G. Talbot,     The Fat Consultant, UK

Abstract:

This book as a whole is concerned with the reduction of saturated fats in foods. The background to this, both in terms of the clinical nutritional studies backing up the need for such reductions to be made and the sources of saturated fats in the diet, are discussed in the first part of the book. The second part of the book deals with ways of reducing saturates in those food categories that contribute the most saturates to the diet. This opening chapter sets the scene for the rest of the book by outlining the background as to why we should be reducing saturated fat intake, but also giving some details of the opposite view. For those unfamiliar with the chemistry of fats and fatty acids a brief introduction to this is given. The chapter then goes on to give some information on the usage of some of the more common ‘saturated’ fats (palm oil, palm kernel oil, coconut oil, butterfat and lard) over the past 15 years in the EU, US and UK. The chapter also discusses what the various options are in terms of the materials that could be used to replace saturates, before concluding with a brief examination of some food categories that are not considered in their own right in later separate chapters – foods such as cakes and doughnuts, ready meals and non-chocolate confectionery.

Key words

saturated fat

chemistry of fats

usage of oils

fat replacers

cakes

doughnuts

ready meals

toffees

1.1 Background to the need to reduce saturated fats

The World Health Organization (2003) has recommended a daily intake of total fat comprising between 15% and 30% of dietary energy. In the same report the WHO recommends that less than 10% of daily energy should come from saturated fats. The UK Food Standards Agency (2008) published its Saturated Fat and Energy Intake Programme and recommended that saturated fat consumption should be reduced from a level of about 13.3% of dietary energy (from the National Diet and Nutrition Survey (HMSO, 2002)) to a level of 11% of dietary energy, a reduction of about 20%. The reason for this is the effects that saturated fatty acids are considered to have on blood cholesterol levels which, in turn, are considered to affect the risk of developing cardiovascular diseases such as coronary heart disease and strokes.

There have been numerous publications showing the effects of saturated fat on blood cholesterol and references to many of these are made in subsequent chapters. One of the most commonly quoted is a meta-analysis of 60 controlled trials carried out by Mensink et al. (2003). In this paper, the authors show that different saturated fatty acids have different effects on total blood cholesterol levels when used to replace 1% carbohydrate (see Fig. 1.1). Within the range of what might be considered long-chain saturates (i.e. C12:0 up to C18:0) there is the suggestion that the longer the chain length the lower is the increase of total cholesterol in the blood, suggesting that stearic acid has a relatively neutral effect compared with lauric acid, which raises blood cholesterol levels significantly. As with many aspects of clinical nutrition, things are not always as clear-cut as they seem and delving deeper into this meta-analysis it becomes clear that much of the increase in cholesterol in the blood from lauric acid is high-density lipoprotein (HDL) cholesterol, the so-called ‘good’ cholesterol. This, and other studies, will be considered in more detail in section 1.4 of this chapter and reviewed in considerably greater detail in later chapters.

Although both the World Health Organization and the UK Foods Standards Agency are calling for reductions in saturated fat in the diet, considerable reductions have already been made between 1986/87 and 2002 in the UK (Table 1.1). In that 15-year period total energy from fat has reduced from about 40.4% down to about 35.4%, a reduction of over 12%. Almost all of this reduction has been to saturated fats (down from 16.8% to 13.3% of energy) and trans fats (down from 2.2% to 1.2% of energy). This reduction in energy from saturates is already one of 20%, but a further 20% reduction is now being called for.

One of the main questions that this book will address is how and where such a reduction can be made. Before trying to answer that, though, it is useful to look at where most of the saturated fat in our diet comes from. Chapter 3 will look at the animal and vegetable sources of saturated fats but, in terms of food groups, we can see from Table 1.2 that, in the UK (HMSO, 2002), 24% of saturates were from a milk (dairy) source, 22% were from meat and meat products, 18% were from cereal-based products (i.e. bakery and baked products) and 11% were from fat spreads (including butter). Three-quarters of our intake was from these four broad food groups. Other groups contributing lesser, but still significant, levels were potatoes and savoury snacks (7% of total saturates) and chocolate confectionery (5% of total saturates). Not surprisingly, these are the areas that this book will concentrate on.

1.2 Chemistry and structure of fatty acids and triglycerides

Fats are triesters of the trihydric alcohol, glycerol, and hence are known as triacylglycerols (TAGs) or, more commonly, triglycerides (TGs). Glycerol forms the backbone to the structure but it is the three fatty acids that are esterified to it that give fats both their functional and nutritional characteristics. All fatty acids are hydrocarbon chains with a methyl (CH3) group at one end and a carboxylic acid (COOH) group at the other. It is the carboxylic acid group that links to the glycerol backbone, reacting with the alcohol group of the glycerol to produce an ester linkage. Saturated fatty acids contain no carbon–carbon double bonds within the fatty acid chain and have a straight, linear structure (albeit with small ‘zig-zags’ moving from one carbon atom to the next) (Fig. 1.2). The structures of the most commonly occurring saturated fatty acids, lauric (C12:0), myristic (C14:0), palmitic (C16:0) and stearic (C18:0) are shown in this diagram. Because they have this straight linear structure, triglycerides that contain significant amounts of saturated fatty acids can crystallize together in a closer crystal structure (because the straight chains can get physically closer together). This gives the fat a thermodynamically more stable structure which results in a higher melting point. Thus, fats containing higher levels of saturates tend to be more solid at ambient temperatures than fats containing higher levels of unsaturates.

Unsaturated fatty acids, on the other hand, generally have a more bent structure (Fig. 1.3). Unsaturated fatty acids contain one or more carbon–carbon double bonds within the fatty acid chain. In naturally occurring vegetable oils these are almost exclusively in the cis configuration. This means that the carbon–carbon chains leading into and away from the two carbon atoms associated with the double bond are on the same side of the double bond as each other. This results in a bend in the chain. Figure 1.3 shows the most commonly occurring cis-monounsaturated fatty acid, oleic acid (C18:1). This has 18 carbon atoms in the chain and the double bond occurs between the ninth and tenth carbon atom (counting from the carboxylic acid end of the chain). Adding another cis double bond three carbon atoms along (i.e. between the 12th and 13th carbon atoms) gives linoleic acid (C18:2), and adding another cis double bond between the 15th and 16th carbon atoms gives linolenic acid (C18:3). As well, of course, as counting the position of the double bond from the carboxylic acid end of the fatty acid chain it is possible to count it from the other end, the methyl group end. This results in the now well-known ‘omega’ nomenclature. If we count from the methyl group end of the chain then the first double bond to be encountered in linolenic acid is after the third carbon atom and so this is known as an omega-3 fatty acid. Similarly, linoleic acid is an omega-6 fatty acid and oleic acid is an omega-9 fatty acid.

The bent structures of these fatty acids are such that a crystal structure with a lower thermodynamic stability is produced which gives these cis unsaturated fatty acids a lower melting point and,...