Genes, Behavior, and the Social Environment Moving Beyond the Nature/Nurture Debate (2006) / Chapter Skim
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Appendix C Social Environmental and Genetic Influences on Obesity and Obesity-Promoting Behaviors
Appendix C Social Environmental and Genetic Influences on Obesity and Obesity-Promoting Behaviors
Pages 236-280
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. The topic of genetic and social environmental influences on obesity, and how they interact, is a unique topic for which conceptual frameworks are scarce.
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The model is intended to reflect much of the current literature, in that correlations or interactions among the social environment and genetic factors are not explicitly posited. However, as reviewed in this report, certain studies challenge this assumption and suggest that expansions of this model may help guide future research.
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. SECTION 3: SOCIAL-ENVIRONMENTAL INFLUENCES ON OBESITY AND OBESITY-PROMOTING BEHAVIORS For the purposes of this report, a broad definition of "social environment" is used.
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Evidence for Interactions Among Social Environmental, Genetic, and Behavioral Factors as They Relate to Obesity 262 6a. Social Environment as a Potential Moderator Variable 263 7.
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. Much of the evidence comes from observational studies that could not control for potential confounding factors or did not directly test associations between participant weight status and exposure to putative environmental risk factors.
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Finally, the authors noted a differential rate of weight gain by SES and attributed that finding to an early onset of weight gain in a person's life, when parental SES may still be influential. Prospective analyses of the National Longitudinal Survey of Youth [19]
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3b. Microenvironmental Influences The two microenvironmental influences reviewed in this section are social facilitation of eating and parental feeding practices.
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APPENDIX C 243 tation effect was greater for meals consumed in the presence of a spouse, family member, or friend compared to less familiar or unknown companions, suggesting that enhanced social interactions and discussions were the underlying mechanisms [31]
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244 GENES, BEHAVIOR, AND THE SOCIAL ENVIRONMENT of overweight was studied in 8,186 girls and 7,155 boys, 9 to 14 years of age, who were participating in a national growth and development study [38]
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APPENDIX C 245 access to foods may have the counterproductive effect of making those "forbidden" foods more desirable [47]
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246 GENES, BEHAVIOR, AND THE SOCIAL ENVIRONMENT i. Externality and Dietary Disinhibition During the late 1960s results from a series of experiments conducted by Schachter and colleagues [58-60]
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APPENDIX C 247 Likewise, studies which examined the effects of varying the portion size [73, 74] or the portion size and the energy density of food [75]
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248 GENES, BEHAVIOR, AND THE SOCIAL ENVIRONMENT search designs need to be developed to further study satiation as a possible phenotype for obesity.
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APPENDIX C 249 paradigm is based on behavioral economics theory, which builds upon an extensive animal literature and research in the additions [88]
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250 GENES, BEHAVIOR, AND THE SOCIAL ENVIRONMENT chew frequency (chews/s)
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APPENDIX C 251 cornerstones of the "toxic" environment. That is, increased consumption of fast foods has been associated with increased weight status.
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252 GENES, BEHAVIOR, AND THE SOCIAL ENVIRONMENT are multifold. For one, increased TVV increases sedentary behavior which in turn is likely to displace time spent in physical activity.
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Heritability of BMI and Fat Mass "Heritability" refers to the extent to which variability in a trait is influenced by genetic variations within a population, and can be subdivided into "narrow-sense" or "broad-sense" heritabilities [118]
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First, most studies find no evidence for shared home environmental influences on fat mass variability in adulthood. Rather, most environmental influences on fat
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Second, among the few studies finding evidence for shared environmental influences on weight status, most examined pediatric samples. For example, in an analysis of over 3,500 twin pairs who were 4 years old, shared environmental factors accounted for 24 percent of variance in weight adjusted for height in boys and 25 percent of the variance in girls [123]
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256 2004 010 166 049 221 204 113 ears,y 10 2003 06/7 055 041 183 139 090 past the 6 2002 00 038 033 168 068 071 during 6 2001 00 025 165 033 058 6 phenotypes 2000 00 024 115 021 048 8 4 a 06 20 40 1999 Map obesity-related 06 6 679 081 9 or 1998 Gene 02 161 55 3 0 212 obesity, 1997 BMI, [125]
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5b. Genetic Influences on Food Intake A relatively small number of studies have tested genetic influences on eating phenotypes, independent from body fat.
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258 GENES, BEHAVIOR, AND THE SOCIAL ENVIRONMENT Effectors Feeding Gastric emptying Metabolic Rate Hypothalamus Hindbrain Second order neurons Nucleus tractus MC3/4R Y1/Y5R solitarius AgRP aMSH Arcuate POMC/ NPY/ nucleus CART AgRP Leptin Insulin Pyy GLP-1 Ghrelin PP OXM Adiposity Satiety Hunger Vagal signals peptides signals afferents FIGURE C-2 Pictorial representation of potential action of gut peptides on the hypothalamus. Access circulating agents into the arcuate nucleus of the hypothalamus is facilitated by a relaxed blood-brain barrier.
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Thus, there may be genes and environmental influences on food intake at specific eating episodes that are different from those factors related to habitual dietary intake. Specific social-environmental influences on meal intake were not reported initially.
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Additive genetic factors accounted for 33 percent of the variance, and nonshared environmental factors accounted for 19 percent of the variance. Thus, the results suggest that both genes and the shared environment can influence total energy intake, although specific aspects of the environment were not measured.
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APPENDIX C 261 ii. Specific Genes Associated with Eating Behaviors There is a dearth of information on specific genes that influence dietary patterns, at least for most individuals in the population [144]
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the potential moderating effects of the social environment on the relationship between genetics and obesity, and (b) the potential moderating effects of genetic factors on the relationship between the social environment and obesity.
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APPENDIX C 263 Moderator: Social Environment a b Genetic Obesity Risk/Genes Putative Behavioral Phenotypes Food Intake: Physical Activity: · Increased Disinhibition · Increased TV Viewing · Impaired Satiation and Satiety · Decreased Non-Exercise · Enhanced Reinforcing Value of Food Activity Thermogenesis (NEAT) · Differences in Food Preferences · Increased Rate of Eating and Sucking Avidity FIGURE C-3 Gene-environment interaction model, with social environment as moderator.
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i. Genetic Factors as a Potential Moderator Variable Bouchard and colleagues conducted a seminal "overfeeding" study in which 12 male MZ twin pairs were fed an additional 1,000 kcal/day beyond their baseline intake levels, for 6 days per week over 100 days [155]
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APPENDIX C 265 TABLE C-3 Effect of 100d Overfeeding in 12 Pairs of Male Twins and Measures of the Similarity Within Pairs Similarity Within Pairs Before Over- After OverVariable Feeding Feeding F ratio ICC Body weight (kg)
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However, the onset of obesity is a developmental process that may be influenced by different genetic or environmental influences at different ages. Thus, research that uses prospective designs to identify genetic and environmental influences on the developmental trajectories of body fat stores would be informative.
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Very little is known about the heritability of behavioral traits that are associated with obesity, particularly those reviewed in Section 4. Studies that clarify the genetic-environmental architecture of these traits would elucidate the extent to which those behavioral traits are genetically influenced, as well as the nature of environmental influences that influence those behaviors (i.e., shared vs.
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However, the identity of specific environmental influences has remained elusive, especially during child development. Adding specific measures of the environment might help address these issues.
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In principle, genetic influences on food intake or physical activity may depend on the access to parks, playground, grocery shops, fast-food restaurants, or other environmental variables associated with SES strata. Recent studies have used Geographic Information Systems to "geocode" the physical distance between individual homes and these other components to the community [14]
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In this model, the effects of social-environmental influences on obesity and obesitypromoting behaviors depend on genotype. signs, in which MZ and DZ twins are used to estimate the heritability of response to an experimental manipulation; or candidate gene designs, in which participants are selected based on specific genotypes.
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· Additional research that builds upon existing conceptual models for "organism-environment interactions." Conceptual models that explicitly address the integration of genetic and social-environmental influences on behavioral traits may help guide future studies. The field of developmental behavioral genetics has addressed this issue, although not in regards to obesity per se.
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environmental factors, as well as the genetic factors, that may be associated with obesity or the onset thereof. Despite their unique focuses, the literature reviewed in this report shows that the two areas have the potential to complement each other and to stimulate future collaborations among investigators.
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9. French, S.A., et al., Fast food restaurant use among adolescents: associations with nutrient intake, food choices and behavioral and psychosocial variables.
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Relation may be accounted for by social factors.
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276 GENES, BEHAVIOR, AND THE SOCIAL ENVIRONMENT 77. Heitmann, B.L.
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APPENDIX C 277 99. Drewnowski, A., Food perceptions and preferences of obese adults: a multidimensional approach.
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134. de Castro, J.M., A twin study of genetic and environmental influences on the intake of fluids and beverages.
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Mediators, moderators, and independent, overlapping, and proxy risk factors. Am J Psychiatry, 2001.
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Genetic and Environmental Influences on Developmental Change. 2001, New York: Oxford University Press.
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