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Obesity: Genetic, Hormonal and Environmental Influences

Abstract

The prevalence of obesity has gradually increased over the last few decades. The rates are almost similar in developed and developing nations. The current study investigates the relationship between obesity (a medical condition) and genetic and environmental factors that influence its occurrence. The study utilizes twins where the general assumption is that the twins share similar genetic makeup. The findings of this paper support the conclusion from other researchers who have found a positive link between genetics and obesity as well as environmental factors and obesity. The conclusion is that obesity occurs because of the interaction between genetics and environmental factors.

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Introduction

The prevalence of obesity is on the increase, especially in many developed nations. The increase is alarming health professionals because of the common morbidities that are associated with it. Initially, it was thought to be a preserve of the developed nations. Currently, obesity affects even the developing nations, which have rapidly increasing obesity rates in the world. Researchers and health professionals use values to define obesity. Weight is the main factor that is considered in the definition of the term.

According to Willyard (2014), obesity is a condition that is defined by the body mass index (BMI) above 30 kg/m2. This condition is associated with the accumulation of body fat with unwanted health effects, with some being fatal. Research into the factors that are associated with obesity shows some modifiable and non-modifiable factors, some of which are genetic and environmental. This research paper discusses and evaluates the link between obesity and environmental, genetic, and hormonal aspects that influence in its occurrence.

Known Obesity Factors

Obesity is frequently associated with several factors such as genetics and environmental setup. According to Willyard (2014), this medical condition is associated with increased fat in the body. However, the main factors that lead to its accumulation are metabolic and environmental elements. Fat metabolism has been the subject of many studies, especially based on its link with obesity. Researchers propose that a significant population of obese individuals has disorders in fat metabolism. Such disorders lead to the accumulation of the same fats in their body (Willyard, 2014).

An important observation in the obesity trend is that the prevalence of the condition is on the rise. Hence, some factors in its occurrence have changed over the years (Willyard, 2014). The abundance of food that is associated with the agrarian revolution is partly responsible for the increased weight of individuals over the past few centuries. However, this situation has been under control for a long period. In most developed nations, food security is not a problem. Citizens can afford different types of food. The availability of fast foods means that individuals can access high caloric diets better than the traditional foods (Willyard, 2014). As such, an important factor in the causation of obesity is the availability of fast foods.

Environmental factors are recognized as the strongest factors in the occurrence of obesity (Willyard, 2014). Changes in environmental factors are recognized as leading causes of the increased obesity as observed over the past few decades. The human race has invented many machines and processes that are aimed at making their work easier. These processes have led to less energy use and hence less caloric loss. The result is that more individuals are obese.

People are now walking and exercising less. Besides, they are eating more and better. Most of the environmental studies take the form of twin studies where twins are identified as having the same genetic makeup and hence equal susceptibility to obesity. The findings indicate that environmental factors such as the availability of abundant food are associated with obesity.

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Many genetic studies have been done on the etiology of obesity. Most of these studies find at least a weak link between obesity and genetics. In most of the studies that have evaluated genetic links of obesity, the human genome has been studied to evaluate the similarities that obese individuals have in relation to their genetic makeup. Similar defects in the genes of individuals who have obesity can answer the genetic predisposition of obesity in certain individuals and races. The high prevalence of obesity in some populations depicts an underlying defect in their genetic makeup that makes them more susceptible to the condition.

Consequences of Obesity

Obesity is an important health condition because of the negative consequences that it has on the health of individuals. Obesity is associated with increased morbidity and mortality for individuals who have the condition. Some of the most common conditions that relate to obesity include myocardial infarction that often leads to death (Willyard, 2014).

The accumulation of cholesterol in the circulatory system leads to a significant reduction in the available spaces in blood vessels. The coronary vessels are frequently affected. Thrombus formation is common in obese individuals. It leads to myocardial infarction that is commonly known as heart attack. In the United States alone, cardiovascular conditions are the leading causes of death (Willyard, 2014). Obesity has a large role to play in the increasing prevalence of these conditions.

Diabetes, which is another condition that is associated with obesity, is on the rise in the US and many other parts of the world. Many researchers have established a relationship between Type II diabetes and obesity, with most obese individuals developing this condition and its many complications (Willyard, 2014). Contrary to earlier studies that stated an older age for the development of diabetes, contemporary studies indicate that the condition now occurs at a much earlier age. The obesity epidemic is to blame for the reduction in the age of the onset of this condition, and hence the increased complications of the condition.

Insulin resistance that accompanies obesity is a well-known precursor for diabetes Type II (Willyard, 2014). From studies that have been carried out on obese young individuals, most of them have significant levels of insulin resistance. A current alarming observation in some of the studies is that the age at which obesity is occurring is reducing, with more and more kids and young adults being obese compared to other times in history (Willyard, 2014).

Some of the other conditions that are associated with obesity apart from cardiovascular diseases and Type II diabetes include erectile dysfunction, orthopedic fractures, eye problems, kidney failure, and metabolic conditions among others. It is the duty of health organizations to sensitize and educate people on obesity and its associated risks.

Literature Review

Many studies on the factors that influence obesity have been established to inform the policies that address the condition. Most of these studies investigate a single factor in the development of obesity. Some researchers also investigate similar factors while using different approaches. A literature review is important in any research since it evaluates a study to allow researchers to develop possible conclusions from their study. In this particular study, a search from relevant databases reveals a number of studies that have been done on the area of interest. The studies from the search will be used in this literature review. Only ten of them qualify for consideration.

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In one of the studies that investigate the genetic links of obesity, Hilbert et al. (2009) confirm the existence of a familial link in some of the participants based on their genetic screening. According to Hinney et al. (2009), some of the 421 women and men who qualified as obese and participated in their study were genetically susceptible to obesity based on their genetic makeup.

The researchers used the Revised Illness Perception Questionnaire that they adapted to obesity, with the Stunkard’s Figure Rating Scale being used to assess family history of the condition (Hinney et al., 2009). This study found a significant predisposition for obesity in women compared to similar tendency in men, which stood at 86.2% versus 59.7% (Hinney et al., 2009).

The above study proved the existence of a genetic link to obesity. The researchers concluded that the weight regulation for individuals who have a genetic predisposition to obesity might not be related to the obesity outcome or the long-term weight outcomes (Hinney et al., 2009). Therefore, the current study will investigate the relative risk for obesity. Besides investigating the risk of obesity in the general population and its relationship to genetics, some researchers also carried out studies on the genetics of weight gain.

Faith, Rha, Neale, and Allison (1999) investigated the genetic links of energy intake that is also related to the prevalence of obesity. It is a well-known fact that increased energy intake is associated with high prevalence of obesity. Therefore, these researchers had an important study on the factors that influence obesity. This study utilized genetic studies that had been done on monozygotic and dizygotic twins to assess the caloric intake and their genetic links (Faith et al., 1999). The researchers hypothesized the existence of a genetic link to the amount of caloric intake that individuals take, their fat mass, and their macronutrient intake. Faith et al. (1999) concluded, “Human obesity may be influenced by behaviors that are themselves genetically regulated” (p. 145).

In another study, the researchers intended to investigate whether there were changes in individuals who had similar genetic makeup on human energy expenditure and substrate utilization (Goran, 1997). In this study, the researcher postulated that energy expenditure in individuals is genetically linked to substrate utilization, which also appears in the obesity causation. Energy expenditure in an individual is significant in obesity. In fact, this form of obesity warrants further investigation (Goran, 1997).

A common relationship that was found between environmental factors and obesity was the increased caloric intake. Binge eating often leads to weight gain and eventual obesity. However, a common question is whether binge eating is genetically coded. Some researchers such as Javaras et al. (2008) set to investigate this link between genetics and binge eating.

They used a case control study that involved twins. In this study, the researchers confirmed the existence of a genetic component of binge eating (Binge Eating Disorder). Therefore, they established this component as a cause of obesity in the long-term (Javaras et al., 2008). The findings of this study illustrate that obesity is genetically linked to eating and hence is a genetically controlled condition.

Binge eating carries a high risk of obesity compared to some of the other genetically determined conditions in obesity. This condition has increased in frequency over the last few years. Sleep problems have resulted to the same situation. According to Trace et al. (2012), women are predisposed to binge eating whenever they have sleeping problems.

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This feeding habit is a catalyst for obesity as indicated by other studies on obesity and binge eating. The researchers verified their “support for an independent association between sleep problems and BE, which is likely due to complex psychological, biological, neuroendocrine, and metabolic factors” (Trace et al., 2012, p. 695).

In yet another study that investigated binge eating, Bulik, Sullivan, and Kendler (2002) sought to establish the genetic and environmental factors in the condition and those in obesity. Their study had the objective of establishing the genetic and environmental links to obesity and binge eating. The study had twins as the participating subjects. The conclusion was that obesity and binge eating were familial and genetically coded (Bulik et al., 2002). Genetic factors lead to the expression of these conditions.

An example of a study that investigated the relationship between caloric intake and obesity was done by Faith et al. (1999). In this study, the researchers found that human behaviors that lead directly to obesity are genetically expressed in the affected individuals. In this study, the researchers used monozygotic and dizygotic twins that were preferred in the current study (Faith et al., 1999). Some of the factors that were investigated for genetic influence include caloric intake, weight gain, and activity among others (Faith et al., 1999).

Other genetic studies support the interaction between genetics and environmental factors to cause obesity. In another study, the researchers investigate the relationship between the body mass indices of individuals in relation to their genetic makeup (Haberstick et al., 2010). In this particular study, the researchers postulate that BMI is under the control of genetics. They conclude that individual BMI variations depend less significantly on genetics (Haberstick et al., 2010).

Available research presents depression as another contributor of obesity apart from binge eating. It is associated with modest risk. Growing evidence suggests that depression is also influenced by an individual’s genetics. The female population has a higher risk (Afari et al., 2010). Afari et al. (2010) investigate the relationship between genetics, obesity, and depression. They conclude that there exists shared genetic risk for obesity and depression.

Obesity is often associated with genetic and environmental factors that are influenced by other hereditary and ecological factors. According to Willyard (2014), the existence of gene coding for certain aspects of obesity does not necessarily mean that individuals will get the condition. Obesity is defined as a condition that has familial roots in its development and outcome (Willyard, 2014).

Most of the available research proposes the availability of genetic links to obesity and other conditions that are associated with this particular condition. In most of the studies, twins are used to investigate the environmental and genetic components of the condition due to the relatively common genetic makeup in most of them.

Methodology

The current study will utilize the methodology that has been used by most of the other studies that have been highlighted in the literature review section. The best type of study for the investigation of genetic, environmental, and hormonal components of obesity is through twin studies by utilizing the dizygotic and monozygotic twins (Willyard, 2014). Monozygotic twins have a similar genetic makeup. Hence, they are equally susceptible to obesity in the same environmental conditions. By shifting these twins to different environments, the study will seek to investigate the independent environmental factors in the causation and occurrence of obesity.

The study will evaluate the prevalence of obesity for twins who had been separated at birth or different ages to the level of growing up in different environments. This separation will be important in assessing whether the existing environmental links are strong factors in obesity development. A case control study is an important research method for the investigation of factors that lead to the occurrence of the condition.

Hence, it will be used in this particular research. Most of the previous researches established that dizygotic twins have different genetic components. Thus, they are susceptible to different conditions in different levels. The incorporation of this type of twins in the study will ensure that the research assesses the link between genetics and environmental factors.

Results

In the study, 26 monozygotic and 17 dizygotic twins were identified for incorporation into the study. The assumption in the study is that the monozygotic twins share a common DNA. When these monozygotic twins were separated after birth or a short period thereafter, they were placed in different environmental conditions.

The differences in environment for these twins included abundance of food, levels of activity in the population that they were in, and the economic status of their respective countries and families. After several years, the research was to establish the BMIs of these individuals in an effort to assess whether they were obese. The findings indicated that in areas of low social economic status, twins who were sent here did not exhibit obesity while those in affluence were most often obese.

In some of the twins who were utilized for the study, the development of obesity was noticed after a short duration into their new area, irrespective of the environmental conditions. Although these twins did not have all the necessary conditions for obesity, they developed obesity that was comparable to that of their twin sisters or brothers.

The existence of this observation further supports the postulation that twins who have similar genetic makeup may have similar results when it comes to obesity (Willyard, 2014). In most of the studies that were done in the same area, twins who were separated at birth and sent to the US and Japan showed different levels of obesity. Therefore, the conclusion is that individuals who have similar genetic makeup often respond differently to the environment whey live in the course of their illnesses.

Discussions

Obesity is one of the health conditions that result from the interaction of both environmental and genetic factors. According to the available literature review, most of the studies were done on twins who had a similar genetic composition (Teixeira, Going, Sardinha, & Lohman, 2005). The main importance of the setup of these studies is the ease of deducing any genetic links in the condition, along with the environmental factors in the etiology of the condition. According to Teixeira et al. (2005), obesity is predetermined by the innate genetic conditions in individuals.

Twins in different environments may share similar genetic contents. However, they can develop a medical condition that is unrelated to genetics. Strong links have been found between obesity and the genetic makeup of individuals. In the existing links, genetic abnormalities predispose individuals to the condition when exposed to different environments that have a high risk of obesity. The participation of twins in this study stresses the importance of genetic coding for obesity. There is strong evidence that the condition is associated with other genetically coded factors.

In this study, genetic makeup of individuals forms a strong link to obesity and hence the frequent reports of obese individuals in the society. Despite the existence of genetic predisposition, not all of the susceptible individuals develop obesity or its related medical conditions (Teixeira et al., 2005). This claim is supported by studies that propose the interplay of genetics and environmental factors in the occurrence of obesity. The current study establishes and confirms the interplay between genetics and the environment in the occurrence of obesity.

The major limitation of this study is the duration that is required to follow up the participating twins and the financial resources that might be put into place. Over the many years that the twins will be followed up, some of the twins are lost. The conditions that are being investigated do not also exist in exclusion and hence the witnessed difficulties in investigating each of these conditions in seclusion. Therefore, there is a need to carry out more studies in the area to establish the link between genetics and environmental factors in the occurrence of obesity.

Conclusions

In conclusion, obesity is a common medical condition that affects many individuals in developed and developing world. The alarming trends include the rapid increase in the number of individuals who are affected by the condition. This study has evaluated the links between genetics and the environment in the causation of obesity using twin studies. Most of the available research that has used twins establishes a link between obesity and genetics. The results support the interaction between these factors in the study.

Reference List

Afari, N., Noonan, C., Goldberg, J., Roy-Byrne, P., Schur, E., Golnari, G., & Buchwald, D. (2010). Depression and Obesity: Do Shared Genes Explain the relationship? Pub. Med., 27(9), 799–806.

Bulik, C., Sullivan, P., & Kendler, K. (2002). Genetic and Environmental Contributions to Obesity and Binge Eating. West Virginia: Virginia Institute for Psychiatric and Behavioral Genetics.

Faith, M., Rha, S., Neale, M., & Allison, D. (1999). Evidence for Genetic Influences on Human Energy Intake: Results from a Twin Study Using Measured Observations. Behavior Genetics, 29(3), 145-154

Goran, M. (1997).Genetic Influences on Human Energy Expenditure and Substrate Utilization. Behavior Genetics, 27(4), 123-138.

Haberstick, B., Lessem, J., McQueen, M., Boardman, J., Hopfer, C., Smolen, A., & Hewitt, J. (2010). Stable Genes and Changing Environments: Body Mass Index Across Adolescence and Young Adulthood, Behavior Genetics, 40(3), 495–504.

Hilbert, A, Dierk, J., Conradt, M., Schlumberger, P., Hinney, A., Hebebrand, J., & Rief, W. (2009). Causal attributions of obese men and women in genetic testing: Implications of genetic/biological attributions. Psychology and Health, 24(7), 749–761.

Javaras, K., Laird, N., Reichborn-Kjennerud, T., Bulik, C., Pope, H., & Hudson, J. (2008). Familiality and Heritability of Binge Eating Disorder: Results of a Case-Control Family Study and a Twin Study. International Journal of Eating Disorders, 41(2), 174–179.

Teixeira, J., Going, B., Sardinha, B., & Lohman, G. (2005). A review of psychosocial pre-treatment predictors of weight control. Obesity Reviews, 6(2), 43–65.

Trace, S., Thornton, L., Runfola, C., Lichtenstein, P., Bulik, C., & Pedersen, N. (2012). Sleep Problems Are Associated with Binge Eating in Women. Int J Eat Disord, 45(1), 695-703.

Willyard, C. (2014). The Family Roots of Obesity. Nature, 508(17), S58-S60.

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StudyCorgi. (2021, December 11). Obesity: Genetic, Hormonal and Environmental Influences. Retrieved from https://studycorgi.com/obesity-genetic-hormonal-and-environmental-influences/

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