Saturday, August 24, 2013

Human Metabolism

The Flexible Human Metabolism

Breedlove, Watson, and Rosenzweig (2010) explained that the human body anticipates future needs, by reading a variety of factors, such as food consumption and energy output. Simply stated, when individuals consume less food, their bodies hold onto fat and energy supplies and slow the metabolism because it senses future need, or rather, future scarcity of food. This, of course, is a highly efficient evolutionary process that compensated for varying food supplies versus the need to maintain energy. It has left the species with somewhat of a conundrum in that although a significant percentage of the population is obese or overweight, losing weight has its inherent challenges. When an individual begins dieting, the body naturally senses future scarcity of food and regulates itself by holding onto stores of fat. The result is that it becomes almost impossible to lose weight (Breedlove, Watson, & Rosenzweig, 2010). In this way, metabolism is one of the powerful influences on body weight.

                                                      Influences on Body Weight

Media Affects Personal Body Awareness

Certainly Americans are subjected to an inordinate amount of media that portrays healthy and happy individuals as thin. Celebrities maintain a physical appearance that has become an ideal by which people measure themselves. People are constantly bombarded with images of unreasonable expectations regarding body weight and other aspects of appearance (Wiseman, Gray, Mosimann, & Ahrens, 1992). These images negatively influence body awareness, which affects how individuals maintain body weight.

Genetics and metabolism

Cultural and racial differences in metabolisms have been found to exist and these differences subject individuals to predispositions in their ability to metabolize food. Because of geographical location and other environmental influences, cultures and races can evolve specific metabolic characteristics suitable for their environment, such as their geographical location. Neel (1962) suggested that when a culture lives in harsh, unstable, or geographically isolated locations, members of that culture develop a culturally specific, highly efficient metabolism. Hawaii is geographically isolated which may predispose Native Hawaiians to biological efficiency (Neel, 1962). He further postulated that if conditions change, the efficient metabolism may no longer be beneficial - and it may become detrimental. In this case, adequate food supplies reach Hawaii today and the idea of food shortage has become obsolete, however Native Hawaiians still maintain biological efficiency. When Native Hawaiians returned to their pre-Western diet, however, they lost weight and were healthier (Shintani, Hughes, Beckam & O'Connor, 1991).

In another example of cultural genetics, excessive carbohydrate consumption has been blamed for the almost epidemic proportion of diabetes in the USA. However, Teuscher, Baillod, Rosman and Teuscher (1987) found that although two West African villages had extremely high carbohydrate intake (84% of their daily calories) none had diabetes and none showed serum levels of blood glucose levels or being pre-diabetic. The main source of carbohydrate for these peoples was cassava root, which is an indigenous plant and staple in their culture (Teuscher, Baillod, Rosman & Teuscher, 1987). It may be that the high consumption of carbohydrates was genetically appropriate for these individuals because this food was natural to their environment and their genetic constitution.

Circadian Rhythms

Circadian Rhythms can influence obesity (Zanquetta, CorrĂȘa-Giannella, Monteiro, & Villares, 2010). Although the exact biological mechanisms by which this influence takes place is unknown, a disruption in these intrinsic mechanisms can provoke obesity and other metabolic disorders as well. The rhythms of the body (the central and peripheral clocks) must maintain synchronization with the adipose tissue clock for the proper regulation of hunger, energy, body weight, and fat deposition (Zanquetta et al., 2010).

Endocrine System

The body's hormonal system has an effect on body weight as well (Schwartz et al., 2010). Many of the body's systems are nourished by sleep and when sleep is inadequate or less than ideal in quality, cortisol and insulin levels can become unbalanced or dysfunctional. Schwartz et al. (2010) explained that a number of lifestyle factors have a tremendous influence on body weight. These include how often an individuals eat, how much they exercise and sleep. Psychological stress, too, has an influence on weight gain or reduction (Schwartz et al., 2010). Schwartz et al. listed ghrelin, glucocorticoids insulin and leptin as a few of the well-researched hormones that have an effect on body weight.

Cultural Influences and Eating Disorders

The system of average American values causes most people to associate thinness with beauty. This affects men and women, but especially women (Knauss, Paxton, & Alsaker, 2008). Such cultural pressure causes individuals, especially females to devalue themselves if their body type deviates from the contrived ideal, which has become thinner during the last few decades (Gardner, Garfinkel, Schwartz, & Thompson, 1980). It is this decrease in self-satisfaction that causes women to create maladaptive eating patterns that can result in disordered eating (Gardner et al., 1980). Because of the expectation to maintain a specific body type, they may resort to disordered eating to help them reach the goal of their perceived ideal body weight.


Breedlove, S. M., Watson, N. V., & Rosenzweig, M. R. (2010). Biological psychology: An introduction to behavioral, cognitive, and clinical neuroscience. (6th ed.) Sunderland, MA: Sinauer Associates, Inc. Publishers.

Brown, D. E., Gotshalk, L. A., Katzmarzyk, P. T., & Allen, L. (2011). Measures of adiposity in two cohorts of Hawaiian school children. Annals Of Human Biology, 38(4), 492-499. doi:10.3109/03014460.2011.560894

Knauss, C., Paxton, S., & Alsaker, F. (2008). Body dissatisfaction in adolescent boys and girls: Objectified body consciousness, internalization of the media body ideal and perceived pressure from media. Sex Roles, 59(9-10), 633-643.

Garner, D. M., Garfinkel, Schwartz, D., & Thompson, M. (1980) Cultural expectations of thinness in women. Psychological Reports: Volume 47, Issue , pp. 483-491. doi: 10.2466/pr0.1980.47.2.483

Neel, J., V. (1962). Diabetes Mellitus: a 'thrifty' genotype rendered detrimental by 'progress'? American Journal of Human Genetics 14, 353-362.

Shintani, T., Hughes, C., Beckham, S., & O'Connor, H. (1991). Obesity and cardiovascular risk intervention through the ad libitum feeding of traditional Hawaiian diet. The American Journal Of Clinical Nutrition, 53(6 Suppl), 1647S-1651S.

Teuscher, T., Baillod, P., Rosman, J. B., Teuscher, A. (1987). Absence of diabetes in a rural West African population with a high carbohydrate/cassava diet. Lancet, 1 8536, 765-738.

Schwarz, N. A., Rigby, R. R., La Bounty, P., Shelmadine, B., & Bowden, R. G. (2011). A review of weight control strategies and their effects on the regulation of hormonal balance. Journal of Nutrition and Metabolism, 1-15. doi: 10.1155/2011/237932

Wiseman, C. V., Gray, J. J., Mosimann, J. E., & Ahrens, A. H. (1992). Cultural Expectations of Thinness in Women: An Update. International Journal Of Eating Disorders, 11(1), 85-89.

Zanquetta, M.M., CorrĂȘa-Giannella, M.L., Monteiro, M.B., & Villares , S.M.F. (2010). Body weight, metabolism and clock genes. Diabetology & Metabolic Syndrome. 2(1), 53. Doi: 10.1186/1758-5996-2-53

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