An imbalance of fatty acids may cause the lung inflammation experienced by cystic fibrosis patients, scientists have suggested.
Cystic fibrosis affects the lungs
They say too much of one acid and too little of another means patients' bodies are more prone to inflammation.
In the New England Journal of Medicine, they suggest Omega-3 oils, found in fish, could help correct the imbalance.
But experts warned CF patients not to change their diets until there is more proof they would benefit.
Each week three young people in the UK die from the disease, which is caused by the faulty CFTR gene.
CF causes an abnormally thick, sticky mucus to be produced in the body, causing chronic inflammation of the lungs leading to life-threatening infections.
The average life expectancy for a person with CF is around 31.
Researchers from the Beth Israel Deaconess Medical Center, the University of Massachusetts and Massachusetts General Hospital took tissue samples from 38 patients with cystic fibrosis.
It was found they had extremely high levels of arachidonic acid (AA) and abnormally low levels of docosahexaenoic acid (DHA).
People who did not have CF did not have the fatty acids imbalance.
Dr Steven Freedman of the gastroenterology division at Beth Israel Deaconess Medical Center, who led the research, said: "Since 1989, we have known that the defective CFTR gene is responsible for CF.
"But we didn't understand how this defective gene leads to the symptoms of the disease.
"This new study sheds light on what may be happening and provides a link between CFTR function and fatty acid metabolism."
He added: "It is known that high amounts of AA and low amounts of DHA would predispose to inflammation.
"This discovery may help explain why there is an excessive inflammatory response among CF patients.
"This is the basis for why Omega-3 fish oils, found in cold-water fish as well as supplements, reduce inflammation since they increase levels of DHA and suppress AA."
'No diet change'
Dr Adam Jaffe, head of the CF Research Group at London's Institute of Child Health, told BBC News Online the research was interesting but not conclusive.
He said: "We need to look more at how the abnormal gene relates to the inflammation and to the fatty acid imbalance.
"We need to know more about the relationship between the three."
CF patients have trouble absorbing fats because their pancreas does not work effectively, so doctors advise a high-fat diet to compensate.
Dr Jaffe said he would not suggest patients start substituting fish into their diet.
He said: "Patients shouldn't change their diet based on spurious associations between fatty acids and inflammation.
"But I would not be against them adding supplements to their diets."