Читать книгу A Statin Nation - Dr Malcolm Kendrick - Страница 16

Whilst there is not such thing as a fat, there are fatty acids. These are generally what people are talking about they use the word fat. Fatty acids come in many different forms, and the terminology can seem quite daunting. For example, there is omega-3 fatty acid, which most people have heard of, usually as a part of super-healthy fish oils.

But what is it? Well, an omega-3 fatty acid is not a single entity. Omega 3s are available in a bewildering variety of forms. It is possible to have myristic omega-3 fatty acid or stearic omega-3 fatty acid. They can also be monounsaturated or polyunsaturated, with a -trans or -cis bond. Some could be considered healthy, others less so.

I know this may seem horribly off-putting, but the naming system is fairly simple to explain. Luckily fatty acids are also one of the simplest molecules in the human body. They consist of three elements. Carbon, oxygen and hydrogen. The backbone is a chain of carbon molecules that can vary in length from one to 80 carbon atoms, although anything over 20 is called ‘long chain’ and we can basically ignore anything over 30.

A fatty acid with 14 carbon atoms in the chain is called myristic acid, and a fatty acid with 16 carbon atoms is called palmitic acid because it was first found in palm oil in high concentrations. And when I tell you that napalm is made from palmitic acid, it does demonstrate that fatty acids contain a lot of energy.

The shortest and simplest fatty acid is acetic acid and still counts as a fatty acid, even though it has no chain of carbon atoms at all. Acetic acid can also be called vinegar (see diagram 8). Chemists do enjoy their world of total confusion.

DIAGRAM 8

So when you visit the fish and chip shop, you could ask for ‘Salt and saturated fatty acid on my chips please.’ I don’t imagine they’d have the faintest idea what you were talking about, though they might say, ‘That’ll raise your blood pressure and cholesterol, don’t you know?’

Diagrams of fatty acids are normally presented as a chain of carbon atoms with hydrogen atoms attached along the chain. In Diagram 9 there are a total of 18 carbon atoms, which makes this one stearic acid. Incidentally, stear is the Greek for tallow, which is a rendered form of beef or mutton fat. And tallow, if you alter it a bit, can be used in jet engines as a biofuel and probably in any car with a diesel engine. At one time, beef tallow was also used by McDonald’s to fry chips until they were told it was terribly unhealthy, and they should stop. Pity, because food fried in tallow is super delicious.

DIAGRAM 9

This stearic acid molecule is, in turn, defined as a saturated fatty acid because every carbon atom in the chain has two hydrogen atoms linked to it. Or, put another way, it is fully saturated with hydrogen atoms. You couldn’t squeeze another one on even if you wanted to. On the other hand, if a fatty acid is defined as unsaturated, it is because there are (at least) two carbon atoms in the chain with only one hydrogen atom linked to them, in which case there is space for more hydrogen atoms. Or, let us say, it is unsaturated with hydrogen atoms.

DIAGRAM 10

The relatively short, unsaturated fatty caproic acid in Diagram 10 is actually a monounsaturated fatty acid because it has two carbon atoms, with no hydrogens attached. The reason for the prefix mono is that there is one double bond between two carbon atoms. Not that there is only one carbon atom with a single hydrogen attached. Please don’t blame me for these naming systems. (Chemically, you could not have a single hydrogen atom missing from one carbon atom because that carbon atom would then have a naked or spare bond, which would be utterly unstable. Kaboom.) If you have more than one double bond in the chain of carbon atoms, the fatty acid is then referred to as a polyunsaturated fatty acid. The unsaturated fatty acid in the diagram below has three double bonds, and is missing six hydrogen atoms. This makes it polyunsaturated.