How Does the Compeosition of Poultry Meat Compare to Beef and Pork

Meat, poultry, and fish composition: Strategies for optimizing human intake of essential nutrients

S. De Smet

1Laboratory for Animal Nutrition and Animal Product Quality, Faculty of Bioscience Engineering, Ghent University, Belgium

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Published:

01 October 2012

Abstract

• Muscle-based food items from farm animals, poultry, and fish contribute significantly to the human intake of essential nutrients (protein, long chain n-3 fatty acids, several trace elements, and most B vitamins) worldwide. The contribution of a food item to the intake of a particular nutrient in a given environment depends on both its level of consumption and its composition.

• Meat, poultry, and fish contribute relatively more to the human intake of protein than calories. In intensive production systems, the body fat content of farm animals has decreased considerably by quantitative genetics selection and optimization of feeding. This has resulted in a concomitant reduction in intramuscular lipid content, which is now generally less than 5% in farm animals, whereas the lipid content of muscle from fish is much more variable. On the other hand, storage fat depots are extensively used in meat processing, thereby contributing largely to the total supply of fat from meat-producing animals.

• The dietary fatty acid composition has a large impact on the fatty acid composition of muscle and fat tissue in both farm animals and fish, but metabolism controls the extent of modification towards a species-specific fatty acid profile (e.g., a higher conservation of n-6 and long chain n-3 polyunsaturated fatty acids in terrestrial animals and fish respectively). Nevertheless, several fold differences in the long chain n-3 fatty content of tissues may be observed.

• The extent to which the content of other micronutrients in animal tissues is responsive to dietary or other strategies depends on metabolic regulation and needs to be evaluated case by case (e.g., selenium and iodine contents in muscle are much more responsive to increasing concentrations in the diet than copper, iron, manganese, and zinc).

• Cost-benefit analyses are required encompassing all levels of the livestock and aquaculture chain for evaluating the human health impact of altering the nutrient composition of animal-derived foods and the efforts and natural resources needed for this purpose, versus alternative strategies.

Introduction

Foods derived from muscle of farm animals, poultry, and fish contribute significantly to the intake of energy and essential nutrients (protein, long chain [LC] n-3 polyunsaturated fatty acids [PUFA], several trace elements, and most B vitamins) in most societies and households. There are very large differences between societies in the level of consumption of animal-derived foods and in the types and characteristics of the prevailing animal production systems. Consequently, the impact of the production and consumption of animal-derived foods on human health and well-being is diverse (FAO, 2009b). For example, the global average meat consumption in 2005 was about 110 g/p/d , with a 10-fold variation between high- and low-consuming populations (FAO, 2009b). It is expected that the demand for animal-derived foods and meat in particular will continue to grow strongly in the coming decades, especially in developing countries, driven by increasing purchasing power, population growth, and urbanisation (FAO, 2009b). A much smaller increase is projected for the developed countries. On the other hand, the current high levels of consumption of meat in developed countries have been criticized for contributing to the burden of chronic diseases (World Cancer Research Fund, 2007) and to climate change and other environmental problems (FAO, 2009b). For these reasons, reducing the intake of meat in developed countries is now advocated, which may pose nutritional challenges for some key nutrients in specific population groups (Millward & Garnett, 2010). The demands for fish are also rapidly increasing worldwide (FAO, 2009a). Facing finite seafish reserves, the fish industry has been rapidly transforming over the last decades with aquaculture supplying now half of the total fish and shellfish for human consumption. Aquaculture increases demand for aquaculture feeds that rely increasingly on ingredients of vegetable origin including grains and vegetable oils (Naylor et al., 2009; Turchini et al., 2009). This evolution affects the nutritional value of fish entering the food chain. Knowing the factors that determine the nutritional value of meat and fish is thus of importance to human nutrition and health, in different scenarios of dietary shifts and production conditions.

It should be remembered that meats and fish are primarily sources of high quality protein. In 2005, the share of livestock products to total calorie and protein intake worldwide was estimated at 12.9% and 27.9% respectively (20.3% and 47.8% in developed countries, and 11.1% and 22.9% in developing countries respectively; FAO, 2009b). The worldwide 2005 to 2007 average per capita protein supply from meat and offals, milk and dairy, and fish was estimated at 14.6, 7.6, and 4.9 g/d respectively (FAO, 2009a). Because total protein intake in developed countries is well in excess of requirements, the role of animal proteins in the human diet is less relevant than in developing countries where the supply of animal proteins is critically important. The potential for steering the amino acid composition of animal tissues is limited and is not the subject of ongoing research. Although nutritionally very important, the protein fraction of animal-derived foods is not further discussed here and the focus is on essential nutrients for which there are deficiencies encountered in major parts of the world.

Fish is the major source of the LC n-3 PUFA eicosapentaenoic acid (EPA, C20:5 n-3) and docosahexaenoic acid (DHA, C22:6 n-3), to which many health effects are attributed (Ruxton et al., 2005). Meat is poorer in these LC PUFA but is the major source in non-fish-eaters (Welch et al., 2010). Meat and fish are also valuable sources of essential trace elements (copper, iron, iodine, manganese, selenium, zinc), most B-vitamins, and a series of other micronutrients (Higgs, 2000; Van paemel et al., 2010). The content of essential nutrients in meat and fish depends on many factors and the potential to alter its composition strongly differs according to the nutrient considered. The aim of the present manuscript is to consider the contents of LC n-3 PUFA and some other micronutrients in meat and fish, and to evaluate the potential of feeding and breeding strategies to alter the micronutrient composition of these food items.

Fat and Essential Fatty Acid Content of Meat and Fish

For a long time, meat has been criticized for its high fat content and inappropriate fatty acid composition. This has initiated a vast amount of research in the last decades on the lipid and fatty acid metabolism in farm animals and the composition of their products. In meat cuts devoid of external fat, the protein content is relatively constant at approximately 20% on a fresh matter basis, whereas the fat content is generally less than 5% and varies between 1 and 10% depending on a variety of things, including species, muscle, and nutrition. Trimming of external fat is widely practiced during carcass processing and contributes to leaner meat supplies. Hence, fresh meat can be considered a lean food item (McNeill et al., 2012). On the other hand, variable amounts of subcutaneous fat and other body fat depots are consumed and used in meat processing worldwide, resulting in meat products with widely varying fat content (Chizzolini et al., 1999). Thus, unless a greater proportion of carcass fat depots is directed to feed and non-food applications in future, the consumption of meat and meat products will continue to contribute significantly to the overall fat and fatty acid intake in populations with a large consumption of these products.

The economic incentive to genetically select for lean animals and to optimize feeding systems in terms of balancing nutrient supplies for fast muscle and low fat accretion has been great in many developed countries. The Piétrain breed (Figure 1) is an example of an extremely lean breed of pig. The carcass fat to lean ratio in this breed declined from 0.49 to 0.19 between 1970 and 2000 (Roehe et al., 2003). Classical breeding programs have been very effective in this respect, and although there is still room for progress, side-effects of mass selection for animal productivity are now appearing, necessitating a revision of breeding objectives to remain in line with changing societal expectations. One of these side-effects is the very low intramuscular fat content of lean meats, reducing the flavor and juiciness of cooked meats and the suitability for processing (Wood et al., 2008). The desired intramuscular fat content of meats strongly varies across the world. In Continental Europe, visible fat in meat cuts is not liked and carcass payment schemes do favour lean carcasses. On the contrary, in most other continents, a certain degree of marbling is wanted and its evaluation is included in carcass grading systems. It is unlikely that conventional animal genetic selection and management strategies will allow for the disentangling of the accretion of body fat depots and the deposition of intramuscular fat. The implementation of new molecular-genetic technologies offers perspectives to steer tissue-specific expression of traits (e.g., to produce lean carcasses with greater intramuscular fat content and improved eating quality), and their potential should at least be investigated.

Figure 1.

The Piétrain breed of pigs have seen a drastic drop in carcass fat to lean ratio since 1970 (source: Wikipedia).

Figure 1.

The Piétrain breed of pigs have seen a drastic drop in carcass fat to lean ratio since 1970 (source: Wikipedia).

The fat content of edible fish is more variable than that of muscle from farm animals and poultry and typically ranges between 1 and 15%, due to large differences in fat storage location in the body among fish species. The total body fat content in farmed fish is also much more related to the dietary fat content compared to terrestrial animals. However, the fat content of fish is no issue from a human nutritional viewpoint, on the contrary, due to the increased proportion of beneficial LC n-3 PUFA. Very generalized, fish lipids have approximately equal proportions of saturated, monounsaturated, and PUFA, the latter dominated by LC n-3 fatty acids.

The fatty acid composition of meat and fat from terrestrial animals is a matter of intense debate and research. Animal fats strongly differ in fatty acid composition dependent on both animal and dietary factors, but are generally considered too high in saturated fatty acids and low in PUFA. Again generalizing, intramuscular fat of terrestrial animals is on average characterized by approximately equal proportions of saturated and monounsaturated fatty acids (in the range of 35 to 50%) and reduced proportions of PUFA (5 to 20%) with a predominance of n-6 PUFA. Dietary factors impacting on the tissue fatty acid composition involve the source and content of dietary fat, and the duration and time of feeding. Paradoxically, the aquaculture industry is currently focusing on replacing LC n-3 PUFA sources by vegetable oils, whereas the livestock and poultry industries display increasing interest in the potential of including LC n-3 PUFA sources in their diets. The outcome of the numerous studies on modification of the muscle fatty acid composition may be summarized as follows.

Meats with less intramuscular fat content are relatively richer in PUFA because of a greater proportion of membrane phospholipids versus triacylglycerols (De Smet et al., 2004; Wood et al., 2008). Nevertheless, the content of essential fatty acids on muscle weight basis (g/100 g) is quite strongly related to the total lipid content (illustrated in Figure 2 for broiler meat). It must be stressed that from a human nutrition perspective, the absolute amounts of a nutrient in a food item are far more important than their relative proportions.

Figure 2.

Illustration of the effect of dietary fat source (3% added palm, soybean, linseed, or fish oil) and intramuscular fat content in broilers on the absolute amount (mg/100g meat) and relative proportions of long chain n-3 PUFA. Breast and thigh muscle contain approximately 1 and 4 to 5% fat respectively (after Poureslami et al., 2010).

Figure 2.

Illustration of the effect of dietary fat source (3% added palm, soybean, linseed, or fish oil) and intramuscular fat content in broilers on the absolute amount (mg/100g meat) and relative proportions of long chain n-3 PUFA. Breast and thigh muscle contain approximately 1 and 4 to 5% fat respectively (after Poureslami et al., 2010).

As a result of microbial metabolism and bio-hydrogenation of PUFA in the rumen, fats from ruminant animals are generally greater in saturated fatty acids and lesser in PUFA compared with fats from monogastric animals, but do also contain a large series of minor fatty acids (e.g., trans fatty acids, conjugated linoleic and α-linolenic fatty acids, odd and branched chain fatty acids; Scollan et al., 2006; Wood et al., 2008). The human health effects of these minor fatty acids is not well established at present. Dietary manipulation of the fatty acid profile of ruminant meats is thus dependent on the efficacy of protecting PUFA from lipolysis and bio-hydrogenation in the rumen (Scollan et al., 2006). On the other hand, although ruminants offer less potential than monogastric animals for contributing to the human intake of LC n-3 PUFA, the abundant supply of α-linolenic acid in grass-based systems is a sustainable opportunity that should be exploited. Particularly the benefits and specific effects of botanically diverse pastures need more investigation (Lourenço et al., 2008).

In monogastric farm animals and fish, dietary fatty acids undergo little transformation during digestion and absorption. Hence, the tissue fatty acid composition is a mirror of the dietary fatty acid composition in these species (Raes et al., 2004; Rymer and Givens, 2005: poultry; Wood et al., 2008: pork; Turchini et al., 2009: fish). The dietary supply of α-linolenic acid (C18:3 n-3), typically present in grass and linseed, results in clearly greater concentrations of this strictly essential fatty acid in muscle and adipose tissue, but as in humans, only marginally increases the concentrations of the LC derivatives EPA and DHA. The elongation and desaturation capacity seems to be inversely related to evolution (fish > broilers ∼ pigs > human; Turchini et al., 2009; Poureslami et al., 2010). However, also in fish the endogenous conversion of α-linolenic acid does not result in greater contents of LC n-3 PUFA. Likewise, a significant increase in the content of LC n-3 PUFA in terrestrial meat and farm-raised fish thus requires the direct supply of LC n-3 PUFA by means of fish oil/meal or micro-algal oil/biomass incorporation in the diet (Figure 2 and 3). Comparable shifts in the meat fatty acid profile (g/100 g fatty acids) as shown in Figure 2 for broilers are observed in fattening pigs, but absolute amounts of LC n-3 PUFA (mg/100 g meat) are on average less in pork compared with poultry meat. Considering the declining fish stocks, the rising need for LC n-3 PUFA in aquaculture, the absolute requirement of most fish species for LC n-3 PUFA, and the greater deposition efficiency of fish versus terrestrial animals of these fatty acids, an increased use of fish oil in the feed of farm animals is not justifiable. The use of cultivated micro-algae as the primary producers of LC n-3 PUFA is a more desirable and sustainable strategy for livestock and aquaculture feeds (Brunner et al., 2009; Turchini et al., 2009; Gibbs et al., 2010).

Figure 3.

Variation in fat content (%) and long chain n-3 PUFA content (mg/100g portion; % recommended nutrient intake) that may be encountered in meat and fish. Please note that these are average values but that also within species the fat content and long chain n-3 PUFA content may vary. Examples are from feeding studies in which modern genotypes during most of the fattening period were fed representative diets with a lipid content within the range of the species-specific requirements and with the indicated dietary oil source making up a considerable part of the added fat.

Figure 3.

Variation in fat content (%) and long chain n-3 PUFA content (mg/100g portion; % recommended nutrient intake) that may be encountered in meat and fish. Please note that these are average values but that also within species the fat content and long chain n-3 PUFA content may vary. Examples are from feeding studies in which modern genotypes during most of the fattening period were fed representative diets with a lipid content within the range of the species-specific requirements and with the indicated dietary oil source making up a considerable part of the added fat.

The feeding strategies that have been studied in the past for increasing the content of beneficial fatty acids do not generally raise the feed cost substantially and do not have negative impact on animal performances when recommended levels of dietary fat are respected. Similarly, replacing fish oil by vegetable oils in fish diets does not affect the fish's performance as long as the minimal requirements for LC n-3 PUFA are met (Turchini et al., 2009). A general concern when using LC PUFA in the diet of farm animals is the negative effect on the oxidative stability and flavor of meat (Melton, 1990; Campo et al., 2006; Wood et al., 2008). Fish oil in the diet above certain levels leads to off-flavors and reduced fat stability. Increased levels of dietary antioxidants are able to retard oxidative rancidity, and it is well established that α-tocopherol is effective in this respect. It is deposited in cell membranes thereby offering protection against lipid and color oxidation (Wood et al., 2008). However, this does not allow for the overcoming of sensory problems in all instances. Particularly fat-rich processed meat products remain vulnerable. Softness of the fat (e.g., in pork bellies) is another commonly reported problem when feeding high levels of PUFA. More work is required in this area to produce meat and meat products with an improved composition without compromising sensory quality.

Genetic tools have been investigated much less than nutritional strategies, although there is significant genetic variation for fatty acid deposition and metabolism (De Smet et al., 2004). Nevertheless, conventional genetic selection for improved muscle fatty acid composition may not be considered a valuable strategy for various reasons, among which unfavorable phenotypic and genetic correlations with intramuscular fat content and the much larger potential of feeding strategies have to be mentioned. Again, molecular-genetic approaches may be envisaged (Dodson et al., 2009). Transgenic pigs functionally expressing a delta-12 fatty acid desaturase gene from spinach (Saeki et al., 2004) and a humanized Caenorhabditis elegans gene, fat-1, encoding an n-3 fatty acid desaturase (Lai et al., 2006) has been reported. Alternatively and probably of more practical relevance, promising research is being conducted in plant molecular science aiming at the expression of several desaturase and elongase enzymes in rapeseed, which should result in plant-derived foods containing LC n-6 and n-3 PUFA (Venegas-Calerón et al., 2010). Although direct human consumption of transgenic plants on a large scale is unlikely to happen in the near future, feeding these modified plants to farm animals and fish might be an interesting avenue for fuelling LC n-3 PUFA into the human food chain.

Trace Element Composition of Muscle

Essential trace elements (e.g., cobalt [cobalamin], copper, iron, iodine, manganese, selenium, zinc) are functional, structural, and regulatory components of numerous bio-molecules in the living organism. The intake of several essential trace elements is suboptimal in many countries around the world (WHO, 2004; Black et al., 2008; WHO, 2008). Low- and middle-income countries are most affected, but the prevalence of iron and iodine deficiency, for example, is also high in high-income countries. Muscle is a good carrier of several essential trace elements, providing these elements mostly in an organic, well-absorbable form. Hence, similarly to essential fatty acids, increasing or optimizing the content of essential trace elements in meat and fish might positively contribute to human health. The homeostatic regulation and metabolism of essential trace elements is, however, complex and differs according to the element (Windisch, 2002). To maintain metabolic equilibrium, absorption and excretion of essential trace elements is actively adjusted in relation to changes in intake. The regulation of some trace elements occurs mainly at the site of absorption (e.g., copper, iron, manganese, zinc), whereas for others renal excretion is the major site of regulation (e.g., cobalt, iodine, selenium). Consequently, the potential to alter the content of essential trace elements will strongly depend on the element and all factors interfering in the regulation and metabolism. These include the source, content and chemical species of the element in the diet, and interfering dietary (e.g., chelating agents, metal ions, other trace elements) and metabolic factors.

We reviewed the literature on concentrations of essential trace elements in edible tissues and products, linked with the dietary supply of various concentrations and forms of the element (Van paemel et al., 2010). A summary is given in Table 1 for muscle and liver across species and type of animals. Species differences are illustrated in Figure 4 for zinc. In muscle, the response to increased dietary concentrations of copper, iron, manganese, and zinc is mostly absent, and the chemical form of the element in the supplement (i.e., inorganic or organically bound) does not appear to affect the response. In contrast, muscle selenium and iodine concentrations increase with increasing dietary concentrations, and the source of the element is also important. Including an organic source in the diet (e.g., algae Laminaria digitata, seaweed Ascophyllum nodosum) is more effective than using an inorganic form, and may result in several fold increases in muscle iodine content. Similarly, for selenium, several studies in different species are available in which dietary supplementation with sodium selenite or selenium-enriched yeast resulted in increased deposition of selenium in muscle, but the response to selenium-enriched yeast is approximately two times greater (EFSA, 2008). It should be mentioned that for the elements discussed here, the concentrations in liver are at least similar but may be 10 times greater compared with muscle and that the response to dietary supplementation is generally also greater in liver tissue.

Table 1.

Range of trace element contents in muscle and liver across species (pigs, ruminants, and poultry) from animal feeding studies.

Table 1.

Range of trace element contents in muscle and liver across species (pigs, ruminants, and poultry) from animal feeding studies.

Figure 4.

Figure 4.

Cobalt is a particular trace element since its only known function is as an essential component of vitamin B12. Humans and monogastric animals (except horses and rabbits) do not require cobalt but they require vitamin B12, whereas the ruminant microflora can synthesize vitamin B12, provided dietary cobalt is available in sufficient quantities. Animal foods (i.e., meat, milk, egg, fish, and shellfish) but not plant foods are considered to be the major dietary sources of vitamin B12 (Watanabe, 2007). Vegetarians, and particularly vegans, are susceptible to vitamin B12 deficiency. Values in food composition tables for vitamin B12 in cooked meat are in the range of 10 to 30 μg/kg with at least 20 times greater concentrations in liver (Watanabe, 2007). Ortigues-Marty et al. (2005) observed increases in vitamin B12 contents in liver and muscle of beef and lamb in response to increased cobalt allowances. However, in muscle there was only a response in the case of deficiency.

In US, trace element compounds are listed that are authorized for use in animal feeds and are generally recognized as safe, but no maximum allowed contents are specified. However, in the EU a maximum allowed total content of trace elements in feeds for farm animals is defined. Levels that are currently recommended and used in feeds in the EU to meet the animal requirements vary according to animal category and are either considerably lower (e.g., iron, iodine, manganese) or close to the maximum allowed content (e.g., selenium). This means that the potential enrichment of animal foods above average current levels is negligible for most elements, taking into account the poor response in muscle for most elements. The greatest potential exists for iodine and for selenium in case an organic source is used. Almost no data are available from fish feeding studies in this respect.

Impact of Altering the Micronutrient Composition of Meat or Fish on Human Health

The contribution of a food item to the intake of a specific micronutrient is the result of the food item intake and its composition. This means that those foods that are consumed in the largest quantities are the most appropriate target foods for enrichment if no major shifts in dietary pattern are assumed. Large differences between countries are apparent for the average per capita EPA+DHA intake (e.g., it was estimated at 950, 244, and 175 mg/d in Japan, UK, and Australia respectively; Givens and Gibbs, 2008; Figure 5). Intake values are at least 5 times less in non-fish-eaters than in fish-eaters. Considering a general recommended intake value of 450 mg EPA+DHA/d, it is clear that there is little benefit of modifying the fatty acid profile of livestock derived foods in Japan in contrast to western countries. Givens and Gibbs (2008) have estimated the impact on the human intake of LC n-3 PUFA following a shift in the meat fatty acid profile due to alternative animal feeding regimens. Adding fish oils to the diets of all farm animals has the potential to provide to the UK adult diet a daily intake of EPA+DHA of about 230 mg, with poultry meat providing the largest amount (74 mg). Poultry is more responsive to dietary changes compared to other terrestrial animals (Figure 3). In addition, the skin of poultry is readily consumed providing a substantial amount of LC n-3 PUFA (Gibbs et al., 2010). However, it is clear that modifying only meat, and for sure meat from only one species, will not result in the desired shift in intake of LC n-3 PUFA. In addition, as mentioned above, making increased use of fish oil in farm animals' diets is not sustainable and is ethically questionable. Brunner et al. (2009) even argued that the official recommendations to stimulate consumption of fish and seafood in rich countries may increase within-country and international inequalities in view of the limited fish stocks.

Figure 5.

Percentage contribution of different food items to the total estimated eicosapentaenoic acid (EPA, C20:5 n-3) and docosahexaenoic acid (DHA, C22:6 n-3) EPA+DHA intake in (A) Australia: 175 mg/d and (B) UK: 244 mg/d (Givens and Gibbs, 2008). The recommended intake is 450 to 500 mg/d.

Figure 5.

Percentage contribution of different food items to the total estimated eicosapentaenoic acid (EPA, C20:5 n-3) and docosahexaenoic acid (DHA, C22:6 n-3) EPA+DHA intake in (A) Australia: 175 mg/d and (B) UK: 244 mg/d (Givens and Gibbs, 2008). The recommended intake is 450 to 500 mg/d.

A more widespread use of the precursor α-linolenic acid in animals' diets (e.g., from grass, linseed) will not raise the same sustainability concerns. Although meat does not contribute greatly to the total supply of α-linolenic acid and the conversion efficiency to the LC n-3 PUFA is low in both animals and in humans, this strategy should nevertheless be considered in view of the large shortage in intake of LC n-3 PUFA and the ease and low cost of application. Stearidonic acid (C18:4 n-3), which is one step further in the n-3 pathway, has been investigated as a more interesting precursor but the conversion to DHA is also limited (Turchini et al., 2009: fish) and plant sources are not readily available. Alternative approaches (e.g., the development of cost-effective cultivated micro-algae and genetically modified crops enriched in LC PUFA) should thus be investigated and encouraged for application in both farm animal and fish feeding.

Similar considerations could be made for other micronutrients. The inclusion of iodine sources or selenium-enriched yeast in feedstuffs for meat-producing animals might induce an indirect but substantial, stable, and easily controllable contribution to the human iodine and selenium supply, without the risk of overdosing or the need for a shift in eating pattern. Again, iodine and selenium enrichment of meat from a single animal species will not suffice to raise the human supply substantially. It is important to mention in this respect that iodine, like selenium, have a narrow range (1:4) between human requirements and tolerable upper intake levels. Compared with other tissues and excreted products (i.e., milk and eggs), muscle is more resistant to modification but at the same time safer in terms of risk of overdosing. Precise estimates of the impact of shifts in meat consumption pattern on the intake of trace elements are lacking (e.g., one might expect that the actual trend for decreasing beef and increasing poultry consumption in many countries might aggravate iron deficiency, but this needs to be assessed).

To allow the successful introduction of nutritionally improved meats in the market, intervention studies are needed that examine the effect of these foods on human metabolic parameters and that may support nutrition or health claims. Only few studies are available in this respect for meat, but there are indications that altered meat may indeed have a positive impact on health indicators. Weill et al. (2002) compared the plasma and erythrocyte fatty acid profile of healthy volunteers that consumed milk, butter, eggs, pork, broiler chicken, beef, and lamb from livestock receiving linseed at 5% in the diet versus a standard diet. Without any change in consumers' eating habits, foodstuffs from animals fed linseed diets induced significant modifications in plasma and erythrocyte fatty acid composition. Larger effects may be expected if LC n-3 PUFA is added to the animals' diets. This was tested by Coates et al. (2009). Pork was enriched in LC n-3 PUFA by including a fortified tuna fishmeal product in the pig finisher diets. Healthy volunteers received a selection of five fresh cuts totalling 1000g/week for 12 weeks from either n-3 enriched pork or regular pork, corresponding to an intake of 1.3 g LC n-3 PUFA per week. The authors concluded that modest increases in LC n-3 PUFA intake resulting from regular consumption of enriched pork improved cardiovascular risk factors. Conversely, patients with coronary heart disease consuming 700 g per week of fish oil fed salmon had more favorable biochemical changes compared to the consumption of rapeseed oil fed salmon (Seierstad et al., 2005).

More generally, cost-benefit analyses are required to evaluate the opportunities of altering the essential nutrient composition of meat and animal-derived foods in general by new breeding and feeding strategies versus alternative approaches at the level of the food processing industry or public health services. Fortification of foods during processing is more versatile and controllable than approaches at the primary production stage. On the other hand, a widespread implementation of relatively simple feeding strategies in meat producing systems guarantees a safe and population-wide, be it modest, health benefit, and may allow farmers to create added value to their products.

Conclusion

Meat and fish consumption contributes significantly to the intake of several essential nutrients in most societies. Knowing the animal and dietary factors that determine the content of these nutrients in edible tissues is thus of importance. The potential to alter the nutrient composition of muscle strongly differs according to the nutrient considered. Enhancing the content of LC n-3 fatty acids in meat has been investigated extensively over the last decades, and it is now clear that muscle fat content and an animal's dietary fatty acid composition has the largest impact. In aquaculture, on the contrary, the challenge is now to maintain the naturally high levels of these beneficial fatty acids in fish muscle in view of the replacement of fish oil by vegetable oils in the feeds. From a human health and global sustainability perspective, cost-benefit analyses should be carried out along the food chain on the use of feed resources to optimize the micronutrient composition of edible tissues from meat-producing animals and fish versus alternative strategies.

Stefaan De Smet is a professor in Animal Science at Ghent University, Belgium. He is responsible for teaching general and advanced courses in animal production, animal breeding, and meat science. He performed his Ph.D. research on the role of rumen protozoa and later moved to meat quality research with particular interest in the relationship between carcass quality and sensory and technological meat quality traits. His current research focuses on the health value of animal-derived foods with emphasis on the optimisation of the fatty acid composition and oxidative stability of meat from various species.

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