Fish oil supplements may have no benefit for type 2 diabetes
Published on 9 September 2019
The benefits of fish oil as part of a healthy balanced diet for people with type 2 diabetes
Analysis of the study by Pam Dyson, Research Dietitian at Oxford Centre for Diabetes, Endocrinology and Metabolism, author of the DRWF leaflet A healthy diet and diabetes and member of the DRWF Editorial Advisory Board:
This high-quality review aimed to evaluate the effects of different fatty acids on the prevention and treatment of diabetes. Most of the studies included in the review looked at omega-3 fatty acids, which are commonly found in fish and are often taken as supplements.
Many claims have been made for omega-3 over the years, including preventing heart disease and obesity, and treating rheumatoid arthritis, asthma and inflammatory bowel disease, although recent reviews of the evidence have disproved many of these claims.
The role of omega-3 in diabetes prevention and treatment is uncertain, and this review confirmed that there is little benefit of increasing omega-3 intake and that there may even be negative outcomes with higher doses.
The results of this review may come as a surprise to many people, when advice from health and well-being authorities (including the NHS and Diabetes UK) generally encourages more fish, especially oily fish such as salmon, mackerel, sardines and herring.
The role of eating fish in the prevention of type 2 diabetes appears to differ in different populations, with a review reporting no association in European populations, increased risk of diabetes in US populations and a protective effect in Asian populations.
However, for those diagnosed with diabetes, fish is recommended because of its beneficial effect on prevention of heart disease. If this is the case, why didn't this review find a positive effect of omega-3?
It is important to remember that the majority of studies used omega-3 supplements, rather than using food, and this may account for the difference. Studies investigating the effects of foods (e.g. fruit, vegetables, wholegrains) rather than single nutrients (e.g. vitamin C, folic acid, β-carotene) on heart disease and overall mortality and have shown similar results.
For example, there is little evidence of any beneficial effect on the risk of heart disease using supplements including multivitamins, vitamins C and D, β-carotene, calcium and selenium, indeed supplementing with antioxidants and niacin appear to increase risk.
Conversely, foods such as wholegrains, vegetables and nuts (which contain many of the nutrients above) are associated with reduced risk.
A recent review looking at overall risk of death concluded that adequate intakes of certain nutrients (vitamins A and K, zinc and magnesium) were linked to a lower risk of death, but only if the nutrients came from food and not supplements.
In summary, it appears that eating food rather than taking supplements is the answer, as there are apparently beneficial effects of foods that are not seen with supplements. In addition, food tastes better and is usually cheaper than supplements.
A note of caution
Some people e.g. women who are pregnant and breastfeeding and children and babies have different recommendations for oily fish.
People diagnosed with specific deficiencies e.g. vitamin D deficiency or who have been advised to take omega-3 supplements should continue to follow medical advice and take their supplements as prescribed.
Read the BMJ report
Read more about fish and shellfish nutrition on the NHS website
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