Fat is a much-maligned substance in the twenty-first century world we find ourselves in; exhortations for it to be burnt or exhumed from one’s diet abound from all sides, and indeed entire industries are now founded on dealing with the unwanted stuff in one form or another. However, fat is not, in fact, some demonic hate figure designed specifically to kill all that is good and beautiful about our world, and since it is at least relatively interesting I thought it might be worth investigating a few bits and pieces surrounding it over the course of a post.
All fats are based upon a molecule called glycerol, or propan-1,2,3-triol to give it its technical IUPAC name. Glycerol is a very interesting substance used for a wide range of purposes both in the body and commercially; it can be broken down to form sugar, can be used as a laxative, is an effective antifreeze, a useful solvent, a sweetener, is a key ingredient in the production of dynamite and, of course, can be used to store energy in fatty form. Glycerol is, technically speaking, an alcohol, but unlike most everyday alcohols (such as the ethanol upon which many of our favourite drinks are based) each glycerol molecule contains not one but three alcohol functional groups. In a fat, these alcohol groups act like sticking points, allowing three different long-chain carboxylic acid molecules known as ‘fatty acids’ to attach to each glycerol molecule. For this reason, fats are also known as ‘triglycerides’, and precisely which fat is formed from this structure depends on the structure of these fatty acids.
Fatty acids consisting of shorter chains of carbon atoms have less atoms with which to interact with their surroundings, and thus the intermolecular forces between the fatty acid chains and other molecules are weaker for shorter-chain acids. This has a number of effects on the properties of the final product, but one of the most obvious concerns its melting point; shorter-chain fatty acids generally result in a product that is liquid at room temperature, and such products are designated as ‘oils’ rather than fats. Thus, not all triglycerides are, technically speaking, fats, and even triglycerides are part of a larger chemical family of fat-like substances known as ‘lipids’ (organic chemistry can be confusing). As a general rule, plants tend to produce oils and animals produce fats (presumably for reasons of storage), which is why you get stuff like duck fat and olive oil rather than the reverse.
The structure of the fatty acids is also important in an important dietary consideration surrounding fats; whether they are saturated or unsaturated. In chemistry, carbon atoms are bonded to one another by covalent bonds, consisting of a shared pair of electrons (each atom providing one electron of the pair) that keeps the two atoms bonded together. Most of the time, only one pair of electrons forms the bond (known as a single bond), but sometimes the relevant carbon atoms have a surfeit of electrons and will create another shared pair, forming a double covalent bond. The nature of double bonds means that the carbon atoms involved can accept more hydrogen atoms (or other electrophiles such as bromine; bromine water is a good test for double bonds) whereas a molecule made up entirely of singly-bonded atoms couldn’t accept any more and would be said to be saturated with hydrogen. Thus, molecules (including fats and fatty acids) with only single bonds are described as saturated, whilst those with double bonds are known as unsaturated*. A mixture of the food industry and chemical fraternity has developed a whole host of more specific descriptive terms that give you more detail as to the chemical structure of your fats (stuff like monounsaturated and such), and has also subdivided unsaturated fats into two more categories, cis- and trans-fats (the names refer to the molecules’ arrangement in space about the double bond, not their gender orientation).
With all these different labels, it’s no wonder people have so much trouble remembering, much less identifying, which fats they are ‘supposed to avoid’. Saturated and trans-unsaturated fats (which occur rarely in nature due to enzyme structure and are usually manufactured artificially) are apparently bad, mono-unsaturated (cis-) fats are good, and poly-unsaturated (cis-) fats good in moderation.
The extent to which these fats are ‘good’ and ‘healthy’ does not refer to the effect they will have on your waistline; all fats you eat are first broken down by your digestive process, and the resulting calories produced are then either used to power your body or turned into other sorts of fat that take up belly space. This process is the same for all types of energy-containing food and I shall come onto a few details about it in a paragraph or two. No, the relative health risk of these different fat types refers instead to the production of another type of lipid; cholesterol, which has such a complex, confusing structure and synthesis that I’m not even going to try to describe it. Cholesterol is a substance produced intentionally by the body and is very useful; it is used in the production of all sorts of hormones and vitamins, is a key ingredient of bile and is used in helping cells rebuild themselves. It is transported through the body by two different substances known as LDL (low-density lipoprotein) and HDL (take a wild guess) that carry it via the bloodstream; and this is where problems arise. The precise mechanism behind it is not known, but an increased consumption of trans-fats and other ‘bad’ triglycerides leads to an increase in the amount of cholesterol and LDL in the bloodstream. If this stuff is allowed to build up, cholesterol can start to ‘stick’ to the sides of one’s blood vessels, slowly reducing the effective size of the blood vessel until it is almost completely shut. This greatly reduces the flow of blood through these vessels, and this can have particularly dramatic consequences if the large, important blood vessels close to or supplying the heart are affected, leading to coronary heart disease and a greatly increased risk of heart attacks. HDL, for some reason, doesn’t apparently contribute to this affect, leading HDL to be (misleadingly, since it’s not actually cholesterol) dubbed ‘good cholesterol’ and LDL as ‘bad cholesterol’.
Clearly, then, having too much of these ‘bad fats’ can have some pretty serious consequences, but public realisation of this has lead all fat to be considered as a disgusting thing to be shunned. Frankly, this is just plain old not true, and it is far easier to live a healthy life with a bit of meat** on the bones than to go down the super-skinny angle. Fat is a vital body tissue, required for insulation, vitamin transport, to store energy, to prevent the disease and provides many essential nutrients; omega-3, the ‘essential oil’ (meaning it is not produced by the body) found in fish that is thought to play a role in brain development and other bodily functions, is nothing more than an unusual fatty acid.
If you want further evidence as to the importance fat plays in one’s body, I refer you to a condition known as lipodystrophy, in which one’s body cannot produce or store fat properly. In some cases this is localised and relatively harmless, but in incredibly rare cases it manifests itself as a hereditary condition that causes abnormal bone and muscle growth, facial disfigurement and requires an incredibly strict diet (in direct contravention of the massive appetite the condition gives you) in order to control one’s levels of cholesterol and carbohydrate intake. In many cases, sufferers of this horrible condition will not live past twenty, if they even get that far.
*Vegetable oils tend to be more frequently unsaturated than fats, as this is another factor that reduces their melting point and makes them liquid. A key process involved in producing margarine involves taking these vegetable oils and adding hydrogen to these double bonds, a process known as hydrogenation, in order to raise their melting point and make the margarine solid and spreadable. Chemistry!
**Although, as anyone who likes their bacon skinny will tell you, fat is most certainly not meat. In fact, it’s not even alive.