Good Fats, Bad Fats
By Nigel Kinbrum aka MuscleTalk member nigeepoo - Taken from his eBook 'Nigee's Guide to Healthy Body Fat Loss'
There's a lot of bad information in the media about fats. Saturated fats are usually described as 'bad' and polyunsaturates are usually described as 'good'. This is simplistic. Everything is bad in excess, even polyunsaturates. The thing about fats is that there are four basic types (saturates, monounsaturates, omega-6 polyunsaturates and omega-3 polyunsaturates), and these must be consumed in roughly the right proportions for optimum health. Suffice it to say, the majority of people in the West do not eat them in anywhere near the right proportions.
What exactly are fats?
Fats are an ester of glycerol and fatty acids.
1 molecule of glycerol + 3 molecules of fatty acid = 1 molecule of triacylglycerol (triglyceride / fat) + 3 molecules of water.
It's the fatty acids that determine whether a fat is saturated, monounsaturated or polyunsaturated. The four different types of fatty acid all have a CH3 at one end and a COOH at the other. The difference is in the middle section.
Saturated fatty acids have a middle section consisting of all CH2. Here's a diagram of stearic acid (the predominant fatty acid in beef fat):
Monounsaturated fatty acids have one C=C bond in the middle, which happens to be 9 from the left-hand end resulting in monounsaturates also being referred to as omega-9 fatty acids, as omega is at the end of the Greek alphabet. Here's a diagram for oleic acid (the predominant fatty acid in olive oil):
Omega-6 polyunsaturated fatty acids have two or more C=C bonds in the middle with the last one being 6 from the left-hand end. Here's a diagram for linoleic acid (the predominant fatty acid in sunflower oil):
Omega-3 polyunsaturated fatty acids have three or more C=C bonds in the middle with the last one being 3 from the left-hand end. Here's a diagram for alpha-linolenic acid (the predominant fatty acid in flax-seed oil):
These diagrams are a bit misleading. Where there is a C=C bond, there are two H's on the 'underside' only of the molecule. This asymmetry causes the H's to repel each other and bend the molecule into a V-shape at each C=C bond. C=C bonds with H's on the same side are known as cis bonds. The above molecule is really cis, cis, cis (c,c,c) alpha-linolenic acid. The other type of C=C bond is known as trans and looks like the following diagram:
This is a diagram of trans, trans, trans (t,t,t) alpha-linolenic acid. As the H's are on opposite sides of the molecule, they do not repel each other and the molecule is straight, as shown above. Note that saturated fatty acid molecules are naturally straight. Therein lies the problem with trans fatty acids, which are straight like saturated fatty acids but have unsaturated bonds which are prone to oxidation. For more details see www.cyberlipid.org/perox/oxid0002.htm for some heavy-duty organic chemistry!
Our bodies take trans fatty acids and incorporate them into cell membranes as if they were saturated fatty acids. This results in atherogenic (artery-clogging) damage to the immune system and other health problems. trans fatty acids are found in partially-hydrogenated vegetable oils and so any processed foods or cooking/spreading fats which has the word 'hydrogenated' high-up in the ingredients list should be avoided. These really are the bad fats.
There are also naturally-occurring trans-fatty acids made by bacteria in the stomachs of ruminant animals, like conjugated linoleic acid (CLA), which looks a bit like the diagram below:
This has one of the C=C bonds shifted to the left and also has one cis bond and one trans bond, so the molecule is always bent. CLA has certain beneficial properties but medical studies show mixed results. It's certainly not artery-clogging, so don't let anyone put you off eating butter from grass-fed cows (e.g. New Zealand butter) by suggesting that it has nasty trans fats in it. CLA is a good trans fat.
Anyway, back to diet. I've read that saturated fat consumption should be about 10% of total calories. This is because, even though saturated fats are not essential (our bodies can manufacture them), this guarantees adequate levels of sex hormones in the body. I've also read that total polyunsaturate consumption should be about 5% of total calories, with a ratio of omega-6 (ω-6) to omega-3 (ω-3) of 2:1. As ω-3 are only found in greater quantities than ω-6 in flaxseeds (linseeds) and oily fish, and many people eat way too little or no oily fish (and who, other than body-builders and some vegetarians/vegans, eats flaxseeds?), the average ω-6 : ω-3 ratio in the West may be as much as 20:1. This is due to the widespread consumption of meats, eggs and milk from grain-fed animals, grains, nuts and seeds. So, it's not surprising that there are high rates of heart disease and other inflammatory diseases in the West, as ω-6 fats end up in types of prostaglandins which are pro-inflammatory. ω-3 fats end up in types of prostaglandins which are anti-inflammatory.
So eat up yer oily fish if you're not vegetarian or vegan. Otherwise, eat up yer ground-up flaxseeds!
Monounsaturates can make up 15% to 35% of total calories, depending on activity levels. Sedentary people on average burn twice as much energy from fats as from carbs. So, if energy from protein is 25% say, 25% of energy can then come from carbs and 50% can come from fats i.e. a 2:1 ratio of fats : carbs. When active, more carbs are needed by everyone.
To see which fats contain which fatty acids, see www.manitobaharvest.com/nutrition/index.asp?itemID=183 for a Comparison of Dietary Fats chart.
For more information on fats see the article Essential Fatty Acids.