The role of meat as a source of n − 3 polyunsaturated fatty acids in the human diet
Introduction
There is now much evidence to show that chronic disease is rapidly increasing worldwide. Data summarised by WHO/FAO (2003) indicate that in 2001, chronic diseases gave rise to approximately 60% of the 56.5 million deaths reported around the world and about 46% of the global burden of disease. It has been projected that by 2020, chronic diseases will account for almost 75% of all deaths worldwide. The cost to national health services for treating chronic disease will also be massive. Almost half of the deaths arising from chronic disease are attributable to cardiovascular disease, although the rapid increase in the obesity/type 2 diabetes-related Metabolic Syndrome (Nugent, 2004) is very concerning, not only because it already affects a large proportion of the population worldwide, but also because it is now starting to affect people earlier in life. Also, and contrary to popular belief, not only Western societies are affected, developing countries are increasingly at risk (WHO, 2002).
It has been recognised for some time that diet makes a major contribution to the risk factors for chronic disease. At a global level there is evidence that major changes to diet have occurred over the last 100–200 years (Simopoulos, 2000) but additionally, very major changes to diet in the developed world have occurred during the last 50 years. Notably, as animal-derived foods have become more plentiful and societies have increased spending power, an increased consumption of animal products has occurred with a consequent increase in fat content and hence energy density of diets (Table 1). Because of the composition of many animal fats, increased consumption of them has been associated with an increase in dietary ratio of n − 6/n − 3 polyunsaturated fatty acids (Simopoulos, 2000) and increased chronic disease. This paper will examine the potential of animal nutrition to improve the composition of fat in ruminant meat and will also discuss how this needs to be related to the evidence that not all n − 3 fatty acids in the human diet are of equal potency.
Section snippets
Contribution of meat to diets
Worldwide, the demand for meat and other animal products is increasing at a substantial rate driven by a combination of population growth, urbanisation and rising income. Table 1 shows the trends in meat and milk consumption over the past 40 years for various parts of the world. For large parts of many societies, meat and animal products represent a source of high quality protein, although high intakes of some animal products can lead to excessive fat intakes. From the late 1960s to the late
Dietary n − 3 fatty acids and chronic disease
The relationship between dietary fat type and intake and the risk of cardiovascular disease (CVD), coronary heart disease (CHD) in particular, has been extensively investigated with strong and consistent associations seen from a wide body of data (see Kris-Etherton et al., 2001, WHO/FAO, 2003). In recent years there has been much interest in the beneficial effects of the very long chain (VLC, carbon chain length ⩾20) n − 3 PUFA, in particular eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic
Contribution of meat to very long chain n − 3 PUFA intake in the UK
In a recent study (Givens & Gibbs, 2006) the current mean intake of EPA + DHA in UK adults was estimated to be about 244 mg/day, only about 54% of the minimum recommended intake (Table 3). In addition, if those who eat oily fish are excluded (27% of adults) the vast majority of the adult population is consuming only about 113 mg/day. Of this amount, poultry meat contributes about 24% with ruminant meat and pig meats contributing only about 5% and 2.2%, respectively. It is likely that the higher
Enhancing the n − 3 fatty acid composition of ruminant meat
In general, fat in meats derived from ruminant animals is composed of approximately 45–55% of saturated fatty acids, 45–50% monounsaturated fatty acids and relatively minor amounts of PUFA (Table 4; adapted from Enser, Hallett, Hewitt, Fursey, & Wood, 1996). The preponderance of saturated fatty acids is a result of the extensive biohydrogenation by the rumen bacteria of any dietary unsaturated fatty acids. Most of the efforts to change the fatty acid composition of beef, and to a lesser extent
Effect of n − 3 fatty acid enrichment on trans and conjugated fatty acids in ruminant meat
It is known that increasing the intake of fish oil and ALNA by dairy cows leads to increased concentrations of trans C18:1 and conjugated C18:2 (CLA) fatty acids in milk (see review of Givens et al., 2006). There are less data for meat, although the data in Table 7, Table 8 point to a similar effect. The outcome of three recent studies (Aharoni et al., 2004, Cooper et al., 2004, Raes et al., 2004) are summarised in Table 9. The results of all studies indicate that feeding increasing amounts of
Conclusions
It is considered that consumption of VLC n − 3 PUFAs in most Western populations is sub-optimal and benefits in relation to chronic disease would be gained from increased consumption. It now appears that dietary ALNA is a very limited source of VLC n − 3 PUFA in humans and increased intake of ALNA may be of limited advantage relative to increased consumption of preformed VLC n − 3 PUFA. Although poultry meat contributes about 24% of VLC n − 3 PUFA to the UK diet, ruminant and pig meat provides only
Acknowledgement
This work was supported by both LIPGENE, an EU Sixth Framework Programme Integrated Project (2004–2009) (http://www.lipgene.tcd.ie), and RELU, a Research Councils UK funded project concerned with The Implications of a Nutrition Driven Food Policy for Land Use and the Rural Environment (http://www.relu.rdg.ac.uk/).
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