A small group of people carry a genetic mutation which helps protect their heart against the harmful effects of fatty foods, scientists said on Thursday.

Several researchers from three universities in the United States carried out a study on 809 volunteers from the Lancaster Amish population, in order to search for genes which play a role in individual differences in the body's handling of triglycerides, a common form of fat in the blood. The participants were given milkshakes that contained particularly heavy cream. After six hours, samples of their blood were taken so as to see how much fat was in their bloodstream.

The levels of triglycerides of most individuals in the study increased gradually for three to four hours and then dropped, as expected. However, fat levels in roughly 5 percent of participants started off low and barely budged.

Scientists found that those 5 percent had a mutation that put out of action one of their two copies of a gene known as apoC-III. The gene codes for a protein, APOC3, which usually reduces the breakdown of fats. Those with apoC-III produced about 50 percent of the normal amount of apoC-III and had the most diminished levels of triglyceride, most probably for the reason that they were able to break down more of the fat in their bloodstream.

According to lead author Dr Toni Pollin, from the University of Maryland, the findings may open the door to improved therapies for cardiovascular disease. Each year, cardiovascular diseases kill more Americans than cancer does.

The gene mutation works by blocking the production of chemical which keeps triglycerides circulating in the bloodstream for longer. The chemical lacking, the fats are passed through the blood more rapidly, researchers said in the journal Science.

“This is among the strongest human evidence we have that APOC3 is quote, unquote, bad,” said Dr. Daniel J. Rader, a heart disease researcher at the University of Pennsylvania. “If you had a drug to turn off the gene to prevent as much APOC3 being made, this study suggests that that would be beneficial to do.”