What’s fishy about the latest seafood study?

You’re not alone if hearing various news reports about scientific studies leaves you confused – or you could end up simply being misinformed. You might think that if the research was published in a reputable journal, the conclusions would be valid but unfortunately, science doesn’t always work that way. Keep in mind that when a number of scientific investigations yield similar results, that’s what makes a consensus of opinion. But there will always be outliers in research which differ from the current thinking. These studies do make great headlines that grab your attention but that’s why you may need experts in the field to offer their opinions.

Recent headlines about eating fish not being linked to heart health benefits for the general population is a perfect example. The findings showed that a minimal fish intake of 175 g (approximately 2 servings) weekly is associated with lower risk of major cardiovascular incidents and death among patients with prior cardiovascular disease but not in general populations.

In other words, they’re saying that fish doesn’t offer you benefits unless you actually have artery disease.

But not so fast. There’s some fishy stuff here.

First the details of the study.

In a recent issue of the journal, JAMA Internal Medicine, scientists looked at the link between fish consumption and the risk of cardiovascular disease and death in a number of different studies and pooled the results together. All in all, there were more than 191,000 subjects included.

But the subjects being evaluated were quite different. In one study, the Prospective Urban Rural Epidemiology (PURE) from 21 countries, more than 139,000 subjects (average age – 54 years)  didn’t have cardiovascular disease while just under 8,000 did actually have the disease. They were followed for about 9 years. In the other 3 studies, all 43,413 patients had either cardiovascular disease or diabetes. Self-reported fish intake was assessed using various questionnaires.

While the exact numbers aren’t important, consider just how many were healthy and then look at what the scientists were measuring as outcomes: heart attacks, strokes, sudden death, and congestive heart failure. In other words, the scientists were measuring pretty serious consequences. These don’t usually happen over the period of less than a decade to healthy people.

It’s well known that the development of cardiovascular disease can take a number of decades and then during that time, having some sort of incident, such as what the investigators were measuring would be quite unusual. So not seeing heart attacks and strokes or having people die from these things if they started out healthy at the beginning of the study is hardly surprising.

Something smells fishy here
An accompanying editorial in the same journal by Dariush Mozaffarian, MD, DrPH,  didn’t receive as much attention but should have as it offered invaluable insight as to how we should view the conclusions. Mozaffarian, besides being a cardiologist, is also dean and a professor at both the Tufts Friedman School of Nutrition Science and Policy, and at Tufts Medical School. He has authored more more than 400 scientific publications on dietary priorities for obesity, diabetes, and cardiovascular diseases.

In other words, he’s definitely an expert. (I’ve heard him speak at a few high powered conferences and he certainly knows his stuff!)

Mozaffarian pointed to a number of issues with the study design and therefore, its conclusions. For one, he didn’t understand the grouping of the studies together as they were different types of investigations.

He said, ”However, drawing such conclusions across different studies (as opposed to within a single study) is treacherous, given the many other differences between such studies as well as the play of chance.”

Treacherous is a pretty strong word for this type of publication.

Another very significant flaw he points to is that the types of fish and how they were prepared were not assessed. So fried fish from a fast food restaurant that was likely cooked in artery-clogging trans fat (as it was likely still being used at the time) would count in the same way as a cold-water omega-3 packed selection like salmon.

It’s hardly surprising then that “fish” didn’t offer the health benefits that we might expect to see.

His takeaway from the research is that previous evidence still holds. After looking at all types of research, in summary he says, “Adults should aim to consume about 2 servings of fish per week, and larger benefits may accrue from nonfried oily (dark meat) fish, which can contain up to 10-fold higher omega-3 levels than white fish.”

In other words, when you see headlines that seem to go against the grain of current thinking, be skeptical and consult an expert who might provide some clarity on the topic. Since it’s Nutrition Month, I suggest the expertise of a dietitian who can help you navigate the potentially murky waters.


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Categories: Nutrition Month, Nutrition News

Author:Rosie Schwartz

Rosie Schwartz is a Toronto-based consulting dietitian and writer.

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