《食品加工营养手册》参考资料（英文版）9 Enhancing the nutritional value of meat.pdf_大学文库

210 The nutrition handbook for food processors swallowing meat. Meat is a highly nutritious and versatile food. The primary importance of meat as a food lies in the fact that when digested its protein is broken down releasing amino acids, which are assimilated and ultimately used for the repair and growth of cells. Meat is a nutrient dense food, providing valu able amounts of many essential micronutrients. Meat supplies fatty acids, vita- mins, minerals, energy and water and is involved in the synthesis of protein, fat and membranes in the bod Traditionally meat was considered a highly nutritious food, highly valued and associated with good health and prosperity. As such, western societies gradually increased consumption with increasing affluence. The healthy image of red meat gradually became eroded during the 1980s, when research on the role of lipids in heart disease focused attention on the fat contributed from meat. The british Government's Committee on Medical Aspects of Food and Nutrition(COMA) report on coronary heart disease(CHD)in 1984 identified meat as a major source of saturated fat, contributing a quarter of UK intakes( Committee on Medical Aspects of Food Policy, 1984). Although the multifactorial nature of CHD risk is now widely acknowledged(British Nutrition Foundation, 1996: COMA, 1994) he health image of red meat remains tarnished due to this negative association. More recently, we have seen the publication of two reports on diet and cancer (World Cancer Research Fund, 1997; COMA, 1998). These reports associated red meat consumption with increased incidence of certain cancers, in particular, colorectal cancer(CRC), despite the existence of conflicting evidence. Both of these reports issued guidelines on the limits of red meat one should consume, to reduce the risk of developing CRC, which negatively influenced the image of red meat The 1990s also saw major publicity on non-nutritional issues including animal health concerns such as bovine spongiform encephalopathy (BSE)and more recently the return of foot and mouth disease(FMD)to Britain. The last 25 years have been the most turbulent regarding issues surrounding meat consumptio with much of the publicity being negative thus downplaying meats nutritional value 9.2 Meat consumption trends The negative nutritional image that surrounds red meat is in some way respon sible for the decrease in expenditure. In 1999, 25.8% of expenditure on home food in Great Britain was spent on meat and meat products(Ministry of Agri- culture Fisheries and Food, 1999).This is a significant drop compared with 32. 1% in 1979. During this time period there have been major changes in the type of meat that people are buying in the UK. Expenditures on beef, lamb, pork, ba and ham each fell, whilst expenditure shares on poultry and on other meats have risen. The major growth area in processed meats and meat products has been frozen convenience meat products, meat based ready meals and other meat prod ucts such as chinese and italian meals c ng meat(Ministry of Agriculture

swallowing meat. Meat is a highly nutritious and versatile food. The primary importance of meat as a food lies in the fact that when digested its protein is broken down releasing amino acids, which are assimilated and ultimately used for the repair and growth of cells. Meat is a nutrient dense food, providing valuable amounts of many essential micronutrients. Meat supplies fatty acids, vitamins, minerals, energy and water and is involved in the synthesis of protein, fat and membranes in the body. Traditionally meat was considered a highly nutritious food, highly valued and associated with good health and prosperity. As such, western societies gradually increased consumption with increasing affluence. The healthy image of red meat gradually became eroded during the 1980s, when research on the role of lipids in heart disease focused attention on the fat contributed from meat. The British Government’s Committee on Medical Aspects of Food and Nutrition (COMA) report on coronary heart disease (CHD) in 1984 identified meat as a major source of saturated fat, contributing a quarter of UK intakes (Committee on Medical Aspects of Food Policy, 1984). Although the multifactorial nature of CHD risk is now widely acknowledged (British Nutrition Foundation,1996; COMA, 1994), the health image of red meat remains tarnished due to this negative association. More recently, we have seen the publication of two reports on diet and cancer (World Cancer Research Fund, 1997; COMA, 1998). These reports associated red meat consumption with increased incidence of certain cancers, in particular, colorectal cancer (CRC), despite the existence of conflicting evidence. Both of these reports issued guidelines on the limits of red meat one should consume, to reduce the risk of developing CRC, which negatively influenced the image of red meat. The 1990s also saw major publicity on non-nutritional issues including animal health concerns such as bovine spongiform encephalopathy (BSE) and more recently the return of foot and mouth disease (FMD) to Britain. The last 25 years have been the most turbulent regarding issues surrounding meat consumption with much of the publicity being negative thus downplaying meat’s nutritional value. 9.2 Meat consumption trends The negative nutritional image that surrounds red meat is in some way responsible for the decrease in expenditure. In 1999, 25.8% of expenditure on home food in Great Britain was spent on meat and meat products (Ministry of Agriculture Fisheries and Food, 1999). This is a significant drop compared with 32.1% in 1979. During this time period there have been major changes in the type of meat that people are buying in the UK. Expenditures on beef, lamb, pork, bacon and ham each fell, whilst expenditure shares on poultry and on other meats have risen. The major growth area in processed meats and meat products has been frozen convenience meat products, meat based ready meals and other meat products such as Chinese and Italian meals containing meat (Ministry of Agriculture 210 The nutrition handbook for food processors

Enhancing the nutritional value of meat 211 Fisheries and Food, 1999). There are many factors responsible for these the tarnished image of red meat being one such Other influencing factor changes in lifestyle trends which saw the drive for convenience foods, and the resultant responsiveness of the industry to this has greatly influenced the chang ing meat-buying habits of consumers. 9.3 Cancer Meat consumption has been implicated in many cancers, as being either protec tive or causative, depending on the type of cancer. Meat consumption has been shown to protect against cancers of the stomach(Hirayama, 1990; Tuyns et al 1992; Azevedo et al, 1999), liver and the oesophagus(Zeigler et al, 1981; Tuyns et al, 1987; Nakachi et al, 1988). These are three of the top five cancers globally On the other hand, meat consumption has been implicated as a cause of colorectal (colon and rectal), breast and prostate cancer, with the main emphasis being on CRC. CRC is the fourth most common cancer in the world, but in Europe and other Western countries it is second in terms of incidence and mortality(after lung cancer in men and breast cancer in women) with 190000 new cases per year in Europe(Black et al, 1997; Bingham, 1996). There is strong evidence from epi demiological studies showing that diet plays an important role in most large bowel cancers, implying that it is a potentially preventable disease(Higginson, 1966: COMA, 1998). The precise dietary components that influence CRC risk have not been fully elucidated. However, epidemiological studies suggest that high intakes of fat, meat and alcohol increase risk, whereas vegetables, cereals and non-starch polysaccharides, found in fruit and many other foods, decrease the risk(Bingham, 1996). For many of these dietary factors the evidence is equivo- cal. In the case of meat, the evidence is conflicting, early cross-sectional com parisons attributed much of the world-wide variation in CRC incidence to fat and animal protein consumption(Armstrong and Doll, 1975). In contrast, subsequent case-control and cohort studies are much less consistent(Hill, 1999a) 4. Meat consumption and CRC became a high profile issue during 1997 and 1998 ith the global launch of the World Cancer Research Fund report (WCRE, 1997), timed to coincide with the publication of the British COMA report, both on diet and cancer. The WCRF report was particularly negative towards red meat, fuelled the launch publicity. This stimulated several critical appraisals report, all challenging the conclusions regarding meat(Hill, 1999b). The scien- ic evidence is not sufficiently robust to recommend a maximum of 80g/day red meat as pronounced by the WCRF and the initial announcement by COMA for a similar recommendation was subsequently revised. Most of the data show- ing an association between meat consumption and CRC are American, whereas several studies conducted outside the US(many in Europe) have shown no such elationship(Hill, 1999a). On final publication, COMA(1998) reassured consumers that average consumption levels(90 g/day of cooked red meat)were acceptable COMA suggests that high consumers, less than 15% of the UK popu

Fisheries and Food, 1999). There are many factors responsible for these changes, the tarnished image of red meat being one such. Other influencing factors include changes in lifestyle trends which saw the drive for convenience foods, and the resultant responsiveness of the industry to this has greatly influenced the changing meat-buying habits of consumers. 9.3 Cancer Meat consumption has been implicated in many cancers, as being either protective or causative, depending on the type of cancer. Meat consumption has been shown to protect against cancers of the stomach (Hirayama, 1990; Tuyns et al, 1992; Azevedo et al, 1999), liver and the oesophagus (Zeigler et al, 1981; Tuyns et al, 1987; Nakachi et al, 1988). These are three of the top five cancers globally. On the other hand, meat consumption has been implicated as a cause of colorectal (colon and rectal), breast and prostate cancer, with the main emphasis being on CRC. CRC is the fourth most common cancer in the world, but in Europe and other Western countries it is second in terms of incidence and mortality (after lung cancer in men and breast cancer in women) with 190 000 new cases per year in Europe (Black et al, 1997; Bingham, 1996). There is strong evidence from epidemiological studies showing that diet plays an important role in most large bowel cancers, implying that it is a potentially preventable disease (Higginson, 1966; COMA, 1998). The precise dietary components that influence CRC risk have not been fully elucidated. However, epidemiological studies suggest that high intakes of fat, meat and alcohol increase risk, whereas vegetables, cereals and non-starch polysaccharides, found in fruit and many other foods, decrease the risk (Bingham, 1996). For many of these dietary factors the evidence is equivocal. In the case of meat, the evidence is conflicting, early cross-sectional comparisons attributed much of the world-wide variation in CRC incidence to fat and animal protein consumption (Armstrong and Doll, 1975). In contrast, subsequent case-control and cohort studies are much less consistent (Hill, 1999a). Meat consumption and CRC became a high profile issue during 1997 and 1998 with the global launch of the World Cancer Research Fund report (WCRF, 1997), timed to coincide with the publication of the British COMA report, both on diet and cancer. The WCRF report was particularly negative towards red meat, which fuelled the launch publicity. This stimulated several critical appraisals of the report, all challenging the conclusions regarding meat (Hill, 1999b). The scientific evidence is not sufficiently robust to recommend a maximum of 80 g/day red meat as pronounced by the WCRF and the initial announcement by COMA for a similar recommendation was subsequently revised. Most of the data showing an association between meat consumption and CRC are American, whereas several studies conducted outside the US (many in Europe) have shown no such relationship (Hill, 1999a). On final publication, COMA (1998) reassured UK consumers that average consumption levels (90 g/day of cooked red meat) were acceptable. COMA suggests that high consumers, less than 15% of the UK popuEnhancing the nutritional value of meat 211

212 The nutrition handbook for food processors lation, eating above 140g/day might benefit from a reduction. Equally impor tantly, this report acknowledged that meat and meat products remain a valuable source of a number of nutrients including iron and that for many a moderate intake makes an important contribution to micronutrient status. The potential effect on iron status of further reductions to red meat intakes was subsequently investi gated, as recommended within the COMA report. Given that a 50% reduction in intake would result in a third of women having low iron intakes(below &mg/d). the appropriateness of public health messages concerning meat consumption should be carefully considered prior to reaching the media( Gibson and Ashwell 2001). Various components of meat (protein, iron, and heterocyclic amines)have been suspected of contributing to the development of CRC. Dietary protein is broken down in the body to amino acids, which are further degraded to ammonia, which may have cancer-initiating effects. The human colon is also rich in amides and amines that are substrates for bacterial nitrosation by nitric oxide(NO)to N nitroso compounds that are found in human faeces. There is no conclusive evi- dence that protein derived compounds can increase cancer risk in humans. It is hypothesised, but not yet established, that the intake of iron from meat and other iron-rich foods may increase the risk of cancer via the production of free radi- cals in the body. Heterocyclic amines are formed by the Maillard reactions that involve amino acids, sugars and creatine during cooking. They are usually pro- duced on the surface of meat during cooking at very high temperatures, such as in frying, grilling or barbecuing but they are minimal when meat is steamed, microwaved or marinated. The heterocyclic amines are known mutagens in vitro and carcinogens in rodents. The most abundant heterocyclic amine produced in meat is phenylimadazo pyridine(PhlP), which is a relatively weak carcinogen compared to other heterocyclic amines such as IQ and MelQ. The role of hete rocyclic amines in causing CRC is not fully elucidated in humans Truswell summarised the evidence in 2000 and showed that 20 out of 30 case- control studies and 10 out of 14 prospective studies showed no relationship between meat intake and Crc with some of the results of the remaining studies being confused and one prospective study showing an inverse correlation between meat consumption and CrC risk(Hill, 2000). If meat consumption were associ- ated with increased risk for cancer, one would expect mortality from cancer to be much lower among vegetarians. In a recent meta-analysis of five cohort studies, results have shown no significant differences in mortality from cancer in general, and more specifically mortality in stomach, breast, lung, prostate and colorectal cancer between vegetarians and omnivores(Key et al, 1998, 1999). If red meat consumption were associated with increased risk for CRC, one would expect a decrease in the incidence of CRC to occur over time as a result of decreasing meat consumption trends. During the past 30 years, red meat con sumption in the UK has decreased by approximately 25%0, while during the same time the incidence of CRC has increased by about 50%(Hill, 1999b). Similarly, if meat consumption were associated with increased risk for CRC, one would

lation, eating above 140 g/day might benefit from a reduction. Equally importantly, this report acknowledged that meat and meat products remain a valuable source of a number of nutrients including iron and that for many a moderate intake makes an important contribution to micronutrient status. The potential effect on iron status of further reductions to red meat intakes was subsequently investigated, as recommended within the COMA report. Given that a 50% reduction in intake would result in a third of women having low iron intakes (below 8 mg/d), the appropriateness of public health messages concerning meat consumption should be carefully considered prior to reaching the media (Gibson and Ashwell, 2001). Various components of meat (protein, iron, and heterocyclic amines) have been suspected of contributing to the development of CRC. Dietary protein is broken down in the body to amino acids, which are further degraded to ammonia, which may have cancer-initiating effects. The human colon is also rich in amides and amines that are substrates for bacterial nitrosation by nitric oxide (NO) to Nnitroso compounds that are found in human faeces. There is no conclusive evidence that protein derived compounds can increase cancer risk in humans. It is hypothesised, but not yet established, that the intake of iron from meat and other iron-rich foods may increase the risk of cancer via the production of free radicals in the body. Heterocyclic amines are formed by the Maillard reactions that involve amino acids, sugars and creatine during cooking. They are usually produced on the surface of meat during cooking at very high temperatures, such as in frying, grilling or barbecuing but they are minimal when meat is steamed, microwaved or marinated. The heterocyclic amines are known mutagens in vitro and carcinogens in rodents. The most abundant heterocyclic amine produced in meat is phenylimadazo pyridine (PhIP), which is a relatively weak carcinogen compared to other heterocyclic amines such as IQ and MeIQ. The role of heterocyclic amines in causing CRC is not fully elucidated in humans. Truswell summarised the evidence in 2000 and showed that 20 out of 30 casecontrol studies and 10 out of 14 prospective studies showed no relationship between meat intake and CRC with some of the results of the remaining studies being confused and one prospective study showing an inverse correlation between meat consumption and CRC risk (Hill, 2000). If meat consumption were associated with increased risk for cancer, one would expect mortality from cancer to be much lower among vegetarians. In a recent meta-analysis of five cohort studies, results have shown no significant differences in mortality from cancer in general, and more specifically mortality in stomach, breast, lung, prostate and colorectal cancer between vegetarians and omnivores (Key et al, 1998, 1999). If red meat consumption were associated with increased risk for CRC, one would expect a decrease in the incidence of CRC to occur over time as a result of decreasing meat consumption trends. During the past 30 years, red meat consumption in the UK has decreased by approximately 25%, while during the same time the incidence of CRC has increased by about 50% (Hill, 1999b). Similarly, if meat consumption were associated with increased risk for CRC, one would 212 The nutrition handbook for food processors

Enhancing the nutritional value of meat 213 expect the rates of CRC to be higher in countries with high meat consumption and lower in countries with low meat consumption. People in the Mediterranean countries eat more red meat than do, for instance, the inhabitants of the UK, yet these countries have lower CRC rates(Hill, 2000). Such paradoxical findings are further evidence that, at current levels, meat consumption is not a risk factor for CRC incidence Epidemiological associations between dietary components, specific foods or food groups and chronic disease, such as cancer, can identify risk factors, but are generally insufficient to establish cause and effect relationships. Findings from epidemiological studies must be combined with other types of evidence(e.g. animal experiments, human clinical trials) before a persuasive causal relation- ship can be established. CRC is multi-factorial; it is confounded by diet, smoking, alcohol, physical activity, obesity, aspirin use, age and family history. There are known protective and causative factors. It is well-known that daily consumption of vegetables and meat reduces the risk of cancer at many sites, whereas daily meat consumption with less frequent vegetable consumption increases risk Hirayama, 1986; Kohlmeier et al, 1995; Cox and Whichelow, 1997). Evidence suggests that it is the reduced intakes of the protective factors such as vegetables ind cereals that are the main determinants of crc risk with meat being coinci- ly related There is a need to assess the role of meat when consumed in normal quant ties, by normal cooking methods, and within the context of a mixed, balanced, diet. The method of cooking meat and the degree of browning are of particular importance to this whole issue. A major effort by International Meat Industry partners has attempted to raise awareness of the complexities of meat prepara tion and cooking habits and how these differ between countries. Dietary assess ment techniques adopted by nutrition scientists currently do not take full account of the diverse differences between meat products world-wide and the consequent influences these may have on the body. For example, it is well recognised that meat is often cooked more evenly through the muscle within Europe, whereas it tends to be blackened on the outside whilst remaining rare on the inside in north America. This may be one reason for the greater negative findings in American studies of the role of meat in CRC, compared with European studies. This hith- erto unexplored facet of meat consumption may have far-reaching implications for interpretation of epidemiological data and ultimately for public health rec ommendations. Certain marinades applied to meat before cooking will reduce the quantity of potential carcinogenic materials present. The application of knowl- edge in this area to the production of processed meat products with all the nutri tional benefits and none of the potentially harmful components would be pro- In summary, it is important not only to examine the relationship between meat consumption and CRC alone, but also to look at meat preparation and cooking differences in conjunction with protective factors, such as vegetables and cereals At a meat and diet workshop, it was stated

expect the rates of CRC to be higher in countries with high meat consumption and lower in countries with low meat consumption. People in the Mediterranean countries eat more red meat than do, for instance, the inhabitants of the UK, yet these countries have lower CRC rates (Hill, 2000). Such paradoxical findings are further evidence that, at current levels, meat consumption is not a risk factor for CRC incidence. Epidemiological associations between dietary components, specific foods or food groups and chronic disease, such as cancer, can identify risk factors, but are generally insufficient to establish cause and effect relationships. Findings from epidemiological studies must be combined with other types of evidence (e.g. animal experiments, human clinical trials) before a persuasive causal relationship can be established. CRC is multi-factorial; it is confounded by diet, smoking, alcohol, physical activity, obesity, aspirin use, age and family history. There are known protective and causative factors. It is well-known that daily consumption of vegetables and meat reduces the risk of cancer at many sites, whereas daily meat consumption with less frequent vegetable consumption increases risk (Hirayama, 1986; Kohlmeier et al, 1995; Cox and Whichelow, 1997). Evidence suggests that it is the reduced intakes of the protective factors such as vegetables and cereals that are the main determinants of CRC risk with meat being coincidentally related. There is a need to assess the role of meat when consumed in normal quantities, by normal cooking methods, and within the context of a mixed, balanced, diet. The method of cooking meat and the degree of browning are of particular importance to this whole issue. A major effort by International Meat Industry partners has attempted to raise awareness of the complexities of meat preparation and cooking habits and how these differ between countries. Dietary assessment techniques adopted by nutrition scientists currently do not take full account of the diverse differences between meat products world-wide and the consequent influences these may have on the body. For example, it is well recognised that meat is often cooked more evenly through the muscle within Europe, whereas it tends to be ‘blackened’ on the outside whilst remaining rare on the inside in North America. This may be one reason for the greater negative findings in American studies of the role of meat in CRC, compared with European studies. This hitherto unexplored facet of meat consumption may have far-reaching implications for interpretation of epidemiological data and ultimately for public health recommendations. Certain marinades applied to meat before cooking will reduce the quantity of potential carcinogenic materials present. The application of knowledge in this area to the production of processed meat products with all the nutritional benefits and none of the potentially harmful components would be progressive indeed. In summary, it is important not only to examine the relationship between meat consumption and CRC alone, but also to look at meat preparation and cooking differences in conjunction with protective factors, such as vegetables and cereals. At a meat and diet workshop, it was stated: Enhancing the nutritional value of meat 213

214 The nutrition handbook for food processors It is time that the meat CRC story was laid to rest, so that we can get back to recommending that young women of childbearing age eat meat as a ready source of available iron (Hill, 2000) Nevertheless, it is sensible to consider that there must be an optimal range for meat intakes in order to ensure a balanced diet is achieved whilst optimal weight is maintained. From this practical perspective COMA's(1998)suggested intake range of 90-140 g cooked meat per day is sensible as a public health message he overemphasis on reducing meat, however, rather than encouraging greater accompanying plant food intake has served only to confuse the public(Hill, 1999b). Evidence suggests that the risk of cancer will be reduced to a greater extent by increasing intakes of fruit and vegetables than by lowering meat intakes Once again, the move towards pre-prepared meal solutions provides opportunity anufacturers to devel cipes with a healthy balance of meat and veg etable ingredients such that the nutritional profile of the dish is optimised. 9. 4 Concerns about fat Regular consumption of red meat is associated epidemiologically with increased risk of coronary heart disease, due to its fat composition. Conversely, a growing bank of evidence is showing that a healthy diet that includes lean red meat can produce positive blood lipid changes(Watts et al, 1988: Scott et al, 1990; Davidson et al, 1999; Beauchesne-Rondeau et al, 1999 ). blood cholesterol levels are increased by inclusion of beef fat, not lean beef in an otherwise low-fat diet Equal amounts of lean beef, chicken, and fish added to low fat, low saturated fat diets, similarly reduce plasma cholesterol and LDL-cholesterol levels in hyper- cholesterolaemic and normocholesterolaemic men and women Meat is a source of arachidonic acid(20: 4n-6), both in the lean and visible fat components(Duo et al, 1998). Assumptions that the 20: 4n-6 content of meat was responsible for increasing thrombotic tendencies in Western societies are too sim- plistic. The presence of large amounts of linoleic acid (18: 2n-6) in current diets results in plasma increases of linoleic and arachidonic acids only. However, in the absence of linoleic acid, the long chain n-6 and n-3 PUFAS present in lean meat can influence the plasma pool, increasing plasma eicosatrienoic acid (20: 3n- 6), 20: 4n-6, and eicosapentaenoic acid (20: 5n-3), and probably reducing throm- botic tendencies. It is the imbalance of n-6: n-3 PUFAS in the diet, brought about by excessive 18: 2n-6, that causes high tissue 20: 4n-6 levels, so encouraging metabolism to eicosanoids(Sinclair et al, 1994; Mann et al, 1997) Meat contributes between a third and a half of the uk daily cholesterol intake Chizzolini et al, 1999: British Nutrition Foundation, 1999). Meats cholesterol content is, for consumers, another negative influence on meats health image, although it is now accepted that dietary intake of cholesterol has little bearing on plasma cholesterol. A review of the cholesterol content of meat indicates sur prisingly that levels of cholesterol are generally not higher in fatty meat or meat

It is time that the meat CRC story was laid to rest, so that we can get back to recommending that young women of childbearing age eat meat as a ready source of available iron. (Hill, 2000) Nevertheless, it is sensible to consider that there must be an optimal range for meat intakes in order to ensure a balanced diet is achieved whilst optimal weight is maintained. From this practical perspective COMA’s (1998) suggested intake range of 90–140 g cooked meat per day is sensible as a public health message. The overemphasis on reducing meat, however, rather than encouraging greater accompanying plant food intake has served only to confuse the public (Hill, 1999b). Evidence suggests that the risk of cancer will be reduced to a greater extent by increasing intakes of fruit and vegetables than by lowering meat intakes. Once again, the move towards pre-prepared meal solutions provides opportunity for manufacturers to develop recipes with a healthy balance of meat and vegetable ingredients such that the nutritional profile of the dish is optimised. 9.4 Concerns about fat Regular consumption of red meat is associated epidemiologically with increased risk of coronary heart disease, due to its fat composition. Conversely, a growing bank of evidence is showing that a healthy diet that includes lean red meat can produce positive blood lipid changes (Watts et al, 1988; Scott et al, 1990; Davidson et al, 1999; Beauchesne-Rondeau et al, 1999). Blood cholesterol levels are increased by inclusion of beef fat, not lean beef in an otherwise low-fat diet. Equal amounts of lean beef, chicken, and fish added to low fat, low saturated fat diets, similarly reduce plasma cholesterol and LDL-cholesterol levels in hypercholesterolaemic and normocholesterolaemic men and women. Meat is a source of arachidonic acid (20:4n-6), both in the lean and visible fat components (Duo et al, 1998). Assumptions that the 20:4n-6 content of meat was responsible for increasing thrombotic tendencies in Western societies are too simplistic. The presence of large amounts of linoleic acid (18:2n-6) in current diets results in plasma increases of linoleic and arachidonic acids only. However, in the absence of linoleic acid, the long chain n-6 and n-3 PUFAs present in lean meat can influence the plasma pool, increasing plasma eicosatrienoic acid (20:3n- 6), 20:4n-6, and eicosapentanoic acid (20:5n-3), and probably reducing thrombotic tendencies. It is the imbalance of n-6: n-3 PUFAs in the diet, brought about by excessive 18:2n-6, that causes high tissue 20:4n-6 levels, so encouraging metabolism to eicosanoids (Sinclair et al, 1994; Mann et al, 1997). Meat contributes between a third and a half of the UK daily cholesterol intake (Chizzolini et al, 1999; British Nutrition Foundation, 1999). Meat’s cholesterol content is, for consumers, another negative influence on meat’s health image, although it is now accepted that dietary intake of cholesterol has little bearing on plasma cholesterol. A review of the cholesterol content of meat indicates surprisingly that levels of cholesterol are generally not higher in fatty meat or meat 214 The nutrition handbook for food processors

Enhancing the nutritional value of meat 215 products. The cholesterol content of a meat is related to the number of muscle fibres so tends to be higher the more red the muscle 9.5 Reductions in the fat content of red meat Twenty years ago red meat and meat products were identified as major contri butor to fat intake in the UK. Most of the visible(subcutaneous) fat in the meat was consumed. In the early 1980s the red meat industry began to shift produc tion systems to favour less fat, reflecting more energy-efficient animal husbandry For many years now there has been emphasis on reducing the fat content of our diets and this continued consumer demand for less fat further prompted the meat industry to consider ways of reducing the fat content of meat. The fat content of the carcase has been reduced in Britain by over 30% for pork, making British pork virtually the leanest in the world, 15% for beef and 10% for lamb, with further reductions anticipated for beef and lamb over the next 5-10 years. The fat content of fully trimmed lamb, beef and pork is now 890, 5% and 4%o respe tively( Chan et al, 1995) These achievements are due to three factors: selective breeding and feeding practices designed to increase the carcase lean to fat ratio; official carcase clas sification systems designed to favour leaner production; and modern butchery techniques(seaming out whole muscles, and trimming away all intermuscular fat). It is easier to appreciate the process and extent of fat reduction by looking at the changes over time for a single cut of meat such as a pork chop(Fig 9. 1) The reduction in fat for pig meat is well illustrated by the trend downwards in P2 fat depth between the 1970s and the 1990s(P2 is fat depth at the position of the last rib)(Fig. 9.2). Since 1992 it has remained stable at around ll mm. Although updated compositional figures for British meat were published from 1986 onwards(Royal Society of Chemistry, 1986: 1993; 1996; Meat and Livestock Commission and Royal Society of Chemistry, 1990), it is only since updated supplements to the McCance and widdowson tables were published in 1995( Chan et al, 1995 and 1996), that the achievement of the meat industry in reducing the fat content of meat has been more widely acknowledged( Depart- ment Of Health, 1994b: Scottish Office, 1996: Higgs, 2000) A fat audit for the UK, commissioned by the Government's Ministry of Agri culture, Fisheries and Food to trace all fat in the human food chain provides a more accurate picture than National Food Survey(NFS)(Ministry of Agriculture Fisheries and Food, 1981-99)data for identifying principal sources of fat in the diet, between 1982 and 1992(Ulbricht, 1995). It illustrates that whereas the fat contributed by red meat decreased by nearly a third, that from fats and oils as a group increased by a third to contribute nearly half of our fat intakes(Fig. 9.3) This striking picture is lost in NFS data since vegetable fats(in particular)are consumed within a broad range of end products-from chips(so here they are hidden within the vegetables section) to meat products (so here they artificially inflate the apparent fat contributed by meat)

products. The cholesterol content of a meat is related to the number of muscle fibres so tends to be higher the more red the muscle. 9.5 Reductions in the fat content of red meat Twenty years ago red meat and meat products were identified as major contributors to fat intake in the UK. Most of the visible (subcutaneous) fat in the meat was consumed. In the early 1980s the red meat industry began to shift production systems to favour less fat, reflecting more energy-efficient animal husbandry. For many years now there has been emphasis on reducing the fat content of our diets and this continued consumer demand for less fat further prompted the meat industry to consider ways of reducing the fat content of meat. The fat content of the carcase has been reduced in Britain by over 30% for pork, making British pork virtually the leanest in the world, 15% for beef and 10% for lamb, with further reductions anticipated for beef and lamb over the next 5–10 years. The fat content of fully trimmed lamb, beef and pork is now 8%, 5% and 4% respectively (Chan et al, 1995). These achievements are due to three factors: selective breeding and feeding practices designed to increase the carcase lean to fat ratio; official carcase classification systems designed to favour leaner production; and modern butchery techniques (seaming out whole muscles, and trimming away all intermuscular fat). It is easier to appreciate the process and extent of fat reduction by looking at the changes over time for a single cut of meat such as a pork chop (Fig. 9.1). The reduction in fat for pig meat is well illustrated by the trend downwards in P2 fat depth between the 1970s and the 1990s (P2 is fat depth at the position of the last rib) (Fig. 9.2). Since 1992 it has remained stable at around 11 mm. Although updated compositional figures for British meat were published from 1986 onwards (Royal Society of Chemistry, 1986; 1993; 1996; Meat and Livestock Commission and Royal Society of Chemistry, 1990), it is only since updated supplements to the McCance and Widdowson tables were published in 1995 (Chan et al, 1995 and 1996), that the achievement of the meat industry in reducing the fat content of meat has been more widely acknowledged (Department Of Health, 1994b; Scottish Office, 1996; Higgs, 2000). A fat audit for the UK, commissioned by the Government’s Ministry of Agriculture, Fisheries and Food to trace all fat in the human food chain provides a more accurate picture than National Food Survey (NFS) (Ministry of Agriculture, Fisheries and Food, 1981–99) data for identifying principal sources of fat in the diet, between 1982 and 1992 (Ulbricht, 1995). It illustrates that whereas the fat contributed by red meat decreased by nearly a third, that from fats and oils as a group increased by a third to contribute nearly half of our fat intakes (Fig. 9.3). This striking picture is lost in NFS data since vegetable fats (in particular) are consumed within a broad range of end products – from chips (so here they are hidden within the vegetables section) to meat products (so here they artificially inflate the apparent fat contributed by meat). Enhancing the nutritional value of meat 215

218 The nutrition handbook for food processors health. Fatty acids play a role in many conditions such as CHD, cancer, obesity, diabetes and arthritis. These roles can be protective, causative or relatively neutral, depending on the disease, the fatty acid, and the opposing effects of other dietary components. Current dietary advice emphasises balancing the intake of the different fatty acids. The Department of Health( COMA, 1994)has recom mended a reduction in the intake of saturated fat and an increase in the intake of unsaturated fat. Within the unsaturated fatty acids it is recommended to increase he omega-3(n-3) PUFAS relative to the omega-6(n-6) PUFAS 9.6.1 Saturated fatty acids Probably the main misconception about meat fat is that it is assumed to be totally saturated. Meat contains a mixture of fatty acids both saturated and unsaturated and the amount of saturated fat in meat has been reduced in recent years. At the present time, less than half the fat in pork and beef and 51% of the fat in lamb is saturated. The saturated fat contributed to the diet from red meat and meat products has gradually fallen from 24%o in 1979 to 19.6% in 1999. Carcase meats now provide 6.7% of total saturated fat intake(Ministry Of Agriculture Fisheries And Food, 1981). In reality, even this figure is an overestimate, since there is a disproportionate wastage in terms of trimming, cooking losses and plate waste (Leeds et al, 1997) The predominant saturated fatty acids in meat are stearic acid(C18: 0) and palmitic acid (C16: 0). In general terms, saturated fats are known as the" fats as they tend to raise blood cholesterol and cause atherosclerosis. However, not all saturated fats are equal in their effects on blood cholesterol. For instance, stearic acid does not appear to raise blood cholesterol (Bonanome and Grund 1988)or other thrombotic risk factors(Kelly et al, 1999, 2001). Stearic acid prominent saturated fat in meat, for example; it accounts for approximately one third of the saturated fat in beef. Similarly, palmitic acid, another major saturated fat in meat does not consistently raise blood lipids. On the other hand, myristic acid(C14: 0)is the most atherogenic fatty acid, having four times the cholesterol raising potential of palmitic acid(Ulbricht, 1995). Myristic acid is found only in minor quantities in meat 9.6.2 Monounsaturated fatty acids Meat contains a mixture of unsaturated fatty acids, polyunsaturated fatty acids and monounsaturated fatty acids(MUFAs ). MUFAs are the dominant unsaturated fatty acid in meat and they account for approximately 40%o of the total fat in meat It is a neglected fact that meat and meat products are the main contributors to 1UFAS in the British diet, supplying 27% of total MUFA intake(Ministry Of Agriculture Fisheries And Food, 1999). MUFAs are considered to be neutral with respect to blood cholesterol levels. The principal MUFA in meat is oleic acid (cis C18: 1n-9), which is also found in olive oil and is associated with the health Mediterranean diet

health. Fatty acids play a role in many conditions such as CHD, cancer, obesity, diabetes and arthritis. These roles can be protective, causative or relatively neutral, depending on the disease, the fatty acid, and the opposing effects of other dietary components. Current dietary advice emphasises balancing the intake of the different fatty acids. The Department of Health (COMA, 1994) has recommended a reduction in the intake of saturated fat and an increase in the intake of unsaturated fat. Within the unsaturated fatty acids it is recommended to increase the omega-3 (n-3) PUFAs relative to the omega-6 (n-6) PUFAs. 9.6.1 Saturated fatty acids Probably the main misconception about meat fat is that it is assumed to be totally saturated. Meat contains a mixture of fatty acids both saturated and unsaturated and the amount of saturated fat in meat has been reduced in recent years. At the present time, less than half the fat in pork and beef and 51% of the fat in lamb is saturated. The saturated fat contributed to the diet from red meat and meat products has gradually fallen from 24% in 1979 to 19.6% in 1999. Carcase meats now provide 6.7% of total saturated fat intake (Ministry Of Agriculture Fisheries And Food, 1981). In reality, even this figure is an overestimate, since there is a disproportionate wastage in terms of trimming, cooking losses and plate waste (Leeds et al, 1997). The predominant saturated fatty acids in meat are stearic acid (C18:0) and palmitic acid (C16:0). In general terms, saturated fats are known as the ‘bad’ fats as they tend to raise blood cholesterol and cause atherosclerosis. However, not all saturated fats are equal in their effects on blood cholesterol. For instance, stearic acid does not appear to raise blood cholesterol (Bonanome and Grundy, 1988) or other thrombotic risk factors (Kelly et al, 1999, 2001). Stearic acid is a prominent saturated fat in meat, for example; it accounts for approximately one third of the saturated fat in beef. Similarly, palmitic acid, another major saturated fat in meat does not consistently raise blood lipids. On the other hand, myristic acid (C14:0) is the most atherogenic fatty acid, having four times the cholesterol raising potential of palmitic acid (Ulbricht, 1995). Myristic acid is found only in minor quantities in meat. 9.6.2 Monounsaturated fatty acids Meat contains a mixture of unsaturated fatty acids, polyunsaturated fatty acids and monounsaturated fatty acids (MUFAs). MUFAs are the dominant unsaturated fatty acid in meat and they account for approximately 40% of the total fat in meat. It is a neglected fact that meat and meat products are the main contributors to MUFAs in the British diet, supplying 27% of total MUFA intake (Ministry Of Agriculture Fisheries And Food, 1999). MUFAs are considered to be neutral with respect to blood cholesterol levels. The principal MUFA in meat is oleic acid (cis C18:1n-9), which is also found in olive oil and is associated with the healthy Mediterranean diet. 218 The nutrition handbook for food processors