#619: How Much Fish Should a Healthy Diet Contain?

Danny Lennon (0:13)

Hello, and welcome to another episode of Sigma Nutrition Radio. My name is Danny Lennon, and of course with me is Dr. Alan Flanagan. Alan, how are you doing today?

Alan Flanagan (0:22)

I'm very well, thanks. I am looking forward to the end of summer, but it's been a great summer.

Danny Lennon (0:28)

Excellent. I'm very glad to hear it. And today we have quite the topic for people that I think is going to be one of the ones that for me is quite interesting because of some of the unknowns and maybe the lesser debated areas around this question that we'll hopefully get into and it kind of sits at that intersection of a number of interesting separate questions. So as we will get to, there are a number of sub-questions that start to come from the original question we'll lead off with. And whilst we are going to be talking about the health impacts of fish consumption broadly as our topic for today, this opens the door to a number of really interesting questions that relate to study design, methodology within studies, how we evaluate evidence, and then how we go from there and interpret that appropriately to give recommendations at both the public health level as well as the individual level. So in particular, what we want to look at is the common recommendations that are given across a variety of different organizations and official guidelines from a variety of different countries that relate to fish consumption. And so as we will mention in a moment, they are worded slightly differently. Some of the recommendations may be slightly different, but by and large, there is quite a lot of coherence amongst where those recommended guidelines end up coming out for fish consumption for general health purposes at the population level. But what we want to look at is where do those actual recommendations come from?

How strong is that evidence behind them relative to what we might presume? How that relates to the specific quantity that's discussed? And then of the evidence itself, what are some of the nuances within it? Now, within that, as we will get to, there's a couple of really interesting things that relate to the background diet or the baseline diet that someone has. And so if we're going to add or remove fish from the diet, what implications that has. But also related to that, as ever, is the comparator food or what are we comparing that with? So if we are increasing or decreasing fish consumption within a dietary pattern, what would that be replacing?

And what is the effect of it replacing different foods? And how should we think about that when it comes to our interpretation? And so just to put in a pin of a couple of ideas that we maybe will get into, one is around the differences we see when we are thinking about what is fish actually replacing in the case where we might be adding it to the diet in replace of something else. And then also a converse question maybe that is worth considering is that if someone doesn't currently consume fish, depending on what their diet actually looks like, there may be differences in what the resulting impact would be from adding that fish in. And so is it implicated in all those situations? And I think there's some really, really interesting nuance to get to.

So before we get to any of those more deeper questions, probably our best point to start from here, Alan, is to take a look at what those recommendations actually are, get some clarity on that, where they tend to converge, and therefore, off the back of that, we can start getting into maybe where that comes from.

Alan Flanagan (3:44)

Yeah, so across most Western countries, the recommendations are largely similar. So for example, in the UK, the Scientific Advisory Committee on Nutrition, or SACN, recommends eating at least two portions of fish per week, and a portion serving size is generally something between 120 to 140 grams. And then there's also a specific recommendation that one of those portions or servings per week be an oily fish. So are like salmon, sardines, mackerel, etc. European Food Standards Agency recommendations are generally similar to that. In America, we also have a broadly similar recommendation. The Academy of Nutrition and Dietetics recommends about two 120 gram servings of seafood per week. Again, it also recommends focusing on choices that are rich in Omega-3 fatty acids, EPA and DHA.

It also then makes specific recommendations for keeping mercury levels low or eating fish that are not high in mercury.

So those would be fish, for example, like bluefin tuna or swordfish.