OKAY, DO YOU KNOW WHAT A FAT IS?

[Guest guest]

Dear Group,

 

I suggest that you read the article at the website as it has diagrams to show

examples which will be deleted by the server when posted here.

 

F.

 

http://www.redflagsweekly.com/kendrick/2003_feb04.html

 

 

February 4, 2003

 

OKAY, DO YOU KNOW WHAT A " FAT " IS?

 

By Malcolm Kendrick MbChB, MRCGP (email - malcolm )

 

I received an overwhelming response to my little primer on lipoproteins, so I

thought I should explain a little more about fats. Excuse my diagrams, I got

them all from the internet, so they have no overall design template, but I hope

that I can keep things clear.

 

A fat has the basic structure shown below (Fig 1).

 

 

 

(Fig 1) My nameless fat

 

 

 

All fats are, basically, a chain of carbon atoms of varying length, where the

carbon atoms are attached exclusively to hydrogen atoms, apart from the group at

the end — COOH - called a carboxyl group. The carboxyl group is what defines

fats as an acid, or fatty acid. So a fatty acid and a fat are actually the same

thing. The terms are interchanged at will. That one caused me endless confusion.

 

You may have noticed that my nameless fat has a gap at the bottom, where no

hydrogen (H) atoms are attached. And there is a double bond between the carbons

with the missing hydrogens. This means that the carbon atoms at either end of

the double bond are not ‘saturated’ with hydrogen. So this fat is ‘unsaturated.’

 

The other thing about my nameless fat is that there is only one double bond, so

this fat would be referred to as a mono-unsaturated fat. Monounsaturated = one

double bond, or two hydrogens missing. If there is more than one double bond,

the fat is referred to as poly-unsaturated.

 

Clearly, therefore, a saturated fat is one with no double bonds, and no

hydrogens missing. It is fully saturated with hydrogen. You can see how this

nomenclature works in Fig 2.

 

In real-life you can tell if a fat is saturated primarily because it is solid at

room temperature. Monounsaturated fats and polyunsaturated fats are usually

liquid are room temperature. Unless you live in Siberia, of course.

 

 

 

Fig 2

 

 

 

So, how come you can spread margarine, it being polyunsaturated and all? Because

in the 1930s a very clever chemist learned how to nail extra hydrogens to

unsaturated fats using a process known as ‘hydrogenation,’ and thus was born

margarine — hoorah. Artificially hydrogenated fats are often called trans-fats,

or trans fatty-acids. These types are fat are not really found in nature at all.

 

As a slight aside, forget GM foods, margarine is as alien as it gets. Even if

you call it Flora and paint pictures of lovely flowers around the tub, and get

highly paid athletes to promote its health giving wonders. ‘Flora….’ (is this

just a UK name?). Sorry, start again with my strap-line (fade-in Beethoven’s

pastoral symphony). ‘Flora, as natural as platinum catalysed hydrocarbon

cracking itself.’ That, by the way, is what we in the UK call a joke. Just in

case the Flora lawyers try to sue me.

 

So, now you know the difference between a saturated and unsaturated fat. And

pretty unexciting it is too. How come it seems so difficult? Because people

start using terms like alpha-linoleic, and stearic and Omega-3, and cis-bonds

and uncle Tom Cobbly and all.

 

All of this is really just a form of nomenclature used by chemists (to confuse

us poor laypeople). However, to keep it simple, if the double bond in a fat is

three along from the ‘Omega’ end of the fat, which is the opposite end from the

carboxyl group, the fat is then called an Omega 3 fatty acid. If the double bond

is six along, it is an Omega 6. And that’s the difference between an Omega 3 and

an Omega 6 fatty acid. Wow — hold onto your seat — is this exciting or what.

 

Where do the other names come from e.g. stearic, and linoleic, and palmatic etc?

Generally, these names are taken from the source of the fat. So palmatic acid

comes from Palm oil/fat. Linoleic comes from linoleum (only joking — it’s

vice-versa). These types of fat/oil are defined primarily by the length of the

carbon chain. Linoleic acid, for example, has eighteen carbon atoms.

 

Thus, fats are named according to a few different variables. Where they come

from, palmatic, coconut (and this also defines the number of carbon atoms),

whether they are saturated, or unsaturated, and where the double bond, or bonds,

sit. The other significant bit of nomenclature is whether or not the double bond

is cis, or trans. To explain.

 

Usually, in natural fats, the hydrogen atoms sit on the same side of the double

bond, causing a ‘kink’ in the chain. See diagram 3. when you get this

‘same-side’ hydrogen structure, the bond is known as a cis bond. If the

hydrogens are spread either side it is known as trans.

 

Because cis bonds have both the hydrogen on the same side, they tend to kink,

causing the chain to bend. This bendyness allows the fat to wiggle around more,

and so the fat is fluid. A saturated fat has no kinks, no bendiness, and thus

remains solid. Trans bonds are also less wiggly than cis bonds, so the fat is

more solid, but no too solid. Which is why margarine can spread ‘straight from

the fridge,’ or in my case, straight into the dustbin.

 

Diagram 3

 

 

 

And that’s about all you need to know about fats — or fatty acids. There are

other ‘naming’ protocols, but they don’t really have much relevance to

non-specialist audiences.

 

But please keep one thing in mind - within the context of heart disease. The

only real connection between fats and cholesterol is that, as they are insoluble

in water, they have to be transported around inside lipoproteins. You don’t make

cholesterol from saturated fats, or any other sort of fat, or vice-versa.

 

So, why do people keep telling you that excess saturated fat consumption raises

your Cholesterol level? Because this has become an article of faith. It is not

susceptible to reason, logic or facts. Metabolically speaking, there is no

connection between these two substances at all. They just happen to sit in the

same lipoproteins. (And it’s the lipoprotein level you’re interested anyway —

you don’t actually have a cholesterol level)

 

Equally, why do unsaturated fats lower your cholesterol level? They don’t. How

could they? Fats, saturated or otherwise, ARE NOT CONNECTED TO CHOLESTEROL

METABOLISM. You might as well argue that eating excess protein will raise your

blood sugar level. For a graphical illustration of the differences between fats

and cholesterol. See diagram 4.

 

 

 

 

 

DIAGRAM 4

 

A SATURATED FAT CHOLESTEROL

 

 

 

 

 

 

 

So now you know what a saturated fat is, and what an Omega 3 fatty acid is, and

what cholesterol is. I hope you will now find what I found. Once you understand

this stuff a bit better, you can’t imagine why anyone ever thought that

saturated fat in the diet had an impact on cholesterol levels in the first

place. There is just no connection.

 

 

 

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