OILS AIN'T OILS

“Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Appreciate your friends. Continue to learn. Do what you love. Live as if this is all there is.” - Mary Anne Radmacher

Call me a kill-joy if you like, call me a spoil-sport, call me a wowser, but today for Food Friday, I’d like to have a chat about dietary fats. It seems particularly apt at this time of the year when people overeat seriously on an almost daily basis. Christmas foods are traditionally full of fats and our intake of fats and oils around this time of the year can be excessive.

The first thing to note about dietary fat is that there is a minimum requirement for fat (not for total fat), but only for the fatty acids linoleic acid (a so-called omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid). These are the so-called “essential fatty acids”. The best way to understand what they do in the body is to see what happens when we do not include them in our diet.

Deficiencies of these two fatty acids have been seen, for example, in hospitalised patients fed exclusively with intravenous fluids containing no fat for weeks. Symptoms of deficiency include a dry skin, hair loss, and impaired wound healing. Essential fatty acid requirements (a few grams a day) can be met by consuming approximately a tablespoon of polyunsaturated plant oils daily. Fatty fish also provides a rich source of omega-3 fatty acids. Even individuals following a low-fat diet generally consume sufficient fat to meet requirements.

However, in the vast majority of the industrialised world, quite the opposite is the problem! Too much fat is consumed in the diet and if this fat is rich in cholesterol (particularly the “bad” cholesterol LDL and other saturated fats) it is linked to obesity, and an increase in heart disease risk. It is widely accepted that a low-fat diet lowers blood cholesterol and is protective against heart disease. Yet, the situation is complicated by the fact that different fatty acids have differing effects on the various lipoproteins that carry cholesterol. Furthermore, when certain fats are lowered in the diet, they may be replaced by other components that carry risk. In general, saturated fatty acids, which are found primarily in animal foods, tend to elevate LDL and total blood cholesterol (and hence risk of fat disease).

When saturated fatty acids in the diet are replaced by unsaturated fatty acids (either monounsaturated or polyunsaturated) LDL and total blood cholesterol are usually lowered, an effect largely attributed to the reduction in saturated fat. However, polyunsaturated fatty acids tend to lower HDL cholesterol levels, while monounsaturated fatty acids tend to maintain them. The major monounsaturated fatty acid in animals and plants is oleic acid. The good dietary sources of this monounsaturated are olive, canola, and high-oleic safflower oils, as well as avocados, nuts, and seeds. Historically, the low mortality from CHD in populations eating a traditional Mediterranean diet has been linked to the high consumption of olive oil in the region, although the plentiful supply of fruits and vegetables could also be a factor.

The two types of polyunsaturated fatty acids found in foods are omega-3 fatty acids and omega-6 fatty acids. Linoleic acid, the primary omega-6 fatty acid in most diets, is widespread in foods (major sources being vegetable oils such as sunflower, safflower, and corn oils). Low cardiovascular disease rates in Eskimo populations eating traditional diets high in omega-3 fatty acids initially provoked the speculation that these fatty acids may be protective against CHD. The primary lipid-altering effect of omega-3 fatty acids is the reduction of blood triglycerides. Omega-3 fatty acids may also protect the heart and blood vessels by lowering blood pressure, reducing blood clotting, preventing irregular heart rhythms, and acting as anti-inflammatory agents.

The long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are derived from alpha-linolenic acid, a shorter-chain member of the same family. Fatty fish such as salmon, herring, sardines, mackerel, and tuna are high in both EPA and DHA. Flaxseed is an excellent source of alpha-linolenic acid, which the body can convert to the long-chain omega-3 fatty acids. Other sources of omega-3 fatty acids include walnuts, hazelnuts, almonds, canola oil, soybean oil, dark green leafy vegetables such as spinach, and egg yolk. A diet high in polyunsaturated fatty acids may increase LDL lipid oxidation and thereby accelerate atherosclerosis; therefore, it should be accompanied by increased intakes of vitamin E, an antioxidant. Fish oil supplements are not advised without medical supervision because of possible adverse effects, such as bleeding.

The safety of trans (as opposed to naturally occurring cis) unsaturated fatty acids has been called into question because trans-fatty acids in the diet raise LDL cholesterol to about the same extent as do saturated fatty acids, and they can also lower HDL cholesterol. Trans-fatty acids are found naturally in some animal fats, such as beef, butter, and milk, but they are also produced during the hydrogenation process, in which unsaturated oils are made harder and more stable. Certain margarines, snack foods, baked goods, and deep-fried products are major food sources of trans-fatty acids.

So what is the moral of this story? Eat as little fat as is practicable. Eat foods with low saturated fat content and consume more of the omega-3 fats. A diet that is low in fats, varied in terms of seasonal fruits and vegetables, high in fibre and low in red meats is a healthier diet. But you didn’t need me to tell you that, you knew it all along. It’s just that we need to put it all into practice. Maybe after the festive season, what do you think?