Eating a diet rich in omega-6 polyunsaturated fatty acids could reduce the risk of type 2 diabetes by more than a third, a new review concludes.
From an analysis of almost 40,000 adults across 20 studies, researchers found that people who had higher blood levels of linoleic acid — a main form of omega-6 — were less likely to develop type 2 diabetes than those with lower levels of the fatty acid.
Study co-author Dr. Jason Wu, of the George Institute for Global Health in Australia, and colleagues recently reported their findings in The Lancet Diabetes & Endocrinology.
Type 2 diabetes occurs when the body is no longer able to effectively use insulin — the hormone that regulates blood glucose — or when the pancreas does not produce enough insulin. As a result, blood glucose levels become too high.
Following a healthful diet is deemed one of the best ways to prevent type 2 diabetes.
Polyunsaturated fats (PUFAs) such as omega-3 and omega-6 should form a part of a healthful diet, albeit in moderation. The new review, however, suggests that we might want to consider increasing our intake of omega-6 to protect against type 2 diabetes.
Omega-6: A help or hindrance?
Omega-6 fatty acids are considered to be essential for health; not only do they aid brain function, but they also play an important role in skin and hair growth, and they help to regulate metabolism and support bone health.
However, since the body is unable to produce omega-6, we can only get these fatty acids from certain foods, including soybean oil, sunflower oil, corn oil, and some nuts and seeds.
Current guidelines from the American Heart Association (AHA) recommend that omega-6 fatty acids should make up no more than 5–10 percent of our daily total energy intake, as they have been linked to increased inflammation and heart disease.
"Based on concerns for harm, some countries recommend even lower intakes," says Dr. Wu.
However, Dr. Wu and team note that while there are an array of studies that have investigated the effects of omega-6 on heart health, little is known about how omega-6 influences the risk of type 2 diabetes.
"[...] only a handful of prospective studies have evaluated associations between linoleic acid or arachidonic acid biomarkers and type 2 diabetes," write the study authors, "resulting in potential limitations of publication bias and inadequate power to assess interactions by demographic, medical, or genetic characteristics."
"Thus," they add, "the potential effects of omega-6 PUFAs, including linoleic acid and its metabolite arachidonic acid, on type 2 diabetes remain unresolved and are of considerable clinical, scientific, and public health importance."
To find out more about the link between omega-6 and type 2 diabetes, the researchers conducted an analysis of 20 prospective cohort studies on the subject.
The studies included a total of 39,740 adults aged 49–76 years from 10 countries, including the U.S., the United Kingdom, Germany, France, Finland, Australia, Iceland, the Netherlands, Taiwan, and Sweden.
All study participants were free of type 2 diabetes at study baseline. During a follow-up period of 366,073 person years, 4,347 new cases of type 2 diabetes occurred.
As part of the studies, participants' blood was assessed for levels of linoleic acid and arachidonic acid, and the team looked at whether or not these levels might be linked to the development of type 2 diabetes.
Compared with subjects who had low blood levels of linoleic acid, the researchers found that those who had higher levels of the omega-6 fatty acid were 35 percent less likely to develop type 2 diabetes.
"This is striking evidence," says senior author Prof. Dariush Mozaffarian, of the Friedman School of Nutrition Science and Policy at Tufts University in Middlesex County, MA.
"The people involved in the study were generally healthy and were not given specific guidance on what to eat. Yet those who had the highest levels of blood omega-6 markers had a much lower chance of developing type 2 diabetes," he adds.
There was no significant link between blood levels of arachidonic acid and risk of type 2 diabetes, the team reports.
These findings persisted after accounting for a number of possible confounding factors, including body mass index (BMI), age, sex, race, and levels of omega-3 fatty acids.
'Little evidence for harms'
Interestingly, the researchers say that their findings — together with results from previous studies — "do not suggest that high levels of dietary omega-6 PUFA[s] are harmful."
"Additionally," the team adds, "although omega-3 and omega-6 PUFA has been hypothesized to compete, we did not identify any evidence of a physiologically relevant interaction in this large, well-powered consortium analysis."
The researchers caution that many of the studies included in their analysis were observational, so they are unable to prove cause and effect between higher linoleic acid levels and reduced risk of type 2 diabetes.
That said, they believe that their results indicate that we may benefit from increasing our intake of omega-6.
"Some scientists have theorized that omega-6 is harmful to health. But based on this large global study, we have demonstrated little evidence for harms, and indeed found that the major omega-6 fat is linked to lower risk of type 2 diabetes."
Dr. Jason Wu