About one-third of women could have a mutated gene that leads to weight gain, a new study claims. The gene could one day help researchers create tests that predict which women are likely to put on pounds.

Researchers from Maastricht University in Holland recruited nearly 5,000 men and women for their study, watched them lose and gain weight for 10 years, and conducted a DNA analysis that discovered a mutation in women that could lead to formation of fatty tissue.

Specifically, the mutant of a gene called the MMP2 gene was more common in women who put on pounds, but not in men who did. Freek Bouwman, lead author of the study for nutrition and toxicology research at Maastricht, said nearly 30 percent of women have this impaired MMP2 gene.

Men, on the other hand, have a faulty gene called FTO that also leads to weight gain.

"Men with a certain mutation of the FTO gene had 87 percent increased risk for gaining weight compared with those without it," the authors wrote in the study.

So what does this FTO gene actually do? According to researchers, it increases the urges in men to eat sugary and fatty foods. The investigators dubbed it the "junk food gene" because men with the mutated version of FTO would eat 100 calories more than the average man at a meal. In one week, that adds up to 2,100 extra calories.

Researchers presented their findings at the European Congress on Obesity in Liverpool, which was held from May 12 to 15. They speculate both FTO and MMP2 are gender-specific since they're regulated by sex hormones.

These findings have the potential to track individuals who are most at risk of gaining weight after they lost it.

John Wilding, professor of the UK Association for the Study of Obesity, said genes are not completely at fault. "People should still worry about what they eat, he told the Daily Mail. "You can't change your genes, but you can change your behavior."