Most people have heard the news that fish oil is good for you. Now, evidence from a new study suggests that using more fish oil than vegetable oil in a person's diet blocks the formation of chemicals, called prostanoids, which cause unhealthy inflammation in bodily tissues and organs.

"Prostanoids help control blood pressure, fight allergies, and modulate inflammation, but too much of them — especially those made from vegetable oils — can also lead to increased pain, swelling, and redness in various tissues," says lead researcher William L. Smith, Professor and Chair of Biological Chemistry at the University of Michigan, Ann Arbor, "Our study shows that prostanoids made from fish oil cause less pain and swelling than those made from vegetable oil and that adding fish oil to the diet decreases the amount of prostanoids made from vegetable oil."

Smith's study is to be published in the August 3, 2007 issue of the Journal of Biological Chemistry. He and his team looked at the mutual effects of both oils by changing their respective amounts in cultured cells. A relative increase in fish oil lowered the amount of prostanoids from vegetable oil, although not always in the expected proportions.

Their research identified for the first time how the body naturally regulates levels of prostanoids produced by fish and vegetable oil.

Besides helping design healthier diets, the results of this study may also help scientists develop anti-inflammatory drugs with fewer side effects than the ones currently available.