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Following up on fish oil -

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Norman Swan: A couple of weeks ago we ran what has become one of our more controversial stories for a wee while and that's because so many of you are wolfing down fish oil capsules every day. Two researchers, one from Harvard and the other from the University of Auckland, reported analysing a variety of fish oil capsules and finding only a fraction of the content where they advertised omega-3 fatty acids, with the rest often containing saturated fat. Not a great idea if you're taking fish oil for your heart perhaps.

And then when they looked at the omega-3 fatty acids they were often oxidised, they were off. We pooh-poohed an industry sponsored study which found the opposite, but received a detailed email from Professor Peter McLennan of Wollongong University who reckons our story was wrong. Peter has researched fish oils and the heart for decades and he is in our Wollongong studio as we speak. Welcome Peter.

Peter McLennan: Good evening Norman.

Norman Swan: So let's start out on a bigger picture before we get to fish oil capsules because I don't want to waste the opportunity of having you on the program because of your experience in this area. Why did fish oil start off with great hope about preventing sudden cardiac death and so on and so forth, and every time a new meta-analysis comes out the effect size of fish oil becomes less such that you question whether it's worth taking at all, even if the stuff inside is good?

Peter McLennan: Well, it really probably comes down to how we understand fish oil is working, Norman. The very first indications suggested that it may be working by preventing thrombosis and clotting because that is a well-known action with very high doses of the omega-3 fatty acids. And the other indication is in atherosclerosis, in coronary artery disease. But as we've followed this research through the epidemiology, we're finding that the main effect is not in preventing heart attacks, preventing the atherosclerosis, but indeed preventing that from causing fatal arrhythmias…

Norman Swan: So sudden cardiac death.

Peter McLennan: Yes, sudden cardiac death.

Norman Swan: But I thought even that had been disproven by the large trials, suggesting no, it doesn't even do that, even though there was hope of it.

Peter McLennan: No, well, the trials that have examined sudden death in clearly defined communities that are at high risk of sudden death have come out in favour of it, the GISSI-Prevenzione trial in particular in Italy. Where we've run into problems is that you can't do sudden death studies in the general population because we don't know who's going to have one and we just can't collect enough data.

Norman Swan: So it's got to be in an at-risk group such as the Michael Vallely's patients.

Peter McLennan: Such as people who have already had a previous heart attack are at very high risk of an arrhythmia that will kill them. And so if we restrict the studies to those patients, then we will see a protective effect. What happens is that even those patients are hard to get in enough numbers. So people have been combining patients who have had a stroke, patients who have had a myocardial infarction, patients who have had angina, and expecting that they will see…it's too mixed a group.

Norman Swan: But 45% of adults over 45 in New South Wales are taking fish oil, they are not all at risk of sudden death and they think it's doing something else for them. It's a massive industry.

Peter McLennan: I would doubt that number because when we do the nutrition surveys, the Australian national survey of all sorts of nutrients, the indication is that intake of omega-3 fatty acids is very low across the population.

Norman Swan: I think it comes from the 45 and Up Study, but we can always check that later. So then the question…and what about the dose? Even if you are taking it for sudden death, are the doses high enough? Because that has been the argument, say, from the group in Adelaide with arthritis, is that you've really got to take a lot of fish oil to get an anti-inflammatory effect.

Peter McLennan: That's correct, the anti-inflammatory effects do take high doses, and it is quite effective in that.

Norman Swan: So what's a high dose?

Peter McLennan: Well, for arthritis I think they are using 10 millilitres or 10 grams a day…

Norman Swan: So 10 capsules or 10 mls of the liquid.

Peter McLennan: Yes, it's a very high dose. Also for lowering clinical hypertriglyceridemia you need 4 to 6 grams of the active omega-3 fatty acids to lower it. So that's, again, to get a therapeutic effect. What we are talking about is protecting the heart through correcting a deficiency more than having a drug-like effect.

Norman Swan: Okay, so let's talk about the fish oil capsules and what's inside them. A New Zealand study looking at Australian and New Zealand products, a Canadian study and a study at Harvard all seem to show the same thing. A third of the content is omega-3 fatty acids when you would imagine it's all omega-3 fatty acids, the rest is significantly saturated fat. And then when they look at the omega-3 fatty acids it's oxidised. In other words, oxygen has got in and it's gone off. But you don't agree with the findings of these three studies?

Peter McLennan: Well, for starters the natural content of most fish oils is about 30% EPA plus DHA, which are the active components, and that has always been the case.

Norman Swan: So that's not a surprise.

Peter McLennan: To find that there is only 30% of them in it is just defined that that's correct. The other conflict was about the presence of saturated fat. Well, saturated fat is present in the fish and in the fish oil at about the same level, about 30%. And indeed when we first started to investigate fish oil, we were looking at the difference between polyunsaturates in general and saturated fatty acids. So at that time in the mid-'80s saturated fat was the baddie, and we started using fish oil because it had less polyunsaturates than the highly unsaturated vegetable oils, and we expected to get findings somewhere in between the two, but in fact the fish oil outperformed the sunflower seed oil and safflower oils manyfold, and we couldn't…if we diluted it with saturated fats we didn't lose the effect.

Norman Swan: So it overwhelmed the effect of whatever saturated fat was in there.

Peter McLennan: Indeed.

Norman Swan: So what about the oxidation issue?

Peter McLennan: Yes, the oxidation, I'm not an expert in the processes, and the degree of oxidation is well...that are specified for safety reasons…are well under the potentially dangerous levels. It's very difficult to actually oxidise fish oil. In the body it oxidises…

Norman Swan: But David Cameron-Smith reckoned it's very easy when you look at the supply chain.

Peter McLennan: I think he has conducted a study where he used oxidised fish oil and had to bubble it with oxygen for 30 days or more to get a significant degree of oxidation. When we first started using fish oils, we actually got it as a waste product from a Safcol cannery in Melbourne, and it was like tar. We didn't consider it satisfactory for human consumption, it was being used for paints and that, but it was very effective in preventing arrhythmias in animal models.

Norman Swan: So consumers can be reasonably relaxed, bottom-line?

Peter McLennan: Absolutely.

Norman Swan: Peter McLennan, we'll have to leave it there, thank you very much for joining us.

Peter McLennan: You're welcome.

Norman Swan: Peter McLennan from the faculty of Science, Medicine and Health at the University of Wollongong. You pays your money, you take your chance.