Do you know the difference between omega-3, omega-6, omega-7 and omega-9? Or saturated, monounsaturated and polyunsaturated fats? Or trans fats, essential fatty acids and triglycerides? It took me a while to understand them, too, so here’s my complete guide.
Fatty acids contain a chain of carbon atoms linked together with single or double chemical bonds. If the carbon atoms are all linked using single bonds the fatty acid is described as saturated, as no spare bonds are available to make new connections with hydrogen atoms.
A fatty acid that contains one or more double bonds is described as unsaturated, as spare bonds remain available to make new chemical links.
- If the carbon chain contains only one double bond, the molecule is classed as a mono-unsaturated fatty acid (MUFA).
- If there are two or more double bonds, the molecules is referred to as a poly-unsaturated fatty acid (PUFA).
Unsaturated fats are further classified according to the position of their first double bond, counting from the omega (methyl) end of the molecule.
- If the first bond involves the third carbon atom, the unsaturated fat is classed as an omega-3. These always have more than one double bond so are known as omega-3 polyunsaturated fatty acids (eg alpha-linolenic acid).
- If the first double bond involves the 6th carbon atom, the fatty acid is classed as an omega-6. These always have more than one double bond, and are known as omega-6 polyunsaturated fatty acids (eg linoleic acid).
- If the first double bond involves the 7th carbon atom, it is classed as an omega-7. As these only have one double bond, omega-7s are also monounsaturated fatty acids (eg palmitoleic acid).
- If the first double bond involves the 9th carbon atom, it is classed as an omega-9. As these only have one double bond, omega-9s are also monounsaturated fatty acids (eg oleic acid).
The number and position of the double bonds within a fatty acid determines how flexible and bendy it is, and whether it acts as a solid or liquid at room temperature.
In general, saturated fats tend to be solid while mono-unsaturated and polyunsaturated fats tend to form oils.
The position of the first double bond also determines how the fatty acid is metabolised and used by cells, and how it affects your overall health.
The fats in your diet, and those in your body stores, are mainly present in the form of triglycerides rather than free fatty acids. Triglycerides are E-shaped molecules that contain three fatty acids linked to a glycerol backbone.
Any three fatty acids can be present, such as two saturated fatty acids and one mono-unsaturated fatty acid; or one saturated fatty acid, one monounsaturated fatty acid and one omega-3 polyunsaturated fatty acid.
Dietary fats (and body fat stores) therefore contain a blend of saturated fats, monounsaturated fats and polyunsaturated fats.
In general, animal-based foods contain a higher percentage of saturated fat than vegetable foods. Even butter, lard and dripping, which are traditionally viewed as saturated fats still contain significant amounts of ‘healthy’ monounsaturated fats and some polyunsaturated fats.
The types of fat found in animal and vegetable foods vary depending on the nourishment they have received, and their individual genetic make-up, but here are some typical values:
|Dietary Fat||% saturated||% monounsaturated||% polyunsaturated|
|Beef fat (dripping)||51%||38%||3%|
|Pork fat (lard)||40%||43%||10%|
|Cod liver oil||21%||45%||31%|
|Macadamia nut oil||14%||81%||5%|
|Evening primrose oil||8%||11%||77%|
Eating excess saturated fat has been associated with an increased risk of coronary heart disease in some studies, but not in others, and it is now recognised that many of the early studies which demonised saturated fat were flawed.
Some saturated fats are converted into cholesterol in the liver, but only saturated fatty acids containing chains of 12, 14 or 16 carbon atoms have an effect on your blood cholesterol levels. Those with chain lengths of up to 10 carbon atoms, and those with over 16 carbon atoms, do not raise cholesterol levels.
Overall, a third of dietary saturated fats – including stearic acid (which has 18 carbon atoms) and is found in milk fat, cocoa butter and meat fat – have no cholesterol raising activity. This does not mean that a high saturated fat intake is harmless, however. Like all types of fat, it has a high calorie content and can contribute to weight gain if you eat too much. And, if you have a high cholesterol level, you may have inherited genes that mean you process saturated fat less efficiently than other people.
If your cholesterol level is raised, aim to replace some foods that are high in saturated fats with foods providing a higher amount of the more beneficial monounsaturated fatty acids (found in olive, rapeseed, macadamia, avocado and walnut oils) or omega-3 polyunsaturated fats (found in fish, flaxseed and walnuts oils). Brazil nuts also have a notable cholesterol lowering activity.
Monounsaturated fats have only one double bond. Some, such as oleic acid are omega-9s (first double bond involves the 9th carbon atom) while some are omega-7s.
Foods rich in omega-9 monounsaturates include macadamia nuts, almonds, hazelnuts, avocado, olive oil and rapeseed oil. Only a few oils are good sources of omega-7s, and these include macadamia nut oil and sea buckthorn oil. Avocado oil contains useful amounts of omega-7, too.
Monounsaturated fats are metabolised in a way that lowers blood levels of ‘bad’ LDL-cholesterol and total cholesterol, but do not lower ‘good’ HDL-cholesterol. A diet high in monounsaturates may help to reduce your risk of type-2 diabetes, atherosclerosis, high blood pressure, coronary heart disease and stroke. This may explain many of the benefits of the Mediterranean diet.
Polyunsaturated fatty acids contain two or more double bonds and are further divided into omega-3s and omega-6s.
Because of the position of their first double bond, your body handles omega-3s and omega-6s in different ways. Omega-6 fatty acids are converted into substances (series 2 prostaglandins, series 4 leukotrienes) that promote inflammation and increase blood stickiness. In contrast, omega-3s are converted into substances (series 3 prostaglandins, series 5 leukotrienes) that have anti-inflammatory and blood-thinning actions.
The omega-6 fatty acid, gammalinolenic acid (GLA, found in evening primrose, blackcurrant and starflower oils) is one of the few omega-6s that can reduce inflammation if intakes are sufficiently high.
Your cells cannot convert omega-6s into omega-3s, or vice versa, so balanced intakes of these two types of fat are important to regulate inflammation.
Omega 3 and omega 6 ratio
Our ancestors evolved on a stone-age diet supplying an omega-6 to omega-3 ratio of around 2:1. The average western diet currently contains a ratio of omega-6 to omega-3 fats of 10:1 due to increased consumption of vegetable oils, vegetables spreads and convenience foods, together with reduced intakes of omega-3 rich nuts and oily fish. This imbalance has been linked with an increased susceptibility to inflammatory diseases such as asthma, eczema and coronary heart disease (which is associated with low-grade inflammation of artery walls).
Good sources of omega-3 essential fatty acids include:
- oily fish such as mackerel, herring, salmon, trout, sardines, pilchards, fresh tuna (not tinned)
- wild game meat such as venison and buffalo
- grass-fed beef
- omega-3 enriched eggs
- omega-3 fish oil supplements.
To reduce your intake of inflammatory omega-6s, cut back on:
- omega-6 rich vegetable oils such as safflower oil, grape-seed oil, sunflower oil, corn oil, cottonseed oil or soybean oil (replace with healthier oils such as rapeseed, olive or walnut oils)
- margarines based on omega-6 oils such as sunflower or safflower oil
- convenience and fast-foods
- bought cakes, sweets and pastries.
Trans fatty acids
Polyunsaturated fatty acids are oils are room temperature. Because they contain spare double bonds, they can be converted into semi-solid margarines and spreads by artificially adding extra hydrogen atoms to convert some of their double bonds to single bonds.
During commercial hydrogenation processes, some of the partially hydrogenated fats produced are twisted and have a rigid structure that is more like that of a saturated fat rather than a nice, flexible cis-unsaturated fat. These twisted partially hydrogenated fats are known as trans-fatty acids.
Trans fats are harmful as they increase the rigidity of cell membranes, are processed to raise blood levels of ‘bad’ LDL-cholesterol while lowering levels of ‘good’ HDL cholesterol. Trans fats are also associated with inflammation, poor glucose control and weight gain. Trans fats have also been shown to increase the risk of cancer, especially those of the breast and prostate gland. Now these health risks are recognised, margarines and low fat spreads which were high in trans fats are now reformulated to reduce their trans-fat content. Check labels and select foods with the lowest content of trans fats or partially hydrogenated polyunsaturated fats.
Naturally produced trans fatty acids found in milk, cheese, butter and meats (such as vaccenic acid, an omega-7 also found in human milk) are structurally different to those generated by artificial hydrogenation of fats, and have not been associated with health risks such as coronary heart disease. This has turned the butter versus margarine controversy on its head. The simplest advice is to eat as wide a variety of foods as possible, including a little of everything (butter and margarine if you wish) in moderation with nothing to excess.
Essential fatty acids
Your cells can make monounsaturated fatty acids, and most polyunsaturated fatty acids from other fats in your diet, but can only make omega-6s from other omega-6s, and omega-3s from other omega-3s.
Because of this, one omega-6 (linoleic acid) and one omega-3 (alpha-linolenic acid) must come from the diet to act as building blocks for making the rest. These two polyunsaturated fats are therefore classed as essential fatty acids.
Linoleic acid (LA, an omega 6) can only be converted into other omega-6 fatty acids, such as gamma-linolenic acid (GLA) and arachidonic acid (AA), while alpha-linolenic acid (ALA, an omega 3) can only be converted on to form other omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
As a result, only around 5% to 10% dietary alpha-linolenic acid is converted on to the important long chain omega-3s, EPA and DHA. These long chain fatty acids are therefore often classed as essential, too (although technically speaking, they aren’t really).
Essential fatty acid deficiency
When your diet provides too few essential fatty acids, or you make too few long-chain omega-3s (EPA and DHA which are important for healthy brain function) your body makes do with the next best fatty acids available. This means incorporating saturated fatty acids and even harmful trans-fatty acids into cell membranes. These fatty acids have a less flexible structure, and reduce the elasticity of artery walls, and the speed at which chemical and electrical messages are passed from one nerve cell to another within the brain.
Lack of essential fatty acids, especially the omega-3 alpha-linolenic acid (and the longer-chain DHA and EPA) has been linked with an increased risk of allergies such as eczema, asthma and hay fever, and with learning difficulties such as dyslexia. Symptoms that may be due to an essential fatty acid deficiency include:
- Dry, scaly, itchy skin – especially on the shins
- Keratosis pilaris (pimply, goosebump-like skin on the upper arms and legs)
- Dull, straw-like hair
- Soft or brittle nails
- Impaired immunity with frequent infections
- Eczema, hayfever and asthma
- Visual difficulties (poor night vision, sensitivity to bright light, visual disturbances when reading)
- Learning difficulties (distractibility, poor concentration, poor working memory)
- Emotional sensitivity (depression, excessive mood swings, undue anxiety)
- Sleep problems (difficulty settling at night, early waking)
- Possibly excessive thirst and urinary frequency (but rule out diabetes)
If you do not eat much fish, an omega-3 fish oil supplement is advisable. If you have dry, itchy skin, a supplement that provides GLA (the anti-inflammatory omega-6) such as evening primrose, starflower, blackcurrant seed or echium seed oils, could help, too.
Have you taken omega 3, 6, 7 or 9 supplements? If so, what for? Did you find them helpful? Please share your experiences below.
Image credits: pixabay; Dorling Kindersley (with permission)