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 body mass index 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 omega-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-omega-6 oils substantially degrades polyunsaturated fatty acid bioavailability. Third, heavy metal co-contamination in arsenic- and mercury-affected watersheds may attenuate omega-3 benefits. Fourth, urbanization 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 realize fish's cardioprotective potential in South Asia.