When we think of protein we usually think of meat. However, there is some protein in fruits, berries, vegetables, nuts and seeds.
Proteins are large molecules that are essentially long chains of amino acids.
The essential elements of an amino acid are carbon, nitrogen, oxygen and hydrogen (R is the rest of the stuff attached).
Proteins do a lot of stuff in your body, everything from being part of cells that make up tissue (example: muscle tissue is full of protein because of actin and myosin, (mechanical structure tissue)) to transporting other molecules around the body and communicating information to cells. Proteins participate in some way in almost every action of your body.
Some amino acids can be synthesized by the cells in your body while others have to be gotten through the protein you eat.
As a molecule, most proteins are linear polymers, which simply means they are large molecules with many repeating subunits.
Just to give you an idea of how complicated protein molecules are here is a "ball and stick" representation of an enzyme protein called hexokinase. The two little clumps in the upper right corner are ATP and glucose.
Okay, so how much of this stuff does the average person need and what are the best sources?
It really depends on age, the size of your body, amount of activity, etc. But, usually the average adult could use about 50 grams of protein a day. The best source of protein is meat, eggs and dairy.
"Meat, eggs, and dairy products from pastured animals are ideal for your health. Compared with commercial products, they offer you more "good" fats, and fewer "bad" fats. They are richer in antioxidants; including vitamins E, beta-carotene, and vitamin C. Furthermore, they do not contain traces of added hormones, antibiotics or other drugs." - http://www.eatwild.com/healthbenefits.htm) (Eggs " These findings suggest that consumption of up to 1 egg per day is unlikely to have substantial overall impact on the risk of CHD or stroke among healthy men and women." - JAMA. 1999 Apr 21;281(15):1387-94. http://www.ncbi.nlm.nih.gov/pubmed/10217054) It is abundant, package nicely for breakdown and absorption into your body and usually offers a complete source, that is to say gives amino acids that your body cannot make. You can get protein from plant sources but they are usually not as abundant and also incomplete (not containing all essential amino acids)
Problems with too much animal protein.
Excessive amounts of protein have been linked to bone mineralization loss (Barzel US. Excess dietary protein can adversely affect bone. J Nutr. 1998 Jun; 128 (6): 1051– 53. ) and kidney problems. ("Protein overload stimulates RANTES production...Given its chemotactic activity, RANTES [Regulated on Activation, Normal T Cell Expressed and Secreted] released into the interstitium might promote inflammatory cell recruitment and contribute to interstitial inflammation and renal disease progression..." - Kidney International (1998) 53, 1608–1615; doi:10.1046/j.1523-1755.1998.00905.x http://www.nature.com/ki/journal/v53/n6/abs/4490199a.html )
However, animal proteins have been shown to increase bone mineral density while plant proteins have been shown to diminish bone mineral density. (Am J Epidemiol. 2002 Apr 1;155(7):636-44. http://www.ncbi.nlm.nih.gov/pubmed/11914191)
Excess dairy might lead to or aggravate symptoms of multiple sclerosis an autoimmune disease. This could be because of the molecular similarity between a certain milk protein and certain proteins on nerve tissue. ("In this study, we demonstrate that Ab specific for the extracellular Ig-like domain of myelin oligodendrocyte glycoprotein (MOG) cross-reacts with a homologous N-terminal domain of the bovine milk protein butyrophilin (BTN)...The demonstration of molecular mimicry between MOG and BTN, along with sequestration of BTN-reactive Ab in CSF suggests that exposure to this common dietary Ag may influence the composition and function of the MOG-specific autoimmune repertoire during the course of MS." - J Immunol. 2004 Jan 1;172(1):661-8. http://www.ncbi.nlm.nih.gov/pubmed/14688379)
Excessive red meat consumption has been linked to certain disease processes like heart disease and colorectal cancer but unfortunately the other factors possibly contributing to these diseases has confounding the data enough to make these conclusions questionable. (" Colinearity between red meat intake and other dietary factors (e.g. Western lifestyle, high intake of refined sugars and alcohol, low intake of fruits, vegetables and fibre) and behavioural factors (e.g. low physical activity, high smoking prevalence, high body mass index) limit the ability to analytically isolate the independent effects of red meat consumption. Because of these factors, the currently available epidemiologic evidence is not sufficient to support an independent positive association between red meat consumption and colorectal cancer." - Obes Rev. 2011 May;12(5):e472-93. doi: 10.1111/j.1467-789X.2010.00785.x. http://www.ncbi.nlm.nih.gov/pubmed/20663065 )
What about the high fat content of meat doesn't that lead to heart disease? According to the American Journal of of Clinical Nutrition, the answer is no. (" A meta-analysis of prospective epidemiologic studies showed that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD. " - Am J Clin Nutr. 2010 Mar;91(3):535-46. doi: 10.3945/ajcn.2009.27725. Epub 2010 Jan 13.http://www.ncbi.nlm.nih.gov/pubmed/20071648?dopt=AbstractPlus)
Red meat actually has a lot of beneficial qualities. One of which is that it contains a lot of B vitamins which are crucial in proper functioning of the cells of your body. Red meat is especially rich in iron and vitamin B12.
("Red meat is a rich source of vitamin B12, which is vital to proper functioning of nearly every system in your body. B12 deficiency can play a role in everything from aging, neurological disorders, and mental illness, to cancer, cardiovascular disease, and infertility. Red meat also contains significant levels of other B vitamins, including thiamin, riboflavin, pantothenic acid, folate, niacin, and vitamin B6. It’s crucial to get these vitamins from whole foods sources, rather than relying on government fortification of processed foods, and red meat is one of the easiest ways to ensure adequate intake." - http://chriskresser.com/red-meat-it-does-a-body-good )
The iron content of beef (more readily available in heme version than in plants) is crucial for red blood cells and deficeincies can not only cause anemia but other disease processes as well like Plummer-Vincent syndrome which promotes esophogeal cancer. ("The Plummer-Vinson syndrome, caused by iron deficiency, has been known for more than half a century to promote the development of esophageal cancer." - Herbert V, The antioxidant supplement myth. Am J Clin Nutr 1994;60:157-8. http://ajcn.nutrition.org/content/60/2/157.full.pdf )
Is all beef the same?
Not all beef is the same. It seems that 100% grass fed beef is better for you than typical corn fed beef. This may be because the omega 3 to 6 ratio is more balanced in grass fed beef not to mention other dietary factors such as higher amounts of vitamin A, E, and antioxidants.
(" Several studies suggest that grass-based diets elevate precursors for Vitamin A and E, as well as cancer fighting antioxidants such as glutathione (GT) and superoxide dismutase (SOD) activity as compared to grain-fed contemporaries. " - http://www.nutritionj.com/content/9/1/10 )
Red meat is rich in something called creatine which is only found in animal foods. Creatine has been shown to be crucial to cognitive function. ( "Creatine supplementation had a significant positive effect (p < 0.0001) on both working memory (backward digit span) and intelligence..." - Proc Biol Sci. Oct 22, 2003; 270(1529): 2147–2150. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1691485/ ) ("... in vegetarians rather than in those who consume meat, creatine supplementation resulted in better memory." - British Journal of Nutrition / Volume 105 / Issue 07 / April 2011, pp 1100-1105 http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8207518 ) getting your creatine from natural sources might also be the best choice since creatine supplementation has been linked to kidney problems. ( " One case report of acute renal failure was reported in a 20-year-old man taking 20 gm/day of creatine for a period of four weeks." - J Herb Pharmacother. 2004;4(1):1-7. http://www.ncbi.nlm.nih.gov/pubmed/15273072 ) (" We report a case of a heretofore healthy 18-year-old man who presented with a 2-day history of nausea, vomiting and stomach ache while taking creatine monohydrate for bodybuilding purposes. The patient had acute renal failure, and a renal biopsy was performed to determine the cause of increased creatinine and proteinuria. The biopsy showed acute tubular necrosis. In the literature, creatine monohydrate supplementation and acute tubular necrosis coexistence had not been reported previously. Twenty-five days after stopping the creatine supplements, the patient recovered fully. Even recommended doses of creatine monohydrate supplementation may cause kidney damage; therefore, anybody using this supplement should be warned about this possible side effect, and their renal functions should be monitored regularly." - NDT Plus (2011) 4 (1): 23-24. doi: 10.1093/ndtplus/sfq177 First published online: October 11, 2010 http://ckj.oxfordjournals.org/content/4/1/23.full )
Carnosine is another nutrient only found in animal foods that has been shown to prevent degenerative affects of aging like eyesight and cognitive problems. (" By controlling oxidative stress, suppressing glycation, and chelating metal ions, carnosine is able to reduce harmful sequelae such as DNA damage. AGEs are known contributors to the pathology of Alzheimer's disease, and carnosine therefore merits serious attention as a possible therapeutic agent." - Sci Aging Knowledge Environ. 2005 May 4;2005(18):pe12. http://www.ncbi.nlm.nih.gov/pubmed/15872311 ("...carnosine seems to delay the impairment of eyesight with aging, effectively preventing and treating senile cataract and other age-related diseases. Therefore, carnosine may be applied to human being as a drug against aging." - http://www.ncbi.nlm.nih.gov/pubmed/10951108 )
"Upon digestion, carnosine is broken down in the gastrointestinal tract into its constituents. Yes, some intact carnosine does escape the GI tract freely but that small amount is quickly broken down in the blood by the enzyme carnosinase. Carnosinase hydrolyzes carnosine and other dipeptides containing histidine into their constituent amino acids. In other words, after consuming meat, all of the carnosine that was ingested is converted to beta-alanine and histidine. Then, oddly enough, the amino acids are converted back to carnosine in the muscles and used or transported where needed. The entire process of carnosine synthesis is not entirely understood, but it's worth noting that consuming carnosine from meat is unnecessary, as it will be converted into beta-alanine and histidine anyway, both of which are available in many raw whole foods. " - http://www.skinnylimits.com/blog/carnosine-and-raw-veganism/
We also hear a lot about omega 3 lipids and health. The active forms of omega 3, DHA and EPA are abundant in animal food and easily converted into useful substrates in the human body. Unlike animal omega 3, plant omega 3 comes in the form of ALA which is harder for the body to convert to useful substrates.
("The parent fatty acid ALA (18:3n-3), found in vegetable oils such as flaxseed or rapeseed oil, is used by the human organism partly as a source of energy, partly as a precursor of the metabolites, but the degree of conversion appears to be unreliable and restricted. More specifically, most studies in humans have shown that whereas a certain, though restricted, conversion of high doses of ALA to EPA occurs, conversion to DHA is severely restricted." Int J Vitam Nutr Res. 1998;68(3):159-73.http://www.ncbi.nlm.nih.gov/pubmed/9637947) ("The vegetarian diet, with an average n-6/n-3 ratio of 10/1, promotes biochemical n-3 tissue decline. To ensure physical, mental and neurological health vegetarians have to reduce the n-6/n-3 ratio with an additional intake of direct sources of EPA and DHA, regardless of age and gender." Ann Nutr Metab. 2008;52(1):37-47. doi: 10.1159/000118629. Epub 2008 Feb 28. http://www.ncbi.nlm.nih.gov/pubmed/18305382)
What about other animal products like chicken, fish, pork, etc. is what they are fed or processed with make a difference?
Processed Meats
Eating processed meat, like sandwich meat, bacon and sausage, seems to be associated with a higher risk of coronary artery disease, colorectal cancer, diabetes, COPD [chronic obstructive pulmonary disease] and bladder cancer.
"...processed meat intake was associated with 42% higher risk of CHD...and 19% higher risk of diabetes mellitus." - Circulation. 2010 Jun 1;121(21):2271-83. doi: 10.1161/CIRCULATIONAHA.109.924977. Epub 2010 May 17. http://www.ncbi.nlm.nih.gov/pubmed/20479151
" The results of our analysis support a moderate positive association between processed meat consumption and mortality, in particular due to cardiovascular diseases, but also to cancer." - BMC Med. 2013 Mar 7;11:63. doi: 10.1186/1741-7015-11-63. http://www.ncbi.nlm.nih.gov/pubmed/23497300
"Consumption of processed meats, but not red meats, is associated with higher incidence of CHD and diabetes mellitus." - Circulation. 2010; 121: 2271-2283 Published online before print May 2010, doi: 10.1161/CIRCULATIONAHA.109.924977 http://circ.ahajournals.org/content/121/21/2271.short
"Frequent cured meat consumption was associated independently with an obstructive pattern of lung function and increased odds of COPD." - American Journal of Respiratory and Critical Care Medicine, Vol. 175, No. 8 (2007), pp. 798-804.
doi: 10.1164/rccm.200607-969OC http://www.atsjournals.org/doi/abs/10.1164/rccm.200607-969OC#.U9WaEKh7Txc
" In these 2 cohorts combined, frequent consumption of bacon was associated with an elevated risk of bladder cancer." - Am J Clin Nutr November 2006 vol. 84 no. 5 1177-1183 [note: not controlled for nitrite or nitrate content, a common ingredient in bacon] http://ajcn.nutrition.org/content/84/5/1177.abstract
What is it about processed meats that research has shown leads to disease processes?
"...addition of nitrite seems to increase, the promoting potency [pre-neoplastic carcinogenic lesions] of cured meat." - Published OnlineFirst June 8, 2010; doi: 10.1158/1940-6207.CAPR-09-0160 Cancer Prev Res July 2010 3; 852 http://cancerpreventionresearch.aacrjournals.org/content/3/7/852.full
It seems that the addition of nitrites to meat creates a disease causing food. What is nitrite?It is a naturally occurring substance in the body and in foods like fruits and vegetables. Of course fruits and vegetables have a combination of nutrients, like vitamin C, that mix with the naturally occurring nitrites preventing them from converting into something called nitrosamines. So, adding nitrite to foods like bacon is not the same as getting nitrite from plant foods. Nitrosamine is a well known carcinogen and when not inhibited by other ingested nutrients from food it can obviously lead to some of the problems associated with processed meats.
Fortunately, the processed food industry knows this and ascorbic acid [vitamin C] along with some other nitrosamine inhibiting products is now added to many preserved or processed meats like bacon. Does this make consuming nitrite preserved meat safe? Hard to say since vitamin C has been added to preserved meat in the U.S. since the 1970's but the research I cite showing processed meats cause all kinds of health problems are much more recent (2007-2013). The 40 year time span that processed meats have had to show that adding vitamin C eliminates the health problems seems to show that it didn't make a difference and that toxic nitrosamines from nitrites are causing just as much problems as ever. There could be some other unknown element to processed meats that causes health problems but the main difference between processed meat and non-processed is the addition of nitrites.
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