What is Protein?
Definition of Protein
Etymology: French protéine, from Late Greek prōteios primary, from Greek prōtos first — more at prot-
Date: circa 1844
1 : any of various naturally occurring extremely complex substances that consist of amino-acid residues joined by peptide bonds, contain the elements carbon, hydrogen, nitrogen, oxygen, usually sulfur, and occasionally other elements (as phosphorus or iron), and include many essential biological compounds (as enzymes, hormones, or antibodies)2 : the total nitrogenous material in plant or animal substances
REFERENCES:
http://www.merriam-webster.com/dictionary/PROTEIN
Established Protein Recommendations
Recommended Dietary Allowances (RDA) for different age groups.2
Recommended Dietary Allowance for Protein
Grams of protein needed each day
Children ages 1 – 3
13
Children ages 4 – 8
19
Children ages 9 – 13
34
Girls ages 14 – 18
46
Boys ages 14 – 18
52
Women ages 19 – 70+
46
Men ages 19 – 70+
56
In the early 1940’s, nutrition thinking moved from minimum requirements to the more general concept of Recommended Dietary Allowances (RDA). The RDA for protein was defined as the level of protein judged to be adequate ... to meet the known nutrient needs for practically all healthy people [13].
REFERENCES:
13. National Research Council: "Recommended Dietary Allowances. Protein and Amino Acids," 10th ed. Washington DC: National Academy Press, pp.52 –77,1989 .
Based on the information available, the Food and Nutrition Board set the RDA at two standard deviations above the average requirement to meet the minimum needs of 97.5% of the population.
The primary measurements used to define average protein requirements are short-term nitrogen balance and amino acid oxidation [14,15]. The primary focus is protein utilization and how to achieve maximum growth or maintenance of lean body mass using the least dietary protein. The experimental methods were based on feeding a range of protein intakes and monitoring changes in nitrogen balance or amino acid oxidation. These measures exhibit an inflection point believed to reflect the minimum protein intake necessary to maintain maximum lean body mass.
REFERENCES:
14. Munro HN, Crim MC: The protein and amino acids. In Shils ME, Young VR (eds): "Modern Nutrition in Health and Disease," 7th ed. Philadelphia: Lea & Febiger, pp1 –37,1988 .
15. Millward DJ: Macronutrient intakes as determinants of dietary protein and amino acid adequacy. J Nutr134 :1588S –1596S,2004 .[Abstract/Free Full Text]
http://www.jacn.org/cgi/content/full/23/suppl_6/631S
“While an inflection point in the nitrogen balance graph is usually clear, the nitrogen balance values above the inflection point are not usually zero as the concept implies. In 1978, Hegsted [16] (reviewed the literature on human nitrogen balance studies including studies ranging up to one year in length. He found that the nitrogen balance graph remained positive at nitrogen intakes above the inflection point. Most investigators point to these data as evidence for methodology flaws in the nitrogen balance approach. So while researchers have dogmatically used the nitrogen balance approach to predict the minimum protein requirement, they have been unwilling to accept the complete data set that protein intakes above the inflection point result in net nitrogen retention and maintenance of higher levels of lean body mass. “ -Donald K. Layman, PhD
REFERENCES:
Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana, Illinois
: Donald K. Layman, Ph.D., 437 Bevier Hall, University of Illinois, 905 South Goodwin, Urbana, IL 61801, E-mail: dlayman@uiuc.edu
16. Hegsted DM: Assessment of nitrogen requirements. Am J Clin Nutr31 :1669 –1677,1978 .[Free Full Text]
The Recommended Dietary Allowances (RDA) by the National Academy of Sciences are revised approximately every five years. The RDA are compromise opinions of highly qualified nutritional scientists based on interpretations of available data. As with any interpretations of available data. As with any, interpretations and opinions not found on definitive information, they are subject to challenges. The RDA for protein for 7-to 9-uear-old children have been adjusted downward from 60 g in 1958 to 36 g in 1974, a 40% reduction. Data from our laboratories have shown positive apparent nitrogen balances on intakes as low as 18 g daily when no allowances were made for integumental and other nitrogen losses, however, based on accumulative data over several years we calculate the protein requirement to be 45 g daily from a typical American diet. If a safety factor of 30% is added the allowance would become 58.5 g. Currently the RDA for protein for the 7- to 10-year-old child supplies 6% of the RDA for Calories which contrasts to 8.30 and 9.20% for adult males and females, respectively. For comparison, energy from protein as a percentage of total energy for some common foods are: white bread, 12%; corn meal 10%; white rice 7%; and wheat flour 13%
REFERENCES:
http://www.ncbi.nlm.nih.gov/pubmed/727009
Adv Exp Med Biol. 1978;105:1-10.
Position paper on RDA for protein for children.
Abernathy RP, Ritchey SJ.
Human Breast Milk is 6% protein according to the USDA.
http://www.nutridiary.com/quantity.asp?fid=01107&ref=http://www.nutridiary.com/query.asp%3Ffd%3Dmilk%26fg%3D0000%26db%3D0%26opt%3D0
The Recommended Daily Allowance (RDA) of protein promulgated by the Food and Nutrition Board of the National Academy of Science in the Dietary Reference Intakes for macronutrients (1) and accepted by the US Department of Agriculture Dietary Guidelines Committee (2) of 0.8 g protein/kg/d is a reasonable estimation of the minimal amount of protein intake needed to maintain nitrogen balance (N-balance) in healthy young adults. This value may be inadequate as even a minimal value for active adults or the elderly.
The N-balance does not have a direct correlation with functional outcomes and therefore is not the most appropriate endpoint for the determination of the optimal level of protein intake considered in the context of the overall diet. Parameters related to muscle mass, strength, and metabolic function are more relevant endpoints. N-balance was chosen as the endpoint for determining the RDA largely because of the prevalence of available data.
The optimal level of protein intake is >0.8 g protein/kg/d. The current RDA for protein is actually <10% href="http://www.ajcn.org/cgi/content/full/87/5/1582S#R1#R1">1) and less than the amounts of protein recommended in the dietary guidelines (2). The amount of dietary protein that could be characterized as optimal is uncertain.
Protein intake can be increased to at least double the RDA, and perhaps higher, without risk of adverse responses in healthy individuals with normal renal function
REFERENCES:
Food and Nutrition Board, Institute of Medicine. Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids (macronutrients). Washington, DC: National Academy Press, 2002. Internet: http://www.nap.edu/books/0309085373/html/2002 (accessed 19 June 2006).
US Departments of Health and Human Services (USDHHS) and Agriculture (USDA). 2005 Dietary guidelines for Americans. 6th ed. Washington, DC: US Department of Health and Human Services, 2005.
ACKNOWLEDGMENTS
The Beef Checkoff provided compensation to the author for speaking engagements through the National Cattlemen's Beef Association.
Reimbursements of travel costs and lodging were provided by the Protein Summit sponsors. The Summit sponsors provided an honorarium for the author's efforts on the Steering Committee for organization of the meeting and preparation of manuscripts.
http://www.ajcn.org/cgi/content/full/87/5/1582S
In general, it's recommended that 10–35% of your daily calories come from protein. Below are the Recommended Dietary Allowances (RDA) for different age groups.
REFERENCES:
2Source for Acceptable Macronutrient Distribution Range (AMDR) reference and RDAs: Institute of Medicine (IOM) Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. This report may be accessed via
www.nap.edu*
Most people eat more protein than they need without harmful effects However, protein contributes to calorie intake, and so if you eat more protein than you need, your overall calorie intake could be greater than your calorie needs and contribute to weight gain. Besides that, animal sources of protein can be sources of saturated fat which has been linked to elevated low-density lipoprotein (LDL) cholesterol, a risk factor for heart disease. In addition, for people with certain kidney diseases, a lower-protein diet may be recommended to help prevent an impairment in kidney function.
Source: NIH Medical Encyclopedia
http://www.cdc.gov/nutrition/everyone/basics/protein.html
Several studies concluded, that active people and athletes may require elevated protein intake (compared to 0.8g/kg).[13][10][9] Suggested amount varied between 1.6g and 1.8g,[10] while a proposed maximum protein intake would be approximately of 25% of energy requirements at approximately 2 to 2.5 g, per body kg per day.[9] However, many questions still remain to be resolved.[10]
REFERENCES:
9. Layman DK, Shiue H, Sather C, Erickson DJ, Baum J: Increased dietary protein modifies glucose and insulin homeostasis in adult women during weight loss. J Nutr133 :405 –410,2003 .[Abstract/Free Full Text]
10. Layman DK, Boileau RA, Erickson DJ, Painter JE, Shiue H, Sather C, Christou DD: A reduced ratio of dietary carbohydrate to protein improves body composition and blood lipid profiles during weight loss in adult women. J Nutr133 :411 –417,2003 .[Abstract/Free Full Text]
^ a b c d Lemon, Peter (2000). "Beyond the Zone: Protein Needs of Active Individuals". Journal of the American College of Nutrition 19 (5): 513–521.
Dangers of excessive protein, defined as when protein constitutes > 35% of total energy intake, include hyperaminoacidemia, hyperammonemia, hyperinsulinemia nausea, diarrhea, and even death (the “rabbit starvation syndrome”). The three different measures of defining protein intake, which should be viewed together are: absolute intake (g/d), intake related to body weight (g · kg-1 · d-1) and intake as a fraction of total energy (percent energy). A suggested maximum protein intake based on bodily needs, weight control evidence, and avoiding protein toxicity would be approximately of 25% of energy requirements at approximately 2 to 2.5 g · kg-1 · d-1, corresponding to 176 g protein per day for an 80 kg individual on a 12,000 kJ/d diet
REFERENCES:
^ a b c d e f Bilsborough, Shane; Neil Mann (2006). "A Review of Issues of Dietary Protein Intake in Humans". International Journal of Sport Nutrition and Exercise Metabolism (16): 129-152. http://hk.humankinetics.com/IJSNEM/viewarticle.cfm?aid=5642. Retrieved 2010-01-05.
http://hk.humankinetics.com/IJSNEM/viewarticle.cfm?aid=5642
by OrganicFitness.Org
WHO and United Nation Protein Establishment
http://whqlibdoc.who.int/trs/WHO_TRS_935_eng.pdf
