Chapter 3 - Meat and health

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Meat consumption role of meat in the diets

Meat consumption

Meat consumption is based largely on availability, price and tradition. Meat production is a very complex operation depending not only on demand (which is usually based on price and income) but on many social and economic influences such as official policy, price support mechanisms, and interrelations such as the interaction between beef and milk production, the availability of animal feedstuffs and competition for food between man and animals.

It is difficult to make accurate comparisons of meat consumption between countries because different methods are used to estimate consumption. Figures may be derived from total supplies available at wholesale level, or from records of household purchases, with or without estimates of what is consumed away from home; the estimate of waste, both in preparation of the food and by the individual adds to the uncertainty. Some national estimates fail to include imports, and some surveys include the weight of non-meat components of the products (for example the amount of meat in a product can range between 100% in some burgers to 10% in some pizzas). FAO Food Balance Sheets are prepared from figures for production, imports, stock changes and exports with allowances for feed, processing and "other uses" and the same methods are applied to all regions so that the figures, as in Table 1-1A, are comparable.

Up to a certain level of income the amount of meat eaten varies with income, in the relatively affluent western world where the proportion of available income spent on food has been steadily falling over the past generation, there is now little if any difference between the amounts of meat eaten by the different income groups. This contrasts with the Third World countries (FAO 1990a).

The amount of meat consumed in different countries varies enormously with social, economic and political influences, religious beliefs and geographical differences. It is very large in meat-producing areas such as Uruguay, Argentina, Australia and New Zealand, at 300 g per head per day compared with an average of 10 g in India Indonesia and Sri Lanka Table 1-1A shows the contrast between total meat supplies in developed and developing countries, allowing for exports, imports and stock changes, and Table 3-1 shows that the production per capita in the former is five times as much as in the developing countries. These tables also show the relative size of production of the different types of animals involved.

Role of meat in the diet of developed and developing countries

Meat is held in high esteem in most communities. It has prestige value, it is often regarded as the central food round which meals are planned, various types of meat are sometimes made the basis of festive and celebratory occasions, and from the popular as well as the scientific point of view, it is regarded as a food of high nutritive value.

While it is clear that meat is not essential in the diet, as witness the large number of vegetarians who have a nutritionally adequate diet, the inclusion of animal products makes it easier to ensure a good diet.

There is a marked difference at the present time in attitudes towards meat between the people of the developing and industrialised communities In the former where meat is in short supply it can be taken as a measure of the nutritional quality of the diet as a whole. Where a typical diet is heavily dependent on one type of cereal or root crop, meat, even in small amounts, complements the staple food. It provides a relatively rich source of wellabsorbed iron and also improves the absorption of iron from other foods, its amino acid composition complements that of many plant foods, and it is a concentrated source of B vitamins, including vitamin B12 which is absent from plant foods. Consequently there is pressure to increase the availability of meat products.

In the industrialised countries where food of all kinds is plentiful and cheap there is concern, whether or not misplaced, about the potentially harmful effects of a high intake of saturated fat from animal foods (discussed later), emphasis on continuous development of regulations dealing with hygiene in slaughter houses and during subsequent handling, concern about hormones administered to cattle, what is perceived as excessive addition of water to some processed products - concerns that can scarcely be afforded in developing countries when balanced against food supplies.

With increasing mechanisation in industrialised communities the steady fall in human energy expenditure and consequently in per capita food consumption poses a potential problem in achieving an adequate intake of nutrients even where there is an abundance of food available. With the variety of food available a diet of 8 Ml (2000 kcal) or more per day is likely to supply enough of all the nutrients, but when the intake is 6.5 to 7 MJ (1600-1800 kcal) per day the consumer needs to make an informed choice of foods to ensure an adequate intake of nutrients.

In western Europe the daily average energy intake of women is about 6.5 Ml and that of men 8 MJ (excluding alcohol) and there are reports of biochemical signs of deficiencies of several B vitamins and iron. It is not clear whether this is accompanied by functional defects.

In industrialised countries there have been slow but continuous changes over the years in the relative amounts of different types of meat consumed (beef, pork, lamb, poultry) depending partly on price and influenced by fashion, advertising, etc. In more recent years health aspects, more correctly, perceived health aspects, have become a factor.

The concerns about public health in industrialised countries where coronary heart disease and other "diseases of affluence. are common have led to recommendations to the public to modify their diet, popularised as Dietary Guidelines. These particularly recommend a reduction in fat consumption, especially saturated fatty acids and consequently, even if incorrectly, in red meat (discussed later). This has led in some sections of their populations to a relative increase in the consumption of poultry and fish at the expense of red meat.

In addition there is concern, whether or not misplaced, about the presence in meat of pesticides, residues of hormones and growth promoters used to increase yields, and concern about human diseases thought to be transmitted by beef, together with an increase, for many reasons, in vegetarianism.

Meat as a source of protein

Human Protein Requirements

Human requirements for protein have been thoroughly investigated over the years (FAD/WHO 1985) and are currently estimated to be 55 g per day for adult man and 45 g for woman. (There is a higher requirement in various disease states and conditions of stress).

These amounts refer to protein of what is termed "good quality" and highly digestible, otherwise the amount ingested must be increased proportionately to compensate for lower quality and lower digestibility.

Protein Quality

The quality of a protein is a measure of its ability to satisfy human requirements for the amino acids. All proteins, both dietary and tissue proteins, consist of two groups of amino acids - those that must be ingested ready-made, i.e. are essential in the diet, and those that can be synthesised in the body in adequate amounts from the essential amino acids. Eight of the 20 food amino acids are essential for adults and ten for children.

The quality of dietary protein can be measured in various ways (FAD/WHO 1991) but basically it is the ratio of the available amino acids in the food or diet compared with needs. In the earlier literature this was expressed on a percentage scale but with the adoption of the S.I. system of nomenclature it is expressed as a ratio. Thus a ratio of 1.0 (100 per cent) means that the amino acids available from the dietary proteins are in the exact proportions needed to satisfy human needs; a ratio of 05 means that the amount of one (or more) of the essential amino acids present is only half of that required. If one essential amino acid is completely absent (a circumstance that can occur only experimentally with isolated proteins since any food, let alone a whole diet, consists of a mixture of many proteins) the protein quality would be zero.

There is a popular impression, originating at one time from nutrition textbooks, that the qualities of proteins from animal sources are greatly superior to those from plant sources. This is true only to the extent that many animal sources have Net Protein Utilisation, NPU, (a measure of the usefulness of the protein to the body) around 0.75 while that of many, but not all plant foods is 0.5-0.6. However, after infancy people consume a wide variety of proteins from different foods and a shortfall in any essential amino acids in one food is usually made good, at least in part, by a relative surplus from another food - this is termed complementation. As a result the protein quality of whole diets even in developing countries rarely falls below NPU of 0.7, a value that can be compared with the average of 0.8 in industrialised countries (FAD/WHO 1985).

The value of meat in this respect is that it is a relatively concentrated source of protein, of high quality (NPU 0.75-0.8), highly digestible, about 0.95 compared with 0.8-0.9 for many plant foods, and it supplies a relative surplus of one essential amino acid, lysine which is in relatively short supply in most cereals.

Effect of Cooking on Protein Quality

Apart from the inherent quality of the various proteins a reduction in quality takes place if there is damage to amino acids when the food is cooked. At a temperature below 100C when proteins are coagulated, there is no change in nutritional quality.

The first changes take place when food is heated to temperatures around 100C in the presence of moisture and reducing sugars, present naturally or added to the food. There is a chemical reaction between part of one essential amino acid, lysine and a sugar to form a bond that cannot be broken during digestion, and so part of the lysine is rendered unavailable.

When proteins are analysed in order to determine their amino acid composition the procedure involves a preliminary hydrolysis with strong acid which does break the lysinesugar bond, so chemical analysis does not reveal this type of damage and special methods are needed. At a higher temperature or with more prolonged heating, the lysine in the food protein can react with other chemical groupings within the protein itself and more becomes unavailable. In addition the sulphur amino acids (cystine which is not essential and methionine which is) are rendered partly unavailable.

The lysine-sugar reaction results in a brown-coloured compound (the so-called browning or Maillard reaction) which produces an attractive flavour in food and is the main cause of the colour of bread crust and roast meat. While such severe heating reduces the amount of lysine available in these foods the loss is nutritionally insignificant since it affects only a very small fraction of the total amount present.

At the temperature needed to cook meat there is little loss of available lysine or the sulphur amino acids but there can be some loss if the meat is heated together with reducing substances, as may be present when meat is canned with the addition of starch-containing gravy or other ingredients.

Overall the damage to protein caused by cooking is of little practical significance and it can be argued that if there is meat in the diet it is likely that the quantity of protein would compensate for any shortfall in quality.

The nutritional quality of the proteins of meat rich in connective tissue is low since collagen and elastin are poor in the sulphur amino acids - there is only 0.8 g of each per 100 g of total protein compared with values of 2.6 and 1.3 of each respectively in "good meat. Meat is tough to eat when it is rich in connective tissue and such meat is often used for canning since the relatively high temperature involved in the sterilisation process partly hydrolyses the collagen so making the product more palatable. However, it still results in a product with NPU as low as 0.5 compared with a value of 0.75 - 0.8 for good quality meat (Bender and Zia 1976).

Adequacy of Dietary Protein

The protein requirement of an individual is defined as the lowest level of protein intake that will balance the loss of nitrogen from the body in persons maintaining energy balance at modest levels of physical activity (FAD/WHO 1985). The "requirement" must allow for desirable rates of deposition of protein during growth and pregnancy. When energy intake is inadequate some of the dietary protein is diverted from tissue synthesis to supply energy for general physical activity - this occurs at times of food shortage and also in disease states where food is incompletely absorbed and utilised.

A diet adequate in energy is almost always adequate in protein - both in quantity and quality. For example, an adult needs an amount of protein that is equivalent to 7 - 8% of the total energy intake, and since most cereals contain 8 - 12% protein even a diet composed entirely of cereal would, if enough were available and could be consumed to satisfy energy needs, satisfy protein needs at the same time. Growing children and pregnant and nursing mothers have higher protein requirements as do people suffering from infections, intestinal parasites and conditions in which protein catabolism is enhanced. During the stress that accompanies fevers, broken bones, burns and other traumas there is considerable loss of protein from the tissues which has to be restored during convalescence and so high intakes of protein are needed at this time together with an adequate intake of energy.

The digestibility of the proteins of various diets varies considerably. For example, the digestibility of typical Western diets and Chinese diets is 0.95 (i.e. 95% digested). That of the Indian rice diet and Brazilian mixed diet is 0.8 (FAD/WHO 1985). Digestibility is high in diets that include milk and meat and low when maize and beans predominate.

An increase in the amount of protein eaten beyond "requirement" figures compensates for any shortfall in digestibility and protein quality.

Meat as a source of vitamins and minerals

Meat and meat products are important sources of all the B-complex vitamins including thiamin, riboflavin, niacin, biotin, vitamins B6 and B12, pantothenic acid and folacin. The last two are especially abundant in liver which, together with certain other organs is rich in vitamin A and supplies appreciable amounts of vitamins D, E and K.

Meats are excellent sources of some of the minerals, such as iron, copper, zinc and manganese, and play an important role in the prevention of zinc deficiency, and particularly of iron deficiency which is widespread.

Meat Iron

The amount of iron absorbed from the diet depends on a variety of factors including its chemical form, the simultaneous presence of other food ingredients that can enhance or inhibit absorption, and various physiological factors of the individual including his/her iron status. Overall, in setting Recommended Daily Intakes of nutrients the proportion of iron absorbed from a mixed diet is usually taken as 10%.

Half of the iron in meat is present as haeme iron (in haemoglobin). This is well absorbed, about 15-35%, a figure that can be contrasted with other forms of iron, such as that from plant foods, at 1-10%.

Not only is the iron of meat well absorbed but it enhances the absorption of iron from other sources - e.g. the addition of meat to a legume/cereal diet can double the amount of iron absorbed and so contribute significantly to the prevention of anaemia, which is so widespread in developing countries.

Zinc is present in all tissues of the body and is a component of more than fifty enzymes.

Meat is the richest source of zinc in the diet and supplies one third to one half of the total zinc intake of meat-eaters. A dietary deficiency is uncommon but has been found in adolescent boys in the Middle East eating a poor diet based largely on unleavened bread.

Health concerns associated with the consumption of meat

Coronary or Ischaemic Heart Disease

A major cause of death in some parts of the industrialised world is coronary heart disease (CHD) and saturated fatty acids have been implicated as an important dietary risk factor. Since about a quarter of the saturated fatty acids in the diet is supplied by meat fat, the consumption of meat itself has come under fire.

The first stage of development of the disease is a narrowing of the coronary arteries by deposition of a complex fatty mixture on the walls - a process termed atherosclerosis. The fatal stage is the formation of a blood clot that blocks the narrowed artery thrombosis. Even if the thrombosis is not fatal the reduced blood flow to the heart muscle deprives it of oxygen and can lead to extensive damage - myocardial infarction.

Despite many years of intensive investigation the real cause of CHD is not known but a large number of what are termed risk factors have been identified, including a family history of CHD, smoking, lack of exercise, various types of stress and certain disease states together with a number of dietary factors. The saturated fatty acids, myristic and palmitic, have been established as the most important of the dietary risk factors in coronary heart disease.

There are three types of lipoproteins (protein-lipid complexes) in the blood; low density lipoproteins (LDL) in which 46% of the molecule is cholesterol; high density lipoproteins (HDL) which include 20% as cholesterol; and very low density lipoproteins (VLDL) which have 8% cholesterol. High levels of total blood cholesterol are associated with the incidence of CHD and high intakes of saturated fatty acids elevate blood cholesterol levels: hence the association between dietary saturated fatty acids and CHD. It is the LDL that appear to be the main problem and HDL appear to be protective.

This lipid hypothesis of causation of CHD has led to the adoption in many countries of dietary guidelines which, among other objectives, are intended to reduce the intake of saturated fatty acids as compared with unsaturated fatty acids and so reduce blood levels of LDL.

Types of Fatty Acids

Saturated Fatty Acids (SFA)

Two of the saturated fatty acids, myristic and palmitic acids, appear to be the principal dietary factors that increase the blood cholesterol and do so by increasing LDL The other main SFA in the diet, stearic acid, does not have the same effect (apparently because it is converted to oleic acid which is monounsaturated - see below); fatty acids of shorter chain length appear to have no effect.

In order to explain the terms saturated and unsaturated fatty acids to the consumer, SFA have been equated with animal fats so meat fat is perceived as being saturated, but, in fact, this is only relative. For example pork lard is 40% SFA, beef tallow is 43-50% SFA, depending on the part of the body from which it is derived. These figures can be compared with 20 - 25% SFA in vegetable oils which are perceived as unsaturated. Table 3-2 shows that except for lamb fat the proportion of SFA is about 40% or less. In four of the six samples of meat listed there is a higher proportion of monounsaturates than SFA.

This perception of meat fat as being saturated has led to the belief that meat, particularly red meat, should be avoided. In fact it has been shown that a reduction of total fat intake while still including in the diet 180 g of lean meat containing 8.5% fat can result in a reduction in blood cholesterol levels (Watts et al 1988). The relation between diet and coronary heart disease is not only a subject of considerable misunderstanding in the minds of consumers but also a subject of some controversy among medical scientists.

Monounsaturated Fatty Acids (MUFA)

The fatty acid of main interest is oleic acid (plentiful in olive, rape seed and higholeic safflower oils). The relatively high intake of olive oil and consequently the proportionately low intake of SFA are believed to be important dietary factors in the low incidence of CHD in Mediterranean countries compared with northern Europe. It is not clear whether oleic acid confers direct protection or simply replaces SFA in the diet. Table 3-2 shows the contribution of meat fat to the intake of MUFA.

Polyunsaturated Fatty Acids (PUFA)

These are fatty acids with between 2 and 6 double bonds and long carbon chains of 18 to 22 carbon atoms (Table 3-3). Linoleic acid (18 carbon atoms and 2 double bonds) and linolenic acid (18 carbon atoms and 3 double bonds) are plentiful in many vegetable oils. The very long chain fatty acids, eicosatetraenoic (20C, 4 double bonds) and docosapentaenoic (22 C, 5 double bonds) are plentiful in fish oils and smaller amounts are present in some meat fats.

These very long chain PUFA appear to offer direct protection against "heart disease", particularly against thrombosis, but it is not clear whether the other PUFA in the diet (from vegetable oils) offer protection or simply displace SFA. Consequently it is often recommended that vegetable oils (rich in PUFA) should not simply be added to a diet but should be used to replace other fats when there is a need for fat in formulating food products.

Linoleic and linolenic acids are essential in the diet (they were at one time termed vitamin F) and the very long chain FA are formed from them in the body. It is possible that the rate of their formation may not be adequate under all circumstances and so there may be benefit from consuming some of these very long chain PUFA ready-made in the diet.

Trans Fatty Acids

PUFA exist in nature in two structural forms, termed cis and bans forms. It is the cis forms that are used in the production of fatty products such as special margarines. The other forms, bans, are formed when oils are hydrogenated to make hard fats for some margarines, and small amounts are found in the fats of ruminants where they are formed by bacterial hydrogenation in the rumen.

Experimentally bans fatty acids have been shown to have an adverse effect on both LDL and HDL and so are considered potentially harmful. When calculating the ratio of PUFA and SFA in diets, the bans fatty acids are often included with SFA.

Cholesterol

Cholesterol is a fatty compound involved in the transport of fat in the blood stream and is also part of the structure of cell membranes of tissues of the body. It is not a dietary essential since adequate amounts are synthesised in the body from other dietary ingredients.

Confusion has arisen between the terms blood cholesterol and dietary cholesterol. For most individuals dietary cholesterol has little or no effect on blood cholesterol levels because reduced synthesis in the body compensates for increased dietary intake. However, there are individuals who are sensitive to dietary cholesterol (Reiser and Shorland 1990) and most authorities advise a general reduction in cholesterol intake for everyone.

Meat supplies about one third of the dietary cholesterol in many western diets with the remainder from eggs and dairy products. Since all these foods are valuable sources of nutrients there could be some nutritional risk in restricting their intake. The cholesterol content of meat and other foods is listed in Chapter 2, Table 2-7.

In addition to playing an important role in CHD dietary saturated fats have been implicated in hypertension, stroke, diabetes and certain forms of cancer, so all dietary guidelines include recommendations to reduce total fat intake and especially that of saturated fats.

Some 20 national authorities have issued dietary guidelines which differ mainly in the amounts of the various foods advised (James 1988). Generally it is recommended that total fat should be reduced to 20-30% of the total energy intake, with not more than 10% from saturates, 10-15% from MUFA and with PUFA at 3% or more; this results in a P/S ratio of 1.0.

Most authorities, but not all, recommend a reduction in dietary cholesterol to around 300 mg or less per day.

Poultry Meat versus Read Meat

Dietary guidelines sometimes include advice to substitute, at least in part, chicken for red meat. Chicken meat including its skin contains about the same amount of fat as does medium-fat red meat, 20%; it is necessary to remove the skin with the adhering subcutaneous fat, to reduce the fat content to around 5% - which is no lower than the figure for lean meat.

However, chicken flesh has less saturated fatty acids (33% of the total) and more PUFA (14%) than lean meat with 45% and 4% respectively.

Duck flesh is very fat, containing about 10% fat - 45% when the skin and subcutaneous fat are included; only 27% of duck fat is saturated.

Meat from game birds, grouse, partridge, pheasant and pigeon, contains about 5, 7, 9, and 13% fat respectively, of which about one quarter is saturated.

Apart from differences in the amounts and types of fatty acids in the various kinds of meat, poultry and game their nutrient compositions are similar.

Toxic compounds formed during processing and cooking

While cooking is necessary to develop the desirable flavours in meat (as well as to destroy harmful organisms) the oxidation of fats, especially at frying temperatures, can give rise to compounds that decompose to aldehydes, esters, alcohols and short chain carboxylic acids with undesirable flavours.

Meats are particularly susceptible because of the unsaturated lipids present which are more readily oxidised and because of catalysis by haeme and non-haeme iron.

The more PUFA present the greater the likelihood of oxidation, and pork (3.6 g PUFA/100 g when grilled), duck (meat and skin, cooked, 3.5 g) and chicken (roast meat and skin, 2.5 g) are the most susceptible. Other types of meat are less susceptible, e.g. Iamb (grilled cutlets, 1.5 g PUFA), turkey (meat with skin, 1.3), and beef (fried steak, 0.6 g per 100 g).

The adverse effect of these oxidation products on eating quality is well recognised but more recently it has been suggested that some of them may be carcinogenic, and also may be involved in the ageing process and CHD. However, it is possible or even likely that the unpleasant flavours would cause rejection of the food at levels below harmful ranges.

Cholesterol can also be oxidised and the oxidation product has been suggested as a possible factor in CHD (Addis 1986).

Carcinogens

A number of epidemiological studies have suggested a link between the intake of animal protein and predisposition to cancers at various sites -pancreas, breast, colon, prostate and endometrium - but there are many contradictory reports. A summary of eleven case-controlled studies of colon cancer, three of stomach cancer and one of breast cancer concluded that the available data do not provide convincing evidence that removal of meat from the diet would substantially reduce the cancer risk (Phillips et al 1983; Kritchevsky 1990).

The products of pyrolysis of organic material (by overheating and charring), polycyclic hydrocarbons, are believed to be carcinogenic. The most thoroughly investigated of these is 3,4-benzpyrene which is formed on the surface of barbecued and broiled (grilled) and smoked meat products (including broiled fish and roasted coffee).

The main source of these compounds is the flame itself, especially from charcoal, and indirect cooking where the flame is not in contact with the food greatly reduced the amount present.

Nitrosamines

Nitrites, used in curing salts can react with amines commonly present in food, to form nitrosamines.

These have been shown to be carcinogenic in all species of animals examined but it is not clear, despite years of intensive research, whether the amounts present in cured meats affect human beings. The problem is particularly difficult because nitrosamines have been found in human gastric juice, possibly formed from nitrites and amines naturally present in the diet. As a precaution, legally enforced in some countries, there is a tendency to reduce the amount of nitrite used in the curing mixture and to add vitamin C which inhibits the formation of nitrosamines.

Erythorbic acid and tocopherol are also effective in reducing nitrosamine formation. The problem is complex since the process of curing is designed to prevent the growth of Clostridium botulinum which is responsible for botulism, and the risk of botulism is increased if the concentration of nitrate-nitrite is reduced too far. (Moreover, cigarettes contribute far greater amounts of nitrosamines, up to one hundred times as much as cured meats).

Other potential problems

Bovine Spongiform Encephalopathies (BSE)

There is a group of diseases called prion disease, also known as spongiform encephalopathies or transmissable dementias, which include some very rare human diseases, scrapie in animals and BSE. It is not clear whether these all represent the same disease but they have in common the presence of an aberrant form of a normal cell protein called prion protein.

In some countries there have been recent outbreaks of BSE in cattle with the suspicion that it might be transmitted to human beings through affected meat.

This is difficult to prove or disprove and the risk may be remote but it has added to other popular suspicions about meat and may be partly responsible for the reduction in beef consumption in some countries.

Excessive Amounts of Vitamin A in Liver

There are reports in the scientific literature of harmful effects of acute and chronic excessive intakes of vitamin A, mostly from pharmaceutical preparations. Recently, however, concern has been expressed at unusually high levels of vitamin A found in some, few, samples of animal liver, which, if eaten during the early stages of pregnancy, might possibly affect the human foetus.

Residues of Drugs. Pesticides. etc.

Residues of drugs, pesticides and agricultural chemicals can be found in small amounts in meat and meat products. Pesticides, for example, may be applied specifically to the animals to control insects or intestinal parasites but may also be present in meat as a result of exposure of the animals to chemicals used on buildings, grazing areas and crops. While there is no clear evidence that these small amounts cause harm to the consumer they are perceived as a risk. For this reason there is widespread legislation to test for and control a range of chemical substances that may be present in meat (Codex 1991A).

The problem is complicated because several hundred substances are used to treat animals, to preserve animal health and to improve animal production. These include antimicrobial agents, beta-adrenoreceptor blocking agents (used to prevent sudden death in pigs due to stress during transport) anti-helminthics, tranquillizers, anti-coccidial agents, vasodilators and anaesthetics.

Potential safety problems arise from the possibility of residues of these drugs and their metabolites remaining in the tissues (and milk) consumed by human beings. Some tranquillizers, for example, are used in pigs in the immediate pre-slaughter period when there is no time for their removal through the normal metabolic processes . They can persist in the human body so that repeated intakes could possibly result in accumulation of the drugs.

In order to protect the consumers from such risks the Codex Alimentarius Commission publishes Draft Codes of Practice for control of the use of veterinary drugs (Codex 1991A). These provide guidelines for the prescription, application, distribution and control of drugs.

Where there is sufficient scientific information available about the drug in question the Codex Commission defines the following:- Acceptable Daily Intake (ADI) as a measure of the amount of a veterinary drug, expressed on a body weight basis, that can be ingested over a life-time without appreciable health risk (the same term and definition as used for food additives). This is set at one hundredth of the maximum no-observed-effect level (NOEL) determined in experimental animals, on the assumption that human beings may be ten times as sensitive as the test animals used to determine NOEL and that there may be a tenfold range of sensitivity within the human population. When data are incomplete the safety factor may be set at a much higher multiple.

The maximum amount of residue of a drug - maximum residue limit (MRL) - is the maximum concentration per kg fresh weight of food that is recommended by the Codex Commission as being legally acceptable. This is based on the amount considered to be without any toxicological hazard to human health and takes account of other relevant public health risks as well as food technological aspects.

A point is made in the 1991 report that the principal problem is not only the safety of the substances and their residues but the public perception of their safety.

There is no doubt that administration of drugs to animals (and birds) is always a potential risk to human health and so there is a need to control the use of these drugs and to measure the extent of any residues left in the food intended for human beings.

Conclusion

Meat is not an essential part of the diet but without animal products it is necessary to have some reasonable knowledge of nutrition in order to select an adequate diet. Even small quantities of animal products supplement and complement a diet based on plant foods so that it is nutritionally adequate, whether or not there is informed selection of foods.

Side by side with these known benefits of including meat and meat products in the diet are problems associated with excessive intakes of saturated fats, risks of food poisoning from improperly processed products, residues of chemicals used in agriculture and animal production and other potentially adverse aspects discussed.

Within these concepts is the major problem of meat production under conditions that avoid food poisoning and satisfy the economic demands of profitability with the traditional, cultural and religious concerns of the community in question.

There is a steadily increasing demand for meat in the developing countries which can be satisfied by increased domestic consumption and/or increased imports. It is thought that the major increase in domestic production will come from small producers rather than from creating large production units but these lack the essential facilities for producing safe and wholesome products.

If there is to be a significant increase in meat production it will require clear policy decisions with the necessary financial, legislative and technical support. There is considerable potential for increased supplies through better management, selection of animals, avoidance of waste and making use of indigenous species.

If exports are to be considered then attention has to be paid to the strict hygienic and safety requirements involved, whatever the domestic market might tolerate.


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