A gene variant, earlier known to protect people against weight gain and insulin resistance, could have an opposite effect in people who eat a high-fat diet and are heavier, according to a study on mice.

The results indicated that the 12 percent of people who carry the so-called Ala12 version of the gene that serves as a master controller of fat differentiation would be more sensitive than most to the amount of fat in their diets.

The fat-moderating gene is called peroxisome proliferator-activated receptor gamma isoform 2, or Pparg2.

However, the researchers said that the Ala12 gene variant is less active and less efficient in driving fat cells' formation than the more common Pro12 version.

Thus, people with Ala12 are generally less obese and more sensitive to insulin, but that can change if they shift to a less sensible, fat-laden meal plan.

Johan Auwerx of Universite Louis Pasteur in France and the Ecole Polytechnique Federale de Lausanne in Switzerland said that genetic testing for the variant could thus be used as a diagnostic tool.

"Through dietary counseling, carriers could be informed that they really need to watch out for high fat in their diets," he said.

Also, he added that the findings raised a potential caution about the long-term effects of drugs called thiazolidinediones (TZDs), which stimulate activity of the Pparg2 receptor and are used for the treatment of diabetes.