioprotective lipid profile. Second, deep frying in high-n-6 oils substantially degrades PUFA bioavailability. Third, heavy metal co-contamination in arsenic- and mercury-affected watersheds may attenuate n-3 benefits. Fourth, urbanisation is eroding fish intake among the highest-risk subgroups, while aggregate dietary data obscure this heterogeneity. Generic eat-more-fish guidance is insufficient; ethnicity-sensitive, sustainability-conscious guidance on species, preparation and contamination risk is needed to realise fish's cardioprotective potential in South Asia.