Meat plays an ever increasingly important role in the diets of the world’s population. Consumption is growing generally around the globe as major populations become more affluent. A significant increase in consumption of beef has been observed in countries like Korea, Japan, Malaysia, Kuwait, Saudi Arabia, Mexico, Taiwan and Brazil. In general, consumption of beef is heavily and disproportionately concentrated in the industrial countries with an average annual per capita consumption in the range of 6.5-6.7 kg per capita. Argentina is the largest consumer of beef accounting for 40 kg per capita followed by Brazil (25.4 kg per capita) and USA (23 kg per capita) whereas in the EU (28 countries) consumption of beef and calve meat is 10.9 kg per capita based on kilograms of retail weight per capita per annum (Ojha et al., 2016). Unlike poultry, cultural and religious factors have implications on consumption trends in some countries. Apart from social factors meat have negative perception in terms of food safety, environmental and health implications. Despite several issues, beef is still a most popular meat product among large section of society.
Like any other meat, beef is an excellent source of high quality protein and contains all essential amino acids. Dietary protein is required for growth, maintenance and repair of the body and can also provide energy. Human requirements for protein have been thoroughly investigated over the years and are currently estimated to be 55 g per day for adult man and 45 g for woman. Average servings of lean beef adequately meet these requirements. It also contains a rich source of many minerals including zinc, iron, selenium, phosphorus, magnesium, potassium and copper. Minerals present in beef are more bioavailable compared to plant sources. Apart from proteins beef also contains high level of lipids. These lipids provide dietary energy and essential nutrients including essential fatty acids. Consumer’s concern and awareness centred on consumption of high fat foods including red meat has some effects on the meat consumption pattern. Nutritional value of meat and beef has been reviewed extensively (Cabrera and Saadoun, 2014). Overall, beef is a rich source of proteins with high biological values and other micronutrients. From this perspective, the current paper reviews the scientific literature in health implications of beef intramuscular fat consumption.
Nutritional Profile of Beef
In October, 2015, 22 scientists from ten countries evaluated the carcinogenicity of the consumption of red meat (unprocessed) and processed meat at the International Agency for Research on Cancer (IARC) (Bouvard et al., 2015) based on 800 epidemiological studies. Epidemiological studies were selected based on the association of cancer with consumption of red meat or processed meat in various countries around the world. The report concluded that the consumption of red meat is probably carcinogenic to humans with strong positive association with pancreatic and prostate cancer. However, the association of meat consumption with cancer was based on epidemiological studies. The IARC report did not include the role of environmental pollutants and processing induced chemical (e.g., N-nitroso-compounds, polycyclic aromatic hydrocarbons and heterocyclic aromatic amines) which are formed as a result of processing (e.g., curing and smoking) at high temperatures or present in raw meat (Domingo and Nadal, 2016). Furthermore, Kurtfield (2015) has recognised there are many limitations of such studies including inability to accurately estimate intake, lack of pre-specified hypotheses, multiple comparisons, and confounding factors – including body weight, fruit/vegetable intake, physical activity, smoking, and alcohol – that correlate significantly either positively or negatively with meat intake and limit the reliability of conclusions from these studies. Nonetheless, despite global attention red meat remains a popular source of protein and has several nutritional benefits.
In addition to the traditional essential nutrients of proteins and lipids, beef meat is a potential source of a number of bioactive substances that have been studied for their potential beneficial effects. These meat-based bioactives include taurine, creatine, conjugated linoleic acid (CLA), carnitine, and several endogenous compounds (Arihara, 2006). Imidazole dipeptides such as anserine and carnosine are antioxidants naturally present in beef and have a role as a metal chelator and free-radical scavenger (Kohen et al., 1988). Although the beef contains low levels of antioxidants and associated antioxidant activity compared to plant foods, presence of certain antioxidants along with high quality proteins is certainly advantageous for health conscious beef consumers. Beef is also rich in many vitamins (e.g., vitamin B12, B6, riboflavin, thiamine and pantothenic acid) and mineral (e.g., zinc, iron, selenium, phosphorus, magnesium, potassium and copper) (Williams, 2007).
Role of nutrients for various health benefits are reported extensively. The nutritional value of macronutrients such as protein, fat, and minerals and its role to integrate as a part of a healthy diet depends on several factors including, the level, composition and their bioavailability. For example, the minerals found in beef are more bioavailable compared to vegetable sources (Hunt, 2003). Half of the iron in meat is present as haem 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. The chemical composition of beef is varies not only based on genotype but also on the type of cut (Jung et al., 2015; Jung et al., 2016; Kim et al., 2002). For example, Oh et al. (2016) reported the chemical composition of high-preference and low preference cuts of Hanwoo beef (Table 1). Table 1 shows significant variations in chemical compositions of various cuts on dry basis. In general, moisture, protein, lipid, and ash content of various retail cuts of beef varies from 58.5% to 71.3%, 18.8% to 21.8%, 4.9% to 19.4%, and ash 2.3% to 3.1% respectively based on fresh weight basis (Jung et al., 2015).
a-eValues followed by same alphabets are not significantly different. 1)Dry matter basis.
Nutritional compositions of various cuts and popular beef breeds allow consumer to make choice and may satisfy their health consciousness. However, a judicious balance between the cost of various cuts and nutritious profile is a challenge to promote consumption of beef for profit margins.
Lipid Profile of Beef
Presence of high level of lipids in beef has been a topic of discussion for beef consumers because of their associated health implications. In general lipid fraction in beef varies from 4-15% on fresh basis depending on several factors including genotype, feeding regime and meat cut. In recent years, strategies for increasing the level of beneficial fatty acid while reducing saturated fatty acids in beef with particular focus on intramuscular fat has been investigated (Scollan et al., 2006).
The relationships between dietary fat irrespective of the food source and their relationship with various incidence of lifestyle diseases including cardiovascular diseases is well established and several health agencies have specific guidelines. According to World Health Organisation (2003) recommendations various dietary fat fractions showed contribute <15-30%, <10%, <5-8%, <1-2% and <1% of total energy intake from total fat, saturated fatty acids, n(6)-polyunsaturated fatty acids, n(3)-polyunsaturated fatty acids and trans fatty acids respectively. In general fatty acid in beef varies depending on the genotype, muscle type and feeding regime (Mapiye et al., 2013). Pavan and Duckett (2013) studied fatty acid profile of eight retail cuts (eye of round, ribeye, top round, striploin, tenderloin, top-sirloin, underblade, ground beef) from grass-fed steers. They reported that the total fatty acids on fresh basis ranges from 1.31-11.08 mg/100 g in retail cuts studied with saturated fatty acids, mono unsaturated fatty acids and poly unsaturated fatty acids ranging from 41.49 to 48.95%, 33.92 to 35.86% and 1.99 to 6.87%, respectively. Presence of these long chain n-3 and n-6 poly unsaturated fatty acids in beef samples has been reported for various health benefits and improve maternal and offspring health, growth and development, cognitive function and psychological status in humans (Mapiye et al., 2015; Pelliccia et al., 2013).
Various nutritional fractions based on beef fats namely total SFA, PUFA, PUFA (n3), PUFA (n6), ratio of PUFA: SFA, PUFA (n3): PUFA (n6) and Atherogenic Index (AI) are becoming increasingly popular to evaluate the nutritional quality of beef fat in regard to the prevention of coronary heart diseases and anticarcinogenic activity (Vannice and Rasmussen, 2014). AI assesses the risk of atherosclerosis and considered as an indicator of impact of fat on the cholesterol concentration. AI is based on those fatty acids (C12:0, C14:0 and C16:0) which can increase or decrease the level of cholesterol. Mathematically, it can be defined as the relationship between key SFA and the total unsaturated fatty acids (Eq. 1) (Nantapo et al., 2014; Ulbricht and Southgate, 1991).
It is believed that all saturated fatty acids have negative effect on human health due to their hypercholesterolic effect. Research has shown that certain saturated fatty acids (e.g., steric acid, C18:0) have no effect on plasma cholesterol level (Ulbricht and Southgate, 1991). Similarly, some fatty acids trans-11 vaccenic acid (C18:1 trans-11) and their isomers i.e., cis-9, trans-11 of conjugated linoleic acid (CLA cis-9, trans-11) found in beef at varying level are known to have anti-carcinogenic and anti-atherogenic effects (Tricon et al., 2005; Turpeinen et al., 2002).
Factors Effecting Intramuscular Fat Content in Beef
The total lipid content of muscle is often termed as marbling fat or intramuscular fat. Marbling fat is the speckles of fatty tissues composed mainly of neutral lipids. It consists of clusters of individual cells (adipocytes). Intramuscular adipocytes increase both in number and size in cattle as beef progresses from being “almost absent” to higher marbling scores. Marbling of muscles has a role in eating quality of beef in terms of tenderness and juiciness of cooked meat. Presence of intramuscular fat is one of the important factors associated with the consumer perception of beef eating quality influencing flavour and sensory attribute (Hunt et al., 2016). The interaction of muscle with the level of intramuscular fat have shown the effect on consumer ranking of beef flavour (Legako et al., 2015). Studies have shown that the composition of intramuscular fat is strongly influenced by both the genotype and production system, including slaughter weight (De la Fuente et al., 2009). A plethora of literature is available, demonstrating that grass-fed cattle have higher levels of n(3), MUFA compared to concentrate fed animals (French et al., 2000; Nuernberg et al., 2005; Realini et al., 2004). However, the composition of intramuscular fat is largely influenced by genetic factors compared to dietary factors. Meat fatty acid composition is influenced by genetic factors, although to a lower extent than dietary factors (De Smet et al., 2004). Increase in fatness of a given species also has an effect on the fatty acid composition influencing the PUFA/SFA ratio. In the case of beef, as fat content increases the level of SFA and MUFA increases at a much faster rate compared to PUFA (De Smet et al., 2004).
Literature reveals that the lipid composition and fatty acid profile of intramuscular fat in beef can be manipulated based on three factors namely (i) genotype, (ii) time on feed and (iii) finishing diet (Wood et al., 2008). For example, in a study by Cho et al. (2005), fatty acid profiles of 3 muscles (Longissimus dorsi, Triceps brachii and Semimembranosus) were compared from 24 mon old Korean Hanwoo and Australian Angus beef on different feeding regime. They reported that the Hanwoo beef from cattle raised on concentrate feeding had higher unsaturated fatty acids (C16:1n7, C18:1n7, C18:2n6 and C20:1n9) compared to Angus beef. However, Australian Angus beef had significantly higher n-3 PUFA, whereas Korean Hanwoo beef contained higher n-6 PUFA for the three muscles being studied. To improve the marbling of the Korean beef breed, a grain based feeding system is performed however, this can also cause an increase in the level of subcutaneous and visceral fat, which may lead to inefficient meat production (Lee et al., 2008). Hence, recent focus on the identification of genes responsible for the marbling effect in beef is important to enhance beneficial fatty acids while reducing subcutaneous and visceral fat which is mainly saturated fatty acid. Pethick et al. (2004) reported that intramuscular fat development within muscle is not late maturing and that the expression of marbling is due to maintained fat synthesis due to energy availability in combination with declining muscle growth as animals get older.
Fatty Acid Profile of Intramuscular Fat
Generally, oleic acid (C18:1) is the most abundant fatty acid in beef followed by palmitic (C16:0) and steric acid (C18:0). Varying the level of α-linoleic acid (C18:3n-3) and conjugated linoleic acid (C18:2cis-9, trans-11) has been reported (Smith et al., 2004). Literature review highlights that the intramuscular fat contains high level of PUFA and MUFA compared to other fats in beef. Insausti et al. (2004) studied the fatty acid composition of five Spanish cattle breeds (Asturiana de los Valles, Morucha, Parda Alpina, Pirenaica, and Retinta). They observed that the intramuscular fat contains higher PUFA/SFA ratio and demonstrated the presence of long chain fatty acids with an increase in intramuscular fat. It can be concluded that an increase in intramuscular fat showed an increase in the level of long chain PUFA (e.g., C22:6n-3 and C20:5n-3) may not always involve higher SFA. Marbling fat contains more oleic acid and less stearic acid than subcutaneous adipose which effects not only the palatability of beef but also has a positive health aspect.
Health Implications of Beef Consumption with High Degree of Marbling
Beef remains a highly valued, nutritious food and associated with good health and prosperity. It contains valuable nutritious components discussed above. Health professionals’ recommendation to reduce the overall consumption of fats and the diet-heart (lipid) hypothesis focussed attention on the saturated fat contributed from meat. A number of epidemiological studies have proposed an association of red meat consumption with development of cardiovascular disease (CVD) and colon cancer. However cause and effect with regard to a direct relationship to many of these studies remains unproven.
Factors such as the inability to accurately measure intake, identification of the proposed causative agents, lifestyle of the subjects greatly limits the reliability of the conclusions of these studies. However different strategies are being developed by producers and processors, aiming to reduce fat level in beef. These approaches include selective breeding and feeding practices designed to increase the carcass lean to fat ratio; improved official carcass classification systems designed to favour leaner production; and modern butchery techniques (seaming out whole muscles, and trimming away all intermuscular fat). Research over past few decades suggests that grass-only diets can significantly alter the fatty acid composition and improve the overall antioxidant content of beef. Grass feeding improves the quality of beef, and makes the beef richer in omega-3 fats, vitamin E, beta-carotene, and CLA. There is tremendous potential to enhance health benefits of beef by the production of high-quality beef from better-bred animals with superior genetics and improved nutritional profile via better feed management.
In the US, Smith and Johnson (2014) produced a “white paper” citing that as the concentration of intermuscular fats in beef loins increased the amount of MUFAs increased also. In particular, an increase in the healthier oleic acid was observed at the expense of SFAs in USDA Select beef (less marbled) and the MUFA / SFA ratio was 0.75 compared with 1.33 in the USDA Prime beef (more marbled). The conclusion being that a more marbled beef cut (especially the brisket) is healthier. The results of this study are very positive for producers and consumers of high marbled beef animals but the authors observe that further studies especially across different breeds is required to substantiate this hypothesis.
Despite several issues centred around safety of raw and processed beef, enjoys popularity among various segments due to the presence of high quality protein and other nutrients. In relation to lipid content of beef, intramuscular fat contains high level of PUFA and MUFA compared to other beef fat. Level and composition of intramuscular fat varies depending on breed and feeding regime. Literature suggests that the marbling is more complex than the development of subcutaneous fat and marbling not only provides good fatty acids but also contributes to the higher eating quality of beef. Most studies conclude that meat plays a pivotal role in nutritious diets, high quality marbled beef is not only of excellent eating quality but may also contain more beneficial fatty acids. In any case a healthy lifestyle will include a well-balanced diet including meat and regular exercise.