A 'double-muscled' pig has been created by editing just one gene by scientists in South Korea and China.

Cattle have been selectively bred over many generations to produce larger amounts of beef. The researchers, led by Jin-Soo Kim, a molecular biologist at Seoul National University, say they are now able to do this with pork without the years of selective breeding.

In a report in Nature magazine, the scientists say they hope their pigs will be among the first genetically modified animals to be approved for human consumption. Regulators are ambivalent about approving such products because of concerns about environmental and health problems.

However, the researchers created the double-muscle pigs by editing just one single gene, meaning the change is far less extreme than those seen in conventional genetic modification.

The team say their method would vastly speed up the selective breeding process in a more natural way than previous GM attempts. "We could do this through breeding, but then it would take decades," Kim told the magazine.

To create the muscly pigs, the scientists targeted a mutation in the myostatin gene that inhibits the growth of muscle cells. In some other species, disrupting this gene leads muscle cells to proliferate, creating an abnormal bulk of muscle.

Kim edited the pig foetal cells using technology known as TALEN, and while the team is yet to publish their results, photos show the pigs are far more muscular than non-GM pigs.

However, of the 32 pigs created, only 13 lived to eight months old and only two are still alive to date. The researchers say that rather than creating the pigs in a lab, they would supply farmers with the sperm that could then be used in normal breeding – these pigs would have one disrupted gene and one normal gene, making them healthier but less muscly than the fully GM pigs.

Kim says he believes China will be the first market they sell the product to as regulations are less strict and the nation is currently investing in gene editing. However, if and when other countries follow is yet to be seen.