Protein and Amino Acid Requirements in the Adults - Essay Example

Protein and amino acid requirements in the adults: This essay is primarily based on critically discussing the principal factors potential of influencing the protein and amino acid (AA) requirements in the adults. Acknowledging the amount of dietary proteins essential to maintain a good health in younger and older adults is important because it helps in “assessment of the nutritional status of individuals or populations and the planning of good diets” (Rand, Pellett, and Young, 2003, p. 109). As life standard continues to increase tremendously in response to technological advancement, so does the average human lifespan and it is frequently claimed by research literature that advancing age forms a critically important factor capable of influencing the protein and AA metabolism and thereby requirements in the adults. The growing incidence of the most frequent health problems in the present age like diabetes, cardiovascular diseases, and cancer is also associated with advancing age and relationship between such diseases and protein and AA requirements is established in myriad research studies. In addition to advancing age which is a heavily recognized factor now, multiple other factors also influence the protein and AA metabolism and requirements in the adults of which the most widely researched ones will be contemplated in this essay. Nitrogen balance studies based data is riddled with variations due to which “despite years of research, amino acid requirements remain a controversial issue” (Duncan, Ball, and Pencharz, 1996, p. 718; Gibson et al., 2002, p. 511). This is also a complex issue because of the variability in proteins AA composition and adult protein intake (Millward, Fereday, Gibson, and Pacy, 2000, p. 112). A dietary protein intake of 118g/d for adults of average weight engaged in average physical activity was considered a standard for most of the late 19th century but the general consensus as reported by historical evidence was that “the protein element should amount to over 100 g a day, and the energy value should be over 3000 calories” (McCay, cited in Rand et al., 2003, p. 109). However, the dietary standard was challenged by Chittenden by the turn of the 20th century who claimed that 118g/d could not be considered an appropriate dietary standard as one-half of this amount taken daily by adults could be more than enough to maintain vigor and meet the physiological needs of human body. It was further stressed that protein and AA requirements differ for people leading an ordinary lifestyle and people engaged in strenuous activities requiring significant muscular activity which proves that physical activity is an important factor which influences the protein and AA requirements. For people living ordinary lives not involving much physical movement, even lower protein intake could suffice and maintain the nitrogen equilibrium. “With most individuals, especially persons not leading an active out-of-door life, even smaller amounts of one-half of 118g/d will suffice” (Chittenden, cited in Rand et al., 2003, p. 109). The protein requirements for adults as set by the UN Expert Consultation in 1985 were introduced after evaluating both short-term and long-term nitrogen equilibrium research literature. The UN Expert Consultation in the end fixed “the adult mean protein requirement at 0.6 g/kg-1/d-1” (Rand et al., 2003, p. 110) which is similar to average intake value of 0.66g.kg-1.d-1 of good quality protein as proposed by the Food and Nutrition Board in 2002 (Humayun, Elango, Ball, and Pencharz, 2007, p. 995). Basically, adult protein requirement is commonly defined as “the continuing intake of dietary protein that is sufficient to achieve body nitrogen equilibrium (zero balance)” (Rand et al., 2003, p. 110) in a healthy adult of normal body weight doing moderate physical activity. Potentially influential factors related to adult nitrogen requirement as identified by Mann-Whitney test and Kruskal-Wallis test (cited in Rand et al., 2003, pp. 114-115) include age, sex, diet, and environment. Aging is one important most factor found to be related to “various metabolic and physiologic changes that may contribute to alter dietary protein requirements for older adults” (Campbell et al., 2008, p. 1322). A research identified that in contrast to women, “men appeared to have a statistically significantly different (P < 0.001) median requirement (higher by almost 20 mg N/kg-1/d-1)” (Rand et al., 2003, pp. 117-118). It was further suggested that the nature of source of dietary protein had an insignificant effect on median protein requirement which sets in contrast with the research study of Millward et al. (2000) which evaluated the difference in the effects of milk and wheat proteins in context of adult AA requirements. The study concluded that “adaptive mechanisms of lysine conservation allow wheat protein to be utilized more efficiently than expected” (Millward et al., 2000, p. 112) which shows that the type of dietary protein source is potential of influencing adult protein and AA requirement. The importance of protein source as a potential factor is also stressed by Young and Pellett (1985, p. 1086) who claim that AA needs can be met even by basic diets if they include wheat in contrast to cassava based diets which lack in essential AAs and hence require higher quantities of milk alongside to fulfill protein and AA requirements. In contrast to this, it is claimed that wheat has a lower postprandial biological value as a research based on subjects consuming wheat-based diet principally reported that all those subjects “required a marked increased in their daily energy intake” (Bolourchi et al., cited in Bos et al., 2005, p. 93) to maintain nitrogen equilibrium. This shows that diet plays the role of an important factor because foods which differ in their AA pattern produce variability in human adults’ dietary requirement (Carpenter, 1992, p. 915). After conducting as many as 19 different studies to evaluate the nitrogen balance responses of 235 participants in a better way, Rand et al. set the median protein requirement of the normal weight healthy adult population at “105 mg N/kg/d (0.65 g good-quality protein/kg/d)” (Rand et al., 2003, p. 120). This sets in slight contrast to the average protein requirement suggested for healthy normal weight adults of both sexes by European Food Safety Authority according to which “the average requirement (AR) is 0.66 g protein/kg body weight per day based on nitrogen balance data” (EFSA, 2012, p. 2557). In contrast to these values, Young and Pellett (1987) argue that the mean minimum physiological requirement “should be increased to 0.75g/kg/d to give a safe protein intake for healthy adults” (Young and Pellett, 1987, p. 1329). Furthermore, the population reference intake (PRI) for adults of both sexes and all ages was set at “0.83 g protein/kg body weight per day” (EFSA, 2012, p. 2557). Research stresses that there should be a basis for evaluating physiological requirements of different indispensable AAs like MIT AA requirement pattern on grounds of which Marchini et al. (1994) refuted the lower requirement valued introduced by William et al. in 1974 (Marchini et al., 1994, p. 85). Some researchers have claimed that elder individuals of good health status do not a require a different, less, or higher protein intake than do younger adults of good health status which overrides the claim made by many that advanced age interferes heavily with dietary protein intake and metabolism as mentioned earlier. Though this has been suggested frequently in the literature, truth is that difference in protein requirements between elderly and young adults could not be suggested with confidence and small percentage of implausibility in this claim still remains that advanced age is an absolute factor. In contrast to this, age is claimed to an absolute factor in another research which suggests that protein intake in the elderly considerably declines due to changes occurring in the “dynamic aspects and distribution of whole body protein and amino acid metabolism during the later adult years” (Gersovitz et al., 1982, p. 6). Also another research based on protein intake in America claims that “there is a trend for decreased protein intake as Americans age” (Fulgoni, 2008, p. 1557). “Factors such as infection, trauma, and disease tend to lower the efficiency of nitrogen utilization and retention and are more common in the elderly than in the young” (Rand et al., 2003, p. 122). So, the importance of factors like stress, injury, and sepsis in relation to AA requirements is established and also highlighted by Young and Marchini (1990) who claim that these factors trigger metabolic responses “characterized by increases in both whole-body protein synthesis and breakdown” (Young and Marchini, 1990, p. 285). This is why age and physiological state of adults are identified in many research studies as two major factors which influence requirements for amino acids (Pellett, 1990, p. 726). Digestibility as a potent factor is also worth mentioning here as some proteins are more readily digested by the human body than others due to intrinsic differences in the composition of food protein. It is claimed that “differences in digestibility affect the utilization of protein” (Pellett, 1990, p. 727) and hence requirements. This also implies that the nutritional value and AA composition of different types of proteins also constitute a potential factor influencing “human protein and amino acid requirements” (Young and Pellett, 1985, p. 1081). Gender, however, is considered by all to be an absolute factor which influences the protein and AA requirements in adults. Different studies have concluded that non-lactating and non-pregnant women have significantly lower dietary protein requirement than male adults owing to variability in physical structure. “Body size is the major determinant of the absolute requirements for protein” (Pellett, 1990, p. 724) which grounds the validity of body size as a potential factor influencing protein and AA metabolism and requirements. Also, physical activity is an important factor as earlier discussed and could significantly affect the nitrogen balance in any study conducted using any scientific method (Rand et al., 2003, p. 123). Concluding, this much becomes clear from the above discussion that the effects of all factors like age, sex, diet etc. have been widely observed and scrutinized by researchers and it is proposed that they play a significant role in adult requirement variability. This remains true that energy and dietary requirements may significantly decline with passing years given the reduced physical activity following retirement and increased incidence of certain diseases. This is also because with advancement in age, changes in appetite, food intake, physical mobility, and general health status are noticed and all such changes have undeniably significant ramifications for the protein and AA requirements. The fact identified repeatedly in several sources that athletes or physically vigorous adults require a higher level of dietary proteins than younger or elder adults do under ordinary living conditions grounds the importance of physical activity as an absolute factor which is why the effects of physical activity along with other factors on protein and AA requirements and metabolism and body nitrogen equilibrium have been comprehensively studied. References: Bos, C, Juillet, B, Fouillet, H, Turlan, L, Daré, S, Luengo, C, Ntounda, R, Benamouzig, R, Gausserès, N, Tomé, D, and Gaudichon, C 2005, Postprandial metabolic utilization of wheat protein in humans, The American Journal of Clinical Nutrition, vol. 81, pp. 87–94. Campbell, WW, Johnson, CA, McCabe, GP, and Carnell, NS 2008, Dietary protein requirements of younger and older adults, The American Journal of Clinical Nutrition, vol. 88, pp. 1322-29. Carpenter, KJ 1992, Protein requirements of adults from an evolutionary perspective, The American Journal of Clinical Nutrition, vol. 55, pp. 913-17. Duncan, AM, Ball, RO, and Pencharz, PB 1996, Lysine Requirement of adult males is not affected by decreasing dietary protein, The American Journal of Clinical Nutrition, vol. 64, pp. 718-25. EFSA 2012, Scientific Opinion on Dietary Reference Values for protein, EFSA JOURNAL, vol. 10, no. 2, pp. 2557-2623. Fulgoni, VL 2008, Current protein intake in America: analysis of the National Health and Nutrition Examination Survey, 2003–2004, The American Journal of Clinical Nutrition, vol. 87, pp. 1554-57. Gersovitz, M, Motil, K, Munro, HN, Scrimshaw, NS, and Young, VR 1982, Human protein requirements: assessment of the adequacy of the current Recommended Dietary Allowance for dietary protein in elderly men and women, The American Journal of Clinical Nutrition, vol. 35, pp. 6-14. Gibson, NR, Jahoor, F, Ware, L, and Jackson, AA 2002, Endogenous glycine and tyrosine production is maintained in adults consuming a marginal-protein diet, The American Journal of Clinical Nutrition, vol. 75, pp. 511-18. Humayun, MA, Elango, R, Ball, RO, Pencharz, PB 2007, Reevaluation of the protein requirement in young men with the indicator amino acid oxidation technique, The American Journal of Clinical Nutrition, vol. 86, pp. 995-1002. Marchini, JS, Cortiella, J, Hiramatsu, T, Castillo, L, Chapman, TE, and Young, VR 1994, Phenylalanine and tyrosine kinetics for different patterns and indispensable amino acid intakes in adult humans, The American Journal of Clinical Nutrition, vol. 60, pp. 79-86. Millward, DJ, Fereday, A, Gibson, NR, and Pacy, PJ 2000, Human adult amino acid requirements: [1-13C]leucine balance evaluation of the efficiency of utilization and apparent requirements for wheat protein and lysine compared with those for milk protein in healthy adults, The American Journal of Clinical Nutrition, vol. 72, pp. 112–21. Pellett, PL 1990, Protein requirements in humans, The American Journal of Clinical Nutrition, vol. 51, pp. 723-37. Rand, WM, Pellett, PL, and Young, VR 2003, Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults, The American Journal of Clinical Nutrition, vol. 77, pp. 109-27. Young, VR, and Marchini, JS, Mechanisms and nutritional significance of metabolic responses to altered intakes of protein and amino acids, with reference to nutritional adaptation in human, The American Journal of Clinical Nutrition, vol. 51, pp. 270-89. Young, VR, and Pellett, PL 1985, Wheat proteins in relation to protein requirements and availability of amino acids, The American Journal of Clinical Nutrition, vol. 41, pp. 1077-1090. Young, VR, and Pellett, PL 1987, Protein intake and requirements with reference to diet and health, The American Journal of Clinical Nutrition, vol. 45, pp. 1323-43. Read More