White fish isn’t a red herring!

Photo credit: Debora Cartagena / CDC website

The BBC’s “Trust Me, I’m a Doctor” broadcast on omega-3 was excellent. The scariest aspect of the study was the fact that all its participants fell into the low omega-3 / high heart disease risk category. There was just one problem. The study used white fish as a control to fish oil supplements and oily fish.

The epidemiology[1] that led to the current enthusiasm for omega-3 rich oils was not based on fish oil supplements. It was about eating fish and sea foods, and white fish would have been a part of that. In “Trust Me, I’m a Doctor”, white fish was used as a control on the basis that it had no fish oils – which is true, but misleading.

  • In white fish the omega-3 is in phosphoglycerides. These form the cell plasma membrane and internal structures. Their composition influences transport, the signalling systems, nuclear receptors and much cell function.
  • Fish oil is a triglyceride. The triglycerides are used for fat depots and energy.
  • Cod liver oil (triglycerides) contains 12% EPA and 8% DHA.
  • Cod flesh phosphoglycerides contain 47% DHA and very little EPA – six times the amount of omega-3 DHA than a corresponding amount of oil from the liver.

“The tissue is the issue”

The important point is that triglyceride oil and phosphoglyceride have different uses. The eating of cod fish meat provides phosphoglycerides which is in the form used by the tissue, in this case the blood cell membranes. The omega-3 index measures whole blood. Hence my question regarding the BBC programme is this. Had they analysed the blood cell membranes separately, would they have found that white fish enhanced the tissue whereas the fish oil did not?

Using the omega-3 index which measures cells and plasma, the study found an increase from the white fish which was not significant. However, if it was concentrated mainly in the tissue, a separate analysis of cell membranes alone could have given a higher proportionate increase and likely reached significance.

The fish oil-derived omega-3, meanwhile, would have been concentrated in the plasma. Little would have been detected in the cell tissue in such a short time.

This could mean that the white fish actually had a better tissue effect than the fish oil. Indeed, there are studies showing a better bio-availability of the phosphoglyceride omega-3 compared to triglyceride oils.

In comparing the benefits of fish oil supplements against oily fish, the researchers would have needed to do a power calculation to test if there was any difference between the two. Their numbers were too small; however, previous tests suggest a better bio-availability from oily fish compared to fish oils.

There is a great deal of misconception about this issue, which is surely a consequence of nutritional science not being taught at schools or medical colleges. This confusion has led to badly designed studies and conflicting results.

None of which detracts in any way from the study’s outcome of an enhanced omega-3 index from fish oil and oily fish, with all the benefits that brings. However, the suggestion that white fish is inconsequential as a source of omega-3 is far from the truth, and needs to be corrected.

The basis of the misunderstanding, and why white fish is being ignored in studies, is that there are two different types of fat in the body: a./Storage (triglyceride). This is the stuff that sits on our waistlines and can clog our arteries if the wrong type. It is basically a storage system for energy, although it also stores fat soluble nutrients such as vitamin A and of course DHA and EPA. b./Structural (phosphoglyceride). This is the building material for cells that forms the structures of the cell. Its fatty acid composition is relevant to cell function.

[1] Epidemiology is the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems. (WHO definition)

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