What Causes Obesity? Nature or Nurture?

What Causes Obesity? Nature or Nurture?


Determination of the cause of a condition is pertinent to its prevention and treatment. The cause of obesity has raised contradicting debates. Some scientists account for nature (genetics) is being the cause of obesity. On the contrary, other scientists account for nurture (environment) as the cause while others explain that the two factors interact to cause obesity. Previous researches have majored on heritability that has been challenged primarily since it only explains the variability and rather not the cause (Moore, 2013).

The proposed research will incorporate molecular genetics to strengthen the inferences made from the quantitative genetics. Twin studies will use a quantitative genetic approach to determine genetic influence on eating behavior and obesity. Molecular genetics will then be used to determine genetic variants that account for individual differences that previous studies have failed to address. An adoption study will be used to confirm twin studies.  Multivariate analysis will be used. Genetic influence on behavioral characteristics will be considered to infer whether there is a clear delineation of nature and nurture or the latter is the product of the former.

The research design will involve keeping of diaries by participants on that will enable evaluation of their eating habits. Participants will be recruited through government health agencies after obtaining approval from ethics committees and the agencies involved. However, the research will be faced by a primary drawback of time. Both quantitative and molecular genetics require long periods of study. The research will collect data for 7 days. The resulting inferences will hence not be genetically viable. However, due to the high cost of a long-term research, the inferences that will be made from the study will prove indispensable in understanding the cause of obesity.


According to Pienar et al. (2013), overweight and obesity incidences have attained epidemic levels. Moreover, the condition has been associated with all the ages, sexes, and races.  The high incidences of the condition have made it be a major health problem worldwide.  The condition has especially raised special concern for the high prevalence of childhood obesity.  The increased incidences of obesity have raised concern in efforts of trying to elucidate the etiology of the disease. An understanding of the etiology of obesity will be critical in paving the way for effective means of prevention, treatment, and control that is often associated with others health problems (Fleming). For instance, obesity is associated with conditions such as diabetes, psychological disorders such as low esteem and hypertension (Fleming).

Obesity is assessed using body mass index (BMI). BMI involves assessment of the weight of an individuals in relation to their height in adults. However, the use of BMI in children is complicated due to the effects of sex and age (Fleming). In response to this, the World Health Organization (WHO) has formulated a method of comparison to assess obesity in children. Children are considered to be obese if their weight is greater than 95 percent that of their peers who have similar height and age. The associations of obesity with other health problems and the increasing incidence rates have results to the need to determine its causal factors.

Scientists are often faced with the need to determine the cause of diseases. Such efforts recapitulate nurture versus nature debates. Determination of the possible cause of diseases is faced with difficulties due to the complex interaction of nature and nurture. According to Kaput (2004), the two factors interact to produce the final phenotype. Moreover, Pizzorno (2007) adds to this inference arguing that nature determines the range of the weight of a person while environment determines the exact point within the range that a person falls. On the contrary, some scientists have proposed that nature does account for a person’s obesity and vice versa. For instance, Pienar et al. (2013) explain that the nurture is the primary factor that causes obesity. The research that will be conducted will aim to ascertain the causative agent for obesity.

Literature Review

Obesity results from body fat accumulation due to homeostatic regulation of energy balance breakdown (Fernández et al., 2008). The possible causative agents causing this disruption of the energy distribution and the reasons as to why different people exhibit variances in their response are understood. However, the specific causative agent between nature and nurture are not yet ascertained. Some scientists account for nature while others claim that nurture is the cause of obesity. Other scientists still claim that nature and nurture interact resulting in obesity. The relationship between nature and nurture and obesity as discussed in previous works of literature are as covered in the following sections.

Nature and Obesity

Components of nature have been related to the susceptibility of a person to gain weight (Fleming). Dumke and Goran (2012) explains that a person’s eating behavior has genetic components that may make a person more susceptible to energy distribution problems. Fernández et al. (2008) explain that genetic components account for the differences in individual differences in body fat distribution. These differences have been shown to persist even when other factors such as education and socio-economic status have been considered. The existence of the individual differences indicates a presence of genetic differences that make some individuals more susceptible to obesity compared to others.

Studies have been conducted to determine the contribution of DNA to energy intake, its expenditure, and fat accumulation. According to Fernández et al. (2008), such studies have used diverse approaches such as genome-wide association, genome-wide linkages, and candidate gene analysis. 253 autosomal regions of the human genome have been associated with obesity in humans. However, Fernández and colleagues explain that the association of genes with adiposity has been made complex by the lack of identification of ‘obesity gene.’ Currently, a gene controlling obesity has been identified. A mutation in this gene results in obesity. However, the role of genes in influencing obesity is indispensable. Studies have indicated that sibling whose parents are obese are five times more likely to be obese (Fleming).

Nurture and Obesity

Nurture concerns with the external environment affecting an individual. The definition of ‘environment’ is of critical importance in studies of nurture and obesity. According to Fernández et al. (2008), environment refers to components such as residential area, dynamics in the community, socio-economic status. Individual experiences and health status. The contribution of the environment to obesity has been a major area of concern to scientists.

Studies have found that social factors may be responsible for the increased incidences of obesity (Dumke & Goran, 2012). Such an inference appeals to many scientists who argue that the increased incidences of obesity are due to the modern living standards. Obesity is said to be due to factors such as physical inactivity, poor sleeping habits, stress and food intake as compared to genetic aspects. For instance, Fleming accounts for the role of large portions of food that is more fatty is associated with obesity. Moreover, poor eating patterns have been associated with obesity.

How the study will close the gap in previous literature

Previous research has majored on the heritability of obesity as compared to the role of the environment. Consideration of heritability of obesity while failing to account for other factors imparts ambiguousness in the results. For instance, the heritability of dietary habits has not been accounted for in previous studies. The proposed research design will incorporate two different but related studies that will be pertinent in separating nature and nurture (Fleming). These studies will involve adoption and twin studies for heritability of obesity. The heritability of behavior will also be conducted to help determine whether ‘environmental conditions’ are determined by genetics. The eating behavior will be used to access the heritability of behavioral characteristics. These studies will help to determine the extent of heritability of obesity. Adoption studies will help to separate nature and nurture. Nurture is primarily concerned with behavioral characteristics. It would hence be prudent to perform a study to determine the heritability of the behavioral characteristics. The evaluation of the heritability of the behavioral characteristics will involve the determination of a possibility of heritability of eating habits using twin studies.

Research Objectives

Previous research has been conducted using approaches that helped to separate nurture and nature. As earlier mentioned, the results of these studies have been diverse. In determining the causative agent for obesity, it would be prudent to perform research that will be considerate of the longitudinal individual differences in people in the same environment while elucidating the role of nature and nurture in influencing obesity. In this case, the objectives of the research will be as outlined below:

  1. To determine the extent to which nature influences obesity
  2. To determine the extent to which nurture influences obesity
  3. To determine causes for individual differences in people in similar environment
  4. Determine what is the causative agent of obesity between nature and nurture
  5. To determine whether genes related to obesity are influenced by eating behavior

Research Method and Data Analysis

Recruitment for both studies to be carried out

The recruitment of the participants will be done through government health agencies. Members in different socio-economic status and education will also be recruited to validate generalizing the results. Moreover, other twin and their families willing to participate will be involved in the research. Participants will be required to keep a diary indicating the various factors mentioned in the above section. To ensure that all the information required will be obtained, the participants will be coached through the process of keeping a diary indicating the various aspects. The special group of twins and their families that will be involved for the molecular genetics will be fully informed regarding the intrusive nature of the research.

Participants will be required to fill a consent form after they accept to participate in the research. A research briefing will also be conducted to ensure that all the stakeholders involved in the process of the research understand the importance of it and its benefits in the improvement of medical information on treatment and prevention of obesity.  An approval will also be required from committees on ethics of the participating agencies and relevant government agencies concerned with research ethics. All the data collected during the study will be treated as confidential. Autonomy of the participants will also be highly upheld. Transparency on the results of the study will be maintained through constant briefing of the stakeholders and the community.

Study One: Twin studies for heritability of eating behavior and obesity

Research Method, Ethical Considerations, and Problems

This study will involve evaluation of adult twin pairs (both monozygotic and fraternal) of the age 18- 50 years living in different and free environments. The study will also involve their first-degree family members in the same age category. The study will involve determining the heritability of various aspects of eating behavior. Such factors include such as emotional, external and restrained eating behaviors. The study will involve keeping a diary for 7 days. The diary recording will involve indicating factors such as the amount, time and hunger level before eating. Beverages taken will also be recorded and the time they are taken. The BMI of the participants will also be determined to access the extent of genetic and environmental influence on the participants. The study of these factors will involve the use of quantitative genetic.

With the current availability of molecular data after completion of Human Genome Project, it would be prudent to incorporate this data in the research. Molecular data will help to counter drawbacks of previous research that failed to account for individual differences in obesity. This study will involve the study of molecular genetics of twins, both monozygotic and fraternal, and first-degree family members. The selection of the twins and the members will be based on observation. The participants will be selected based on their weight with the sample comprising individuals of varying weight.

Data Analysis

Data analysis will be preceded by ascertainment of zygosity through genotyping. Data related to quantitative analysis will be analyzed using multivariate analysis. The means for emotional, restrained and external eating behaviors for the monozygotic, fraternal and other family members will be evaluated. Correlation of the various means in the different sample groups will then be evaluated to determine their significance. There will be determination of the mean of BMI for each of the sample groups. An evaluation of the correlation between the BMI and the various eating behaviors will be determined.

The molecular aspect of this study will involve the use of Genome-Wide Association (GWAS). GWAS will help to identify specific genes responsible for obesity. A linkage analysis will be performed to identify genetic variants. According to Bush and Moore (2012), linkage analysis will be pertinent in explaining individual differences in weight predisposition for people in similar environments.

Study Two: Adoption Studies

Research Method and data analysis

It would be prudent to separate the effects of nature and nurture. As earlier mentioned, adoption studies will help to separate the effects of nature and nurture (Fleming). Thornton, Mazzeo, and Bulik (2011) explain that adoption studies will also help to infer shared environmental influences. The adoption study will involve examination of the eating behavior in a similar manner to that in the previous study. The sample population will be divided into three groups. The eating behavior of the biological and adoptive relatives and that of the children will be evaluated. Participants will be required to keep a diary similar to that in the previous studies. Recruitment and ethical issues will be addressed in a similar manner.

Data Analysis

Data will be analyzed using a multivariate approach. The mean values of restrained, emotional and external eating habits for each of the groups will be determined. Moreover, the BMI mean for each of the groups will also be calculated. Correlation analysis will be used to determine if the differences in the mean values of the restrained, emotional and external eating habits for the various groups will be significant. Data analyzed from this research will be used to infer how eating behavior and obesity are influenced by the environment and genetics in separated environments.


The research will conduct both studies as a way of countering concerns that have been raised in twin studies and adoption studies alone. According to an evaluation conducted by Moore (2013) on twin studies, researchers have failed in various ways. In one of the accounts, Moore explains that researchers have failed to consider molecular data. The inclusion of linkage analysis in this research will be pertinent in countering this drawback in the previous researches. Moore further discredits the use of heritability to explain whether nature or nurture is the cause of obesity. This research will involve an analysis of whether eating habits are genetically influenced. In this case, an inference of the genetic influence of behavioral characteristic such as eating behavior that are considered as ‘nurture’ help to explain the interplay of nurture and nature. Genetic influence on the behavioral characteristic will imply that nature determines factors that are considered to be associated with nurture, and hence environment does not affect obesity. The absence of genetic influence on the eating behavior will imply that the nurture acts independently and is not predetermined by genetics. Such will be accessed using twin correlation as illustrated in the following data graphs.

Fig 1: Graph illustrating assessment of similarity among the identical, fraternal and other family members.

According to Faith and Kral (2006), there is need for the consideration of how obesity genes are moderated by the environment. The incorporation of molecular aspects using linkage analysis will help explain individual differences in obesity in the population. Moore (2013) also accounts for the failure of heritability studies based on twin studies to explain the cause. Studies of heritability help to explain the variability of obesity rather than the cause. The incorporation of molecular and evaluation of genetic influence to behavioral characteristics will help to make advancement in countering this drawback of heritability studies. In this case, behavioral characteristic, for instance, eating behavior, will help to determine whether there is a clear delineation of nurture and nature. Findings indicating nature and nurture as being distinctive will imply that despite genetics accounting for variability as Moore (2013) indicates, it also accounts for the cause. Else, environment or an interplay of the two factors will be inferred to be the cause of obesity. Moreover, the use of adoption studies will help to explain whether eating and weight of children is more related to that of the adoptive or biological relatives. Incorporating eating habits in the adoptive study is pertinent in confirming the presence of lack of genetic heritability of eating habits. It would also be pertinent in separating nature and nurture of the adopted children and their biological relatives to determine whether their weight values are related.

Correlations of the mean values of restrained, emotional and external eating behaviors are used to determine whether their differences in monozygotic, fraternal and other family members will be significance. The significance difference will be used to explain whether the eating behavior is genetically influenced. In a similar manner, the significance of the difference in BMI and the various eating behaviors will be evaluated using relevant correlations. The finding will be used to explain if obesity is influenced by eating behavior. The findings on the role of genetic influence on eating behavior will be combined with those on influences of BMI to infer how obesity and eating behavior are related to nature and nurture. The presence of genetic influence of eating behavior will help to nullify the previously inferences of nurture on obesity. Genetic influence of the eating habit will imply that nurture is a product of genetic factors. In such a case, nature will be seen as a component that causes obesity and defines the external environment that in return influences weight gain.

Adoption studies will be used for the confirmation of the inferences made in the twin studies above. In the case of twin studies, the twins and their relatives live in similar environmental conditions. Therefore, it will be prudent to exploit a situation of environmental separation of the relatives and children. Adoption studies play a critical role in achieving this. The biological relatives and the adoptees live in different environments. Therefore, comparison of inferences in twin and adoption studies will allow their confirmation. Linkage analysis will be incorporated in the research will be used to identify genetic variants (Bush & Moore, 2012). The presence of genetic variants will be used to explain the individual differences in obesity. The combination of quantitative and molecular genetics in making inferences pertaining nature or nurture as the cause of obesity will strengthen the results of the study.

Research Problems and Drawbacks

The research aims at involving quantitative and molecular genetics. Both of these studies require extensive studies based on a large number of samples (Bush & Moore, 2012; Llewellyn & Wardle, 2013). However, this research will only use a small sample for making the relevant studies. Therefore, research approach will be limited due to the short time of data collection. Inferences on genetic role require extensive time and large samples of study. However, the sampling will be critical in making essential inferences regarding possible genetic, or else environmental influences on the eating behavior. According to Llewellyn and Wardle (2013), the research paper does not account for the specific genes involved. The research does not consider the possibility of genetic linkage of the weight and eating associated genes.

According to Dumke and Goran (2012), obesity shows a trend that has been associated with low-income populations. Such correlation implies presence of economic contribution to obesity. The proposed research design does not account for this factor and hence generalizing its result presents ambiguousness.




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