This month’s newsletter was curated and edited by: Dr. J.W. Holloway and his Team

Synopsis

Meat is an excellent source of several minerals that are limiting in plant-based foods. Meat is one of the best sources for zinc, selenium, phosphorus, and iron. A serving of beef, lean cuts (100 g) provides about 37% of selenium RDA, 26% of zinc RDA, and 20% of the potassium RDA (USDA, 2011). Dietary minerals are essential nutrients in human diets, and it is usually recommended by dietitians that they are supplied from foods in which they occur naturally so that they can be maximally absorbed in the gut. Although the prevalence of obesity is rapidly increasing, attaining the level of 33.8% for U.S. adults, many Americans are not meeting the recommended dietary allowance for many nutrients (Flegal et al., 2012; and ARS-USDA, 2011). Of the commonly consumed protein foods, red meat is one of the best sources of readily absorbed iron and zinc. However, limited information is available regarding the content and natural variation in many nutrients in red meats or the extent to which that variation is the result of genetic differences or associated with meat palatability traits. Evaluation of relationships between the concentrations of these nutrients and sensory traits is essential for understanding the impact of this natural variation of traits like tenderness, juiciness, and flavor, which is critical to consumer acceptance and satisfaction. The nutrient density of foods is immaterial if the foods are not acceptable to the consumer.

Analysis

Calcium

Calcium is an essential dietary nutrient in that it is required for bone growth and health, vascular contraction and vasodilation, muscle function, nerve transmission, intracellular signaling, and hormonal secretion (Anderson et al., 1993; Ambudkar, 2011; Fearnley et al., 2011; and Rosenberg and Spitzer, 2011). Insufficient dietary calcium impacts health through its relationship to bone health and osteoporosis, cardiovascular disease, blood pressure regulation, and hypertension, kidney stones, and weight management (Burtis et al., 1993; Flynn, 2003; Tylavsky et al., 2008; Astrup, 2011; and Meier and Kranzlin, 2011). Mateescu et al. (2013) reported that the average calcium concentration in longissimus was 38.71 μg/g muscle. Therefore, beef has only a minor role in the provision of the daily human requirement, providing, on average, 3.87 mg calcium per 100 g serving of beef for the 1,000- to 1,300-mg daily needs of the average adult.

Copper

Copper is a trace element essential for the well-being of most animals in that it is a critical functional component in enzymatic processes. Specifically, copper is required for cytochrome oxidase and superoxidase dismutase, enzymes involved in energy production and protection from free radical damage (Yim et al., 1993; and Gezer et al.,1998). Mateescu et al. (2013) reported copper content in beef longissimus of 0.78 μg/g muscle. Based on this value, a 100 g serving of beef would contribute 0.08 mg of copper or about 6% of the recommended dietary allowance for adults. The most important metabolic role of copper is its contribution to iron metabolism through ferroxidase I and II. Two copper-dependent enzymes are required to oxidize ferrous iron to ferric iron so that iron can be transported through transferring to the site of red cell formation (Osaki et al., 1971; and Garnier et al., 1981).

Iron

Iron is an important dietary mineral necessary for the transport of oxygen in the blood. Dietary iron is crucial to human health, and its deficiency leads to impairment of several physiological functions resulting in disturbances in growth and development for young people (Grantham-McGregor and Ani, 2001; and Lozoff and Georgieff, 2006). There are obligatory losses from endogenous sources, regardless of the level of intake, via the skin (sloughing of skin cells), feces (bilirubin and sloughing of intestinal tract cells), urine, airways (sloughing of respiratory cells), and menstrual bleeding in premenopausal women. Red blood cells have a relatively constant half-life, and the heme portion is rid through the feces in the form of bilirubin (Mateescu et al., 2013). Therefore, the diet plays an essential role in maintaining iron balance (Hurrell and Egli, 2010). Mateescu et al. (2013) reported iron concentrations in beef longissimus of 14.44 μg/g muscle translating to 1.44 mg iron per 100 g serving of beef

The recommended dietary allowance ranges from 8 to 18 mg/d depending on gender and age. Therefore, a 100 g serving of beef would provide between 8% and 18% of the recommended dietary allowance. For most foods, the amount of iron absorbed compared with the amount ingested is typically low so that the source of iron is an important factor determining the efficiency of absorption (Kapsokefalou and Miller, 1993; Andrews, 2005; West and Oates, 2008; and Han, 2011). Most animals and some plant products contain iron in the form of heme, which is more efficiently absorbed than non-heme iron. Heme iron in meat is of two sources from blood and heme-containing proteins in muscle cells, including mitochondria. In plants, on the other hand, heme iron is present only in mitochondria as in all cells that use oxygen for respiration. The high heritability of this mineral in beef longissimus (0.54) and the natural variation of iron content in beef indicate that it may be possible to increase the iron content of beef through both selection and management (Mateescu et al., 2013).

The maximum iron concentration in beef longissimus reported by Mateescu et al. (2013) was 27.43 μg/g muscle so that a 100 g serving represents about 15 to 34% of the recommended dietary allowance depending on gender and age. Although iron can be found in a wide variety of foods, its two forms are far from being equal in value. Heme-iron arises from meat hemoglobin and myoglobin. It is totally digested, highly bioavailable, and easily absorbed from the intestinal lumen (Pereira and Vicente, 2013).  The porphyrin rings of hemoglobin and myoglobin, unlike most other complex compounds, are absorbed as intact molecules by enterocytes (Hallberg and Hulthén, 2000; and Simpson and McKie, 2009). Non-heme iron, which is present mainly in dark-leafed vegetables such as spinach, cruciferous vegetables, and legumes has a much lower digestibility, absorption rate, and bioavailability (Turhan, Altunkaynak, and Yazici, 2004). Vegetable iron sources also often contain iron absorption inhibitors such as phytate (Kumar et al., 2010) and polymerized flavans (Petry, Egli, and Zeder, 2010).

However, controversies remain as some of these foods such as cabbage (kale) are also good sources of ascorbic acid, which improves iron absorption (Thumser et al., 2010). It is clear, however, that heme-iron, even when consumed in small amounts, is two to three times more bioavailable and 15 to 35% more easily absorbed than non-heme iron (Turhan et al., 2004). Since meat is the best source of heme-iron, it is the preferred source of dietary iron. Meat, however, can vary from 26.2 to 75.6% of its iron content as heme-iron (Pereirra and Vicente, 2013). Of all meats, beef has the highest heme iron content: beef loin ranges from 45% to 78% with an average of 58% ((Kongkachuichai, Napatthalung, and Charoensiri, 2002; and Pereira and Vicente, 2013). Iron and heme-iron contents are lower in lighter colored meats such as chicken. For chicken, dark meat heme iron is 39%, whereas white meat is 26% (Clark, Mahoney, and Carpenter, 1997).

Thus, beef is a superior source of iron to chicken. Meat and meat products can contribute up to 18% of iron RDA, which makes it important in a healthy, balanced diet and crucial in preventing one of the most common nutritional deficiencies, anemia (Geissler and Singh, 2011). However, high intake of iron has been reported to damage the intestinal mucosa and lead to systemic toxicity (Mills and Curry, 1994). Excesses also have been reported to induce free radical damage to several surrounding tissues (McCord, 1998). Very high iron intake has been associated with increased risk of colorectal cancer, cardiovascular disease, systemic infection, and neurodegenerative diseases and inflammation (Balder et al., 2006; Qi et al., 2007; and Kontoghiorghes et al., 2010). For these reasons, it is recommended in the US, that adult iron intake not exceed 45 mg/d (Geissler and Singh, 2011). Czerwonka and Tokarz (2017) reviewed the literature as to the relative advantages and disadvantages of red meat as a source of dietary iron.

They concluded that “red meat is a good source of iron and excluding it from the diet may result in too low a supply of this nutrient, and thus an increased risk of its deficiency. However, the bioavailability of iron, in particular in the form of heme, from red and processed meat, is very high, and therefore, substantial, regular intake of this group of products may burden the body with iron, and thereby increase the risk of some non-communicable diseases.” The role of iron in cancer pathogenesis is through its catalysis of N-nitroso compounds, oxidation of polyunsaturated fatty acids, and increased iron levels in the body, which collectively resulting in an intensification of oxidative processes, but also possible changes in the activity of transcription factors (NF-κB and AP-1) and the efficacy of the immune system. High iron intakes can also increase the risk of type II diabetes because of its oxidative damaging effect on pancreatic β cells. This damage can cause a decrease in insulin secretion, an increase in insulin resistance, and liver dysfunction.

Excessive consumption of red meat has been associated with an increased body iron pool and severity of oxidative processes, which in turn may promote atherosclerosis, thereby increasing the risk of cardiovascular disease. However, the epidemiological studies on the impact of red meat consumption are inconsistent. Due to the high nutritional value, the presence of red meat in the diet is preferable, but according to the World Cancer Research Fund International, its consumption should not exceed 500 g per week (Czerwonka and Tokarz, 2017). The challenge for the red meat industry is to use the opportunities provided by genomics to respond to concerns of consumers with respect to the healthfulness of beef. If improving the healthfulness of beef is deemed important by a significant market niche, increasing iron and zinc concentration could be of priority as they are important minerals for human health and beef is one of the best dietary sources of these minerals (Zanovec et al., 2010).

Because these traits are not expressed until the slaughter of offspring, it is impractical to improve them through traditional selection, but they make ideal candidates for genomic selection if genetic markers that account for a worthwhile proportion of the variation can be identified. Mateescu et al. (2013) reported that the amount of variation that could be accounted for by Single Nucleotide Polymorphysm genotypes was concordant with reported pedigree-based heritabilities and was medium-high (0.37) for iron. Mateescu et al. (2013) also found that 7 regions on the 6 chromosomes (chromosomes 1, 2, 7, 10, 15, and 28) have major effects on the iron content of longissimus in Angus cattle. The accuracy of direct genomic values estimated as the genetic correlation with the phenotype (muscle iron concentration) adjusted for contemporary groups was 0.59.

Magnesium

Dietary magnesium is essential to the well-being of animals because of its role in maintaining muscle and nerve function, keeping heart rhythm steady, supporting the immune system, and maintaining skeletal integrity (Clarkson and Haymes, 1995; Saris et al., 2000; Tam et al., 2003; Spiegel, 2011; and Genuis and Bouchard, 2012). Magnesium is also involved in regulating the blood glucose concentration and blood pressure, as well as being involved in ATP metabolism and protein synthesis (Wester, 1987; and Saris et al., 2000). The role of magnesium includes the prevention and management of hypertension, cardiovascular disease, and diabetes (Bo and Pisu, 2008; Champagne, 2008; and Houston, 2011). Mateescu et al. (2013) reported that the magnesium concentration in beef longissimus was 254.5 μg/g muscle (Table 3). Therefore, a 100 g serving of beef would provide between 6.4 and 8.5% of the 300- to 400-mg daily recommended allowance for magnesium intake for adults. Mateescu et al. (2013) also reported a high variability for magnesium concentration among beef longissimus samples. A 100 g serving could provide as much as 14% of the daily recommended allowance for adults (Table 3).

Manganese

Manganese is a trace mineral found primarily in bones, liver, kidneys, and pancreas. Manganese is important for the formation of connective tissue, blood clotting factors, and sex hormones (Santamaria and Sulsky, 2010) and plays a role in lipid and carbohydrate metabolism, calcium absorption, and blood glucose regulation (Kehl-Fie and Skaar, 2010; and Bae et al., 2011) and is necessary for brain and nerve function. Manganese is also a component of the enzyme superoxide dismutase, one of the key antioxidants in the body (Miriyala et al., 2012). Mateescu et al. (2013) reported the manganese concentration in beef longissimus averaged 0.07 μg/g muscle but was highly variable (Table 3). The 0.007 mg provided by a 100 g serving of beef longissimus only provides a small proportion of the daily requirement of 1.8 to 2.3 mg per d depending on gender and age.

Phosphorus

Phosphorus is present in every cell of the body, though it makes up only 1% of the body. Its primary function is in the formation of bones and teeth. It plays an important role in the metabolism of carbohydrates and lipids and in the synthesis of structural proteins (van den Broek and Beynen, 1998; and Civitelli and Ziambaras, 2011). It is also an integral component of adenosine triphosphate critical in supplying energy for many metabolic processes. Phosphorus is a component of the coenzyme form of most B vitamins. It also is involved in the contraction of muscles, in kidney function, in maintaining heartbeat regularity, and in nerve impulse conduction (Horl et al., 1983; Clarkson and Haymes, 1995; and van den Broek and Beynen, 1998). The main food sources of phosphorus are the protein food groups of meat and milk. A diet that provides adequate levels of calcium and protein also provides an adequate level of phosphorus. Mateescu et al. (2013) reported the phosphorus concentration of beef longissimus of 1,968 μg/g muscle, allowing a 100 g serving to provide 196.8 mg of phosphorus or 28% of the 700-mg daily recommended allowance for phosphorus intake for adults. Mateescu et al. (2013) also reported that the phosphorus concentration of beef longissimus was highly variable so that a serving of beef could contribute a maximum of 45% (3,163 μg/g muscle) of the daily recommended allowance for phosphorus intake (Table 3). The heritability of phosphorus, however, was low (0.04, Mateescu et al. 2013).

Potassium

Potassium is a very important mineral for the human body It is primarily involved in electrical and cellular body functions being essential for the proper function of all cells, tissues, and organs (Tylavsky et al., 2008). Beef is one of the best sources of potassium in the human diet (O’Neil et al., 2011; and Nicklas et al., 2012). Mateescu et al. (2013) reported the potassium concentration in beef longissimus was 3,433 μg/g muscle, with one,100 g serving of beef providing 343.3 mg of potassium, equivalent to about 10% of the daily recommended value.

Zinc

Dietary zinc is essential for human growth and development is involved in DNA and RNA synthesis and the catabolism of carbohydrates, lipids, and proteins for ATP generation (Saper and Rash, 2009). Zinc plays an integral role in immune function and aids in wound healing and the maintenance of normal blood glucose concentrations (Jansen et al., 2009; John et al., 2010; Kehl-Fie and Skaar, 2010; Morgan et al., 2011; and Mocchegiani et al., 2012). Adequate zinc intake is essential for human health through its function in enzymatic systems, cell division and growth, and gene expression as well as through its role in immunity and reproduction (Pereirra and Vicente, 2013). Animal and plant foods supply zinc, but as with iron, zinc is more efficiently absorbed from beef than from other sources. Thus, beef is an excellent source of dietary zinc. Mateescu et al. (2013) reported the zinc concentration in beef longissimus was 38.9 μg/g muscle. Therefore, a 100 g serving of beef contains 3.89 mg of Zn, or 26% of the recommended dietary allowance (Table 3). High coefficients of variation (c.v. = 0.20 mg) and moderate heritability (h2 = 0.10) indicate a potentially successful increase of beef zinc content through selection (Mateescu et al., 2013).

Selenium

Selenium is also an essential trace element in human nutrition being the component of selenoproteins which have antioxidant functions in the prevention of cardiovascular disease and cancer (Rayman, 2000) and as a component of the glutathione peroxidase pathway thereby being instrumental in liver detoxification processes. One hundred grams of beef provides about 26% of zinc RDA. (USDA, 2011). Selenium, though present in meat, is more concentrated in some seafood. The recommended dietary allowance of selenium is 55 μg/d for adults (Food and Nutrition Board, and I. of M., 2000). Its content in fresh meat is about 45 µg/100 g of fresh meat with good bioavailability (Fairweather-Tait, Collings, and Hurst, 2010).

Conclusion

Interestingly, science does unequivocally disclose that red meat contains many minerals, such as iron, truly crucial for human health, therefore, we must recall this knowledge and so inform those who may not remember. Specifically, red meat is the best source of heme-iron (the most bio-available and efficiently absorbed iron form). Note that red meat is also a source of the less critical dietary minerals of calcium, copper, and manganese, and is a fair source of magnesium and selenium, which are important for heart health, as well as playing a critical role in the normal functioning of the body. Principally, calcium is necessary for muscles contraction, but magnesium is also necessary for both voluntary and involuntary muscle function as well as energy metabolism. It is needed for muscles to relax back to their full length. Nevertheless, having a daily proportion variable in red meat, having an adequate diet of calcium and protein means an adequate level of phosphorus. Furthermore, beef is a good source of zinc providing (26%) twenty-six percent of the recommended daily allowance in a (100g) one hundred grams serving and is its best source! Finally, we may have the opportunity to make a genomic selection to increase the quantity of iron and zinc contained and enhance the healthfulness of beef. Now you may ask yourself, what else does red meat contain? The next post will help you to find the answer!