3. FATS

Fat is an important dietary component as it is a key energy source, and in addition is vital to proper human growth and development. Fat provides essential fatty acids necessary for the structure of cell membranes and prostaglandins and also acts as solvent for many substances including vitamins A, D, E and K. Although fat is essential in the human diet, it has been established that the free use of fats leads to numerous degenerative diseases such as cardiovascular disease and various forms of cancer. Findings such as these have prompted the US National Academy of Science to recommend a lower intake of fat, whilst encouraging the consumption of more fibre, fruits and vegetables. Moreover, they suggested an increase in the consumption of complex carbohydrates (e.g. starch), and a decrease in the consumption of pickled, salted or smoked foods.¹

The consumption of fat in the Western world is very high and the average Western diet contains some 30-40% fat. In the United States, it has been found that both men and women consume an average of 36% to 37% fat, which is far higher than the level recommended by most health organizations.² Because fat is a solvent for many organic molecules it can be a powerful flavourant, and besides this attribute, fat provides a desirable mouth feel and contributes to the feeling of satiety after a meal. These attributes of fat have encouraged the use of increased quantities of fats in many traditional and commercial foods and made it extremely difficult for consumers to switch to a lower fat intake. Although the public is aware of the potential danger of high-fat diets, many are not willing to give up the tastes to which they have become accustomed, and the chemical industry has responded by developing a host of artificial foods which simulate fats. These modern fat replacement foods have similar properties to fats, but they are manufactured from carbohydrates, proteins or modified fats.³ The modified fats differ from normal fat, in that less is required to obtain the desired effect, or in that the modified fat is not absorbed, thus enabling one to eat without concern for weight gain or other disadvantages associated with a high-fat diet.

Reduced-fat products are appearing on supermarket shelves in increasing numbers, and they contain blends of altered nutrients designed to replace fats. Protein-based fat replacements are manufactured from milk and/or egg proteins and combined with water, sugar, pectin and citric acid. Carbohydrate-based replacements include dextrins, modified food starches, polydextrose and gums, which are used as such, or combined with fats to produce the desired effects. For all the potential benefits that these replacements may provide, the long-term effects of their use must still be evaluated. It has been estimated that their use can account for 30% to 40% of the food which a person consumes instead of the 1% to 2% of other food additives.⁴ The long-term effects of the fat replacement practice, particularly in young children, must surely be a matter of concern. A switch to a whole-food programme will not only solve the problem of high-fat intakes, but will also provide a solution to the taste and texture question.

Fats in the diet

Triglycerides

Most of the fat consumed by humans is in the form of neutral fats which are formed when three fatty acids combine with glycerol to form a triglyceride (Fig. 3.1).

Figure 3.1. Formation of a triglyceride (a neutral fat)

Saturated and unsaturated fatty acids

Fatty acids consist of hydrocarbon backbones which terminate in a carboxyl group (-COOH). Carbon has a valency of four, which means that it can combine with four other atoms, and in a saturated fatty acid all the additional bonds of the carbon chain are occupied by hydrogen atoms. There are thus no double bonds in the carbon chain of a saturated fatty acid. Animal fats are rich in saturated fatty acids and they contain mainly palmitic acid which contains sixteen carbon atoms, and stearic acid, which contains eighteen carbon atoms (figure 3.2)

Figure 3.2. The structure of palmitic and stearic acid.

Figure 3.3. The structure of oleic acid.

Unsaturated fatty acids have one or more double bonds between carbon atoms, and the carbon molecules are therefore “unsaturated” with hydrogen atoms. Unsaturated fatty acids are commonly found in plant foods, and can be either monounsaturated fatty acids or polyunsaturated fatty acids, depending on the number of carbon atoms which contain double bonds. The unsaturated fatty acids are classified according to the position of the double bond which they contain ie, omega-9 (n-9), omega-6 (n-6), or omega-3 (n-3), then they can also have different isometric configurations, namely cis or trans. The principle fatty acid found in olive oil, for example, is oleic acid, and because oleic acid contains only one double bond in its carbon chain, it is a monounsaturated fatty acid (fig. 3.3).

Polyunsaturated fatty acids contain more than one double bond in the carbon chain and they are more common in plant foods than in animal foods. The most important polyunsaturates are linoleic acid, linolenic acid and arachidonic acid, of which linoleic acid is the most abundant. A further fatty acid in this group is eicosopentanoic acid which is a long-chain fatty acid found in fish oil. The double bonds between the carbon atoms of polyunsaturated fatty acids make the fat more fluid and lower the melting point, which is the reason why plant oils are normally liquid and animal fats are solid.

Essential fatty acids

Essential fatty acids are fatty acids which we cannot manufacture ourselves and which must therefore be obtained from the diet. Animals and humans are capable of elongating fatty acid chains and they can also desaturate fatty acid chains but they cannot desaturate the fatty acid carbon chain at positions six and three. Because linoleic acid and a-linolenic acid are unsaturated at these positions, they cannot be manufactured from other fatty acids and must therefore be obtained from the diet. These two fatty acids are essential components of cell membranes and act as precursors to a group of molecules known as prostaglandins. They are not required in large quantities, and it has been found that if they comprise 1% of total calories, then this is sufficient to prevent deficiency manifestations. Arachidonic acid is similar in structure to linoleic acid and α-linolenic acid, and originally it was also considered to be an essential fatty acid, but since it can be manufactured from linoleic acid, it is no longer considered an essential fatty acid. The structures of linoleic and linolenic acid are given in figure 3.4 and in figure 3.5 the distribution of fatty acids in plant foods is presented. In table 3.1 the major fatty acids in Western diets are presented.

Figure 3.4. The structure of linoleic and linolenic acid.

Cholesterol

Cholesterol belongs to a group of fats known as steroids. Cholesterol has been blamed for the coronary havoc wreaked in the world today, but cholesterol is an essential compound in all animals, and it forms an important substrate for several biosynthetic pathways. Cholesterol occurs in almost all samples of animal fats as well as in blood and bile and is thus mainly derived from the consumption of animal foods. Another source of cholesterol is endogenous cholesterol, which is synthesized in the liver and intestine. Contrary to popular belief, plants do not produce cholesterol although they do produce phytosteroids. The consumption of plant foods per se, can therefore not increase cholesterol levels. In the absence of dietary cholesterol, the liver will synthesize enough cholesterol to meet all the needs of the body and a vegetarian diet will thus not lead to shortages in cholesterol.

Figure 3.5. Fatty acid distribution in vegetable oils. (Adapted from reference 5)

Cholesterol is usually bound to two kinds of protein carriers which are called high-density lipoprotein (HDL) and low-density lipoprotein (LDL). High levels of LDL are associated with vascular disease as these molecules tend to infiltrate arterial walls, whereas HDL seems to attract cholesterol out of the walls and transports it to the liver where it is metabolized. The consumption of animal fats will lead to increased levels of the harmful LDL-cholesterol, whereas plant foods tend to lower cholesterol levels. In table 3.2 the concentration of cholesterol in various foods is presented.

Table 3.1. The major fatty acids in the US diet. Besides these long-chain fatty acids the diets also include small quantities of short- and medium-chain fatty acids as well as other long-chain fatty acids. (From reference 6).

Table 3.2. The cholesterol content of selected foods. The amounts are for 100g edible portions. (Adapted from reference 7)

Digestion and absorption of fats

The digestive system breaks down food into simple components that can be readily absorbed, and these are then reconstituted into the various components of the body. Because fats are water-insoluble, their digestion and absorption is different from that of the other nutrients we eat. Fats must first be emulsified, which means that they must be dispersed in the aqueous medium of the intestinal contents before they can be broken down by enzymes. Emulsification is achieved by the addition of bile salts and lecithin to the gut contents which, together with the churning of the ingested material, breaks the fat up into droplets. These tiny droplets are then acted upon by enzymes known as lipases which are released by the pancreas. Lipases break the fat down into fatty acids, monoglycerides and diglycerides. By the further action of bile, still tinier droplets called micelles are formed which are polar and consist of bile and bile salts, monoglycerides, fatty acids and glycerol. Once these products have been absorbed by the absorptive cells of the intestines, they are again converted to triglycerides which together with phospholipids form protein-coated droplets known as chylomicrons.

About 80% of chylomicrons find their way into the lymphatic system via the lymph ducts of the gut villi, whilst the other products of digestion, such as the sugars and amino acids enter the bloodstream via the capillaries. The lymphatic system acts as a filter to remove harmful residues and bacteria before returning the fatty acids to the bloodstream. Excessive fat intake thus places severe demands on the lymphatic system and can lead to increased susceptibility to disease and common ailments such as fatigue, headaches, colds and flu.

As there are no lipases nor emulsifiers secreted in the saliva or stomach, lipid digestion does not commence until the ingested food has left the stomach. Excess fat in the diet will also retard the digestive processes in the stomach, and protein digestion thus takes considerably longer if free fat is present. Moreover, the fat coats the ingested food making it difficult for the water-soluble enzymes in the stomach to penetrate and commence the process of digestion. This is particularly true if the protein is of animal origin, as animal proteins take longer to digest than plant proteins and also require a lower stomach pH than do plant proteins. Meat, for example, takes some 3-6 hours preparation time in the stomach, but the presence of free fat will lengthen the digestion time well beyond this point. A further consequence of this delay is that the products of carbohydrate digestion will start to ferment under these circumstances and lead to a build up of acid fermentation products. Protein foods prepared by frying or grilling will give a satisfied after-dinner feeling, but this is because of the longer time that the food remains in the stomach, and not because of the better nutrient quality of the food consumed. The presence of fats in the food retards the digestive process in the stomach because fat induces the release of a hormone known as gastric inhibitory peptide (GIP) which slows down the gastric activity.

Once the food has left the stomach and entered the duodenum, fatty acids in the duodenum will cause the release of another hormone known as cholecystokinin-pancreozymin, which induces the gall-bladder to contract and to release bile into the small intestine. This same hormone will also induce the pancreas to release sodium bicarbonate into the duodenum to neutralize the acid in the chyme so that the alkaline phases of digestion can commence. The phospholipid lecithin, which is produced in the liver and assists in the emulsification of fats, is also released into the duodenum. The presence of these emulsifiers makes it possible for the water-soluble enzymes in the duodenum to operate optimally, even in the presence of fat. In whole foods the fats are not in a free form (they are still surrounded by the phospholipid bilayer), and thus remain water-soluble until acted upon by the lipases in the duodenum. Even whole foods that are rich in fats, such as oilseeds, nuts and oil rich fruits such as avocado pears and olives will thus not interfere with the digestive process in the stomach. Only once the fat has been extracted in its free form will it retard the digestive processes.

Lecithin plays a significant role in the metabolism of fats in general, and it protects against the accumulation of fatty deposits in the arteries. Lecithin is a phospholipid consisting of fatty acids, phosphoric acid, glycerol and the B-group vitamin choline. The pancreatic enzyme phospholipase-A liberates lysolecithin from lecithin and lysolecithin then acts as a detergent and assists in the emulsification process. As the liver can only produce a limited amount of lecithin per day, the regular consumption of fatty foods, particularly animal products, will lead to a reduction of lecithin reserves and lay the foundation for the development of arteriosclerosis. A regular supply of whole foods such as fruits, vegetables, grains, seeds, nuts and legumes will ensure that the body’s lecithin needs are met. Legumes in particular are an excellent source of lecithin, but all whole foods will help the body to produce natural lecithin and aid in the emulsification of dietary lipids.

Fats and disease

Fats have been positively linked to numerous degenerative diseases such as cancer and cardiovascular disease, but a number of common ailments can also be attributed to a high-fat consumption. It is, however, not only the quantity of fat that is implicated in disease, but also the type of fat. In countries where fat consumption is low, the incidence of degenerative diseases is far lower than in Western countries with their high-fat consumption. The Japanese have a fat intake of only 10%-20% of their food intake and they do not seem to suffer from the diseases prevalent in Western society, and also seem to enjoy greater longevity of life. This phenomenon is definitely linked to their lifestyle, because Japanese communities that have adopted Western lifestyles suffer from the same diseases that are prevalent in these societies. Different fatty acids exert different effects, and though research into the role of fatty acids in disease causation is still in its infancy, some information is available. Precisely how fatty acid imbalances cause disease, is unknown, but because they are incorporated into cell membranes, changes in dietary intake of fatty acids can cause changes in membrane fluidity, responses to outside signals such as hormones, binding of ligands (ie, lipoproteins) to their membranes, lipid mediators of the intracellular signalling cascade (ie, inositol triphosphat, prostaglandin, and leukotrine production). Moreover, the oxidation products of fatty acids can cause damage and even cell death.⁶

Fats and cancer

The role of fats in cancer promotion has received much attention of late, as there is a strong correlation between various forms of cancer and total fat intake. Carcinogenic processes have two distinct stages: Initiation and Promotion. Initiation involves an irreversible interaction between a carcinogen and the genetic material of its target tissue. Not much is known about initiators, but asbestos (lung cancer), viruses (lymphatic cancers and cervical cancer) as well as tobacco smoke (lung cancer) are known to initiate cancer. Initiation does not generally lead to observable tumours unless promoters are present. These promoters can cause the transformed cells to form tumours. As the consumption of excess fats and certain types of fat can promote cancer, it is important to plan dietary strategies accordingly. In table 3.3 the association between fat and certain other parameters is presented. Clearly, fat is strong promoter of colon and prostate cancer, and fruits and vegetables act as anti-promoters.

Table 3.3. The association between selected dietary components and cancer.(From Ref. 8)

Cancer of the breast, colon and prostate is common in countries with Western lifestyles such as Switzerland, the US and South Africa, but is rare in Japan. Japanese migrating to the US soon develop the same incidence of US prevalent cancers in view of a change in diet. In developing countries as much as 80% of total calories come from cereals and grains, but in industrialized countries there is a calorie intake shift towards animal fat, vegetable oil and refined sugar. This latter diet reduces the incidence of gastric cancer but increases the incidence of colon, ovarian, prostate and breast cancer. The drop in gastric cancer has been attributed to refrigeration, which has replaced salting, pickling and smoking as a means of food preservation. Countries such as Austria where smoked foods are used extensively, also have high incidences of gastric cancer.⁹

International correlation studies have shown that a high-fat intake increases the incidence of prostatic, breast and colon cancer. Prostate cancer has been correlated with diets high in animal fats such as fatty meats, cheeses, cream and eggs. The US, Britain, the Netherlands, Denmark and South Africa have some of the world’s richest diets, and also have the highest incidence of breast cancer.⁹ Diabetes and pancreas cancer are also positively correlated with a high-fat diet.¹⁰ Saturated fatty acids in particular are associated with breast cancer, particularly in postmenopausal women,¹¹ colorectal adenomas,¹² and ovarian cancer, where a 20% increase in risk was observed for every 10g of saturated fatty acids consumed.¹³ The association between polyunsaturated fats and cancer is even more profound. Animal studies have shown that high linoleic acid consumption in particular promotes mammary tumours to a greater extent than saturated fatty acids. Safflower oil and corn oil, both rich sources of linoleic acid, where more likely to induce tumours than were olive oil or even coconut oil because these oils are poor in linoleic acid.⁶

Fibre, vitamin A, C and E, the trace element selenium, and some phytochemicals in certain vegetables, beans, seeds and herbs have been identified as anti-promoters which offer protection against cancer. The food types that offer this protection, as well as the distribution of phytochemicals, are discussed in chapter 7 and summarized in figure 7.3 and figure 7.4. These foods contain sulfides, phytates, flavonoids, glucerates, carotenoids, coumarins, mono- and tri-terpenes, lignans, phenolic acids, indoles, isothiocyanates, phthalides, and polyacetylenes which interfere with the processes of cancer initiation or promotion, and in this way block the formation of tumours (fig. 3.6).¹⁴

Figure 3.6. The effect of dietary phytochemicals on the processes of cancer initiation and promotion. (From reference 14).

Vitamin A probably acts as an anti-promoter for lung, colon, stomach, bladder, oesophagus and oral cavity cancers. Vitamin C and E are associated with reduced incidence of gastric cancer and selenium with a reduced incidence of breast and colon cancer.⁹ Fibre on the other hand protects against cancer by decreasing the length of time that faecal matter stays in the digestive tract, thus limiting the build up of potential carcinogens.¹⁵ Finns for example have a high consumption of whole grains and the associated high faecal mass has been cited as a contributing factor to the low incidence of colon cancer in this nation. The vegetarian lifestyle thus offers considerable protection against cancer, and a vegan diet seems to be more effective than other vegetarian diets. In studies conducted on vegetarians it was found that ovo-lacto vegetarians (vegetarians that include dairy products and eggs in their diet ) have a higher incidence of prostate and ovarian cancer than do their vegan (vegetarians that do not use any animal products) counterparts.¹⁶

Cardiovascular disease

Coronary heart disease has become one of the biggest killers in modern societies, and the consumption of animal fats has been positively associated with this phenomenon. Arteriosclerosis does not only lead to heart disease, but can also be responsible for strokes and kidney diseases. Arteriosclerosis is a slow insidious disease which progresses slowly as a result of the deposition of fat and cholesterol in the walls of the arteries. These fatty deposits become hardened, making the blood vessels less elastic, and eventually clogging them with plaque (a mass of fat and cholesterol). It sometimes happens that blood platelets become caught on the rough edges of plaque, thus initiating clot formation. In this way blood flow to the tissues can be further diminished or stopped. If a clot stays in place it is called a thrombus but if it becomes dislodged and travels around it is called an embolus. Clogged blood vessels in turn

lead to a host of secondary effects such as ischaemia (lack of blood supply and oxygen in the area supplied by the blood vessel) or coronary or cerebral infarct where the supply of oxygen is completely cut off as in the case of a heart attack or stroke. Angina attacks are an indication that the coronary arteries are clogged to the extent that only a quarter of the normal blood supply is being sent to the heart muscle.

It has been clearly established that high cholesterol levels can pose a serious risk of contracting cardiovascular diseases. Besides cholesterol, there are other compounding factors which increase the risk of getting a heart attack, such as high blood pressure and smoking. What is more, the risk is more than additive, as being exposed to more than one of these factors will more than double the risk of having a heart attack. Cholesterol levels per se are however not necessarily a good indicator of the overall risk, but it seems as if the relationship between HDL- and LDL-cholesterol is a better criterion to use when determining the risk factor. HDL-cholesterol has been firmly established as a predictor of protection from atherosclerotic disease. People with low HDL cholesterol levels have the highest heart attack rates, even if their cholesterol levels are in the supposedly safe range of 116 to 192 mg/dl for men and 124 to 211 mg/dl for women. LDL-cholesterol, on the other hand, appears to remain a risk factor throughout life.¹⁷

An elevated serum triglyceride level is also a risk factor for arteriosclerosis. This could be because high triglyceride levels are associated with low HDL-cholesterol levels. When triglyceride metabolism is efficient, the triglyceride concentration is low and the HDL concentration is high. When triglyceride metabolism is sluggish, the triglyceride concentration is high and the HDL concentration is low.¹⁸ Elevated triglyceride levels will also lead to obesity which has also been established as a leading cause of disease. The incidence of obesity also increases with age, as do the risks of contracting cardiovascular disease.

The ratio of saturated to unsaturated fats in the diet is also of significance when determining the risk of contracting cardiovascular disease. Saturated fat is highly correlated with the incidence of coronary heart disease.⁶ A high intake of total fat, cholesterol and saturated fatty acids can also lead to thrombosis, as such diets increase the levels of fibrinogen and factor VII which could cause an increase in thrombosis tendency. Clinical studies have shown, that stearic acid is the most thrombogenic fatty acid,⁶ and diets high in animal products will thus increase the risk of thrombosis. Research has focused for many years on the benefits of polyunsaturated fatty acids in the diet, and these fats have become the desirable replacement for saturated fats to lower cholesterol levels. However, this practice has raised some concern, as studies showed that polyunsaturated fats lowered the levels of the desirable HDL-cholesterol, which was not the case if foods rich in monounsaturated fatty acids were consumed.^19,20 Moreover, it was found that diets high in polyunsaturated fats increased the cancer risk²¹ and had a negative influence on the immune system.²² Trans fatty acids in the diet have been positively associated with cardiovascular disease. In the Nurses’ Health Study, ²³ a 50% increase in risk of heart disease in the highest versus the lowest levels of trans fatty acid consumption was reported, although there were no differences at the intermediate level of consumption. Clinical studies have also shown, that hydrogenated vegetable fats (corn, soy, cottonseed, peanut, or safflower) consistently increased blood cholesterol levels compared to the natural unhydrogenated oils.⁶ Mediterranean diets rich in monounsaturated fats, on the other hand, seem to afford protection against heart disease and cancer.

Mediterranean diets include mainly olive oil as the main fat, and they contain lower levels of polyunsaturated and saturated fats. Mediterranean diets are also rich in grain products such as all kinds of breads, baked goods and pastas. They also include many legumes, seeds, nuts, fruits and vegetables. Populations on this type of diet have low cholesterol levels and a low incidence of coronary heart disease compared to counterparts in other regions of the same country.²¹ Olives, canola oil, monounsaturated safflower and sunflower oils, and almonds are rich in oleic acid which is a monounsaturated fatty acid. In figure 3.7 the relationship between the various fatty acids in foods commonly used in Mediterranean countries is presented.

Vegan vegetarians consume very similar foods to those prevalent in Mediterranean diets. It has also been established that a vegan vegetarian diet can afford protection against cardiovascular diseases. Vegan vegetarians have lower LDL-cholesterol and triglyceride levels than are prevalent in the general population, but HDL-cholesterol levels are not depressed.²⁵ Thus the ideal relationship between these components can be maintained by a vegan diet and this lifestyle can help both adults and children to maintain or achieve desirable blood lipid levels. In view of the increase in the prevalence of cardiovascular diseases with age, a vegan vegetarian diet can contribute substantially to the quality of life during old age. There is also quite a body of evidence, that coronary lesions can even be reversed by extremely stringent diets combined with other lifestyle changes.²⁶ Having said this, it is essential to note, that stringent lifestyle changes may be acceptable for adults who want to reduce fat intake to prevent cardiovascular disease, but care should be taken not to enforce similar changes on children, who require higher fat intakes than adults.²⁷ For a more detailed discussion of these criteria see chapter 5.

Dietary lipids and immune function

The influence of fat on the immune function has only recently come under serious study. It is known that polyunsaturated fatty acids, particularly linoleic acid, are required for optimal functioning of the immune system, but there is an optimum level which should not be exceeded. In recent years there has been a tremendous increase in the consumption of polyunsaturated fats to combat heart disease, but this has brought to the fore a host of problems not previously envisaged. High levels of fats, particularly polyunsaturated fats, impact negatively on the immune system and decrease its ability to cope with cancer tumours, allergies, infections by microbial organisms and both thymic-dependent and thymic-independent antigens.²⁸

Immune responses can thus be enhanced or depressed, depending on the concentration and extent of unsaturation of dietary lipids. It has been found that high-fat diets consistently depress resistance to malaria and tuberculosis in rats, and respiratory infections in chickens, but the same seems to be true for humans. Lower respiratory tract infections in infants, for example, are significantly more common in obese infants than in non-obese infants, and in one third of obese infants, adolescents and adults studied there was impairment of cell-mediated immune responses.²⁹

The mechanism whereby fats interfere with the body’s ability to combat the growth of cancerous tumours has also been investigated. A subpopulation of T-lymphocytes, known as natural killer cells, specifically react to destroy tumour cells before they can proliferate. Recently it has been found that diets high in polyunsaturates, particularly those rich in n-6 fatty acids (e.g. linolenic acid), impact negatively on the ability of these killer cells to seek out and destroy cancer cells.³⁰ The three types of blood cell associated with the immune response are the granulocytes, monocytes, and lymphocytes. The neutrophils are the most abundant granulocyte and they destroy antigens by simply engulfing them. Macrophages of monocytic origin, are also phagocytes but they carry out other functions as well. They secrete substances known as lymphokines and prostaglandins that affect B- and T-cell activity in many ways.

Examples of lymphokines are interferon and interleukon 1, of which interferon stimulates T-cell proliferation and interleukon 1 stimulates a broad range of cells, including the natural killer cells, neutrophils, and B-and T-lymphocytes. T-cells do not produce antibodies, but B-lymphocytes produce antibodies which combine with antigens, rendering them inactive and enabling phagocytes to engulf the invaders.

Figure 3.7. The fatty acid profiles of foods high in monounsaturated fats. (From reference 25)

Prostaglandins, thromboxanes, and leucotrienes are eicosanoids which are produced from the essential fatty acids, linolenic and linoleic acid. Generally, prostaglandins function as vasoconstrictors, thromboxanes affect platelet aggregation, and leucotrines contract smooth muscle cells. Those prostaglandins that have a relaxing, anti-inflammatory and anti-clotting effect are generally formed from alpha-linolenic acid (Triene prostaglandins) whilst those with the opposite effect are manufactured from linoleic acid (Monoene prostaglandins) and arachidonic acid (Diene prostaglandins). More than one hundred different prostaglandins have been identified, and they promote or inhibit basic bodily functions such as fever, blood clotting, vasodilation and constriction, stress, allergy response, membrane permeability, eye pressure, inflammation, steroid production, appetite, fat metabolism and the functioning of the immune system.³¹ When prostaglandins occur in a balanced relationship they tend to relax arteries and reduce blood pressure as well as slow down tumour formation and decrease platelet aggregation, thus lowering the risk of thrombus formation. If the balance of prostaglandins is, however, disturbed then the opposite effects are achieved. It is interesting to note that tumour cells produce large amounts of the prostaglandin PGE₂ and cancer patients can produce four times the normal amount of this prostaglandin and has an immunorepressive effect and leukotrine B₄ is a potent chemotactic and chemokinetic agent.⁶ For a summary of the effects of eicosanoids see figure 3.8.

A reduction in the amounts of polyunsaturated fats in the diet, inclusive of the essential fatty acids, can provide a substantial anticarcinogenic effect.^32,33 A whole-food diet, which includes grains, legumes, seeds and nuts will provide the ideal blend of fatty acids and total fat composition to ensure the optimal functioning of the immune system.

Processed fats

In today’s world the appearance, texture and colour of food is often considered of greater importance than the nutrient value of such food. In an instant world we need instant food, and to avoid spoilage and financial loss, such food is often chemically manipulated to obtain all these desired effects. When the chemical nature of our food is changed so that it meets the requirements of the market place, then the risk is great that it no longer meets the requirements of the body. Our bodies are designed to interact with the environment in a highly specialized way, and any interference with this delicate balance may impact negatively on the system.

Modern oil refining techniques

Extracted oil undergoes a series of steps which adversely affects its nutritional value. Free fatty acids are removed by vacuum extraction and precipitation. Furthermore, the oil is filtered and heated to 220 ^oC to obtain a clear liquid. In order to obtain a less fluid oil, suitable for the production of margarine, the oil is further subjected to the process of hydrogenation, to which liquid oils nowadays are also partially subjected. This process was developed by W. Norman in the year 1900 and involves a catalytic reaction which changes cis fatty acids to trans fatty acids, thus rendering them less fluid by changing the shape of the molecules.

Polyunsaturated fats contain double bonds, and this gives rise to the possibility of cis-trans conversions. In nature, fatty acids occur mainly in the cis configuration, which means that the carbon chains on either side of the double bond are spatially arranged on the same side of the double bond, whereas in the trans configuration the chains are on opposite sides of the double bond. The cis and trans configurations of oleic acid (which has just one double bond) are presented in figure 3.9.

Trans fats do not form part of the normal diet and should not be introduced into the system as they can result in a number of biochemical changes, and together with saturated fats and cholesterol, can lead to altered membrane structure and concomitant hardening of the arteries. The essential fatty acids (linoleic and linolenic acids) also naturally have the cis configuration, and in linoleic acid the atoms are arranged in such a fashion that there is a 60^o bend at each of the two double bonds, resulting in a U-shaped molecule. Trans-linoleic acid however has a Z-shape as the chains on either side of the double bond do not project into the same plane. The free use of extracted, partially hydrogenated oil, rich in linoleic acid (found in corn, safflower and sunflower oils), has been associated with cancer promotion. Linoleic acid is the substrate from which prostaglandins are manufactured, and trans-linoleic acid can result in altered prostaglandins, thus modifying the effect of these hormones or even producing opposite effects. Because leucotrines play an essential role in regulating the immune system in that they are involved in the production of antibodies and the destruction of viruses and cancer cells, it is essential that these molecules be produced from essential fatty acids that have the correct configuration so that the delicate balance and the function may not be jeopardized.

Figure 3.8. The effects of eicosanoid imbalances on various diseases. (From reference 6).

Figure 3.9. The cis and trans configuration of oleic acid.

The molecular changes found in even partially hydrogenated oils can adversely affect the relationship between the various prostaglandins as well as changing them structurally. Trans fatty acids depress serum levels of prostaglandins, and both PGE₁ and PGE₂ were affected in a study done on rats, presumably because linoleic acid could not be converted to long chain fatty acids in the presence of a large influx of the trans-isomer.^34,35 Moreover, hydrogenated oils do not share the properties of normal unsaturated fats and will also not lower cholesterol levels as do the natural oils in whole foods.^6,36 The consumption of trans fatty acids in the Western world is quite high, and it has been estimated that in the US and in Canada, men of 20-39 years of age consume 11-12g per person per day of these fats.³⁶ The British Medical Committee on Cardiovascular Diseases proposed new guidelines in 1994 on recommended consumption of fatty acids. Recognizing that trans fatty acids have an undesirable effect on HDL and LDL cholesterol and coronorary disease mortality, they suggested that no more than 2% of caloric intake come from this source, and that the amount should even be reduced.³⁷

Margarine

Margarine is typically manufactured from the oil of soya beans, maize, sunflower seeds, olives, coconut and palm, with the addition of substances which enhance the flavour and act as preservatives and texturisers. The typical ingredients of margarine include a combination of oils, water, sodium chloride, vitamins A, D and E, lecithin or other emulsifier, preservatives such as sodium benzoate and/or potassium sorbate, milk solids including casein, colorants such as beta-carotene and retinyl esters, flavourants such as butter distillate or simulated butter taste chemicals. The manufacturing process of margarine involves a combination of a number of steps. The fat-insoluble gums and other substances from the crude oil are first removed and then the oil is neutralized with alkali. Subsequently it is bleached, filtered, deodorized and in most cases hydrogenated. After this the product is again subjected to further filtration, neutralization, bleaching, deodorization and blending. Finally, colorants, flavourants, vitamins, emulsifiers and preservatives are added, and proportioning (creating the desired balance between water and fat), emulsification, chilling and packaging round off the final product.

In most cases, margarines exceed the recommended maximum levels for saturated and trans-unsaturated fatty acids, but some countries (Germany) have taken cognizance of the detrimental effects of trans fatty acids and many of the margarines, shortenings and cooking fats in Germany are being produced essentially free from trans fatty acids. Nevertheless, a concentrated, chemically manipulated, unnatural food such as margarine must place excessive demands on the system, and viable alternatives should be sought. Artificial foods are however the vogue, and large quantities of spreads and non-dairy creamers are consumed annually. Non-dairy creamers also contain extracted saturated and hydrogenated plant oils of coconut and palm origin, and therefore contain no less fat than dairy cream.

There are many ways to prepare palatable meals without the use of extracted oils, and their use can thus be limited. The best way of obtaining chemically sound fats, suitable for maintaining the fine chemical balances of the body, is to eat whole food that has not been changed by modern refining techniques. Whole grains, seeds, nuts as well as oil-rich fruits such as avocado pears and olives, together with other plant sources will supply an abundance of fats of the variety required by the body.

The use of oil in the frying of food

The frying of food in oil or lard also has detrimental effects. Studies have shown that heated oils and fats undergo autoxidation and that the rate of autoxidation is proportional to the degree of unsaturation and the presence or absence of pro- and anti-oxidants. It has been established that animal fats undergo autoxidation more readily than oils of plant origin, in spite of the fact that animal fats are saturated fats, but this has been attributed to the virtual absence of natural antioxidants in animal fats. Polyunsaturates, however, sustain the most thermo-oxidative damage when oil is heated. In this regard it is enlightening that a tri-unsaturated fatty acid will undergo autoxidation 10 000 times more readily than a monounsaturated fatty acid.³⁸ The rate and degree of autoxidation of unsaturated and saturated fats is presented in figure 3.10

Figure 3.10. Heat damage sustained by oil. (Adapted from reference 20)

The products formed in fats and oils that are heated to high temperatures are peroxides, aldehydes, ketones, hydroperoxides, polymers and cyclic monomers, any one of which can have toxic effects. Subjecting saturated and polyunsaturated fats, such as butter and sunflower oil to temperatures of 170°C for two hours will so alter the composition that if fed to experimental animals they will induce liver ailments in these animals. If animal fat, polyunsaturated oil, and even monounsaturated oil such as olive oil, is however heated to 180°C for longer periods of time, serious liver disorders are induced in experimental animals that are fed these oils.³⁹ The peroxidised fatty acids in heated fats also affect the cardiovascular system, possibly even causing lesions in the cardiac muscles and arterial lining as well as enhancing clot formation.⁴⁰

As most processed oils are heated to 220°C during the manufacturing process, and are still further heated during the frying process, the use of free oil should for these reasons alone, not be encouraged. The frying of food should therefore be avoided if healthful living practices are introduced into the household. This does not necessarily mean that taste must be sacrificed, but it does mean that age-old habits will have to be revised and substituted with a little bit of ingenuity. If oil is used at all, it should be used in moderation and the cold-pressed variety should be used as this has been least subjected to heat during the extraction and clarifying processes. Also oils rich in monounsaturated fats, such as olive oil, should be the oils of choice as monounsaturated fats undergo the least damage during heating.

Whilst it is true that increased dietary consumption of polyunsaturated fats has led to a decrease in cholesterolaemia and associated drop in cardiovascular disease, it has been accompanied by a rise in deaths from nonvascular diseases such as cancer,⁴¹ cholelithiasis^42,43 and a general drop in life expectancy,⁴⁴ probably resulting from the peroxidation of the polyunsaturates. Peroxidation of polyunsaturates takes place because these molecules are unstable, and the more double bonds there are in the molecules the more readily the process of peroxidation takes place. During this process “free radicals” are formed which are extremely reactive in view of their unpaired electron. Free radical formation is largely prevented in whole foods, as natural antioxidants, which are present in these foods, prevent their formation. A natural balance exists between antioxidants such as the fat-soluble vitamins A and E and the quantity of polyunsaturated fats that are present in whole foods. An imbalance between polyunsaturates and antioxidants will result in a rise in free radical formation with concomitant harmful results such as an increase in the rate of the aging process,^44,45,46 inflammation,⁴⁷ carcinogenesis,^48,49,50 liver disorders⁵¹ and arteriosclerosis.^52,53

Unfortunately modern food processing techniques often strip food of the essential fatty acids and vital prepacked antioxidants and in this way deprive the system of these essential nutrients. During the refining process grains, for example, are stripped of the germ, which contains the essential oils and fat-soluble antioxidant vitamins in a perfect biorelationship, and the lack is then substituted for with large intakes of disproportionate combinations of processed oils and fats. In this regard it is enlightening to note that the daily vitamin E requirements (which amount to about 10mg per day) increases 200 fold if polyunsaturates are added to the diet.⁵³ It is doubtful whether any diet will supply this additional requirement without supplementation, and it is therefore not surprising that the degenerate diseases are so prevalent in Western societies. The eating of whole foods that have not been stripped of their essential components will supply all the essential oils required in healthful combinations and should therefore be encouraged.

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