by Craig Weatherby
There’s more good news about omega-3s and bowel health.
Affirming prior indications, Harvard researchers reported last year that diets high in omega-3 fats may help deter colon cancer (Hall MN et al. 2008).
Now, the results of a large, pan-European epidemiological study suggest that diets high in omega-3 fat may cut the risk of ulcerative colitis—a type of inflammatory bowel disease—by 77 percent.
In contrast, higher intakes of the omega-6 fat called linoleic acid (LA)—the dominant polyunsaturated fat in American diets—may double the risk of colitis.
The study adds to a fast-growing body of evidence supporting the importance of balance between omega-3 and omega-6 fatty acids.
Study author Dr. Andrew Hart of the UK’s University of East Anglia said that the findings may ultimately be more relevant to people already suffering from ulcerative colitis.
“I think it is a balance between the omega-3 and omega-6,” said Dr Hart. “We’ve shown a positive correlation for omega-6 with a plausible biological mechanism, and a negative correlation for omega-3 with a plausible biological mechanism for that.”
Dr. Hart stressed that other studies need to replicate these findings.
Inflammation, disease, and America's omega-6 excess
Omega-6 fatty acids are present in the cell membrane of colon cells in the form of arachidonic acid, which the body makes from the omega-6 fat LA, in which the American diet is overly abundant.
Omega-6 LA abounds in the cheapest and most common cooking oils (soy, corn, safflower, cottonseed, and sunflower), red meat (particularly beef and pork), and margarines.
Processed and prepared foods are usually made with these oils, so they, too, are awash in omega-6 fats. This explains why the American diet is so gravely imbalanced in favor of omega-6s.
Humans evolved on diets with about three parts omega-6 fat to one part omega-3 fat—a 3:1 ratio—but that ratio has risen to 20:1 or more.
Omega-6 arachidonic acid is used to produce pro-inflammatory immune system chemicals such as prostaglandin E2, leukotriene B4 and thromboxane A2.
Conversely, omega-3 fatty acids yield immune system chemicals with anti-inflammatory effects.
Colitis study details
These findings flow from the European Prospective Investigation into Cancer and Nutrition (EPIC), which involved 203,193 men and women.
Dr. Hart analyzed data from EPIC volunteers in the UK, Sweden, Denmark, Germany, and Italy, aged between 30 and 74.
Questionnaires were used to assess dietary intakes.
Dividing the participants into four groups depending on their omega-6 LA intakes, Dr Hart‘s team calculated that highest average intake of LA was associated with a 149 percent increase in the risk of ulcerative colitis.
Conversely, the highest average dietary intakes of DHA were associated with a 77 per cent reduction in ulcerative colitis risk.
As he wrote, “An estimated 30 percent of [ulcerative colitis] cases could be attributed to having dietary intakes higher than the lowest quartile of linoleic acid intake. The positive association [between omega-6 and ulcerative colitis] may reflect a causal association because of both a plausible biological mechanism and supportive evidence from other epidemiological studies.”
- Hall MN, Chavarro JE, Lee IM, Willett WC, Ma J. A 22-year prospective study of fish, n-3 fatty acid intake, and colorectal cancer risk in men. Cancer Epidemiol Biomarkers Prev. 2008 May;17(5):1136-43. Erratum in: Cancer Epidemiol Biomarkers Prev. 2008 Oct;17(10):2901.
- Hart AR. Linoleic Acid, a Dietary N-6 Polyunsaturated Fatty Acid, and the Aetiology of Ulcerative Colitis - A European Prospective Cohort Study. Gut. 2009 Jul 23. [Epub ahead of print]