Increasing omega-3 fats in the diet has little or no effect on risk of type 2 diabetes, finds a new review of evidence.
As such, the researchers say omega-3 supplements should not be encouraged for diabetes prevention or treatment.
Previous studies have suggested that polyunsaturated fatty acids (PUFAs) derived from oily fish and from plants (alpha-linolenic acid and omega-6’s) may have beneficial effects on the body that could help protect against type 2 diabetes, but results have been inconclusive.
To explore this further, researchers at the University of East Anglia analysed the results of 83 randomized controlled trials involving 121,070 people with and without diabetes, all of at least six months duration.
Trials assessed the effects of increasing intake of omega-3’s, alpha-linolenic acid, omega-6’s or total PUFAs on new diabetes diagnoses or measures of glucose metabolism (how well the body processes sugar) taken either as supplements or from enriched foods or natural food sources. The quality of evidence for each trial was also measured.
2 grams of omega-3’s from fish oil has no effect on diabetes risk
The researchers found that increasing long-chain omega-3 fats from fish oil by 2 grams per day over an average duration of 33 months had little or no effect on the likelihood of being diagnosed with diabetes or on glucose metabolism, and this did not change with longer duration.
Effects of alpha-linolenic acid, omega-6 and total PUFAs on diabetes diagnosis were unclear (as the evidence was of very low-quality). Meta-analysis (combining the results of the trials) suggested little or no effect of these fats on measures of glucose metabolism.
The evidence hinted that high doses of long-chain omega-3 fats (more than 4.4 grams per day) may have negative effects on diabetes risk and glucose metabolism, but the researchers emphasize that this finding should be interpreted with caution.
The researchers point to some weaknesses, including missing data and risk of bias in some trials. Nevertheless, when they restricted their analyses to only include the highest quality trials there was still no effect on diabetes risk or glucose metabolism.
The researchers say this is the most extensive review to date assessing the effects of polyunsaturated fats on diabetes and glucose metabolism in long-term randomized controlled trials.
Larger, high quality trials of at least 12 months duration looking at the effects of omega-3 fats and polyunsaturated fats on diabetes risk would be helpful, they conclude.
Source: BMJ, August 21, 2019.
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