The right fats: omega-3 fatty acids soothe inflamed colons. (Science News This Week).

A diet containing fish oil, which is rich in healthful omega-3 fatty acids, reduces symptoms of a colitis-like condition in rats, according to new research. The finding suggests that a proper dietary balance of beneficial fats could be an effective component of therapy in similarly affected people.

Ulcerative colitis, an inflammation of the colon that results in chronic abdominal pain and bloody diarrhea, and a related disorder called Crohn's disease, which produces similar inflammation in the small intestine, are together known as inflammatory bowel disease (IBD). Genetic factors (SN: 5/26/01, p. 327), infectious agents (SN: 11/9/96, p. 302), and diet all appear to play roles in these diseases, which affect up to 5 individuals per 1,000 in industrialized countries. Steroids and other treatments can reduce inflammation, but a cure remains elusive.

To test whether the relative amounts of essential fatty acids in the diet affects colitis-related damage, Natalia Nieto and her colleagues at the University of Granada in Spain induced ulcerative colitis in a group of rats by administering a substance known as trinitrobenzene sulfonic acid through a tube into the animals' colons.

The researchers then divided the rats into three groups and fed each a diet that differed in its sources of fats but had the same low amount of fat overall. One group of rats received its fat allotment in oils from olives, soybeans, and coconuts. Another group consumed these vegetable oils plus animal fat--from pig brains. The diet of a third set of rats contained a mixture of the vegetable oils plus fish oil.

Fish oil, fatty fish such as tuna, canola off, flaxseed, and some nuts are good sources of omega-3 fatty acids, which are nutritionally essential polyunsaturated fats. Most essential fatty acids in other foods belong to the omega-6 family. Animal fats and many vegetable oils also contain large quantities of nonessential saturated fats.

The rats on the diet containing fish oil got less than twice as much omega-6 fats as omega-3 fats, while animals receiving the other two regimens got up to 12.5 times as much omega-6 as omega-3 fat. By many indicators, including visual and microscopic evaluation of the colon and analysis of blood enzymes that indicate the degree of colon injury, the rats on the diet containing the fish oil fared the best. According to some of these indicators, the rats receiving only vegetable oils were significantly healthier than those on the diet containing pig fat, but they still suffered more colon injury than those consuming fish oil, the researchers report in the January Journal of Nutrition.

The study bolsters evidence that "dietary fat manipulation ... can be a supportive or additional treatment option for IBD patients," says Ryosuke Shoda of the International Medical Center of Japan in Tokyo.

However, under clinical conditions, it's difficult to achieve the low ratio of omega-6 fats to omega-3 fats used in the rat diet containing fish oil, Shoda says. He cautions also that artificially induced colitis may not be a suitable model for the human disease.