Credit: Brian Jackson

Omega-3 fatty acids, such as those found in fish oils, are known to be effective in treating conditions associated with insulin resistance and chronic inflammation, such as diabetes. Now, thanks to new research from Jerrold Olefsky of the University of California, San Diego School of Medicine and colleagues, the mechanisms underlying these anti-inflammatory properties is somewhat better understood. Their results could lead to the development of a dietary supplement to treat the inflammation that characterizes obesity and other conditions.

Inflammation is part of the body's immune response to perceived threats. It is caused by cytokines secreted by specialized white blood cells called macrophages. Obese fat tissue contains numerous macrophages, producing relatively large quantities of cytokines. Overexposure to cytokines may cause chronic inflammation and insulin resistance in neighboring cells. In insulin resistance, insulin loses its effectiveness at controlling the level of blood sugar in the body; this can create various health problems, including type 2 diabetes mellitus.

Olefsky and his group identified a key receptor expressed by macrophages in obese body fat. This receptor, called GPR120, has inflammatory effects when it is turned off. But when it is exposed to omega-3 fatty acids, it becomes activated and has strong anti-inflammatory effects (Cell 142, 687–698; 2010). “It's just an incredibly potent effect. The omega-3 fatty acids switch on the receptor, killing the inflammatory response,” stated Olefsky in a press release.

The researchers studied the effects of the omega-3 fatty acids docosahexaenoic acid and eicosapentaenoic acid (the main ingredients in fish oil) on inflammation and insulin resistance in wild-type mice and in mice genetically engineered to lack the GPR120 receptor. All of the mice were fed a high-fat diet, and some of each genotype were given omega-3 fatty acid supplements. Both wild-type and GPR120-knockout mice became obese when fed the high-fat diet. The fatty acid supplements inhibited inflammation and enhanced insulin sensitivity in wild-type obese mice but not in GPR120-knockout mice.

Olefsky noted that the study's result “...suggests a possible way to treating the serious problems of inflammation in obesity and in conditions like diabetes, cancer and cardiovascular disease through simple dietary supplementation.” Further research will be needed to identify a safe, effective dose. Consumption of large quantities of fish oil has been linked to increased risk of bleeding and stroke in some people. Furthermore, it is not known whether dietary supplements or fatty fish supply enough omega-3 fatty acids to activate GPR120.