Oily Fish and the risk of type 2 diabetes

People who report eating regularly oily fish had a significantly reduced risk for developing type 2 diabetes. There is also a slightly positive relationship between the regular use of fish oil supplements and a drop in the incidence of type 2 diabetes, according to a report involving some 400,000 UK residents.

Two aspects of this study are particularly important: the number of participants and the follow-up time of the study. This is the largest study on this topic, and at the time of inclusion in this study, over 392,000 adults did not have type 2 diabetes or cardiovascular disease. After more than 10 years of follow-up, only 7,262 participants developed diabetes.

Perhaps the most interesting part of the study is the comparison of the results for the two groups of the participants: those who ate oily fish and those who took fish oil supplements. The participants who ate either one, two, or more, servings of oily fish weekly had a significant 22% lower rate of type 2 diabetes incidence than those who did not eat fish. In contrast, those who reported regularly taking a fish oil supplement had a significant 9% lower incidence of type 2 diabetes than those who did not take the supplements.

Photo by Caroline Attwood on Unsplash

Which fish are good oily fish?

Cold-water fish such as

• Salmon
• Anchovies
• Herring
• Mackerel (Atlantic and Pacific)
• Tuna (bluefin and albacore), and
• Sardines

These fish have the highest levels of long-chain n-3 fatty acids, notably eicosapentaenoic acid and docosahexaenoic acid, also collectively known as Omega-3 fatty acids.

The cardiovascular benefits offered by eating fish, preferably oily ones, are well-known. Many current dietary guidelines recommend consumption of two servings of fish per week, primarily based on cardiovascular benefits. The guidelines generally do not mention the prevention of type 2 diabetes.

More clinical evidence is needed, however, for a formal recommendation to eat fish to prevent the development of type 2 diabetes. Other studies attempted to show the protective effects of oily fish to prevent the onset of diabetes.

One of them demonstrated that in older Dutch men and women with a low habitual level of fish intake, the hypothesis of protection against the risk of type 2 diabetes could not be supported. It is worth mentioning this result was mainly due to lean fish intake, which accounted for 81% of total fish intake.

In another study published in 1991, with the follow-up of 175 elderly people (64–87 years) for about 4 years, suggested that the habitual consumption of a small amount of fish may protect against the development of impaired glucose tolerance and diabetes mellitus.

What we can say for now is that the newer UK study uncovers important new evidence indicating the potential benefits of regular consumption of oily fish. It is worth noting three observations from some of the researchers of this topic:

• It would be prudent to recommend the consumption of fresh fish oil as part of a healthy diet in place of fish oil supplements to prevent diabetes.
• It is certainly necessary to determine the effect of fish oil supplements on glucose metabolism in people who cannot or choose not to eat oily fish regularly. This grows in importance as a potential beneficial effect from fish oil supplements can mean “better than nothing” for people who cannot add oily fish to their regular diet.
• It cannot be assumed that omega-3 fatty acids alone will have the same effects as oily fish, which certainly contain many other components.

References:

• Rossing, Peter, et al. “Fish oil in diabetic nephropathy.” Diabetes Care 19.11 (1996): 1214–1219.
• Van Woudenbergh, Geertruida J., et al. “Eating fish and risk of type 2 diabetes: a population-based, prospective follow-up study.” Diabetes care 32.11 (2009): 2021–2026.
• Feskens, Edith JM, Carel H. Bowles, and Daan Kromhout. “Inverse association between fish intake and risk of glucose intolerance in normoglycemic elderly men and women.” Diabetes care 14.11 (1991): 935–941.
• Guo-Chong Chen et al. Diabetes Care 2021 Mar, 44 (3), 672–680