The ability of n-3 long chain polyunsaturated fatty acids (PUFAs) to prevent high fat diet-in- duced obesity in rodents is well documented. Evidence for a similar effect in humans is, how- ever, limited. Intervention studies in humans are inconclusive and epidemiological studies are dichotomous. Our recent finding that sucrose and other high glycemic index carbohydrates abrogate the antiobesity effect of n-3 PUFAs might, at least in part, provide an explanation to the apparent discrepancy between human
and rodent intervention studies, and the lack of effect in some human trials. In addition to the amount and type of carbohydrates, the levels of n-6 PUFAs, linoleic acid in particular, in the background diet might influence the antiobesogenic effect of n-3 PUFAs. Lastly, it is plausible that the quantity of persistent organic pollutants in fish oil, and seafood rich in n-3 PUFAs, might influence on the outcome of the trials.