If you are popping fish oil supplements to protect yourself against diabetes, you may be mistaken. According to the researchers, Omega-3 fats have little or no effect on risk of Type 2 diabetes.
Increased consumption of omega 3 fats is widely promoted because of a common belief that it will protect against, or even reverse, conditions such as diabetes.
According to the team from University of East Anglia (UEA), omega 3 supplements offer no benefit.
"Our previous research has shown that long-chain omega 3 supplements, including fish oils, do not protect against conditions such as heart disease, stroke or death. This review shows that they do not prevent or treat diabetes either," said Lee Hooper, from UEA's Norwich Medical School.
"Omega-3 supplements should not be encouraged for diabetes prevention or treatment," he added.
If people do choose to take supplementary fish oil capsules to treat or prevent diabetes, or to reduce levels of triglycerides in their blood, then they should use doses of less than 4.4 grams per day to avoid possible negative outcomes.
"The most trustworthy studies consistently showed little or no effect of long-chain omega 3 fats on diabetes," said the paper.
Omega 3 is a type of fat. Small amounts are essential for good health and can be found in the food that we eat. Omega 3 fats are also readily available as over-the-counter supplements and they are widely bought and used.
The research team assessed the effects of long-chain omega-3 fats, ALA, omega-6 and polyunsaturated fatty acids (PUFAs) - taken as supplementary capsules, or via enriched or naturally rich foods.
Participants included men and women, some healthy and others with existing diabetes, from North America, South America, Europe, Australia and Asia, in studies published from the 1960s until 2018.
Participants were randomly assigned to increase their polyunsaturated fats or to maintain their usual intake for at least six months.
There was clearly no effect of increasing long-chain omega-3 fats on diabetes, but there was insufficient information from trials of ALA, omega-6 or total polyunsaturated fats to assess either protective or harmful effects.
The results show that increasing long-chain omega-3 had little or no effect on diabetes diagnosis or glucose metabolism, but high doses, at levels found in some supplements, could worsen glucose metabolism.
"Oily fish can be a very nutritious food as part of a balanced diet, but we did not find enough trials that encouraged participants to eat more oily fish to know whether it is useful in preventing diabetes or improving glucose metabolism," said Dr Julii Brainard from Norwich Medical School.
"Future trials need to measure and assess baseline omega-3 intakes, and assess effects of eating more oily fish -- not just supplements," she added.