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The Science — And Environmental Hazards — Behind Fish Oil Supplements

Jul 9, 2018
Originally published on July 12, 2018 11:14 am
Copyright 2018 Fresh Air. To see more, visit Fresh Air.

TERRY GROSS, HOST:

This is FRESH AIR. I'm Terry Gross. Today's interview is about human health and the health of the oceans. My guest Paul Greenberg has written a new book whose focus is omega-3 dietary supplements, capsules containing the fatty acids derived from fish and other sea life. He examines the claims the omega-3 industry makes about the health benefits of these supplements and what the latest research has to say.

He also writes about the effect these supplements are having on the populations of fish used to create them and how this is affecting the ecosystems of our oceans. Later, we'll talk about Greenberg's year-long experiment eating fish at every meal to see if it would have a positive effect on his health. One outcome of the diet - it increased the level of mercury in his system - not a result he was hoping for. Greenberg is also the author of "American Catch" and the James Beard Award-winning best-seller "Four Fish."

Paul Greenberg, welcome back to FRESH AIR.

PAUL GREENBERG: Oh, thank you so much for having me back.

GROSS: So what are the health claims made by advocates of omega-3 supplements?

GREENBERG: Basically, they fall into two categories. One is for cardiovascular health, and the other is for brain health. And within those two mega categories are sort of sub things relating to joints, on one hand. Vision is a part of it because vision is sort of a subset of the brain. But I would say that if you really want to talk about omega-3 fatty acids, it's good to talk about the heart and the brain.

GROSS: So how does omega-3 function in the human body, and why do we think we need more?

GREENBERG: So in the heart, it seems to play a role in inflammation. Inflammation is sort of one of these boogeyman words that has entered the discourse around public health in the last I would say five to 10 years. And inflammation is actually a really serious problem. It's basically the body's reaction to infection. And when things don't subside after inflammation, you can have long-lasting effects of one kind or another. So when we talk about cardiovascular health, generally speaking, people who are pro-omega-3 tend to think that omega-3s reduce inflammation and thereby help our cardiovascular system be more resilient overall.

In the brain, omega-3s are actually a major part of the human brain. Somewhere between 5 and 10 percent of the mass of the human brain is DHA omega-3 fatty acid. So it seems to be directly involved in cell signaling. It seems to imply that a healthy amount of omega-3 fatty acid in the brain causes our brains to work faster. That's at least the theory anyway. It's hard to prove once and for all that that is actually happening. But that is in fact what people seem to suggest in the scientific community.

GROSS: So what is omega-3?

GREENBERG: So omega-3 fatty acids are found in seafood. They're also found in green leafy vegetables. There are different kinds of omega-3s. But basically what they are are fats. And omega-3s differ from other fats in that they are what are called polyunsaturated. I won't go into the sort of details of how many carbon bonds they have and so forth, but what they are is they're much more fluid than other forms of saturated fat, for example. And they seem to impart a certain kind of flexibility to our cell membranes.

And people who are really advocates of omega-3s, people that I sort of group together in the book as members of omega world - people within omega world think that this flexibility, this fluidity within omega-3s somehow gets imparted to our cell membranes and makes us similarly flexible and fluid and prone to resolving things like inflammation.

GROSS: So what does the latest scientific research say about ingesting omega-3s through supplements?

GREENBERG: Lately not so many positive things. There have been these raft of studies that came out in the last, say, 10, 15 years really coming to fruition in the last five years that have shown really very limited effect, especially having to do with heart health, these large studies of studies that are also called meta-analyses. For example, one was published in The Journal of the American Medical Association back I think in 2012. And they found pretty much no effect on cardiovascular health at all from omega-3 supplements.

The other side, the brain side of omega-3s - I think it's still kind of - we haven't seen these big studies come out that say very clearly one way or the other, does taking a supplement help our brain? The fact that omega-3s are 5 to 10 percent by mass of the human brain does imply that, gosh, you know, if so much of our brain is this essential fat, will - would more make our brains bigger and faster? And that's the assumption, but it's not necessarily being borne out by scientific research.

GROSS: So how is the supplement industry responding to this research that you've been describing that says, you know, the omega-3 supplements might not be doing what we want them to do?

GREENBERG: Well, the supplement industry tends to respond with more and more studies. The problem that I found as a lay person going into this book was that there are so many omega-3 studies, almost 30,000 studies that have been done about omega-3s - you know, this health factor omega-3s and that health factor. And generally, what the industry tends to do is that when a major study comes out and says omega-3s don't work, they point to this raft of other studies that say that they do. And you can kind of get lost within these - all these different studies.

But actually - so my partner is a statistician. And she just got her Ph.D. And she really helped me understand that there are studies and then there are studies. So most of the studies that the omega-3 industry falls back on are what are called association studies. And those are sort of like - I mean, to use a very sort of crude example, association studies show that when there are chickens, there are eggs. They don't show that necessarily chickens cause eggs. They just say that chickens and eggs tend to be around each other.

So what those association studies tend to look at is if people are eating a lot of fish, if they tend to have, say, high omega-3 levels in their blood, they tend to have better cardiovascular health. But it doesn't show necessarily that eating the omega-3 thing did actually improve your health. The issue becomes more complicated because people who are generally following an omega-3 lifestyle are generally kind of healthier overall. They tend to eat more vegetables. They tend to eat more fish. They tend to exercise. So it's hard to say that this one single factor is causing all of these positive health things.

Now, the thing that scientists really use to prove effect is something called a randomized control trial where you actually have a group of people taking the medicine and a group of the people not taking the medicine. And they don't know if they are taking the medicine, and the other people don't know if they are taking the medicine. And then they look at health results over time to see if the people actually taking the medicine versus the people taking the placebo are showing improved health results. When they actually do the hard work of doing randomized control trials, up until now those randomized control trials haven't been showing very strong effect of omega-3s, particularly when it concerns heart health.

GROSS: I think part of the reason why a lot of people take omega-3 supplements is that they know omega-3 is important to brain functioning. So like you said, why not have more? Can the human body make omega-3 by itself?

GREENBERG: So, yes, it can. The human body can take what's called alpha-Linolenic acid, ALA, from - which is a source of vegetable omega-3, will come to us from leafy greens, various vegetable sources. And we actually can take that and elongate that into EPA and DHA omega-3 fatty acids, which are in our heart and in our brain. So we can make it. But we only can do it at a very low conversion rate. So the supplement industry has sort of seized onto that little, you know, deficiency we have in elongating these fatty acid chains and saying, OK, well, the human body can't quite do it, so we're going to jump in and help the human body add more EPA and DHA to its system.

Interestingly, pregnant mothers actually are much more efficient at creating omega-3s. And the reason is because infants when they're in the womb need to have DHA into their brain to build their brain. So actually, mother's milk is quite high in omega-3 fatty acids. And pregnant mothers can synthesize omega-3 fatty acids from vegetable sources.

So it's kind of unclear whether - do we get that sort of initial load of omega-3s when we're in vitro and then we put it all in our brain and that's enough, or do we have to kind of keep eating it to keep building our brains over time? And to tell you the truth, I didn't find an entirely satisfactory answer in all the research that I did. I think it's open to question whether or not we have to do this.

GROSS: So does the human body absorb omega-3s equally well through a supplement or through fish - when the omega-3 is within the fish itself?

GREENBERG: My impression when talking to health professionals was that, generally speaking, it's better to get omega-3s in food form, just like it's better to get many different forms of nutrition in food rather than through a supplement. I think that the human body was - did not evolve to take isolated amounts of certain chemicals or certain vitamins or nutrients. We evolved to eat whole food. And I truly believe that if you're going to have omega-3s in your body. You should be having them through your food. What I think is interesting is that when you look at studies of indigenous people that live pretty far from the water, they look at health effects in people that don't eat a lot of seafood but who generally live healthy lives - that eat a fair amount of vegetables, that are very physically active - that you don't see this market deficiency that the omega-3 industry warns us that we're going to see.

GROSS: Some of the eggs I buy have omega-3 in them. Is that because the eggs have been supplemented, or are there omega-3s naturally in eggs?

GREENBERG: So, interestingly, there's a doctor in the book named Artemis Simopoulos. She noticed that in Greece, chickens were always browsing on wild field greens, purslane in particular. And so she smuggled a few of those eggs back to the United States. And then together with a guy named Norm Salem, they did a lipid analysis of the grass-fed eggs with the corn-fed eggs that are normally sold in American supermarkets. And they found that the omega-3 levels were much, much higher in the grass-fed eggs. So I would say, you know, when you see pasture-raised eggs, if the chickens involved are truly on pasture and truly eating grasses, they will have higher omega-3 levels. The other way around this, of course, is to supplement chicken feed with fishmeal and fish oil, which is done. It's less and less now, but in the early days of sort of promoting omega-3s, quite often, chickens were fed fishmeal and fish oil to raise the level of omega-3s in their bodies, which would then get passed on to their eggs.

GROSS: Well, let's take a break here. And then we'll talk some more. If you're just joining us, my guest is Paul Greenberg. He's a journalist who's been focusing on issues related to fish for years now. And his new book is called "The Omega Principle: Seafood And The Quest For A Long Life And A Healthier Planet." When we come back, we'll talk about what the source is for over-the-counter omega supplements and what Greenberg says that's doing to the oceans and the oceans' ecosystems. So we'll be right back. This is FRESH AIR.

(SOUNDBITE OF YO LA TENGO'S "HOW SOME JELLYFISH ARE BORN")

GROSS: This is FRESH AIR. And if you're just joining us, my guest is journalist Paul Greenberg, who has written extensively about fish over the years. And his new book is called "The Omega Principle." It's about omega-3 supplements and what the research has to say about whether they're effective or not and what the harvesting of fish for omega-3 supplements is doing to the oceans.

So you're concerned about what omega-3s supplements are doing to the ecosystems in the oceans because the omega-3 supplements come from fish or at least largely come from fish. So what are some of the main sources of the omega-3 supplements?

GREENBERG: So omega-3 supplements come from this critical layer of the ocean biosphere that are small - what are called pelagic fish. They're the silvery, little fish like anchovies and herring and other fish called menhaden that most people haven't heard of, but it's actually the most caught fish in the lower 48 of the United States. These fish are really essential for ecosystem dynamics in the ocean.

So the way that oceans work is that all the energies coming from the sun - it goes - all that energy is processed by plankton, by phytoplankton. And it's really these fish that are - these little fish that are used for omega-3 supplements that transfer the energy from plankton to larger fish. So in other words, you know, you have the solar energy going into the plankton. The little fish then eat the plankton. And then they are in turn eaten by larger fish. So if you harvest this middle layer - if you overharvest this middle layer of anchovies, of herring, of menhaden - if you take them out of the picture, there's no way for the energy to be transferred from phytoplankton up to larger predators. So I guess that's my main concern here.

So in particular, where are the omega-3 supplements coming from? Most of the omega-3 supplement oil is coming from a fish called a Peruvian anchoveta. And it is the most caught fish in the world. In some years, Peruvian anchoveta harvests have equaled as much as 10 million metric tons. Just to give you some perspective, that's like one-eighth of all the fish caught in the world. And the crazy thing about it is that those fish are completely, totally edible. I've eaten them. They're delicious. You can have them on a pizza. You could do anything with them. But 99 percent of those Peruvian anchoveta are ground up into animal feed, boiled down into oil and turned into supplements. So to me, to my mind, that is not necessarily the wisest use to be made of this really, really important source both for the ecology of the ocean but also for humans.

GROSS: So these Peruvian anchoveta - are they anchovies.

GREENBERG: Yeah, they're basically anchovies. They're in the same family as the anchovies that we've eaten - that we all eat from the Mediterranean or are off the coast of Africa. And yeah, it's just - the only reason that we don't eat them is because of this massive - what's called the reduction industry has sort of cornered the market on them all. Now, I also think it's important not to necessarily blame the supplement industry for this because, really, omega-3 supplements are just the latest incarnation of the reduction industry trying to market their products. We've had a reduction industry around for 200 years.

And, actually, the first target of the reduction industry was whales. And really, you know, in the early 20th century, over 350,000 great whales in the Southern Ocean were reduced largely to make margarine. And remember all the time we were always hearing in the '60s and '70s that margarine was this great, heart-healthy replacement for butter and all this kind of thing? Well, it turns out it's not true. And it also turns out that it was probably entirely unnecessary to reduce all of these great whales. Now - there used to be 400,000 great whales in the Southern Ocean. Now there are probably less than 15,000. And all of that was because of this reduction industry. Today, obviously, we're not targeting whales for reduction, but instead we're targeting this major chunk of the ocean. Something like 20 to 25 million metric tons are reduced every year. Twenty to 25 million metric tons of fish are reduced each and every year. How much is that? That's like a quarter of all the fish that we catch - a quarter of all the fish that we catch that never hits the human plate. Most of it goes to feeding animals. Some of it goes to making fertilizer. And again, some of it goes to making omega-3 supplements.

GROSS: So when you talk about reduction and the reduction industry, explain what you're talking about.

GREENBERG: So the reduction industry basically takes all these little fish, catches them buy the millions of pounds or billions of pounds, puts them in a cooker and boils them down into oil that is used for dietary supplements, also used in animal feed. And then the other product is called fish meal, sometimes called fish flour, which is basically this sort of dust that gets incorporated into pellets and fed to animals. The reduction industry was really focused on terrestrial animal feed at first. So a lot of chickens were fed fish meal. Pigs were also fed fish meal and fish oil to some degree. But most recently, more and more of that fish meal and fish oil is being used to feed salmon and to create aquaculture throughout the world.

GROSS: So if a lot of the small fish that are being harvested in order to be reduced for animal feed and for supplements - what happens to the fish that eat those smaller fish that are being harvested?

GREENBERG: The fish that are harvested by the supplement industry are keystone species. They are essential for growing larger fish. And if we remove those smaller fish from the system, then we're going to see fewer bigger fish. I mean, I think some of your listeners might remember the big cod crashes of the 1980s. And Mark Kurlansky famously wrote that book "Cod." And we all know about how we lost all these cod and we overfished them and so forth and so on. But what people don't generally know is that prior to the cod collapse, there was a huge assault on the prey base of cod on the Grand Banks.

It's a fish called capelin. Capelin are also oily fish. They are also used by the reduction industry. And it was really during the '70s and '80s as the animal feed business started to ramp up and started catching all those little fish that we started to see a real impact upon predators. And I did - when I was working on an earlier book, I did go back and interview some of the sources that Mark Kurlansky used for his book "Cod."

And one of them, I remember, in particular in Canada said, you know, the overfishing of cod did occur. But look at all the little fish that we were catching. Look at how that may have affected the cod crash. And, you know, he seemed to feel pretty strongly that the overharvest of those little fish could have had a very strong effect on that cod collapse.

GROSS: My guest is Paul Greenberg, author of the new book "The Omega Principle." We'll talk more after a break. And David Edelstein will review a new documentary about three identical twins separated at birth adopted by three different families. I'm Terry Gross, and this is FRESH AIR.

(SOUNDBITE OF HERBIE HANCOCK'S "DOLPHIN DANCE")

GROSS: This is FRESH AIR. I'm Terry Gross. Let's get back to my interview with journalist Paul Greenberg, who writes about fish, health and our oceans and rivers. His new book, "The Omega Principle," is about the health claims made for omega-3 supplements and what the research has to say about that. The book is also about the small fish and other sea creatures that are boiled down or reduced to make these supplements and for meal for livestock feed and pet food. Greenberg says that the harvesting of these small fish and sea creatures is affecting the food chain in the oceans.

In addition to the small fish we've been talking about being harvested for the reduction industry, krill has become a major source in the past 10 years. What are krill, and how are they being used?

GREENBERG: So krill are a crustacean. They're found generally in the higher latitudes both in the North and the South Pole. But the krill that are the subject of the reduction industry are in the Southern Ocean. They are the primary keystone species for prey, for whales, for penguins, for all these other creatures. Krill eat the algae, the phytoplankton at the bottom of the food web. They put it - you know, incorporate it, build energy, build body mass. And then they are in turn eaten by everything - by whales, by seals, by penguins.

There's actually a seal in the Antarctic that has this weird almost baleen-like mouth. And it's specifically adapted so that it can take gulpfuls of krill and then push the water through its teeth and then eat the krill. So it's really, really essential to all these different creatures.

GROSS: So do you think it's sustainable to extract the fish that we're extracting to sustain the omega-3 supplement industry?

GREENBERG: Well, really, we're talking about the reduction industry, right? So it's not just omega-3s.

GROSS: Ok, yeah.

GREENBERG: It's animal feed and everything. So it used to be a lot worse. Nowadays, it is much better. And I would say that almost every reduction industry that I've looked at has criteria by which they judge sustainability. It's not like they're just fishing pell-mell and catching whatever they want all the time. They do have quotas. They do try to follow rules. So whenever I talk to people with it, whether they're within menhaden or with Peruvian anchoveta, they all say, what we're doing is sustainable. And within maybe the small box of what they're thinking, maybe it is sustainable in that they'll catch this many fish next year, and it'll allow them to keep catching that many fish the next year.

But my point is we need to really widen the box. We need to say, if we count up all of these different production industries, we end up with 20 to 25 million metric tons - a quarter of the world catch. It's a lot of fish. And also, one of the things - and this is really important, Terry - people need to really think about what's called ecosystem-based management. So typically, fisheries management is really about, if I catch as many fish this year, will there be enough left over to produce a similar amount of fish next year? But they don't always take into account the number of the other things that are eating those fish - the seabirds, the whales, the larger fish predators that we like to eat.

More and more what I found doing research for this book was a real push to try and get reduction industry people to look at ecosystem-based management so that we're not just thinking about how many fish we need for next year to have more fish next year. We're really looking at the whole entirety of the ecosystem and really considering how much we're going to take out of the ocean so that everybody is well-fed, and everything is in balance.

GROSS: So early in our interview, we talked about how there's, like - what'd you say? - like 30,000 studies related to investigating whether omega-3 supplements are actually effective or not in improving various health functions. Omega-3 as a supplement falls out of the purview of the Food and Drug Administration, the FDA, because it's categorized as neither food nor drug. Now, this is something else you write about in your book - how the supplement industry came to be outside of the regulatory power of the FDA. So can you give us a little background on how that happened?

GREENBERG: The sort of modern era of supplements really begins with Linus Pauling. He was very much involved in the early discoveries around DNA. But in the 1970s, as his sort of career was starting to fade, he became totally obsessed with vitamin C. And he was recommending these huge amounts of vitamin C - like 3,000 milligrams a day which is like 50 times what the recommended daily allowance was at the time. And this caused the FDA to kind of suddenly sit up and say, you know what? That's a lot. And maybe we ought to try and put some restriction on these kind of huge amounts of recommendations that some people were making about supplements.

Then Orrin Hatch, who actually put himself through college selling vitamins door to door - and I should say that, actually, a lot of the supplement industry is based in Utah for whatever reason - he introduced into Congress a bill called the 1994 Dietary Supplement Health and Education Act. And this really created a third category that was neither food nor drug. And it basically allowed supplements to kind of be put out there where it wasn't judged by criteria for food, and it wasn't judged by criteria for drugs. And so no science or evidence of any kind is really necessary to put these supplements out on the market.

And if you notice, a lot of supplements will often have a star next to them. You know, they'll say kind of very vague health claims. And then there'll usually be an asterisk at the bottom that will say this is not backed up by any particular medical science. You know, omega-3s I would say, to be fair to the omega-3 supplement industry, have been more rigorously tested than a lot of supplements. But it is interesting to note that their rise to prominence throughout the '80s and '90s more or less tracks with the rise of the supplement industry. And I think that omega-3s have benefited from this general legislative environment which allows these nonmedically tested things onto the market.

GROSS: So you wanted to find a way of eating fish that would be both good for you and for the ecosystem of the sea. So you went on this fish diet for a year where at every meal - breakfast, lunch, dinner - you had fish. Did you have things besides fish? Did you have fruits and vegetables and grains?

GREENBERG: Yes, I had fruits, vegetables and grains.

GROSS: OK. So it raised the level of omega-3s in your body.

GREENBERG: Yep.

GROSS: It also raised the level of mercury in your body, which is not a good thing.

GREENBERG: (Laughter) No, no, no. No, in fact, actually, it went up to 5 parts per million. And it was funny - at the time, I was also working on a Frontline documentary which covered some of the same material. And I remember we were interviewing somebody from the state of Alaska, which checks mercury levels, particularly in Inuit communities because they do eat so much seafood, and they eat seals, and they eat whales. But basically, I realized after that interview that if my hair sample - and they usually use a hair sample to determine history of mercury contamination. If my hair sample had ended up at the health lab in Anchorage - that they would have sent somebody out to my village and told me to stop eating so much blubber. So I had very high mercury levels.

But curiously, when I went off of my fish diet, mercury levels dropped again. And now they're pretty much normal. And that kind of led me to this realization that there is a pathway forward, I think, to eating well for yourself and eating well for the ocean and eating well for the planet. And that's when I kind of came up with this idea of what I call a pesca-terranean diet. Pesca-terranean is like a - a Mediterranean diet is the diet that many clinicians have pointed to when they want to talk about an ideal human eating pattern. And basically, what that means is very little animal protein, large amounts of fruits and vegetables, whole grains. Olive oil is your principal fat.

What I think makes the most sense is this Pesca-terranean diet - very low levels of animal protein - talking maybe a couple servings a week. But if you made those servings particular kinds of seafood, you would both have really high nutrition, good levels of omega-3 but also have a much lower impact overall ecologically on the ocean and on the planet. So what are the seafoods that I include in this pesca-terranean diet? Two things that I mainly focus on. One is these little forage fish - anchovies, herring. These fish are extremely high in omega-3 fatty acids, high in all sorts of other nutrients and tend to be quite low in mercury, tend to be quite low in contaminants because, again, they're very low on the food chain. They don't have the mercury load that, say, a tuna would have. But it turns out that environmentally, harvesting an anchovy, harvesting a herring requires very little carbon. There's very little carbon footprint because these fish are caught with nets that don't drag the bottom. So it actually is a way of getting animal protein on our plate without a huge carbon burden.

And again, if we were to eat these fish instead of reducing them, I think we could cut the harvest and actually have this really, really great source of protein on our plates. The other thing that I've really incorporated into my diet are farmed bivalves. That is mussels, clams, oysters - again, super high in omega-3 fatty acids but also all kinds of other nutrients. And actually, mussels, clams, oysters - they actually improve the marine environment even as we grow them. They filter the water. They make the water cleaner. They actually provide structure for all sorts of other animals to exist.

So I feel that a diet that mostly has vegetables and whole grains maybe at the base of the pyramid and then has a little bit of these forage fish, these sardines, anchovies and so forth and a fair amount of these filter feeders like mussels, clams and oysters - that's about the best diet we can get both environmentally and from a health perspective.

GROSS: I thought that shellfish were supposed to be the kinds of bottom feeders that are dirty and that you had to be careful when eating shellfish. Was I misinformed?

GREENBERG: (Laughter) Well, you know, it is true that you need clean water to have good shellfish. And you certainly wouldn't want to be eating clams and mussels and oysters from contaminated waters. But to me this is a positive feedback loop. Once upon a time, for example, you know, New York City was the largest producer of oysters in North America, perhaps in the world. Once we lost New York as a food system and started polluting it and we lost all the oysters, the water just got dirtier and dirtier. So, you know, there are still many clean pieces of water out there. And we should clarify what we mean by bottom feeder.

GROSS: Yeah, thank you, 'cause I'm realizing, like, mussels kind of live on the shore, like, near the shore. So...

GREENBERG: You know, the whole...

GROSS: ...They're not exactly at the bottom of the ocean.

GREENBERG: The whole bottom feeder term is a really weird thing. If you want, I can go off in a really weird digression. There was this rabbi in the Middle Ages called Nachmanides. And he's the one who kind of classified fish are on a kind of continuum of kosher or not kosher. And he's the one who pretty much introduced the idea of bottom feeders as being these kind of dirty things that's better left - consider them kosher. And so catfish got lumped into there. Bivalves and so forth were excluded because of the Torah to begin with.

But I think that that's a kind of Middle Age ancient concept. Really, when you talk about bivalves - clams, mussels, oysters - they live throughout the water column. But even if they're on the bottom, it doesn't mean that the bottom is necessarily inherently bad. We make it bad. But if we were to see the ocean as our primary food source, as a vital, vital food source - I mean, the other Jewish element here is this - a famous Yiddish expression - you know, don't poop where you eat. It's a little stronger in Yiddish I think.

But we shouldn't be doing that. We shouldn't be looking at the ocean as this disposal system. It's really a food system. And if we didn't get into these sort of medieval hang-ups about what's a bottom feeder and what's not, if we looked at the whole ecology of the ocean and understood that we could be a part of that ecology, I just think we could be much healthier as a planet and as a species.

GROSS: Let's take a break here, and then we'll talk some more. If you're just joining us, my guest is Paul Greenberg. And his book - he's written extensively about fish over the years, and his new book is called "The Omega Principle: Seafood And The Quest For A Long Life And A Healthier Planet." And it's about the omega-3 supplement industry and its impact on the ecosystems of the oceans. And in writing about that, he also writes about the whole reduction industry, which harvests fish and uses it for animal feed and food supplements and other products. So we'll be right back after a break. This is FRESH AIR.

(SOUNDBITE OF DANILO PEREZ AND CLAUS OGERMAN'S "RAYS AND SHADOWS")

GROSS: This is FRESH AIR. And if you're just joining us, my guest is Paul Greenberg, a journalist who's written extensively about fish over the years. And his new book is called "The Omega Principle: Seafood And The Quest For A Long Life And A Healthier Planet." And its focus is omega supplements. And it looks at, like, are they actually healthy for you? What does the research say? How are the omega supplements created? And it turns out they're created through harvesting a lot of fish that are then reduced, that are then processed into things like supplements and animal feed and fertilizer.

You previously recommended something on our show that was - that seemed counter-intuitive, which is, like, buy the frozen salmon...

GREENBERG: Yeah.

GROSS: ...Instead of the salmon that's sitting on the ice.

GREENBERG: Yeah.

GROSS: I would always assume that, you know, the seemingly fresh salmon would be the way to go. So are you still recommending the frozen?

GREENBERG: Well, generally speaking, yes. I mean, what most consumers don't know is that outside of the July-August window, any time you see Alaskan salmon in the supermarket, it would have been previously frozen. So what a lot of times supermarkets will do is they'll buy the salmon frozen from the processors, defrost it, put it out on the ice, and it looks all beautiful and stuff. But it's already been frozen. And any time you expose fish to air, you're exposing it to contamination and to, you know, degrading.

So it's much better, rather than going to the fresh seafood case - if you want wild Alaska salmon, it's much better and much cheaper actually to go to the frozen section where you have vacuum-packed things like sockeye salmon that are, you know, really delicious. If you just defrost them overnight in the freezer, they come out really well. Also, from a carbon perspective, you know, if you're worried about your carbon footprint, frozen fish that is frozen on site where they're caught are a much lower carbon footprint than fresh fish. Fresh fish have to be - often they have to be airfreighted.

And so you can imagine if you're flying fish around the world, that's very expensive from a carbon point of view. Frozen fish, once you bring it down to temperature, put it in the hold of a boat, it actually can stay at temperature without very little additional energy and can get to the consumer with a lot less carbon footprint.

GROSS: So your book does include a couple of recipes. And you say kind of your publisher insisted this would help...

(LAUGHTER)

GROSS: ...Sell the book. A recipe I find very appealing because of the five-minute aspect is five-minute salmon.

GREENBERG: First of all, I like to start with sockeye salmon. It cooks quickly. It is lower in fat. Take the fish. If it's frozen, defrost it overnight in the refrigerator. Take it out of the vacuum-packed sealed package. You can scale it if you like. You don't have to because sockeye salmon scales are actually quite small, and they don't really affect the taste or the flavor of the skin. And I actually like a nice crispy skin.

So what I do is make sure to blot it nice and dry. And that's really, really key because if you put a wet piece of fish under a broiler, it'll kind of boil in its own liquid. So you want to make it nice and nice and dry. Then turn it over with the flesh side up. Sprinkle it liberally with just salt and pepper. That's really all you need. If you're watching your salt, you don't really actually need too much salt because sockeye is very, very flavorful.

Put it down on a broiler - and I should say it's really good to have that broiler be nice and hot before you put the fish in. Turn the broiler on before you start blotting the fish dry. By that point, it'll be nice and hot. Put the fish on the broiler, skin side up, and just cook it for five minutes. And as soon as the skin starts to bubble and blacken a little bit, that's it. And you can eat the fish. You can eat the flesh. You can eat the skin - super delicious. You can have it on a Caesar salad. You can do it just as a main course on your plate. It works out really well.

GROSS: So I was going to ask you the temperature. But the temperature's on broil.

GREENBERG: Just put - yeah, I just put it on high broil. I mean, you know, I'm not a professional chef. But I did cook over 800 seafood meals in one year (laughter). So I do know my way around the kitchen. And I guess I would say just make sure that you're broiling rack isn't right up against the flame. But I'd say like three or four inches below the flame should do it.

GROSS: And so if you've blotted dry the salmon before putting it in the broiler, is it less likely to splatter and smell while it cooks and smell up your broiler?

GREENBERG: I guess. You know, probably the less - personally, I don't mind the smell that much. I will say that it is interesting when you ask Americans, time and again, why they don't eat more fish, they always give three reasons. I don't want to touch it. I don't know how to cook it. And I don't want it smelling up my house. So you're right to be concerned about that. But I think, yes, getting as much liquid as possible probably stops some of the spattering. But, again, remember. We're only cooking it for five minutes. So there's just a limit to how much smell can be spread through your house in five minutes of cooking, right?

GROSS: Right. Paul Greenberg, great to have you back on the show. Thank you so much.

GREENBERG: Thank you, Terry. It was really fun.

GROSS: Paul Greenberg is the author of the new book "The Omega Principle." After we take a short break, film critic David Edelstein will review a new documentary about three triplets who were separated at birth and adopted by three different families. They didn't know about each other until years later. This is FRESH AIR.

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