Trans-fatty acids are blamed for a host of health problems, from high cholesterol to increased risk of heart disease, but in the July Journal of Lipid research, a new study of rats suggests that trans-fats - while still relatively unhealthy -- do not increase the risk of insulin resistance and diabetes.

Earlier epidemiological studies had indicated that heavy consumption of trans-fats may affect muscle insulin sensitivity, lessening muscles' ability to burn energy, which would result in reduced fat oxidation and increased insulin resistance. So Beatrice Morio of the French National Institute for Agricultural Research and her colleagues launched a dietary study of rats, wherein the rats got an eight-week diet enriched in either industrial trans-fats (processed oils), natural trans-fats (dairy fat), or regular unsaturated fats.

At the end of the trial, none of the rats displayed altered insulin or glucose responses, nor was their muscle capacity significantly affected. In further cell culture studies, there was no noticeable difference in the insulin sensitivity of the cells.

The researchers concluded that trans-fatty acids are still generally unhealthy, but muscles treat them like regular fats, meaning that trans-fat metabolites won't remain in muscles and increase the risk of insulin resistance and diabetes.