People who get plenty of omega-3 fatty acids in their diets may have a lower risk for type 2 diabetes, two new reports in the American Journal of Clinical Nutrition suggest.
In one study, of more than 3,000 older US adults, researchers found that those with the highest blood levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were about one-third less likely to develop diabetes over the next decade than those with the lowest levels.
In the other, researchers found that among 43,000 Singapore adults, those who got the most alpha-linolenic acid (ALA) in their diets had a decreased diabetes risk.
EPA and DHA are found in fish, whereas ALA is found in plant foods, including flaxseed, canola oil and soy.
Findings not proven
But the researchers say their findings do not prove that omega-3 fats fight diabetes. They may just be markers for some other aspect of diet or lifestyle that influences diabetes risk.
People often hope there is a dietary "magic bullet" against disease, noted Andrew Odegaard of the University of Minnesota in Minneapolis, one of the researchers on the Singapore study.
In fact, studies have come to conflicting conclusions on the connection between omega-3s and diabetes. A few have even found that people with a high intake of omega-3s have an increased diabetes risk.
But the new US study did something most previous ones have not: it looked at blood levels of omega-3 fatty acids.
Researchers led by Dr Luc Djousse of Harvard University used information on 3,088 older US adults taking part in a heart-health study. At the outset, they measured participants' blood levels of EPA, DHA and ALA. Over the next decade, 204 were diagnosed with diabetes.
Among patients in the top quartile of EPA/DHA levels, 5% developed diabetes. That compared with 6.5% in the bottom quartile.
The difference was greater when it came to ALA levels: just under 4% of people with the highest levels developed diabetes, versus 8.5% of those with the lowest.
When the researchers accounted for other factors-like weight and exercise habits- omega-3 levels were still tied to a lower diabetes risk.
For the other study, Odegaard and his colleagues looked at records from 43,176 Singapore adults ages 45 to 74 who were interviewed about their diet habits, then followed over the next decade. During that time, 2,252 developed diabetes.
Overall, 5% of subjects in the highest quintile of ALA intake developed diabetes, compared to 6% in the lowest quintile.
After accounting for weight, exercise and other factors, the researchers found that high ALA intake was linked to a 22% reduction in diabetes risk.
Omega-3s from fish, however, were not tied to diabetes risk.
It's not clear why ALA appeared to protect against diabetes, Odegaard said. Some lab research, he said, has suggested that omega-3s, and particularly ALA, might improve insulin sensitivity.
Good overall diet
However, Odegaard also pointed out that people who consume a lot of ALA are likely to have a good diet overall, and probably healthy lifestyle habits like regular exercise.
And while he and his colleagues tried to factor in those variables, it's still possible that it is not the ALA, specifically, that offers the anti-diabetes benefit.
As for why omega-3 from fish was not linked to diabetes risk, Odegaard said that a potential explanation might rest in how people prepare their fish. If it's fried and served with less-than-healthy side dishes, any protective effect of omega-3s might be washed out.
"There are many things to consider," Odegaard said, "in this inherently complicated nutritional topic."
(Reuters Health, Amy Norton, June 2011)