Diabetes is one of the major degenerative disorders driven by chronic, “silent” inflammation.
Omega-3s help moderate and resolve inflammation, so it's been presumed that diets rich in these fatty acids should help prevent or dampen diabetes – especially the majority of cases caused in part by carrying excess pounds – and substantial evidence supports that idea.
As the authors of a recent evidence review wrote, “Obesity is associated with low-grade chronic inflammation … the key link between obesity and development of insulin resistance … [Omega-3s] may therefore offer a useful anti-inflammatory strategy to decrease obesity-induced insulin resistance” (Oliver E et al. 2010).
Conversely, the omega-6 fatty acids that predominate in most vegetable oils and prepared/packaged foods – therefore in most Americans' diets – tend to promote or sustain inflammation.
(The main exceptions are olive, macadamia, canola, and hi-oleic sunflower oils, which are relatively low in omega-6 fats.)
And it's becoming clear that diabetes is one of the disabling diseases promoted by America's grossly excessive intake of omega-6s.
A number of population studies have looked for links between intake of omega-3s and risk of diabetes.
Some epidemiological (population) studies link diets rich in fish and/or their omega-3s to a modestly reduced risk of diabetes… but others have found no drop or a slight rise in risk. For example, see “Diabetes-Fish Study Raises Doubts.”
Why would omega-3s help?
In addition to their anti-inflammatory influences, studies involving healthy and diabetic animals and people show that omega-3s exert beneficial metabolic effects.
These metabolic benefits include improved blood fat and inflammation profiles – which promote and sustain diabetes – in healthy and diabetic people alike.
Surprisingly, only a minority of the studies that have looked at omega-3s' potential to deter “insulin resistance” – a primary promoter of and integral part of diabetes – indicate that fish fats help.
For more on the entire topic, see the “Omega-3s & Metabolic Health” section of our news archive.
Encouragingly, two recent studies – from the U.S. and Singapore – lent support to the hope that omega-3-rich diets can help deter diabetes (see “Omega-3s Linked to Lower Diabetes Risk”).
Now, the results of a joint U.S-Chinese epidemiological (diet-health) study conducted in Shanghai add more evidence to the positive side of the scale … especially for women.
Unusually, new study looked at all kinds of omega-3s
As in the Singapore-based study we summarized last month, the team behind the Shanghai study looked for links between diabetes rates and intake of the two major kinds of omega-3s: seafood-source and plant-source.
Most studies have only looked at the long-chain, seafood-source or “marine” omega-3s our bodies actually need to survive and thrive, called DHA and EPA.
When necessary – in the absence of seafood and fish or krill oil supplements – the body can make DHA and EPA, very inefficiently, from the short-chain, plant-source “green” omega-3 called ALA.
Omega-3 ALA – obtained by Americans from canola oil, beans, dark leafy greens (e.g., spinach and chard), flaxseed, and walnuts – has been studied less much in relation to diabetes.
The Singapore-based study we reported on last month linked higher intakes of plant-derived omega-3 ALA to a 21 percent reduction in the risk of diabetes … finding no links between higher intakes of seafood-source omega-3s and either a higher or lower risk of diabetes.
The new Shanghai study also examined peoples' reported intake of all omega-3s – ALA from plant foods and DHA/EPA from seafood – as separate and joint influences on the risk of developing diabetes over several years.
But this time, all omega-3s came out winners … within the known limitations of epidemiological studies that rely on people's diet recollections, and do not measure people's omega-3 blood levels.
Remember that in the Harvard study we reported last month, which used blood tests, high levels of seafood-source omega-3s and plant-source omega-3 ALA were both linked to a risk reduction … with ALA showing a slight edge at a 43 percent cut, versus a 36 percent drop with high blood levels of seafood-source EPA and DHA.
Shanghai study links seafood to reduced diabetes risk
The new study involved 116,156 Chinese people – 51,963 men and 64,193 women – living in Shanghai. All were middle-aged and free of diabetes and cardiovascular disease at the outset of the six-year study.
The researchers visited the participants three times, at two-year intervals, to collect information about their diets and activity and to take physical measurements.
A subsequent data analysis by the U.S.-Chinese team linked higher seafood intake to a reduced risk of diabetes … and this beneficial association was stronger for women than for men.
Specifically, women's diabetes risk was 11 to 14 percent lower among the one-fifth who reported the highest levels of fish and shellfish intake, respectively.
For men, those in the one-fifth who reported the highest shellfish intake were 16 percent less likely to develop diabetes within six years – with the risk dropping by 30 to 34 percent in the next two highest-intake groups.
The U.S.-Chinese team found no significant link between fish intake and diabetes risk in men from Shanghai.
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