The Major Fat Constituents in the Typical Western Diet

The typical Western diet is the modern diet of the developed nations of North America, Western Europe and Australasia. Evidence suggests that insulin resistance is caused by consumption of the typical Western diet, and this relates to the presence of refined and processed foods within the diet that can alter the biochemical balance of the body through changes to normal metabolic regulation. Of the food components that may contribute to these metabolic changes, dietary fats have been identified as playing a role. The typical Western diet is generally high in both cholesterol and saturated fat, and these have been blamed for both the cardiovascular disease epidemic that is currently sweeping through developed nations and for the rise in the rates of obesity. However, this might be unfair and a gross oversimplification of human nutrition as both dietary cholesterol and saturated fat have been part of the human diet since history began, but the cardiovascular disease and obesity epidemics are only recent phenomenon.

The main problem identified with saturated fat is the amount of calories that it contains. We are told that this increases the risk of overeating and this is turn increases the risk of weight gain. However, as we have seen previously, the energy balance theory of weight gain is not established as the cause of weight gain or obesity. While it is possible to overeat saturated fat, it is just as likely that carbohydrate could be overeaten, and there is with carbohydrate, particularly that which is refined, good reason to suspect that it can cause metabolic dysfunction. Many of the detrimental effects of saturated fats on human physiology have also been, either deliberately or mistakenly, attributed to plasma levels of fasting triglycerides, the largest contribution to which originates not from the diet, but from the de novo lipogenesis pathway using carbohydrate as a substrate. That the Massai of Africa eat large amounts of saturated fat but are not overweight also argues against its role in weight gain.

A number of modified fats are present in the typical Western diet. These include oxidised fats that are the products of lipid peroxidation and trans fats that are the result of the hydrogenation of vegetable oils. Both of these groups of fats are novel dietary additions that were not present in the human diet in great quantities before the mass processing of food, and as such are a relatively new addition to the nutritional research. Increasingly oxidised and trans fats are being identified as possible metabolic poisons. In particular, they may lead to inflammation, oxidative stress and this may subsequently lead to a decrease in insulin sensitivity. Both trans fats and oxidised fats may therefore contribute towards the development of insulin resistance. Interestingly, trans fats may be responsible for some or all of the detrimental effects of saturated fats. This relates to some earlier research that did not differentiate between trans and saturated fats in studies, but simply grouped them together as a single category.

The last group of fats that make up the typical Western diet are the unsaturated fats. There are two nutritional groups of unsaturated fats and these include the monounsaturated fatty acids and the polyunsaturated fatty acids. Unsaturated fatty acids have one or more double bond in their carbon chains, and this gives the molecules less stability in the presence of oxygen, heat and light when compared to saturated fat. This means that unsaturated oils are prone to rancidity, and when consumed in their rancid state, can cause specific health problems. Olives contain high amounts of monounsaturated fatty acids, and vegetable oils such as sunflower, rape, safflower and corn oils contain high amounts of polyunsaturated fatty acids. Because of their chemical structure unsaturated fats tend to be liquid oils at room temperature in contrast to saturated fats which tend to be solid at room temperature. Some animal products such as lard and fish contain high amounts of unsaturated fatty acids.

One subgroup of polyunsaturated fats are the omega-3 and omega-6 categories of fatty acids. These groups are championed by alpha linolenic acid and linoleic acid, the parent compounds and the omega-3 and -6 metabolic pathways, respectively. Both alpha linolenic acid and linoleic acid have vitamin like effects, as they are both essential nutrients and they are required to form short-lived hormone molecules called eicosanoids. Generally the typical Western diet contains too many omega-6 fatty acids and too few omega-3 fatty acids and this causes an imbalance in eicosanoid formation in cells. As eicosanoids regulate inflammation, and imbalance of omega-6 to omega-3 fat in the diet leads to a proinflammatory state, and this subsequently causes oxidative stress and associated metabolic damage. Trans fats also interfere with essential fat metabolism. Metabolites of alpha linolenic acid in the diet include eicosapentaenoic acid and docosahexaenoic acid from fish.

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