There has been much published over the past 10-15 years regarding the health benefits of a diet containing foods rich in omega-3 polyunsaturated fatty acids (PUFAs), in particular eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Some of the best sources for these protective bioactive lipids are cold water fishes and krill. I won't delve into the science here that clearly shows the health benefits of these PUFAs so if you need more information go to either http://themedicalbiochemistrypage.org/omegafats.php or http://supplementscience.org/pufas.html for the details.
But are all omega-3 PUFAs created equally, do they confer the same level of protection? Well in many studies there is clearly a difference in the efficacy of EPA over DHA and visa versa. But with respect to the growing epidemic of obesity in the US and other "Western" diet consuming countries it appears that DHA may be the fat to increase in ones diet. Due to rising obesity rates there has been a significant increase in the incidence of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). While both NAFLD and NASH are characterized by hepatosteatosis, NASH is characterized by hepatic damage, inflammation, oxidative stress, and fibrosis. Both of these disorders ultimately lead to severe cirrhosis and liver failure resulting in death.
Research from the University of Oregon Health Sciences Center, conducted in the lab of Dr. Jump, has recently shown that mice consuming a typical Western diet but supplemented with DHA showed a reduced incidence of developing NASH and that this coincided with a reduction in the level of expression of numerous genetic markers correlated to NASH development such as inflammatory genes and oxidative stress-related genes. The decrease in the development of NASH in these animals was significantly greater when the diet was supplemented with DHA compared to one supplemented with EPA. The take-home from these animals studies is that dietary supplementation with DHA may be useful in combating NASH in obese humans.
The results of this study were published online in the Journal of Nutrition: http://jn.nutrition.org/content/early/2013/01/07/jn.112.171322.abstract?sid=c4c2eb61-7b15-40c3-9a8d-71715fc0b8b7
I should point out here that simply taking supplements containing purified DHA may not be sufficient to obtain the necessary uptake of the fat as research has shown that DHA is not readily absorbed from the human gut and that a large percentage is excreted in the feces. This means that it may require very large intake doses to obtain the desired effects within the body. Research has shown that absorption of DHA obtained from dietary krill oils is much higher than fish oils or free DHA itself.