Discover Portal

Omega 3 Supplement

NIHR Signal Boosting omega-3 fatty acid intake is unlikely to prevent type 2 diabetes

Published on 12 November 2019

doi: 10.3310/signal-000833

Increasing the intake of polyunsaturated fats in the diet with supplements of omega-3 fatty acids, for example, is unlikely to affect people’s risk of developing type 2 diabetes. However, this review only looked at the effect of supplements on diabetes, not wider health.

This large systematic review included 83 long-term trials comparing higher and lower intake of omega-3 and omega-6 fatty acids and total polyunsaturated fats in healthy adults and those with existing diabetes. It found no convincing evidence that a higher intake of these fatty acids affected people’s risk of developing type 2 diabetes or improved control of existing diabetes. There was a suggestion that high doses of long-chain omega-3 fatty acids might worsen glucose metabolism.

The finding supports existing recommendations not to offer omega-3 supplements to prevent or treat type 2 diabetes.

Share your views on the research.

Why was this study needed?

Around 4.7 million people in the UK have diabetes, costing the NHS more than £10 billion per year. Around 90% of these people have type 2 diabetes, a condition in which the hormone insulin, which controls the uptake of glucose from the blood, either can’t work properly or is not produced in enough quantities.

People with diabetes are often advised to eat plenty of oily fish and plant oils. These are rich in polyunsaturated fatty acids (PUFA), such as omega-3 and omega-6 fatty acids, but the impact of these substances on diabetes development and glucose metabolism is unclear. Some experimental data has suggested that omega-3 may worsen the control of diabetes.

This study aimed to review the effects of PUFA on diabetes risk and glucose metabolism and to answer these uncertainties. It also looked specifically at omega-6 fatty acids, short-chain omega-3 (α-linolenic acid), long-chain omega-3 (eicosapentaenoic acid [EPA], and docosahexaenoic acid [DHA]) fatty acids.

What did this study do?

This systematic review compared the effects of higher and lower omega-3, omega-6 and total PUFA intake on new diagnoses of diabetes, pre-diabetes, maintenance of normal blood glucose, serum insulin and insulin resistance. Eligible interventions could be dietary advice, supplementation (taken orally as oil, foods or capsules), or diet provided.

The review included 83 randomised controlled trials lasting at least 24 weeks, involving a total of 121,070 adults at any risk of diabetes or with diabetes. Half of the studies were conducted in Europe. They evaluated increasing PUFA on its own, not the effect of a wider change in diet or lifestyle.

There was limited data on the effect of increasing α-linolenic acid, omega-6, and total PUFA, and the authors identified a risk of bias in many of the included trials, though this might be expected to magnify any treatment effect. Also, most trials assessing the impact of boosting long-chain omega-3 consumption involved supplements, making it difficult to draw conclusions about the impact of increasing oily fish consumption.

What did it find?

  • Increasing consumption of long-chain omega-3 fatty acids had little or no effect on the likelihood of being diagnosed with type 2 diabetes. This occurred in 3.7% of people over the course of these trials, relative risk 1.00 (95% CI 0.85 to 1.17; 17 trials; 58,643 participants). It also had little or no effect on measures of glucose metabolism, including glycated haemoglobin, insulin resistance (HOMA-IR), plasma glucose or fasting insulin.
  • High dose supplementation with long-chain omega-3 (more than 4.4 g/day) may worsen glucose metabolism, although this finding should be interpreted with caution, as subgrouping by dose did not reveal statistically significant differences.
  • The impact of increasing α-linolenic acid, omega-6, and total polyunsaturated fatty acids on diabetes diagnosis remains unclear because the evidence was of very low quality.
  • There is no evidence that the ratio of omega-3 to omega-6 is important for type 2 diabetes or glucose metabolism.

What does current guidance say on this issue?

The NICE guideline on cardiovascular disease risk assessment and reduction states that omega-3 fatty acids should not be offered to people with type 2 diabetes. However, NICE’s guideline on the management of adults with type 2 diabetes advises including oily fish in the diet.

The American Diabetes Association also recommends consuming a Mediterranean-style diet high in polyunsaturated fats, omega-3, and α-linolenic acid, without taking supplements.

What are the implications?

This study supports recommendations that omega-3 fatty acid supplements should not be offered to people with type 2 diabetes, for their diabetes. Neither should the supplements be offered to prevent diabetes in people at high risk of developing the disease.

People with diabetes or at risk of developing it should still be encouraged to eat a healthy Mediterranean-style diet, including oily fish, as part of a healthy lifestyle.

Citation and Funding

Brown TJ, Brainard J, Song F et al. Omega-3, omega-6, and total dietary polyunsaturated fat for prevention and treatment of type 2 diabetes mellitus: systematic review and meta-analysis of randomised controlled trials. BMJ. 2019;366:14697.

The study was funded by the World Health Organization’s Nutrition Guidance Expert Advisory Group (NUGAG) subgroup on Diet and Health.

Bibliography

Diabetes UK. Tackling the crisis. London: Diabetes UK; 2019.

NICE. Cardiovascular disease: risk assessment and reduction, including lipid modification. CG181. London. National Institute for Health and Care Excellence; 2014 (updated 2016).

NICE. Type 2 diabetes in adults: management. NG28. London: National Institute for Health and Care Excellence; 2015 (updated 2017).

Why was this study needed?

Around 4.7 million people in the UK have diabetes, costing the NHS more than £10 billion per year. Around 90% of these people have type 2 diabetes, a condition in which the hormone insulin, which controls the uptake of glucose from the blood, either can’t work properly or is not produced in enough quantities.

People with diabetes are often advised to eat plenty of oily fish and plant oils. These are rich in polyunsaturated fatty acids (PUFA), such as omega-3 and omega-6 fatty acids, but the impact of these substances on diabetes development and glucose metabolism is unclear. Some experimental data has suggested that omega-3 may worsen the control of diabetes.

This study aimed to review the effects of PUFA on diabetes risk and glucose metabolism and to answer these uncertainties. It also looked specifically at omega-6 fatty acids, short-chain omega-3 (α-linolenic acid), long-chain omega-3 (eicosapentaenoic acid [EPA], and docosahexaenoic acid [DHA]) fatty acids.

What did this study do?

This systematic review compared the effects of higher and lower omega-3, omega-6 and total PUFA intake on new diagnoses of diabetes, pre-diabetes, maintenance of normal blood glucose, serum insulin and insulin resistance. Eligible interventions could be dietary advice, supplementation (taken orally as oil, foods or capsules), or diet provided.

The review included 83 randomised controlled trials lasting at least 24 weeks, involving a total of 121,070 adults at any risk of diabetes or with diabetes. Half of the studies were conducted in Europe. They evaluated increasing PUFA on its own, not the effect of a wider change in diet or lifestyle.

There was limited data on the effect of increasing α-linolenic acid, omega-6, and total PUFA, and the authors identified a risk of bias in many of the included trials, though this might be expected to magnify any treatment effect. Also, most trials assessing the impact of boosting long-chain omega-3 consumption involved supplements, making it difficult to draw conclusions about the impact of increasing oily fish consumption.

What did it find?

  • Increasing consumption of long-chain omega-3 fatty acids had little or no effect on the likelihood of being diagnosed with type 2 diabetes. This occurred in 3.7% of people over the course of these trials, relative risk 1.00 (95% CI 0.85 to 1.17; 17 trials; 58,643 participants). It also had little or no effect on measures of glucose metabolism, including glycated haemoglobin, insulin resistance (HOMA-IR), plasma glucose or fasting insulin.
  • High dose supplementation with long-chain omega-3 (more than 4.4 g/day) may worsen glucose metabolism, although this finding should be interpreted with caution, as subgrouping by dose did not reveal statistically significant differences.
  • The impact of increasing α-linolenic acid, omega-6, and total polyunsaturated fatty acids on diabetes diagnosis remains unclear because the evidence was of very low quality.
  • There is no evidence that the ratio of omega-3 to omega-6 is important for type 2 diabetes or glucose metabolism.

What does current guidance say on this issue?

The NICE guideline on cardiovascular disease risk assessment and reduction states that omega-3 fatty acids should not be offered to people with type 2 diabetes. However, NICE’s guideline on the management of adults with type 2 diabetes advises including oily fish in the diet.

The American Diabetes Association also recommends consuming a Mediterranean-style diet high in polyunsaturated fats, omega-3, and α-linolenic acid, without taking supplements.

What are the implications?

This study supports recommendations that omega-3 fatty acid supplements should not be offered to people with type 2 diabetes, for their diabetes. Neither should the supplements be offered to prevent diabetes in people at high risk of developing the disease.

People with diabetes or at risk of developing it should still be encouraged to eat a healthy Mediterranean-style diet, including oily fish, as part of a healthy lifestyle.

Citation and Funding

Brown TJ, Brainard J, Song F et al. Omega-3, omega-6, and total dietary polyunsaturated fat for prevention and treatment of type 2 diabetes mellitus: systematic review and meta-analysis of randomised controlled trials. BMJ. 2019;366:14697.

The study was funded by the World Health Organization’s Nutrition Guidance Expert Advisory Group (NUGAG) subgroup on Diet and Health.

Bibliography

Diabetes UK. Tackling the crisis. London: Diabetes UK; 2019.

NICE. Cardiovascular disease: risk assessment and reduction, including lipid modification. CG181. London. National Institute for Health and Care Excellence; 2014 (updated 2016).

NICE. Type 2 diabetes in adults: management. NG28. London: National Institute for Health and Care Excellence; 2015 (updated 2017).

Omega-3, omega-6, and total dietary polyunsaturated fat for prevention and treatment of type 2 diabetes mellitus: systematic review and meta-analysis of randomised controlled trials

Published on 23 August 2019

Brown, T. J.,Brainard, J.,Song, F.,Wang, X.,Abdelhamid, A.,Hooper, L.

Bmj Volume 366 , 2019

OBJECTIVE: To assess effects of increasing omega-3, omega-6, and total polyunsaturated fatty acids (PUFA) on diabetes diagnosis and glucose metabolism. DESIGN: Systematic review and meta-analyses. DATA SOURCES: Medline, Embase, Cochrane CENTRAL, WHO International Clinical Trials Registry Platform, Clinicaltrials.gov, and trials in relevant systematic reviews. ELIGIBILITY CRITERIA: Randomised controlled trials of at least 24 weeks' duration assessing effects of increasing alpha-linolenic acid, long chain omega-3, omega-6, or total PUFA, which collected data on diabetes diagnoses, fasting glucose or insulin, glycated haemoglobin (HbA1c), and/or homoeostatic model assessment for insulin resistance (HOMA-IR). DATA SYNTHESIS: Statistical analysis included random effects meta-analyses using relative risk and mean difference, and sensitivity analyses. Funnel plots were examined and subgrouping assessed effects of intervention type, replacement, baseline risk of diabetes and use of antidiabetes drugs, trial duration, and dose. Risk of bias was assessed with the Cochrane tool and quality of evidence with GRADE. RESULTS: 83 randomised controlled trials (mainly assessing effects of supplementary long chain omega-3) were included; 10 were at low summary risk of bias. Long chain omega-3 had little or no effect on likelihood of diagnosis of diabetes (relative risk 1.00, 95% confidence interval 0.85 to 1.17; 58 643 participants, 3.7% developed diabetes) or measures of glucose metabolism (HbA1c mean difference -0.02%, 95% confidence interval -0.07% to 0.04%; plasma glucose 0.04, 0.02 to 0.07, mmol/L; fasting insulin 1.02, -4.34 to 6.37, pmol/L; HOMA-IR 0.06, -0.21 to 0.33). A suggestion of negative outcomes was observed when dose of supplemental long chain omega-3 was above 4.4 g/d. Effects of alpha-linolenic acid, omega-6, and total PUFA on diagnosis of diabetes were unclear (as the evidence was of very low quality), but little or no effect on measures of glucose metabolism was seen, except that increasing alpha-linolenic acid may increase fasting insulin (by about 7%). No evidence was found that the omega-3/omega-6 ratio is important for diabetes or glucose metabolism. CONCLUSIONS: This is the most extensive systematic review of trials to date to assess effects of polyunsaturated fats on newly diagnosed diabetes and glucose metabolism, including previously unpublished data following contact with authors. Evidence suggests that increasing omega-3, omega-6, or total PUFA has little or no effect on prevention and treatment of type 2 diabetes mellitus. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42017064110.

Expert commentary

The result of this study does not support any change in practice.

Dietary intervention is one approach for the prevention and treatment of type 2 diabetes. Mediterranean diet, complete in nutrients and rich in vegetables and fruits is often advised.

The key factor in the prevention of type 2 diabetes is the daily caloric intake. This should be reduced to correct overweight status or obesity. Regular exercise is advised in conjunction with a dietary intervention.

Dr Luigi Gnudi, Professor of Diabetes and Metabolic Medicine, King’s College London; Consultant in Diabetes and Endocrinology, Guy’s and St Thomas’ NHS Foundation Trust

The commentator declares no conflicting interests