Fish for your heart: the state of the evidence

A team of researchers recently assessed the quality of the available evidence regarding fish consumption and the risk of chronic diseases by performing what is known as an umbrella review, which essentially an overview of reviews. In this case, the authors identified studies that grouped together multiple smaller studies (these are known as meta-analyses) and synthesized their findings (Adv Nutr 2020;11:1123-1133).

The meta-analyses were all prospective cohort studies - that is, studies in which a group of people are identified at the start of the study and their progress is tracked over time. For their article, the authors identified 34 meta-analyses (298 total studies) that reported on fish consumption and the risk of chronic diseases such as death from any cause, heart disease, stroke, heart attack, type 2 diabetes, and cancers.

Using the data in the articles, the authors were able to standardize the amount of fish consumed and synthesize the results in the meta-analyses while also evaluating the quality of the evidence.

It's not surprising that there were no meta-analyses that the authors rated their evidence quality as High - prospective cohort studies can only show association between (for example) fish and heart disease but can't prove conclusively that eating fish prevents heart disease.

That said, the quality of the evidence was rated as Moderate for heart attack, heart failure, stroke, and all-cause mortality - with every increase of 100 grams of fish consumption per day reducing the risk of these diseases by as much as 25%.

The quality of the evidence with respect to high blood pressure, atrial fibrillation, and type 2 diabetes was considered Low, and of 20 different specific cancer types considered, only the evidence showing a reduction in risk of liver cancer with higher fish consumption was considered Moderate.

One thing this umbrella article does not do is look at the different types of fish. The authors note that while they found no association between overall fish intake and type 2 diabetes, consuming more fatty fish seemed to be protective against type 2 diabetes.

What this means for you

More research is being done all the time into all 9 elements of the Mediterranean Diet - both individually and as a pattern. This umbrella review shows us where more research needs to be done - but it also shows us that fish is good for your heart. Try to eat fish at least twice a week, and mix it up: one day salmon, another day shrimp, the next time something else.

First posted: November 3, 2020