Meat: Where Lean and Fat Get Together

On a recent trip to the grocery store, I overheard a female customer ask the meat counter assistant which beef roast would be the most lean.  The customer was a trim figure in athletic attire, and a young girl (presumably her daughter) loitered by the shopping cart.  This customer embodied the ever-more health conscious consumer eager to provide the most nutritious food for her family.  However, the public is often bombarded with vague or contradictory statements about food (“Beef is bad,” “Eggs are good,” “Beef is good,” “Eggs are bad,” “Chia seeds and acai berries!”), making purchasing decisions difficult.  Fortunately, nutrition labels and ingredient statements on processed foods can allow shoppers to make comparisons and choices that fit their health needs.  But for many raw foods such as meats, fruits, and vegetables, the nutrient information is often not displayed.  This can lead to questions like that of the aforementioned customer. This post of Meat Salads offers some clarification on the types and amounts of fat found in different fresh meats.

Perhaps one of the most misunderstood concepts of food composition is “fat.”  The word is heavy with negative connotation, but without fat in the diet, humans and animals would fare very poorly.  After all, dietary fat facilitates the absorption of vitamins A, D, E, and K; allows for the formation and function of skin, brain, and nervous tissues; encourages the feeling of satiety, and enhances the flavor, aroma, and texture of food (Meat Poultry Nutrition, 2013).  Still, overconsumption of fat can be detrimental for human health, so limiting fat intake to only 20-35% of total daily calories is recommended for almost everyone (Centers for Disease Control and Prevention [CDC], 2012a).  Also, the Dietary Guidelines for Americans 2010 recommends further that calories from saturated fat constitute only 10% of total daily calories (CDC, 2012a).  Saturated fat and its counterpart, unsaturated fat, exist in animal muscles in different ratios depending on the species and muscle function/location.  This means different types of meat will have various levels of saturated and unsaturated fat.  Table 1 gives a simplified explanation of the two fat types, and Table 2, with data from the USDA National Nutrient Database for Standard Reference, Release 26, gives examples of how fat differs among fresh meats.

 

Table 1: A simplified explanation of saturated and unsaturated fats (fatty acids).  Saturated fatty acids are more often used for energy storage and insulation whereas unsaturated fatty acids are used for cell membrane structure, signaling molecules, and other functions.

Fat Type	Definition‡	Diagram‡
Saturated	Every carbon atom in the hydrocarbon chain is bound to as many hydrogen atoms as possible.  The fat has a rigid structure at room temperature.
Unsaturated	At least two carbon atoms in the hydrocarbon chain are not bound to as many hydrogen atoms as possible.  At least 1 double bond (circled in illustration) is present.  The fat has a fluid structure at room temperature.  When only 1 double bond is present, the fat is “monounsaturated.”  When 2 or more double bonds are present, the fat is “polyunsaturated.”

‡ Carnegie Mellon University, 2006

Table 2: A comparison of meat from beef, pork, poultry, eggs, and fish.  Meat will vary in saturated and unsaturated fats depending on the species and muscle of origin.

Species	Cut*	Saturated fat (g/100 g meat)^	Monounsaturated fat (g/100 g meat)^	Polyunsaturated fat (g/100 g meat)^
Beef	Chuck pot roast (1/8” exterior fat)	7.254	7.697	0.684
Beef	Top blade steak (0” exterior fat)	2.817	3.409	0.389
Beef	Strip steak (1/8” exterior fat)	2.100	2.545	0.208
Beef	Tenderloin roast (0” exterior fat)	2.363	2.578	0.454
Beef	Brisket flat half (1/8” exterior fat)	8.951	9.498	0.844
Beef	Flank steak (0” exterior fat)	2.978	2.924	0.277
Pork	Shoulder	4.140	5.367	2.474
Pork	Loin chops	2.450	2.985	0.878
Pork	Cured ham steak	1.440	1.960	0.470
Chicken	Breast (skinless)	0.479	0.586	0.360
Chicken	Thigh (skinless)	0.932	1.272	0.799
Turkey	Breast (skinless)	0.344	0.284	0.355
Turkey	Thigh (skinless)	0.782	0.749	0.722
Egg	Large, whole	1.563	1.829	0.956
Salmon	Atlantic, wild	0.981	2.103	2.539

*Except for the cured ham steak, the given values are for the raw meat servings.

^All values are presented as “g fat/100 g meat” except for the egg (g fat/50 g).

From Table 2, differences in fat content among species and cuts are clearly seen.  Since the CDC recommends limiting fat, especially saturated fat, intake, the values listed above might not be so welcoming for beef fans.  However, the CDC also reports that saturated fat intake can be lowered when customers choose beef cuts with less marbling and then trim all visible fat from the outside of a cut (CDC, 2012b).  Marbling refers to the amount of intramuscular fat (the white flecks or specks) visible in meat.  As Figure 1 below shows, meat can be heavily laced with intramuscular fat or essentially devoid of it.  While more marbling is appropriate for a very indulgent filet mignon at a steakhouse, less marbling is more appropriate for cuts eaten more frequently at home, especially if limiting saturated fat intake is part of your lifestyle.

 

Figure 1: Marbling in cuts of fresh beef.  “Marbling” can be used to give beef a quality grade.  To limit saturated fat intake, consumers should pick cuts with the least amount of marbling that will still allow for a successful cooking and eating experience (Good, 2008).

Just like the lady at the meat counter, more and more people want to know the advantages and disadvantages of foods to make better choices for themselves and their families.  Though following the CDC’s recommendation of limiting fat calories to 20-35% of total daily calories is key to avoiding many health problems, not all foods in the grocery store come with nutrition labels that declare their fat content.  However, having a basic understanding of saturated and unsaturated fats, comparing values from the USDA National Nutrient Database, and being able to differentiate leaner cuts from those with more fat will enable consumers to buy a wide range of meats for all needs, tastes, and occasions.  Remember: variety is key.  Enjoy salmon, eggs, chicken, turkey, shrimp, pork, beef, lamb, and other meats to experience a multitude of flavors while providing your body with essential nutrients.

*To explore more foods and their nutrients, explore the Database by clicking here.*

References
 

Carnegie Mellon University (2006).  Department of Biological Sciences: Interactive Animations.  Retrieved from http://telstar.ote.cmu.edu/biology/MembranePage/index2.html

Centers for Disease Control and Prevention (2012a).  Dietary Fat.  Retrieved from http://www.cdc.gov/nutrition/everyone/basics/fat/index.html

Centers for Disease Control and Prevention (2012b).  Saturated Fat.  Retrieved from http://www.cdc.gov/nutrition/everyone/basics/fat/saturatedfat.html

Good, C. (2008).  Beef Grades.  Retrieved from http://www.thebeefsite.com/articles/1279/beef-grades

Meat Poultry Nutrition (2013).  Skinny on Dietary Fat.  Retrieved from http://www.meatpoultrynutrition.org/ht/d/sp/i/26061/pid/26061.

USDA (NA).  National Nutrient Database for Standard Reference Release 26.  Retrieved from http://ndb.nal.usda.gov/ndb/search/list

 

 

 

 

The Science Behind the Hot Dog: Part 2

The last time I was at my parents’ house, my dad jokingly made a reference to “cow lips” in hot dogs.  I had to cringe.  With labeling requirements that reveal all ingredients in food products, why does the myth of hot dogs being made of "unspeakable" animal parts still exist?  Its longevity may be due to a hot dog’s inner appearance.  The springy, smooth, reddish brown hot dog is a far cry from marbled, fibrous beef chuck.  However, that beef chuck can be turned into a hot dog with the right machinery, ingredients, and cooking process and still deliver the protein, iron, and other nutrients promised by a fresh cut of beef.  In a previous post, I explained the non-meat ingredients of a hot dog.  Today, let’s talk about the meat.

A hot dog is an “emulsified” meat product.  An emulsion is a stabilized mixture of solid particles dispersed throughout a liquid component (Aberle, Forrest, Gerrard & Mills, 2001).  In an emulsified meat product, the particles are fat and the liquid component is water containing salts and proteins (Aberle et al., 2001).  While water and fat would naturally not mix together, proteins with both hydrophobic (“water-fearing”) and hydrophilic (“water-loving”) parts can hold the fat and water together (Figure 1).  Myofibrillar proteins (the stringy, fibrous muscle proteins that allow for movement) hold fat and water together well, but for the myofibrillar proteins to be of use, they must first be extracted from their original positions in skeletal muscle.  A bowl chopper (think of a king-size food processor) will first dice ground lean meat into tiny pieces, thereby increasing the surface area of the meat.  Salt will extract the tightly bound myosin and actin from each other, and these liberated proteins will then interact with the fat and water which are later added to the mix (Aberle et al., 2001). 

Figure 1: Proteins coat fat particles to allow the fat to be held within the water phase of an emulsified product.

If you are unfamiliar with proteins and how they are put together, this might be a little confusing.  The main point, though, is that parts of the animal with LOTS of myofibrillar protein (i.e., skeletal muscle) can interact with water and fat much better than parts of the animal with little myofibrillar protein.  Another type of animal protein is called “stromal protein,” perhaps better known as “connective tissue.”  The main stromal proteins are collagen and elastin.  Collagen is found in skin, lips, ligaments, bones, and blood vessels, and is, in fact, the most abundant protein in an animal’s body (Lodish, Berk, Zipursky, et al., 2000).  However, it is an “insoluble” protein, meaning it is not broken down as myofibrillar proteins are broken down by salt. 

Now, you might be wondering, “What does this have to do with hot dogs?”  Remember that hot dogs are emulsified products, and the emulsion can only be stable if the components bind together well under stress.  Meats that have high binding capabilities are those high in myofibrillar proteins such as bull and cow meat, skinless poultry meat, lean pork trimmings, and beef chucks (Aberle et al., 2001).  Meats with a high percentage of stromal protein include the infamous “filler meats:” lips, stomachs, snouts, skin, and tripe (Aberle et al., 2001).  If hot dogs contain a large percentage of collagen-rich meat, the collagen will melt during heat processing and then congeal as gelatin when the hot dogs are cooled (Aberle et al., 2001).  These hot dogs will undoubtedly not be what the producer or consumer wanted. Since skeletal muscle already contains some collagen due to the presence of blood vessels and connective tissue (Figure 1), deliberately increasing the amount of stromal protein by adding lips or snouts is not greatly practiced. 

Hopefully you now understand why the joke of “cow lips” in hot dogs is not so funny.  Producers want their customers to be happy with tasty, nutritious, good looking products, and this can only happen with the right ingredients.  If you are still curious about what’s in your hot dogs, check the ingredients label.  All filler or “variety meats” must be declared on the label, including the specific meat’s name (e.g. “heart”) (National Hot Dog & Sausage Council, 2013).  So the next time you’re at a weenie roast and someone doesn’t want to eat something made of the “less savory parts of an animal,” show them the ingredient list and enlighten them!  You can even whip out words like "emulsified" or "myofibrillar" to really impress them.

References

Aberle, E.D., Forrest, J.C., Gerrard, D.E. & Mills, E.W.  (2001).  Principles of Meat Science (4^th ed.).  Dubuque, IA: Kendall/Hunt Publishing Company.

Lodish, H., Berk, A., Zipursky, S.L., et al.  (2000).  Molecular Cell Biology (4^th ed.).  New York, NY: W. H. Freeman.

National Hot Dog & Sausage Council (2013).  How hot dogs are made: The real story.  Retrieved from http://www.hot-dog.org/ht/d/sp/i/38597/pid/38597.

hot dog picture: http://www.afdr.org/v2933-HOT-DOG-BEEF-HD-F-DELI-STYLE-BEEF-FRANKS-51.aspx

emulsion diagram: http://lpoli.50webs.com/Tips.htm

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Hey, Tyson: What's your Beef with the Beef?

   Perhaps you have heard that Tyson Foods Inc. has stopped purchasing cattle that have been fed Zilmax, a feed additive meant to improve carcass quality.  The subsequent flood of news stories peppered with phrases like “beta-agonists,” “growth promotants,” and “animal welfare” can understandably raise questions from the public.  What are beta-agonists?  Are they safe for animals to consume?  If fed to an animal, is the meat safe for me to eat?  A very comprehensive article published by the American Society of Animal Science’s Taking Stock newsletter explains beta-agonists well.  The entire article can be found at http://takingstock.asas.org/?p=9145.  Here’s a brief summary of this article’s explanation of beta-agonists and what they do:

·         As animals mature, lean muscle is more difficult to produce than fat.  At the finishing stage (the time period before slaughter), beta-agonists encourage the formation of muscle mass rather than fat.  This means more lean meat (about 30 pounds per head of beef) will be available for the consumer.

·         Beta-agonists used for livestock are called ractopamine and zilpaterol hydrochloride; both are approved by the FDA Center for Veterinary Medicine.  While ractopamine can be used for swine and cattle, zilpaterol hydrochloride is only fed to cattle.  Its trade name, as sold by Merck & Co., is Zilmax.

·         Meat from beef cattle fed Zilmax is safe to eat.  Beta-agonists break down quickly before animals are slaughtered, and no human illnesses or ailments have ever been tied to the consumption of meat from Zilmax-fed cattle.

·         Tyson Foods Inc. has cited joint problems for its concern over cattle fed Zilmax with the logic that additional weight gained due to Zilmax would add pressure to joints.  However, no direct connection between Zilmax consumption and the loss of joint integrity has been found (McCurry-Schmidt, 2013).

   So there we are.  Zilmax is FDA-approved, increases the amount of lean muscle on a carcass and does not harm consumer health.  Of course, since the health of animals is a top priority for farmers and processors, the appearance of cattle with obvious joint problems has raised concerns.  According to a recent article in The Wall Street Journal, Merck & Co. will temporarily suspend sales of Zilmax and conduct studies on how the additive affects the health of cattle (Newman & Gee, 2013).  Research into this issue will hopefully reconfirm Zilmax’s safety, identify how it may affect cattle negatively, or reveal a different cause for joint problems.

   Of course, while all cases of endangered animal welfare are important, taking a “guilty until proven innocent” approach can trigger resentment from producers.  Cattle farmers all over the world have accepted the use of Zilmax for the last twenty years, the FDA has approved it in the U.S. since 2007, and documented research has supported its use for over 30 years (Rich, 2013).  Why, then, is the blame for beef cattle walking stiffly being thrown on Zilmax?  The National Cattlemen’s Beef Association CEO Forrest Roberts commented recently that specific additives “can be used responsibly when managed properly,” (Coffeen, 2013).  Providing cattle with the necessities to develop strong skeletons and feeding promotants for only a short time are parts of proper management; overuse of a muscle developer on an animal with a weak skeleton can understandably cause problems. 

   The world’s population is growing and, of course, needs to be fed.  Beef and pork are choice sources of nutrients are being demanded more and more by a growing middle class.  Being able to increase the yield-to-feed ratio for livestock will benefit producers, consumers, and animals as long as the means to do this are safe for all concerned.  To understand how much impact Zilmax or other additives can have on the beef supply, consider this quote from Richard Raymond, a former Undersecretary for Food Safety, USDA:

“If only half of the 24 million head of cattle harvested annually, a conservative estimate to be sure, yielded an additional 30 pounds of meat, this would provide 360 million more pounds of lean beef during a time when drought and high grain prices are forcing a reduction in the size of the American cattle herd. That would equate to 1.4 billion additional quarter pounders to help feed the world’s children, too many of whom go to bed hungry every night,” (Raymond, 2013).

References

Coffeen, Peggy.  (2013).  Tyson no longer taking cattle fed Zilmax.  Retrieved from http://www.agriview.com/news/livestock/tyson-no-longer-taking-cattle-fed-zilmax/article_130e0790-6166-5da2-bc5c-a7888abeee49.html.

McMurry-Schmidt, M. (2013, August 16).  What are beta agonists?  Taking Stock.  Retrieved from http://takingstock.asas.org/?p=9145.

Newman, J. & Gee, K.  (2013, August 18).  What’s ailing America’s cattle?  The Wall Street Journal.  Retrieved from http://online.wsj.com/article/SB10001424127887323423804579020953889322782.html.

Raymond, R. (2013).  Having agony over the agonists?  Perspective from a former USDA Food Safety official.  Retrieved from http://factsaboutbeef.com/2013/08/02/having-agony-over-the-agonists-perspective-from-a-former-usda-food-safety-official/.

Rich, D. (2013, August 19).  Tyson to ban cattle fed with Zilmax.  High Plains/Midwest Ag Journal.  Retrieved from http://www.hpj.com/archives/2013/aug13/aug19/0813ZilmaxbanDRdbsr.cfm.

The Science Behind the Hot Dog

Have you ever read the ingredients list on a package of hot dogs or lunch meat and found yourself wondering, “What’s this doing in here?”  Many processed meat products contain ingredients both familiar (e.g., pork, beef, sugar, salt) and unfamiliar to consumers.  Unfortunately, some consumers are turned away by ingredients that sound more like they belong in science labs than in kitchens.  However, these compounds are used to increase the quality and safety of products while keeping them affordable and accessible to the consumer (Why ship something that will spoil en route?).  So to answer your question of, “What’s this doing in here?”, here are the purposes of several components found in many processed meat products explained.

       

               

Sodium Phosphates

·         “Phosphates” can encompass a variety of compounds including mono-, di-, and triphosphates.

·         Whereas monophosphates act as buffering compounds, di- and triphosphates are used to increase the water-holding capacity in meat products (Aberle, Forrest, Gerrard, & Mills, 2001).

o   Increased water-holding capacity leads to products with greater tenderness and juiciness (Aberle et al., 2001).

o   These phosphate compounds act similarly to adenosine triphosphate (ATP), the major energy unit produced in most living things.

·         Phosphates may also deter the development of rancidity and improve product texture (Aberle et al., 2001).

Sodium Lactate

·         This weak acid is added to processed meats to control the growth of Listeria monocytogenes, a bacterium of concern in the world of processed, packaged foods (Zink, N.A.). 

·         Sodium lactate is able to disrupt the pH gradients that bacteria set up in their cellular membranes.  These gradients are vital for energy-producing machinery to work, so disruption of the gradient severely reduces a bacterium’s ability to thrive (Zink, N.A.).

Sodium lactate

Sodium Diacetate

·         Sodium diacetate is also added to meat to reduce the growth of L. monocytogenes (Zink, N.A.).

·         This compound dissociates into acetic acid (the active ingredient in vinegar) and sodium acetate.  Acetic acid can donate protons to the environment, thus lowering pH.  This action disrupts the proton gradient and weakens a bacterium’s ability to survive (Zink, N.A.).

Sodium diacetate

Sodium Ascorbate/Erythorbate

·         Sodium ascorbate and erythorbate are “isomers;” that is, their atomic makeup is the same but their conformations are different. 

·         Sodium ascorbate is naturally found in citrus fruits and vegetables, and its biologically active form, ascorbic acid, is commonly known as vitamin C (NCBI, N.A.).

·         Sodium erythorbate is more commonly used in processed meats since it is cheaper and its pH is much closer to that of meat (Mancini et al., 2007).

·         Both sodium ascorbate and sodium erythorbate act as cure accelerators: they reduce the amount of time needed for a product treated with nitrite to develop cured properties (Aberle, 2001).

So don’t fear those scientific-sounding ingredients on the back of a package.  Those ingredients are added with the consumer’s safety and satisfaction in mind.  Keep enjoying those hot dogs and brats at grill-outs this summer, and stock up on lunch meat for kids heading back to school.

References

Aberle, E.D., Forrest, J.C., Gerrard, D.E., & Mills, E.W. (Eds.).  (2001).  Principles of Meat Science (4^th ed.). Dubuque, IA: Kendall/Hunt Publishing Company.

Mancini, R.A., Hunt, M.C., Seyfert, M., Kropf, D.H., Hachmeister, K.A., Herald, T.J., Johnson, D.E.  (2007). Comparison of ascorbic acid and sodium erythorbate: Effects on the 24 h display colour of beef lumbar vertebrae and longissimus lumborum packaged in high-oxygen modified atmospheres.  Meat Science 75(1), 39-43.

NCBI (N.A.).  Ascorbic Acid—Compound Summary (CID 23667548).  Retrieved from http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=23667548&loc=ec_rcs#itabs-2d.

Zink, D.L.  (N.A.).  Post-processing interventions to control listeriosis  [PDF].  Retrieved from http://www.fsis.usda.gov/wps/wcm/connect/3ceeab5b-0bed-4bf6-8513-05f79df03e2b/Listeria_DZink_12.pdf?MOD=AJPERES&CACHEID=d548190c-c5e0-49ba-8771-52a14f42b830.

All compound images are courtesy of PubChem (http://pubchem.ncbi.nlm.nih.gov/).

B12: Of Beef and Bacteria

Just as hamburgers, steaks, chicken wings, pork chops, and other meat products bring unique flavors and aromas to the dinner table, they provide many components necessary for human health.  In fact, meat and other animal products provide some nutrients not found in other foods.  Among those is cyanocobalamin, more commonly known as vitamin B12.

Vitamin B12 is produced by microorganisms that can be found in the environment and inside animals.  Those inside animals make the vitamin in the intestine, and the vitamin can then travel to other organs, muscles, and products (milk and eggs) which can then be incorporated in the human diet (Vitamin B12, n.d.).  Beef liver and clams are the best sources of the vitamin, followed by fish, poultry, meat, milk, eggs, and other dairy products (Office of Dietary Supplements [ODS], 2011).  Red meat is a particularly affordable and diversifiable source of B12.  For example, a single 100 g serving of red meat (such as a 3.5 oz. hamburger patty) can provide 66% of an adult’s daily need for the vitamin (McAfee et al., 2010).  If an insufficient level of vitamin B12 is maintained, weakness, weight loss, tiredness, confusion, loss of appetite, and other health problems may develop (ODS, 2011).  However, though some people may consume enough of the vitamin B12 through their diet, they may not be able to use it.  Vitamin B12 must first be separated from its bound protein and then affiliate with an “intrinsic factor” in the stomach before being absorbed (Vitamin B12, n.d.).  When dietary vitamin B12 cannot be utilized, a supplement is necessary to avoid a deficiency.

According to the National Institute of Health’s Office of Dietary Supplements, the amount of vitamin B12 people need to consume each day varies by age but is essential during all stages of life, as shown in Table 1 (2011).  Problems with metabolism, red blood cell formation, and nervous system performance can result from a vitamin B12 deficiency, and the best way to ensure adequate vitamin B12 levels is to incorporate a variety of animal products into the diet (New York Times, 2011). 

Table 1: Daily recommended amount of vitamin B12 in micrograms (mcg).  The daily recommended amounts increase due to age or special conditions such as pregnancy or lactation (ODS, 2011).

Life Stage	Recommended Amount
Birth to 6 months	0.4 mcg
Infants 7–12 months	0.5 mcg
Children 1–3 years	0.9 mcg
Children 4–8 years	1.2 mcg
Children 9–13 years	1.8 mcg
Teens 14–18 years	2.4 mcg
Adults	2.4 mcg
Pregnant teens and women	2.6 mcg
Breastfeeding teens and women	2.8 mcg

While adults can endure a vitamin B12 deficiency for several years before showing its symptoms, newborns can show its effects soon after birth (Dror & Allen, 2008).  In a healthy pregnant woman, vitamin B12 will travel to the placenta and then to the growing child (Vitamin B12, n.d.).  If the mother, unable to absorb the vitamin or, by choice or not, lacking vitamin B12 in her diet, maintains a low level of this vitamin before and during pregnancy, her unborn child will not receive enough of the vitamin (Dror & Allen, 2008).  In a study by Majchrzak and colleagues (2006) comparing B-vitamin levels in people with different diets, omnivores possessed adequate levels of vitamin B12 whereas vegetarians and vegans displayed inadequacies of the vitamin.  It could then be conjectured that pregnant women eating a balanced diet that includes meat, poultry, eggs, and dairy are much more likely to deliver enough B12 to their unborn children than women avoiding these foods.  Being unable to absorb vitamin B12, not having access to animal products, or choosing not to consumer animal products can cause irritability, failure to thrive, poor development, and apathy in newborns if the mother does not receive a vitamin B12 supplement.

In conclusion, people who enjoy a variety of protein sources including red meat, poultry, eggs, and dairy and effectively absorb and use these food’ nutrients can avoid multitudes of deficiencies, especially that of vitamin B12.  Those who cannot absorb the vitamin, cannot obtain animal products, or choose not to consume animal products need to receive a vitamin B12 supplement to avoid a deficiency.  As for me, I am happy to obtain my vitamin B12 from a bacon-topped turkey burger or ham and cheese omelet rather than the encapsulated products of a bacteria culture. 

References

Dror, D.K., Allen, L.H.  (2008).  Effect of vitamin B12 deficiency on neurodevelopment in infants: current knowledge and possible mechanisms.  Nutrition Reviews 66(5), 250-255. DOI: 10.1111/j.1753-4887.2008.00031.x

Majchrak, D., Singer, I., Maenner, M., Rust, P., Genser, D., Wagner, K.H., Elmadfa, I.  (2006).  B-vitamin status and concentrations of homocysteine in Austrian omnivores, vegetarians and vegans.  Annals of Nutrition and Metabolism 50(6), 485-491. DOI: 10.1159/000095828

McAfee, A.J., McSorley, E.M., Cuskelly, G.J., Moss, B.W., Wallace, J.M.W., Bonham, M.P, Fearon, A.M.  (2010).  Red meat consumption: An overview of the risks and benefits.  Meat Science 84(1), 1-13.

New York Times (2011, February 15).  Vitamin B12.  Retrieved from http://health.nytimes.com/health/guides/nutrition/vitamin-b12.

Office of Dietary Supplements (2011, June 24).  Dietary Supplement Fact Sheet: Vitamin B12.  Retrieved from http://ods.od.nih.gov/factsheets/VitaminB12-QuickFacts/.

Vitamin B12 – Compound Summary. (n.d.)  In PubChem Compound.  Retrieved from http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=16212801&loc=ec_rcs