Norman Swan: Hello and welcome to the Health Report with me, Norman Swan. Today, what's four times a quarter, 0.25, all you maths experts? One, you might say. Well, it's actually two when it comes to reducing your risk of heart attack and stroke. Well, it could be.

Also on the Health Report today, how to get better behaviour in diabetes control. How it really matters who you are referred to when it comes to your chances of surviving cancer. And shocking news about what's really in that fish oil capsule a lot of you swallow every day.

A US study which, as you'll discover, replicates findings in New Zealand and Australia, has found that it is far from what you think you are paying for. Preston Mason is a pharmacologist (that's someone who studies the action of drugs) at Brigham and Women's Hospital and Harvard Medical School in Boston.

Preston Mason: It's a huge industry. We went to the local stores and started purchasing a number of very popular brands of these dietary supplements, brought them back to the lab, opened up the capsules and began to examine them for their content. And there were several interesting observations. One, the omega-3 or the desired part of the fish oil supplement only represented in many cases a third of the overall product, the other two-thirds being other fats, including significant levels of saturated fat.

Norman Swan: Saturated fat? Where did that come from?

Preston Mason: That is just the way it comes from the source, and many of the preparations, they do not remove these other fats, they just put it in as it's harvested. The other problem which is as serious is that we found that the omega-3 fatty acids themselves were generally oxidised…

Norman Swan: Meaning they had interacted with oxygen, like rust, like biological rust.

Preston Mason: Absolutely, so they are no longer effective. So we actually would test them. And because they were oxides they had no benefit, they were not able to have some of the biological activity that we associate with these important omega-3 fatty acids.

Norman Swan: So could this explain why when the Cochrane collaboration and others bring all the trials together of fish oil, they are not finding a cardiovascular effect, that in fact there is an effect from fish oil when it's not oxidised, but most people are taking crap?

Preston Mason: Absolutely. Because of the quality issues we can't have any confidence in any of these studies unless they have used a well-characterised or well qualified product. But many of these trials don't involve such products.

Norman Swan: So how can a manufacturer avoid this oxidisation? It sounds as if it's inevitable.

Preston Mason: In most cases, in order to produce a low-cost product, they do not do any extraordinary efforts to isolate the unoxidised forms of the omega-3s. The general production of omega-3 is a by-product in the formation of proteins for poultry farmers.

Norman Swan: If we think this is an American problem, there has been a recent study in our part of the world…

Preston Mason: Yes, so what got us interested is a large study done in New Zealand, a group out of Auckland looked at 30 different products from both Australia and New Zealand and found I believe over 80% had higher than accepted levels of oxidation. They didn't look at some of these other parameters we were looking at but they did see high levels of oxidation, and that has been confirmed now in other labs in Canada, in other parts of North America.

Norman Swan: So what's the poor consumer to do?

Preston Mason: They have to be very careful. This is an industry that's not carefully regulated, so it's consumer beware. It's not obvious or clear, at least in our country because of a lack of oversight, we do not know exactly the levels and the quality of the omega-3 fatty acids in fish oils.

Norman Swan: Preston Mason is at the Brigham and Women's Hospital in Boston. As you heard, this all started a couple of years ago when a research group at the Liggins Institute at the University of Auckland published an extensive analysis of fish oil capsules. One of the authors was Professor David Cameron-Smith who is on the line from New Zealand. Welcome to the Health Report, David.

David Cameron-Smith: Good evening.

Norman Swan: David, so, broadly the same results?

David Cameron-Smith: Indeed that was exactly the case. We commenced our research on the back of not demonstrating the effect that we thought we would with fish oil. So we conducted a study to look at the ability of fish oil to mitigate the risk of diabetes, particularly some of the oxidative effects or the inflammatory effects of diabetes. To our surprise we kind of demonstrated two key events. One was there was no mitigation of diabetes. And two, when we looked at some of the inflammatory events that are associated with elevated blood glucose, we tended to see a worsening of the effect. So that led us very naïvely to start the process of trying to understand what was in the fish oil that we were giving our participants in that clinical research.

And very broadly we had exactly the same results that Preston described. The first thing was that we were shocked at the level of saturated fatty acids and other things that are normally present in different forms of fatty foods within those capsules. Two, we were unable to demonstrate that the capsules gave you the doses of omega-3 fatty acids that we thought you would get. And then really to our surprise we started to discover that there was very high rates of oxidation.

Norman Swan: Meaning that it had gone off, basically.

David Cameron-Smith: Yes, meaning that…so one of the important things to remember is that long chain omega-3 fatty acids are one of the most unstable compounds on earth. They are long, they are very complicated, and they are very prone to oxidation. So they start to go rancid very quickly, just like leaving fish on the bench, it starts to go rancid and taste awful very quickly.

Norman Swan: But David, this morning I get an email from a CSIRO researcher saying they had published a similar study in November, sent me a copy of it, saying they found exactly the opposite from you and from Preston Mason.

David Cameron-Smith: Indeed that was the data that they've presented just prior to Christmas. But I'd like to draw you back to a number of anomalies with that research. So we've recently published an open letter to the editor of that journal where we've made two important points. The first important point is all of the authors were involved in the Omega-3 Centre. So that's effectively a mouthpiece or an organisation that is devoted to propagating the benefits of omega-3, irrespective of where those omega-3s come from.

The second is the study was conducted by a commercial laboratory, and all the analyses were performed using techniques that were commercially in confidence. So despite our best efforts to understand what they did, how they did it, why they chose those supplements, exactly what the methodologies were that underpinned their results, all we've got back from the company so far is a lovely letter stating that their methodologies are confidential and I would like to be able to describe them but I cannot.

Norman Swan: So what's the poor consumer to do? Because you talk about this, that really fish oil supplements are just a by-product of a huge industry for food stock.

David Cameron-Smith: That's exactly right. At least 75% of the fish oil…and so let's remember where most fish oil comes from. Most fish oil is farmed from ocean fish off the coast of Peru and Chile. They are hauled out of the water in very large trawling vessels. They are then processed onshore, so the conditions from a ship to the shore, subsequently the processing, is all done under conditions that I simply can't verify the quality of that.

Secondly, that fish oil is then transported right across the ocean, to places like China where it engages in high throughput processing. And really it's designed to achieve two things. One is, most of that fish oil goes back to feeding fish. Fish meal is the single biggest product of those fisheries. The second, the smaller by-product and be less valuable by-product is to turn it into fish oil.

Norman Swan: Are there any reliable products on the market, do we know?

David Cameron-Smith: My advice is to go back to the source, and the source is…we have an abundant supply of fresh oily fish. It's unfortunate that our salmon is increasingly farmed under conditions where there is less fish meal fed to those salmon, so there is less omega-3s. And so I'd go to the reliable source. And the other thing to remember is increasingly we are able to manufacture omega-3s from algal sources, and that's an unoxidised source of omega-3.

Norman Swan: So if it says 'algal sources' on the bottle you might be in a bit better shape.

David Cameron-Smith: Exactly.

Norman Swan: David Cameron-Smith, thanks for joining us on the Health Report.

David Cameron-Smith: My pleasure.

Norman Swan: Professor David Cameron-Smith is a human nutritionist at the Liggins Institute at the University of Auckland.

And you're listening to the Health Report here on RN, ABC News Radio and CBC Radio across Canada. I'm Norman Swan.