Читать книгу A Statin Nation - Dr Malcolm Kendrick - Страница 17

DIAGRAM 11

The other point of interest about this polyunsaturated fatty acid is that it is also an omega-3 unsaturated fatty acid. Fatty acids all have CH₃ at one end and COOH at the other, with a different number of CH₂s in the middle. The generic chemical formula is CH₃(CH₂)_nCOOH. The COOH is the chemical part that makes all fatty acids mildly acidic.

The CH₃ end is called the omega end, and the COOH end is called the alpha end (as in from alpha to omega, the Greek for A to Z). However, weirdly, if a double bond is three from the omega end, it is called an omega-3 fatty acid, which means omega (minus) three, though if you want to show off then write ‘ω-3 fatty acid’. In other words, you count backwards from the omega end of the fatty acid to get your omega number. I have never bothered to find out why it is done this way, it just is, probably to add yet another layer of confusion to a topic of almost maximum confusion. In fact, I suppose it is easier to count backwards towards the first double bond you can find.

There are two other points you need to know about fatty acids that are highly relevant to CVD. The first is that the double carbon bond in an unsaturated fatty acid can be in the -cis or -trans form. In nature, virtually every bond is cis. However, in margarine and other fats that are chemically altered, most of the bonds are trans. So, this means that the other type of fatty acids that I need to give special mention to are transfatty acids, or just trans-fats. You may have heard that they are extremely bad for your health, which they are. It will not surprise you to know that they are (or at least were) primarily made by the chemical industry – sorry, the food industry.

Why are they called trans? Well, you can have two types of bond in an unsaturated fatty acid. The first is a -cis bond, where both hydrogens are missing from the same side (yes, any chemist reading that will no doubt choke on their morning Oreo). On the other hand, a trans-fat is where the hydrogen atoms are missing from different sides.

DIAGRAM 12

As you can see from this highly oversimplified molecule, a cis-fatty acid is bent in the middle. A trans-fatty acid is straight. For the food industry, this very slight difference becomes highly important. Because … sorry, aaarrrggghhh, when I started writing about fatty acids I thought it would take a couple of pages. As with almost anything it ends up more complicated than you thought. Oh well, onwards and upwards.

Anyway, most saturated fatty acids, especially the longer ones, are solid at room temperature (clearly, acetic acid is not) because they tend to be straight. Unsaturated fatty acids, at least those with -cis bonds, can bend and wobble in the middle and will not pack together so tightly, which makes them liquid at room temperature. At this point they are not called fats, they are oils. Yes, an oil is just a liquid fat or, to be more accurate, liquid fatty acids.

Therefore, if you want a healthy polyunsaturated substance to put on your toast you have a problem. Whilst you can dip bread into olive oil at fancy restaurants, you cannot really spread oil, it makes a hell of a mess and drips all over your clothes. If you want to create semi-solid polyunsaturated fatty acids, you need to convert the bonds from cis to trans. Then they won’t bend in the middle, can be packed together more tightly and will be solid at room temperature. Clear?

Twisting, superheating and mangling polyunsaturated fats in this way results in that super-healthy substance called margarine. You may remember margarine. Indeed, I think it is now only possible to remember it because it seems that it no longer exists. It was pointed out to me recently that margarine has disappeared, like the Cheshire Cat, leaving only a smile. It cannot be found on the shelves of supermarkets. What we have instead are low-fat spreads. And last time I walked round Sainsbury’s, there was no margarine, only new, improved, low-fat spreads. How strange.

What is the difference between a low-fat spread and margarine? I had a quick look on Google, and this was what I came across from some PR company blub. ‘Choose low-fat and reduced-fat spreads and oils such as rapeseed or olive oil (monounsaturated) instead of hard margarine, lard or butter. To have a low level of saturated fat, which is very important for your heart, you need to limit butter to once a week … Choose lower fat options.’ And that’s distinctly weird because low-fat spreads are still made, almost exclusively, from fatty acids, chemically mangled or not. So, a low-fat spread has the same amount of fat in it as butter – see terminology transforming in front of our eyes.

Margarine was, at one point, advertised as super-healthy because it was high in polyunsaturated fatty acids rather than those deadly, saturated fatty acids. However, the polyunsaturated fatty acids in margarine were primarily transfats, which were later found to be uniquely bad for health. So bad that they now been banned in many countries. The consequence of this is that margarine has transformed from being uniquely healthy to uniquely unhealthy. In a strange coincidence, margarine has magically disappeared from supermarket shelves to be replaced by ‘low-fat’ spreads, i.e. ‘low fat’ to anyone in an advertising agency. Oh well, language is a funny old thing, is it not? George Orwell would, no doubt, be spinning in his grave. ‘Eat low-fat fat instead of high-fat fat.’ You know it makes perfect sense. That thudding noise in the background is a chemist beating his head repeatedly against the wall.

One thing that I find intriguing, but have not yet found an answer to, is the following question. How have the manufacturers of these new ‘high-fat low-fat’ (HFLF) spreads managed to make them solid at room temperature without changing the bonds from cis to trans? I have looked at the website of one leading manufacturer in some detail, and it claims that there are no longer any trans-fats or partially hydrogenated fats in in its product, although I know that there were in the past. If this is true, their product should be an oil, but it is not. I think they have hydrogenated the plant sterols instead – if, indeed, that is possible. Their explanations how they now make polyunsaturated fats solid are totally … well, let’s be kind, beyond my understanding.

Of course, there is a delicious irony to the entire trans-fat saga, which would be funny if it had not resulted in so many premature deaths. We now know that trans-fats are one of the unhealthiest things you can put in your mouth. To quote Wikipedia: ‘Trans-fats, or trans-unsaturated fatty acids, trans-fatty acids, are a type of unsaturated fat that occur in small amounts in nature, but became widely produced industrially from vegetable fats for use in margarine, snack food, packaged baked goods and frying fast food starting in the 1950s. Trans-fat has been shown to consistently be associated, in an intake-dependent way, with increased risk of coronary artery disease, a leading cause of death in Western nations.’

However, at one time, such were the unquestioned benefits of polyunsaturated fatty acids, which included trans-fats, that in the 1980s there was a mass movement to ban McDonald’s from using beef tallow to fry chips, as this was seen as terribly unhealthy. McDonald’s always get it in the neck from everyone.

Under extreme pressure, McDonald’s and many other restaurants were forced to give up beef tallow and started frying in the newer ‘super-healthy trans-fats’. This was primarily due to a campaign run by an organisation called the Centre for Science in the Public Interest (CSPI). The CSPI is now the most active critic of trans-fats. The whole sorry saga of replacing super-healthy, saturated fatty acids with deadly trans-fats is well covered by an article entitled ‘The Tragic Legacy of Centre for Science in the Public Interest (CSPI)’.1

Anyway, where was I? Oh yes, there is no such thing as fat. There are fatty acids, which can be of different lengths, and they can be fully saturated or unsaturated. They can have a -cis or -trans double bond, and if the double bond is three along from the omega end, they are called omega-3 fatty acids, which you find in fish oil. If the double bond is six along from the omega end they are called omega-6 fatty acids, etc.

Apart from trans-fats, they are all perfectly healthy, and there is no strong evidence that any are better or worse for you. Certain animal-sourced omega-3s may have specific benefits, but I wouldn’t go overboard about them.

The final thing that you need to know about fatty acids is that they rarely travel alone in nature. They are normally bundled together in threes. To be more accurate, three fatty acids are attached to a glycerol molecule and create a triglyceride. A triglyceride is what’s found in fat cells and is sometimes called fat, as in ‘triglycerides are fats’.