Oils and fats form an important part of a healthy diet. Structurally they are esters of glycerol with three fatty acids (called either triacylglycerols or triglycerides). It is these fatty acids that give the functionality to fats. Chemically, they can be divided into four main types – saturated, cis-monounsaturated, cis-polyunsaturated and trans fatty acids. In very broad terms, saturated fatty acids and trans fatty acids are solid at room temperature while the cis-unsaturates are liquid at room temperature. Although no naturally occurring fat is either 100% saturated or 100% unsaturated (but is a mix of the two), fats are often referred to as ‘saturated’ or ‘unsaturated’ because of the predominance of one or other type of fatty acid.
The choice of fat used in any given type of food product often comes down to the required functionality. The main aspects of this functionality choice are (a) melting point and melting profile (how the solid fat content changes with temperature), (b) crystallization characteristics, (c) storage stability (particularly oxidative stability) and (d) nutritional characteristics.
From a product functionality point of view, different groups of food products will have different requirements. Bakery products (e.g. pastry and biscuits) require a fat with a moderate amount (25-40%) of solid fat to be present during dough preparation to give a light texture without undue oil exudation in the final product. Chocolate needs to be based on cocoa butter from both a legislative and functionality point of view and any fats used to replace cocoa butter need also to conform to legislation and to melt and crystallise in the same way as cocoa butter. In general, ice cream needs to be based on a fat which is at least 50% solid at 0°C and which melts below mouth temperature. Frying oils need to have as good an oxidative stability as possible to allow both an extended ‘fry life’ and also good shelf stability in the end product.
Often, there is no single natural fat, or even combination of naturally occurring fats, that give the exact functional requirements for a given product application and so oils and fats need to undergo some form of processing. There are three main types of oil modification process used in foods. Hydrogenation is a reaction between hydrogen and the carbon-carbon double bonds in an unsaturated fatty acid. It changes the cis-unsaturated fatty acid either to saturated or to trans-unsaturated. Both saturated fatty acids and trans-unsaturated fatty acids are higher melting than the naturally occurring cis-unsaturated fatty acids so hydrogenation increases the hardness and solid fat content of the fat. Fractionation starts with oils that can be partially liquid and partially solid at a particular temperature (palm oil, shea butter and palm kernel oil are oils that are commonly fractionated). The solid and liquid phases are separated and used in different applications. Unlike hydrogenation, no chemical changes to the fatty acids themselves take place – it is purely a separation process. Interesterification is a process in which the ester linkages between the fatty acid and glycerol are broken and then re-formed usually in a random (but predictable) conformation. However, specific enzymes can be used as catalyst to avoid breaking the ester linkage in the central position of the triglyceride molecule and so allow the production of deliberately structured triglycerides. Each of these modification processes allow the formation of fats with different melting, crystallisation and stability functionalities from the starting oils.
On top of all this, the oils and fats used should give rise to no adverse health concerns. During the course of the 20th century, hydrogenation was probably the most commonly used modification process. However, it produces high levels of trans fatty acids. These have been shown to be adverse to health particularly in terms of their effects on blood cholesterol levels. They increase the detrimental low density lipoprotein (LDL) cholesterol and decrease the beneficial high density lipoprotein (HDL) cholesterol giving rise to a greater risk of cardiovascular disease (CVD) in some individuals. As a consequence of this, the early years of the 21st century saw widespread reformulation of many food products and the development of non-hydrogenated alternatives to previously hydrogenated fats.
cis-Unsaturated oils, on the other hand, show positive effects on blood cholesterol levels insofar as they decrease LDL cholesterol and increase HDL cholesterol levels.
Saturated fatty acids are somewhere in the middle – they increase both the detrimental and the beneficial cholesterol levels but they also do this to varying extents depending on their fatty acid chain length. Lauric (C12), myristic (C14) and, to a slightly lesser extent, palmitic (C16) acids show an overall adverse effect on blood cholesterol, whereas stearic acid (C18) is considered to be neutral in its effects. Overall, the recommendations from governmental and global health organisations is to limit the consumption of saturated fatty acids to about 10-11% of dietary energy. These recommendations are largely based on research carried out some 15 years or more ago and recent research has shown a greater leniency towards saturated fats. Nevertheless, saturated fats should still be used with some caution. One recent example is the fashion for coconut oil. This oil is over 90% saturated and about 50% of that is lauric acid, one of the acids which, in clinical trials, has been shown to have adverse effects on blood cholesterol levels.
‘Modifying lipids for use in foods’ – ed. Gunstone FD. Published by Woodhead Publishing, Cambridge.
‘Reducing saturated fats in foods’ – ed Talbot G. Published by Woodhead Publishing, Cambridge.
Mensink RP, Zock PL, Kester ADM, Katan MB (2003). ‘Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials’ Am. J. Clin. Nutr. 77 1146-1155
Keywords: Fats, saturated, unsaturated, trans, hydrogenation, fractionation, interesterification, bakery, confectionery, ice cream, frying, blood cholesterol, cardiovascular disease.
Oils and fats are important nutrients in a healthy diet. Structurally, they are esters of glycerol with three fatty acids. As such, they are scientifically called triacylglycerols but are commonly referred to in the food industry as triglycerides. Although the terms 'oils' and 'fats' are often used interchangeably, they are usually used to distinguish triglycerides in the liquid state at ambient temperatures (oils) from those in the solid state (fats).
They are commonly of vegetable origin (e.g. palm oil, rapeseed oil, soyabean oil, olive oil, cocoa butter, etc) or animal origin (e.g. pork lard, beef tallow, fish oils) as well as from animal milk fats.
The fatty acids found in most commonly consumed oils and fats are composed of long carbon and hydrogen chains, typically containing from 8 to 20 carbon atoms, mainly with even numbers of carbon atoms, although animal fats also contain significant levels of odd-chain fatty acids. They have a methyl (CH3) group at one end and a carboxylic acid (COOH) at the other. It is this carboxylic acid group that reacts with the hydroxyl groups on the glycerol molecule to form the ester linkages of the triacylglycerol molecule.
Fatty acids can be grouped into four main types:
Saturated fatty acids are straight chains of carbon atoms consisting of methylene (CH2) groups between the end methyl and carboxylic acid groups. The most common saturated fatty acids are lauric acid (C12), palmitic acid (C16) and stearic acid (C18). Shorter chain saturated fatty acids are found in butterfat (e.g. C4, butyric acid) and coconut oil (e.g. C8, caprylic acid, and C10, capric acid).
Monounsaturated fatty acids contain a single carbon-carbon double bond in the carbon chain. This is usually in the cis configuration. The most common monounsaturated fatty acid is oleic acid, containing 18 carbon atoms. In oleic acid, the double bond is between carbon atoms 9 and 10 (counting from the COOH group)
Polyunsaturated fatty acids have more than one double bond in the carbon chain. Common polyunsaturated fatty acids are linoleic acid (18 carbon atoms and 2 double bonds between carbon atoms 9/10 and 12/13) and linolenic acid (18 carbon atoms and 3 double bonds between carbon atoms 9/10, 12/13 and 15/16).
It is, of course, possible to count the position of these double bonds from the other end of the chain, the methyl group end. In these two examples, the first double bond to be encountered in linoleic acid is at the sixth carbon atom and, for this reason, linoleic acid is also called an omega-6 polyunsaturate. In linolenic acid, the first double bond is at the third carbon atom and so linolenic acid is called an omega-3 polyunsaturate.
The fourth type of fatty acid, trans fatty acids, are also unsaturated but, in this case, some or all of the double bonds are in the trans configuration. These are most commonly found as a result of either hydrogenation of fats (see below) or by holding fats at a very high temperature (>200°C) for extended periods of time. As such, they can gradually be produced and build up in used frying oils. However, trans fatty acids are also found naturally in the milk and meat of ruminant animals such as cattle. Typical natural trans fatty acid levels in cow’s milk are about 5%, although levels as high as 9% have also been observed (IFST, 2015). The trans fatty acids in milk are mainly vaccenic acid (a trans-monounsaturate with a double bond between carbon atoms 11 and 12) and conjugated linoleic acid (CLA) with a cis double bond between carbon atoms 9 and 10 and a trans double bond between carbon atoms 11 and 12. These fatty acids have not been found to have adverse consequences and may, indeed, be positive.
Increasing the chain length of a fatty acid increases its melting point - so stearic acid (C18) melts at a higher temperature than lauric acid (C12). Increasing the number of cis double bonds in a fatty acid decreases its melting point - so, considering the group of fatty acids with 18 carbon atoms, the melting point decreases going from stearic (no double bonds) to oleic (one double bond) to linoleic (two double bonds) to linolenic (three double bonds) acids. Changing the double bond configuration from cis to trans increases the melting point - so elaidic acid (the trans equivalent of oleic acid) has a higher melting point than oleic acid.
Different food applications require different melting points and different melting profiles (the change in percentage of solid fat with temperature) for both processing and sensory functionalities. The ability to have a range of fats and oils available with different physical characteristics is of fundamental importance to food product developers. However, fatty acids in these different groups (and, in some cases, fatty acids within the same group) have different nutritional effects, particularly their effects on blood cholesterol levels which, in turn, can impact on cardiovascular disease risk. This will be considered in more detail later in this document.
Despite dividing fatty acids into these four groups, no naturally occurring fat is composed 100% of a single fatty acid group. We refer to saturated fats but this only says that they are naturally occurring fats in which saturated fatty acids predominate. The same thing can be said about monounsaturated fats, polyunsaturated fats and trans fats.
Coconut oil is the most highly saturated naturally occurring fat (typically about 94% saturates – Gunstone et al, 1994). Other 'saturated' fats are palm kernel oil (typically, 82% saturates – Gunstone et al, 1996), cocoa butter (typically, 60-64% saturates – Lipp and Anklam, 1998) and palm oil (typically 51% saturates – Talbot, 2011). Lard and beef tallow are also often considered to be in this category of saturated fats despite typically containing only 40% and 37% saturates, respectively (Talbot, 2011).
Olive oil and rapeseed oils are rich in monounsaturates – typically, 56-83% and 50-66% respectively (Gunstone et al, 1994). Soyabean oil typically contains 53% linoleic acid and 8% linolenic acid (Gunstone et al, 1994). Sunflower oil contains 69% linoleic acid and <1% linolenic acid (Gunstone et al, 1994) but there are also newer, high-oleic, varieties which contain less linoleic acid and more oleic acid.
Different food applications require fats with different functionalities and, therefore, different fatty acid compositions. These different requirements for specific applications will be considered in more detail in a later section. Sometimes, the requirements can be completely fulfilled by a naturally occurring fat or a combination of naturally occurring fats. For example, chocolate can be made purely from cocoa butter or, in the case of milk chocolate, from cocoa butter and butterfat. In some applications, though, the portfolio of fats as they occur in nature do not totally fulfil the functional requirements and so the fats need to undergo some kind of processing to obtain the required functionality.
One of the earliest oil processing methods was hydrogenation (List and King, 2006). In the presence of a catalyst (usually nickel) the double bonds in a liquid oil can react with hydrogen in two ways. Either a hydrogen molecule can react with the carbon atoms in an unsaturated bond to convert it into a saturated single bond. This has a higher melting point and so a liquid oil can be converted into a solid fat. The other way it can react is to convert the cis double bond into a trans double bonds. As trans fatty acids are higher melting than the corresponding cis unsaturated acids the liquid oil is again converted into a higher melting fat. Apart from the natural occurrence of low levels of trans fatty acids in some milk and meat fats, trans fatty acids are only produced by the industrial process of hydrogenation (or by gross thermal mistreatment of oils). Hydrogenation, therefore, converts liquid oils into potentially more functional solid fats and changes the fatty acid composition of the starting mix of oils significantly.
There are considerable health and nutritional problems associated with trans fatty acids (see below for details of these) and so the use of hydrogenation as an oil modification technique has now been largely phased out both in the UK and in many other countries throughout the world, either voluntarily or as a result of legislation (WHO, 2015).
Fractionation is another modification process in which harder, higher melting fats can be produced (Gibon, 2006). In this case a fat is held at a temperature at which it is partially liquid and partially solid. The solid crystals are separated by filtration to give a solid stearin fraction which is higher melting than the starting oil and a liquid olein fraction which is lower melting than the starting oil. Generally, only fats that melt over a wide temperature range are suitable for fractionation. The most commonly fractionated fats are palm oil, palm kernel oil, butterfat and shea butter, although coconut oil and cocoa butter are also occasionally fractionated. In most cases, the oil is fractionated once to give the two fractions mentioned – stearin and olein. Palm oil, though, can be fractionated twice to give three fractions – a very high melting (>50°C) stearin or top-fraction, a middle melting (about 34°C) fraction and a low-melting, liquid at room temperature, olein fraction (Talbot, 2011).
Oils are normally fractionated in one of two ways (Gibon, 2006). ‘Dry’ fractionation involves simply holding the oil at the required temperature to obtain both solid and liquid fractions. ‘Wet’ fractionation uses a solvent, usually acetone, to dissolve the whole of the fat. This solution is then chilled to the point that the stearin fraction crystallises out. The benefits of dry fractionation are that it is cheaper, has no requirements for flameproof processing and gives a very good quality olein. Wet fractionation, on the other hand, is used where the quality of the stearin or, in the case of palm oil, the mid-fraction is of paramount importance. It does, though, require a flameproof plant and good solvent recovery processing, which makes it a significantly more expensive process.
Unlike hydrogenation, there are no chemical changes made to the fatty acids in the oil as a result of fractionation, but there will be a concentration of saturated fatty acids in the stearin and of unsaturated fatty acids in the olein.
The third method of oil modification is interesterification (Xu et al, 2006). In this an oil or a blend of oils is held at an elevated temperature in the presence of either a chemical catalyst or, more commonly these days, an enzyme catalyst. Under these conditions, the ester linkages between the glycerol backbone of a triacylglycerol and the fatty acids that are present break and then re-form. During this, the fatty acid groups can move around in the reaction mix so that they do not necessarily re-form the linkage in the place where it was broken. Hence a randomisation of the positions of the fatty acids on the triacylglycerol molecules occurs. As melting and crystallisation functionalities of fats are dependent on fatty acid position as well as on fatty acid type, the physical characteristics of the end fat are completely different - but predictably so - from that of the starting blend. Interesterification does not alter the overall fatty acid composition, only the positions of the fatty acids on the glycerol backbone.
In a further modification of the interesterification process, some enzyme catalysts have the ability to break only the linkages between the glycerol backbone of the triacylglycerol and those fatty acids in the outside 1- and 3-positions, leaving any fatty acids esterified in the central 2-position alone. This enables so-called structured triacylglycerols to be produced for specific properties and functionalities.
Different food products have different requirements as far as the functionality of the fat they contain is concerned. These requirements can often be condensed down to four basic headings:
- melting point and melting profile
- crystallization characteristics
- storage stability (oxidative and hydrolytic stability)
- nutritional requirements.
Fats used in bakery products, for example biscuits and pastry, need to have a certain level of solid fat present at the temperature at which the dough is mixed in order to give enough structure to hold a light aerated structure and to stop more liquid triglycerides from separating from the baked end product. Biscuit and pastry doughs are often mixed at about 25°C, which is close to the ambient temperature in many bakeries. At this temperature, the dough fat used needs to, ideally, contain between 25% and 40% solid fat. Higher solid fat levels make the dough difficult to mix; lower solid fat levels risk some of the liquid fat exuding from the final biscuit or pastry making it oily to the touch.
Historically, animal fats such as lard and beef tallow were used in many of these applications and, it has to be said, lard makes excellent pastry, largely because of the form in which it crystallises. However, these were phased out partly for ethical and religious reasons and partly because these kinds of animal fats were considered to be ‘unhealthy’ due to high levels of saturated fat and, therefore, high risks of cardiovascular diseases. This is quite ironic when one considers that they were replaced by partially hydrogenated fats with high levels of trans fatty acids which were subsequently found to have an even worse effect on cardiovascular disease risks. As with all hydrogenated fats, these two animal fats have now been almost completely removed from bakery products and have largely been replaced by either palm oil (Atkinson, 2011) or blends of palm oil and its fractions or with oils such as rapeseed oil. To an extent, considering the history of these changes, this is also quite ironic because palm oil contains about 50% saturates which is higher than the levels of saturates typically found in lard and beef tallow!
Bread, particularly factory produced bread, has a very specific requirement for a small amount (typically about 3%) of a very high melting fat to be present. This crystallises around the bubbles formed during the time the bread dough is proving and rising and forms a crystal monolayer around these bubbles (Brooker, 1996). Because of the high melting point of the fat used it can retain its structure during the early stages of baking and so holds the aerated structure of the bread.
Chocolate and confectionery coatings
Chocolate and chocolate like coatings need to be solid at ambient temperatures but then melt quickly at mouth temperature. Cocoa butter does this and is obviously the gold standard as far as this is concerned. Chocolate manufacturers in the EU (European Union, 2000) and a number of other countries across the world (not the USA, though) permit a small amount of non-cocoa vegetable fat (called cocoa butter equivalents) to be used in chocolate. There are various limitations put on this both in terms of the amount that can be used and the types of fat that are used. Cocoa butter is rich in what are called symmetrical monounsaturated triglycerides – SOS (i.e. triglycerides with a saturated fatty acid (mainly palmitic and stearic acids) in the 1- and 3-positions and an oleic acid group in the 2-position. As these triglycerides make up over 80% of the composition of cocoa butter they give it its very sharp melting properties. They are also polymorphic (i.e. they crystallise in a number of different crystal forms – six to be precise). These different crystal forms have different stabilities. The two with the greatest stability are in the beta (β) form. Cocoa butter in chocolate must crystallise in the beta form rather than any of the lower stability forms, otherwise it will be soft, difficult to demould and will show fat bloom (a recrystallisation of fat on the surface of the chocolate). To ensure the correct crystal form, chocolate is ‘tempered’, a process which involves cooling and slightly re-heating the chocolate (Smith, 2009). Any non-cocoa vegetable fats used in chocolate also need to have the same basic SOS triglyceride structure and, because this makes them also polymorphic, they have the same requirement to be tempered. Typical fats used in this way are the middle melting fraction of palm oil and the stearin fraction of shea butter.
Non-cocoa butter confectionery coatings are also produced and used (Talbot, 2009). These cannot legally be called chocolate. The best of these is called a supercoating and is essentially a cocoa butter equivalent used at a much higher level than that allowed in chocolate itself. Cocoa butter replacers are based on fractions of palm oil that have a fairly limited compatibility with cocoa butter, thus allowing low levels of cocoa butter to be present in the coating. Cocoa butter substitutes are based on palm kernel oil, usually the stearin fraction, and these have effectively no compatibility with cocoa butter meaning only low-fat cocoa powder can be used with them.
In general, fats for ice cream need to have at least 50% solid fat at 0°C to structure the ice cream but should have a melting point below normal mouth temperature because, during ice cream consumption, the mouth cools. Dairy ice cream must contain only dairy fat, i.e. normally cow’s milk fat (unless labelled otherwise). Non-dairy ice cream can be based on vegetable fats. Because of these melting requirements, palm kernel oil or coconut oil are usually used as the base oil in non-dairy ice cream. Palm oil is occasionally used but this does retain some solid fat above mouth temperature, which can change the texture of the ice cream. Palm oil is sometimes used in soft-whip ice cream as it holds the shape and texture of the ice cream longer than palm kernel oil.
Frying oils need to have a high degree of oxidative stability because of the high temperature of use. Saturated fatty acids and trans fatty acids have a much higher degree of oxidative stability than do cis unsaturated fatty acids. As these oils are being used at 180°C for frying, the higher melting points and levels of solid fat in more saturated or trans-rich fats is irrelevant and so, historically, frying oils have been based on lard, beef tallow and partially hydrogenated fats. For the same reasons that these have now been removed from bakery products, they have also been eliminated from frying oils. These changes have had a drastic effect on the stability of both the frying oil and of the product being fried (as this will inevitably pick up some of the oil). The main choices of oil for frying are palm olein (acceptable stability but contains about 40% saturates), sunflower oil or rapeseed oil (much lower stability but also much less saturates) or the high-oleic variety of sunflower oil. Because oxidative stability is linked to the degree of unsaturation, conventional sunflower oil, which is rich in linoleic acid, is less stable than the newer variety which is rich in oleic acid. High-oleic sunflower oil is, therefore, seen as a good compromise between high oxidative stability and low levels of saturates.
On top of all these functionality requirements in the different applications described, the fats need to be nutritionally 'acceptable'.
Recommendations relating to both total fat intake and that of individual fatty acid groups vary but all are generally agreed that industrially produced trans fats are nutritionally unacceptable and should be eliminated from the diet and that saturated fats have questionable nutritional benefits and should therefore be minimized. This latter recommendation has, though, been the subject of considerable controversy in recent years.
Much of the dietary advice relating to fatty acid intake has rested on the relationship between the effect of different fatty acid groups on blood cholesterol levels, particularly on low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol levels, and the relationship between the level of cholesterol in the blood and the risk of cardiovascular diseases (CVD). This is the so-called ‘Lipid Hypothesis’ (Stanley, 2010). This hypothesis says that:
- some fatty acids (notably trans and saturated fatty acids) increase blood cholesterol levels, particularly the ‘bad’ LDL cholesterol levels,
- increases in blood cholesterol levels, again particularly LDL cholesterol levels, increase the risk of CVD,
- therefore, consumption of trans and saturated fatty acids increase the risk of CVD.
The validity of this hypothesis, which was initially based on work in the 1940s and 1950s carried out by Ancel Keys (Andrade et al, 2009), has often been called into question. For example, Stanley (2010) summarises the evidence for the lipid hypothesis as ‘weak’. He cites the Nurses Health Study which began in the United States in 1976 and now has over a quarter of a million ‘participants’. Over those years it has monitored health and lifestyle factors and the incidence of a wide range of chronic diseases. Stanley (2010) says that, despite there being an association between saturated fat intake and coronary heart disease found in the early years of the study, after 20 years of follow up, the study ‘was no longer able to demonstrate an association between intakes of saturated fat and risk of developing coronary heart disease’.
There is a large body of evidence for the effects of different fatty acids on blood cholesterol levels. Mensink et al (2003) carried out a large meta-analysis of 60 controlled trials. In this he and his co-workers looked at the effects of the major groups of fatty acids and also at individual saturated fatty acids on total, HDL and LDL blood cholesterol levels.
They found that trans fatty acids were the most harmful of all the fatty acids studied in that they both raised the levels of harmful LDL cholesterol and lowered the levels of beneficial HDL cholesterol. This, and other similar studies carried out around the same time, prompted a wide-scale removal of hydrogenated fats from food products across the UK, Western Europe and North America. The UK Food Standards Agency have long given the advice that no more than 2% of dietary energy should come from trans fatty acids (Food Standards Agency, 2007). In the early part of this century about 1.6% of dietary energy came from trans fatty acids but with the removal of hydrogenated fats from most foods this fell to much less than 1% of dietary energy (almost all of this then coming from the naturally occurring trans fatty acids found in dairy and beef fats). Interestingly, the UK Government’s current ‘Eatwell’ guidelines and the NHS Choices ‘Live Well’ guidelines no longer mention trans fatty acids other than to say that current government guidelines are that adults shouldn't have more than about 5g of trans fats a day.
Advice on saturated fat consumption is more problematic because of the conflicting views and evidence for effects of this in health, and particularly on the risk of CVD. Mensink et al (2003) showed that saturated fat intake increased levels of ‘bad’ LDL cholesterol but also increased levels of ‘good’ HDL cholesterol, albeit by a lesser amount. Delving into individual saturated fatty acids, similar effects were seen (both LDL and HDL cholesterol levels increased with LDL cholesterol increasing more than HDL cholesterol levels). However, there was also a chain length effect in that increases were greatest with lauric acid (C12) and myristic acid (C14), less so (although still significant) with palmitic acid (C16) and statistically insignificant with stearic acid (C18). These effects on individual fatty acids are all very interesting and may have some impact on choice of fats in the diet. It is worth noting that recent research has shown that some of these saturated fatty acids are vital for the maintenance of good health. For example, myristic acid is necessary for the myelination of nerve fibres and much else. It is also worth noting that a high cholesterol level is only a risk for a proportion of the population and depends strongly on genotype. Indeed, some parts of the population, e.g. those over the age of 65, are generally in need of more cholesterol to maintain their cognitive health.
For example, there is a current fashion for coconut oil with a school of thought that this is a very healthy oil to consume. Much of this is based on a paper by St-Onge et al (2003) which stated that ‘long-term consumption of MCT (medium-chain triglycerides) enhances EE (energy expenditure) and fat oxidation in obese women, when compared to LCT (long-chain triglycerides) consumption’. The benefits (or otherwise) of coconut oil rest on the definitions of MCT and LCT and at what chain length MCTs become LCTs. Many scientists would argue that medium chain fatty acids are those with eight and ten carbon atoms and long chain fatty acids are those with twelve of more carbon atoms. The distinction is quite important because proponents of coconut oil as a healthy oil class lauric acid, with twelve carbon atoms, as being a medium chain fatty acid. About 50% of the fatty acids in coconut oil are lauric acid, so it is important to know into which group it falls. Most scientific and nutritional experts (Sacks et al, 2017) would put it into the long-chain fatty acid group and, certainly, the effects of lauric acid significantly increasing both types of cholesterol found by Mensink et al (2003) would suggest that coconut oil does not have the health benefits that its proponents suggest. Recent research by Cunnane et al (2016) has, though, suggested that the low levels of MCT in coconut oil and palm kernel oil (i.e. not the lauric acid component) may have benefits in addressing the risk and treatment of Alzheimer’s disease.
Another conclusion that could be drawn from the effects of individual saturated fatty acids on blood cholesterol levels is that fats like cocoa butter and shea butter, although saturated, are not as bad for cardiovascular health as would be predicted from their saturated fatty acid levels because a significant proportion of those saturated fatty acids are stearic acid.
cis-unsaturated fatty acids, on the other hand, have a beneficial effect on blood cholesterol levels, increasing the beneficial HDL cholesterol and lowering the detrimental LDL cholesterol. cis-monounsaturates are generally regarded as the best type of fat – or, at least, the type of fat with the fewest drawbacks and so the type that can be consumed relatively freely, although it should be remembered that all fats contribute 9 kcal/g of energy to the diet. cis-polyunsaturates are also beneficial in terms of their effects on blood cholesterol levels but there is growing opinion that having switched on a large scale a few decades ago from butter and lard in cooking and as spreads over to sunflower oil and spreads that we have gone too far and that these fats should be limited to between 6% and 10% of dietary energy.
There is also evidence that, as we have switched to oils such as sunflower oil and soyabean oil – oils that are rich in omega-6 fatty acids, we have reduced our intake of the nutritionally important omega-3 fatty acids. In fact, the ratio of omega-6:omega-3 in a typical Western diet is now between 15:1 and 20:1 compared to a ratio of 1:1 in Paleolithic times (GB Healthwatch, 2017). Omega-3 and omega-6 fatty acids compete for the same enzymes to generate long chain polyunsaturates that are essential for our wellbeing (Simopoulos, 2016). The fact that we consume much more omega-6 than omega-3 means that this competition for enzymes is very one-sided and the metabolic pathway from omega-3 gets swamped by that from omega-6 fatty acids. This makes it important for us to consume some omega-3 directly from long-chain polyunsaturate sources, i.e. fish oils, either from oily fish or in the form of supplements. The most important omega-3 fatty acids from fish are EPA (eicosapentaenoic acid – 20 carbon atoms, five double bonds) and DHA (docosahexaenoic acid – 22 carbon atoms, six double bonds). SACN recommend an intake of at least 450mg per day of these two fatty acids (GOED, 2014).
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