Their technology could be adapted for use in livestock that produce meat, milk and eggs fortified with omega-3 fatty acids, they say, foods that could rival fish oil supplements.
Omega-3 fatty acids have been shown to significantly reduce the risk of heart disease and related cardiovascular events. They are also thought to play an important role in mental health, with studies suggesting that they could reduce risk of Alzheimer's disease. But Western diets tend to contain about ten times more omega-6 fatty acids than omega-3.
However producers of the most common source of omega-3 fatty acids, fish oils, face a technical challenge when adding the fishy ingredient to foods. There have also been recent scares over the safety of eating fish - just last week the US Environmental Protection Agency doubled its estimate of how many newborns had unsafe levels of mercury in their blood.
At the same time, a new study in the Journal of Pediatrics (doi:10.1016/j.jpeds.2003.10.059 (2004) shows that children exposed to mercury in the womb may suffer permanent damage to their heart function.
The study of more than 1,000 mothers and children living in Denmark's Faroe Islands, where the population eats large amounts of fish and whalemeat often contaminated with mercury, measured mercury in blood taken from the children at birth and then in hair samples taken at ages seven and 14.
Later the researchers used electrodes on the heads of the children to measure electrical signals in the brain and found delays in brain signaling. The higher the mother and child's mercury load at birth, the more distinct the irregularities. They also found these neurological changes led to poorer system control of heart function.
The news will prompt some nutritionists to advise alternative non-fish sources of omega-3 fatty acids. Several research groups have investigated changes to animal diets that could produce higher quantities of beneficial oils in the resulting food produce. But this also raises the cost of animal feed.
Researchers at Harvard Medical School describe in Nature how they transferred the fat-1 gene, which encodes an enzyme that converts omega-6 to omega-3 fatty acids, into mice. Mammals cannot usually change omega-6 fats into omega-3s.
The animals were raised on a diet rich in omega-6 and lacking omega-3 fatty acids. In a control group, tissue polyunsaturated fatty acids consist primarily of linolenic and arachidonic acids, both omega-6 fatty acids. But the engineered mice produced a balanced mix of omega-6 to omega-3 fatty acids in muscle, milk, and other tested organs, said the researchers.
In a report by Reuters Health, the team said it is now attempting to cross fat-1-producing animals with obese mice that develop diabetes to find out if this could change the disease process or development.