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

Enhancing the nutritional value of meat J. D. Higgs, Food To Fit; and B. Mulvihill 9.1 Introduction The most common dietary problems in developed countries are due mainly to over nutrition. The incidence of overweight, obesity and adult onset-diabetes is increasing steadily. Cancer is now the most common cause of death in many developed countries. The most common cancers are breast, lung, bowel and prostate, which are virtually absent in some developing countries. However,even in our affluent society, we also see signs of nutritional inadequacies. For instance in the UK nearly half of females aged between 1l and 14 are not getting enough iron in their diet, while more than a third are not getting enough zinc( Gregory et al, 2000). We are living in a society where both signs of over-and under nutrition occur side by side. To correct for these nutritional paradoxes we as consumers have to get the balance of nutrients, energy and physical activity right he objective of this chapter is to highlight the nutritional role that meat can play in modern societ The National Food Survey for 1999(Ministry of Agriculture Fisheries and Food, 1999)included a special analysis on meat and meat products consumption in the UK. It stated that 'meat, meat products. are important contributors to the intakes of many nutrients in the British diet. Data from this survey showed that meat and meat products supply: energy 15%0, protein 30%, fat 22%(SFA 22%,MUFA27%,PUFA15%), vitamin d19%,B214%,B621%,B1222%, vitamin A equivalents 20%, niacin 37%, zinc 30%o, iron 149 Meat has been a major part of the human diet for at least 2 million years Human genetic make-up and physical features have been adapted over 4.5 million years for a diet containing meat. An example of this adaptation is our present teeth and jaw structure, that has developed to become efficient at chewing and

9 Enhancing the nutritional value of meat J. D. Higgs, Food To Fit; and B. Mulvihill 9.1 Introduction The most common dietary problems in developed countries are due mainly to over nutrition. The incidence of overweight, obesity and adult onset-diabetes is increasing steadily. Cancer is now the most common cause of death in many developed countries. The most common cancers are breast, lung, bowel and prostate, which are virtually absent in some developing countries. However, even in our affluent society, we also see signs of nutritional inadequacies. For instance, in the UK nearly half of females aged between 11 and 14 are not getting enough iron in their diet, while more than a third are not getting enough zinc (Gregory et al, 2000). We are living in a society where both signs of over- and under￾nutrition occur side by side. To correct for these nutritional paradoxes we as consumers have to get the balance of nutrients, energy and physical activity right. The objective of this chapter is to highlight the nutritional role that meat can play in modern society. The National Food Survey for 1999 (Ministry of Agriculture Fisheries and Food, 1999) included a special analysis on meat and meat products consumption in the UK. It stated that ‘meat, meat products... are important contributors to the intakes of many nutrients in the British diet’. Data from this survey showed that meat and meat products supply: energy 15%, protein 30%, fat 22% (SFA 22%, MUFA 27%, PUFA 15%), vitamin D 19%, B2 14%, B6 21%, B12 22%, vitamin A equivalents 20%, niacin 37%, zinc 30%, iron 14%. Meat has been a major part of the human diet for at least 2 million years. Human genetic make-up and physical features have been adapted over 4.5 million years for a diet containing meat. An example of this adaptation is our present teeth and jaw structure, that has developed to become efficient at chewing and

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 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 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 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, 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 prod￾ucts 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 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 190 000 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). 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 scien￾tific 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 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 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 popu￾Enhancing 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 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 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 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 (PhIP), which is a relatively weak carcinogen compared to other heterocyclic amines such as IQ and MeIQ. 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%, 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 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 and cereals that are the main determinants of CRC risk with meat being coinci￾dentally related. There is a need to assess the role of meat when consumed in normal quanti￾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￾gressive 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