Representatives from Cancer Research UK say that the news is concerning, because the public might take it as a green light to shirk responsibility for their own health.
Researchers at University College London claim that 77 percent of variations in waist size and body mass index are caused by genes.
Speaking to Sky News, Director of Health Information at Cancer Research UK, Sara Hiom, said: "This is not evidence of one fat gene. What it does tell us is that our genes are obviously very important for determining whether we will or won't put on weight as we age.
"This study has actually shown that for those people whose genes make them more susceptible to weight gain that they need to work even harder to cope with the modern environment that has been created around us."
Ms Hiom pointed out that while the gene pool has not changed over the years obesity has still increased, so lifestyle factors must also be to blame.
Senior Science Information Officer at the charity, Dr Julie Sharp, added: "It is important that people do not become fatalistic about this and decide that it is all in their genes therefore they cannot do anything.
"The obesity problem we have now has been caused by the environment, it has been caused by the fact that people aren't eating healthily, they aren't getting exercise."
