We have to thank mice, again. Researchers in Japan, fed overweight mice a diet that was 30% fat. One group of mice received 8% of that in the form of fish oil. 5 months later, the mice that were given fish oil had significantly reduced weight gain than the poor fellas that were given no fish oil.
The cool thing is that the fish oil had an effect on lipid metabolism genes, as well as lipid metabolism related enzymes. The fish oil group also had higher levels of fatty acid ß-oxidation. Even though this study was looking at one of the mechanisms in which fish oil could lower body fat, namely intestinal lipid metabolism, it's another piece to the puzzle that will let us appreciate the many ways fish oil reduces fat levels.