Epidemic obesity: are genetic factors involved via increased rates of assortative mating?

Putative contributors to the secular increase in obesity: exploring the roads less traveled

OBJECTIVE

To investigate plausible contributors to the obesity epidemic beyond the two most commonly suggested factors, reduced physical activity and food marketing practices.

DESIGN

A narrative review of data and published materials that provide evidence of the role of additional putative factors in contributing to the increasing prevalence of obesity.

DATA

Information was drawn from ecological and epidemiological studies of humans, animal studies and studies addressing physiological mechanisms, when available.

RESULTS

For at least 10 putative additional explanations for the increased prevalence of obesity over the recent decades, we found supportive (although not conclusive) evidence that in many cases is as compelling as the evidence for more commonly discussed putative explanations.

CONCLUSION

Undue attention has been devoted to reduced physical activity and food marketing practices as postulated causes for increases in the prevalence of obesity, leading to neglect of other plausible mechanisms and well-intentioned, but potentially ill-founded proposals for reducing obesity rates.

Familial resemblance in eating behaviors in men and women from the Quebec Family Study

OBJECTIVE

It is commonly recognized that genetic, environmental, behavioral, and social factors are involved in the development of obesity. The family environment may play a key role in shaping children's eating behaviors. The purpose of this study was to estimate the degree of familial resemblance in eating behavioral traits (cognitive dietary restraint, disinhibition, and susceptibility to hunger).

RESEARCH METHODS AND PROCEDURES

Eating behavioral traits were assessed with the Three-Factor Eating Questionnaire in 282 men and 402 women (202 families) from the Quebec Family Study. Familial resemblance for each trait (adjusted for age, sex, and BMI) was investigated using a familial correlation model.

RESULTS

The pattern of familial correlation showed significant spouse correlation for the three eating behavior phenotypes, as well as significant parent-offspring and sibling correlations for disinhibition and susceptibility to hunger. According to the most parsimonious model, generalized heritability estimates (including genetic and shared familial environmental effects) reached 6%, 18%, and 28% for cognitive dietary restraint, disinhibition, and susceptibility to hunger, respectively.

DISCUSSION

These results suggest that there is a significant familial component to eating behavioral traits but that the additive genetic component appears to be small, with generalized heritability estimates ranging from 6% to 28%. Thus, non-familial environmental factors and gene-gene and gene-environmental interactions seem to be the major determinants of the eating/behavioral traits.

Longitudinal Modeling of Adiposity in Periadolescent Greek Schoolchildren

PURPOSE

Obesity has an etiology that is multidimensional in nature. Given the dearth of longitudinal data, we examined changes in adipose tissue (Ad) in relation to physical activity levels (PA), aerobic fitness (AF), and energy intake (EI) in Greek schoolchildren, as they progressed from age 12 to 14 yr.

METHODS

This was a 2-yr and three-time-point (TP) study. Participants (N=210 (TP1); =204 (TP2); =198 (TP3)) were assessed for anthropometry, maturity status, Ad, PA, AF, and EI. Mean values were used for exploratory analyses, whereas two generalized estimating equations (GEE) models examined for longitudinal associations between the studied parameters. The first (GEE1) aimed to extract inherent associations between the dependent (Ad) and independent (PA, AF, EI) variables for the entire study period. For further evidence of association, the second analysis (GEE2) used the independent variables at TP1 and TP2 to predict the dependent variables at TP3.

RESULTS

Levels of Ad in boys decreased significantly (P<0.05) from TP1 to TP3, whereas the same variable demonstrated a nonsignificant increase (P>0.05) in girls. GEE1 revealed that longitudinal changes in Ad were significantly associated only with PA (beta=-0.16; P<0.001) and AF (beta=-0.09; P<0.05) for all schoolchildren. Similarly, GEE2 revealed that the main factors (at TP1 and TP2) predicting the development of Ad (at TP3) were PA (beta=-0.14; P<0.001) followed by AF (beta=-0.10; P<0.05).

CONCLUSION

With respect to data presented, we established that longitudinal changes in Ad are mainly accompanied by changes in PA and, to a lesser extent, AF levels.

Prevalence and risk factors for overweight and obesity in Portuguese children

AIM

To identify risk factors for overweight and obesity in Portuguese children.

METHODS

A cross-sectional study of children 7 to 9.5 y old was performed between October 2002 and June 2003. A total of 2,274 girls and 2,237 boys were observed. Weight and height were measured, and parents filled out a questionnaire about family characteristics. Overweight and obesity, using age- and sex-specific body mass index (BMI) cut-off points as defined by the International Obesity Taskforce, were used.

RESULTS

After adjustment for age and sex, the odds ratio for childhood obesity increased by television viewing (reference 0-2 h; 2-3 h: 1.51; 3-4 h: 1.72; 4 h: 1.63), paternal obesity (reference <18.5 kg/m(2); 25.0-29.9: 3.06; 30.0: 7.09), maternal obesity (reference <18.5 kg/m(2); 25.0-29.9: 9.06; 30.0: 18.13) and birthweight (reference <2,500 g; 2,500-3,000 g: 1.55; 3,000-3,500 g: 1.87; 3,500-4,000 g: 2.13; 4,000 g: 2.74), and decreased by sleeping duration (reference 8 h/d; 9-10 h/d: 0.44; 11 h/d: 0.39), paternal education (reference primary school; secondary: 0.91; university: 0.42), maternal education (reference primary school; secondary: 1.13; university: 0.56), being a single child (reference yes; no: 0.56) and family size (reference one child; two children: 0.59; three children: 0.44; more than four children: 0.37).

CONCLUSION

Our data support the perspective that education about energy intake and energy expenditure should be used much earlier in those families with high-risk children, namely those with high parental BMI or high birthweight. Protective factors were parental education and family size.

Parental growth at different life stages and offspring birthweight: an intergenerational cohort study

Using three generations of the 1958 British national birth cohort we investigated ways in which parental size is related to offspring birthweight. By age 41 years, 4566 singleton female and 4050 male cohort members (born 3-9 March, 1958) had become parents and provided information on their singleton offspring. Mother's birthweight (standardised for gestational age and sex) was the strongest determinant of offspring birthweight (effect size [ES] per SDS 112 g [95% CI 97, 128]), which was little affected by adjustment for maternal height or BMI (ES 95 g and 105 g respectively). The intergenerational birthweight association was not observed for mothers born very small or large. Mother's childhood height at age 7 (ES 46 g [24, 67]), but not BMI (ES 3 g [-18, 23]), was associated with offspring birthweight after adjustment for grandparental size, own birthweight, and adult size. Controlling for other growth measures strongly attenuated the association between mother's adult height and offspring birthweight: (ES 90 g, unadjusted, and 25 g, adjusted), while the association between adult BMI and offspring birthweight was little affected (ES 55 g and 51 g respectively). Father's BMI did not affect offspring birthweight, while the associations for height were similar, albeit weaker, than those observed for the mother. Our results suggest that intergenerational associations in birthweights are largely independent of postnatal size. Maternal height in childhood was positively related to offspring birthweight, while the effect of her BMI was restricted to adulthood.

Melanocortin-4 receptor gene: case-control study and transmission disequilibrium test confirm that functionally relevant mutations are compatible with a major gene effect for extreme obesity

We initially performed a mutation screen of the coding region of the MC4R in 808 extremely obese children and adolescents and 327 underweight or normal-weight controls allowing for a case-control study. A total of 16 different missense, nonsense, and frameshift mutations were found in the obese study group; five of these have not been observed previously. In vitro assays revealed that nine [the haplotype (Y35X; D37V) was counted as one mutation] of the 16 mutations led to impaired cAMP responses, compared with wild-type receptor constructs. In contrast, only one novel missense mutation was detected in the controls, which did not alter receptor function. The association test based on functionally relevant mutations was positive (P = 0.006, Fisher's exact test, one-sided). We proceeded by screening a total of 1040 parents of 520 of the aforementioned obese young index patients to perform transmission disequilibrium tests. The 11 parental carriers of functionally relevant mutations transmitted the mutation in 81.8% (P = 0.033; exact one-sided McNemar test). These results support the hypothesis that these MC4R mutations represent major gene effects for obesity.

Assortative mating by body height and BMI: Finnish twins and their spouses

Assortative mating by body height and weight is well established in various populations, but its causal mechanisms remain poorly understood. We analyzed the effect of phenotypic assortment and social homogamy on spousal correlations for body height and body mass index (BMI, kg/m(2)). Our data derived from a questionnaire administered to the adult Finnish Twin Cohort in 1990 (response rate 77%) yielding results from 922 monozygotic and 1697 dizygotic adult twin pairs who reported information about their body height and weight and that of their spouses. Assortative mating was evident for body height and BMI. For body height, the effects of social homogamy (0.24 in men and 0.29 in women) and phenotypic assortment (0.27 and 0.28, respectively) were about the same. For BMI, the effect of social homogamy was stronger (0.31 in men and 0.28 in women) than the effect of phenotypic assortment (0.13 in both men and women). When assortative mating was taken into account, shared environmental factors had no effect on phenotypic variation in body height or BMI. Our results show that assortative mating needs to be considered in population genetic studies of body height and weight.

Eating patterns and obesity in children. The Bogalusa Heart Study

BACKGROUND

Childhood obesity is a growing public health problem. This study examined the association between eating patterns and overweight status in children who participated in the Bogalusa Heart Study.

METHODS

A single 24-hour dietary recall was collected on a cross-sectional sample of 1562 children aged 10 years (65% Euro-American [EA], 35% African American [AA]) over a 21-year period. Overweight was defined as body mass index greater than the 85th percentile using Centers for Disease Control and Prevention reference standards. Multivariate logistic regression was used to investigate the association between eating patterns and overweight.

RESULTS

Consumption of sweetened beverages (58% soft drinks, 20% fruit flavor drinks, 19% tea, and 3% coffee) (p<0.001); sweets (desserts, candy, and sweetened beverages) (p<0.001); meats (mixed meats, poultry, seafood, eggs, pork, and beef) (p<0.051); and total consumption of low-quality foods (p<0.01) were positively associated with overweight status. Total amount of food consumed, specifically from snacks, was positively associated with overweight status (p<0.05). There was a lack of congruency in the types of eating patterns associated with overweight status across four ethnic-gender groups. The percent variance explained from the eating pattern-overweight models was very small. The interaction of ethnicity and gender was significantly associated with overweight status (p<0.001). The odds of being overweight for EA males were 1.2 times higher than for AA females.

CONCLUSIONS

These results demonstrate that numerous eating patterns were associated with overweight status, yet the odds of being overweight were very small. Additional studies are needed to confirm these findings in a longitudinal sample having multiple days of assessment.

Assessing risk factors for obesity between childhood and adolescence: I. Birth weight, childhood adiposity, parental obesity, insulin, and leptin

OBJECTIVE

To assess the effects of body weight, body composition, parental obesity, and metabolic variables on the development of obesity in a large cohort of 5-year-old Native American children with a high propensity for obesity.

METHODS

During the summer months of 1992 to 1995 and again 5 years later, 138 (65 boys and 73 girls) 5-year-old Pima Indian children were studied. Height; weight; body composition; parental obesity; and fasting plasma insulin, glucose, and leptin concentrations were determined at baseline and follow-up. Linear regression models were used to assess the effect of the baseline variables on the development of obesity.

RESULTS

At both 5 and 10 years of age, Pima Indian children were heavier and fatter than an age- and gender-matched reference population. All anthropometric and metabolic variables tracked strongly from 5 to 10 years of age (r > or = 0.70). The most significant determinant of percentage of body fat at 10 years of age was percentage of body fat at 5 years of age (R(2) = 0.53). The combined effect of high maternal body mass index, elevated fasting plasma leptin concentrations, and low fasting plasma insulin concentrations at baseline explained an additional 4% of the total variance in adiposity at follow-up.

CONCLUSIONS

Although parental obesity and metabolic variables such as insulinemia and leptinemia at baseline account for a small percentage of the variance in adiposity at follow-up, early childhood obesity is the dominant predictor of obesity 5 years later. These results suggest that strategies to prevent childhood obesity must be initiated at a very early age.

The Canadian obesity epidemic: an historical perspective

OBJECTIVE

To examine temporal trends in stature, body mass, body mass index (BMI), and the prevalence of overweight and obesity in Canada.

RESEARCH METHODS AND PROCEDURES

Data for adults 20 to 64 years of age were compared across eight Canadian surveys conducted between 1953 and 1998. Temporal trends in stature and body mass were examined using regression, and changes in weight-for-height were expressed as changes from 1953. BMI data were available from 1970 to 1972 to examine changes in overweight and obesity. Qualitative changes in the BMI distribution were examined using Tukey mean-difference plots.

RESULTS

Significant temporal trends in stature and body mass have occurred since 1953 in Canada. Median stature increased 1.4 cm/decade in men and 1.1 cm/decade in women, whereas median body mass increased 1.9 kg/decade in men and 0.8 kg/decade in women. Increases in the 75th percentile of body mass were larger than the median. The average weight-for-height increased 5.1% in men and 4.9% in women from 1953. Furthermore, the prevalences of overweight and obesity have increased from 40.0% and 9.7% in 1970-1972 to 50.7% and 14.9% in 1998, respectively. The entire BMI distribution has shifted to the right since 1970-1972 and has become more skewed to the right for men than for women.

DISCUSSION

There have been significant increases in stature and body mass in Canada over the last 45 years. Body mass has increased more than stature, particularly in the upper percentiles, which has resulted in the currently observed high prevalences of overweight and obesity.

Familial resemblance of 7-year changes in body mass and adiposity

OBJECTIVE

To investigate the familial resemblance of 7-year changes in body mass and adiposity among Canadian families.

RESEARCH METHODS AND PROCEDURES

The sample consisted of 655 women and 660 men from 521 families who participated in the Canada Fitness Survey in 1981 and the follow-up Campbell's Survey in 1988. Indicators of baseline and 7-year changes in body mass and adiposity included body mass (kilograms), body mass index (BMI; kilograms per square meter), sum of five skinfolds (SF5; millimeters), and waist circumference (WC; millimeters). The data were adjusted for the effects of age and sex, and the change scores were adjusted for baseline levels. A familial correlation model was used to determine the heritability of each phenotype using maximum likelihood techniques.

RESULTS

Significant familial resemblance was observed at baseline and for 7-year changes in all phenotypes. At baseline, moderate heritabilities were observed [body mass: heritability coefficient (h(2)) = 56%; BMI, h(2) = 39%; SF5, h(2) = 41%; and WC, h(2) = 39%], whereas values were attenuated for each change score except for WC (Deltabody mass, h(2) = 23%; DeltaBMI, h(2) = 14%; DeltaSF5, h(2) = 12%; and DeltaWC, h(2) = 45%).

DISCUSSION

Changes in body mass and adiposity significantly aggregate within families over 7 years. However, baseline values are characterized by higher heritability levels except WC. The significant heritabilities observed for change scores suggest that lifestyle, transient environmental factors, and possibly age-related gene effects are important determinants of changes in body mass and adiposity.

Associations of body mass index and obesity with physical activity, food choices, alcohol intake, and smoking in the 1982-1997 FINRISK Studies

BACKGROUND

Recent increases in the prevalence of obesity worldwide are suggested to be caused largely by an environment that promotes sedentariness and excessive food intake.

OBJECTIVE

We investigated associations of body mass index (BMI) and obesity with physical activity, food choices, alcohol consumption, and smoking history. In addition, we examined the consistency of these associations over time, with the aim of assessing whether the significance of lifestyle variables as correlates of obesity increased over a 15-y period.

DESIGN

Independent cross-sectional surveys were carried out in 1982, 1987, 1992, and 1997. Altogether, 24604 randomly selected men and women (aged 25-64 y) participated in these surveys. The subjects' weights and heights were measured, and data on lifestyle were collected with self-administered questionnaires.

RESULTS

In men and women, perceived general health, leisure-time physical activity, and daily vegetable consumption were inversely associated with obesity, as were bread consumption in women and activity at work in men. Consumption of sausages, milk, and sour milk and heavy work (in women only) were positively associated with obesity. Obesity was also associated with alcohol consumption and smoking history. Most associations were constant over the 15-y period. However, the inverse associations of BMI with physical activity in women and with perceived health in men seemed to strengthen over time.

CONCLUSIONS

A physically active lifestyle with abstention from smoking, moderate alcohol consumption, and consumption of healthy foods maximizes the chances of having a normal weight. The significance of avoiding sedentariness increases over time as a factor associated with normal weight.

Spousal resemblance in the Canadian population: implications for the obesity epidemic

OBJECTIVE

To determine the extent of the spousal resemblance for adiposity and leanness in the Canadian population.

DESIGN

Cross-sectional population survey.

METHODS

The sample comprised parents and offspring from 1341 families (n=4023) of the Canada Fitness Survey. Indicators of adiposity included the body mass index (BMI) and the sum of five skinfolds (SF5). Both offspring and parents were ranked by their BMI and SF5 percentile position in the population using the entire Canada Fitness Survey database (n=15 818).

RESULTS

Pearson correlations indicated significant spousal resemblance for both BMI (r=0.14; P<0.0001) and SF5 (r=0.13; P<0.0001). However, the magnitude of the spousal correlations varied by the adiposity status of the offspring, with spousal correlations tending to be stronger in parents of lean or obese children and lower among parents of 'average' children. Bivariate histograms indicated that among lean (<or=5th percentile) and obese offspring (>or=95th percentile), the parental pairs tended to cluster among the lower and higher percentiles of adiposity, respectively.

CONCLUSIONS

There are spousal similarities in adiposity, particularly among parents of lean or obese offspring in the Canadian population. The degree to which these similarities are due to a loading of spouses with genes predisposing to obesity or a shared household environment cannot be determined from the present study. However, these results are compatible with the notion that genes and mutations predisposing to obesity are more prevalent among obese parents while those for pronounced leanness are more prevalent among lean parents.

Management of obesity in patients with Type 2 diabetes

Although prevention is clearly a logical first step in the management of the obese Type 2 diabetic patient, such programmes have had little long-term success. Diet, exercise and behavioural modification still form the cornerstones of treatment and relatively small weight loss results in improvement of all major obesity-related co-morbidities, including Type 2 diabetes. The obese diabetic patient faces extra impediments to weight loss, including the adverse effects of diabetic medication, poor glycaemic control and diabetes-related complications. New drugs may offer some additional help, in general by providing the benefit associated with the weight loss as such. Bariatric surgery can produce major long-term weight loss in the severely obese.

Interaction of genetic and environmental programming of the leptin system and of obesity disposition

Possible adverse interactions between an usually inconspicuous genetic trait and early environmental factors favoring the development of obesity were investigated in rats heterozygous for the leptin receptor defect "fatty" (fa). Pups were exposed to early postnatal overfeeding by reducing litter size from normally 10-12 to only 4. Rearing +/+ and +/fa pups from day 3 to 21 in small litters increased fat-free dry mass and body fat, but only in the latter did a significant interaction with genotype occur. Pronounced differences in the responsiveness of +/+ and +/fa pups to "prophylactic" leptin treatment (from day 1 to 21) were observed, with +/fa females from small litters being nearly as fat and unresponsive as previously reported for normally reared fa/fa pups. Clear heterozygous differences in total hypothalamic leptin binding, but no litter size effect, paralleling the differences in leptin responsiveness, were observed. By early postnatal overfeeding an usually inconspicuous genetic trait may thus become etiologic for the development of obesity via physiological changes other than the decreased leptin binding characterizing the genetic defect.

Zur Erblichkeit der Adipositas im Kindes- und Jugendalter

Zusammenfassung. Zwillings-, Familien- und Adoptionsstudien haben gezeigt, daß in westlichen Industriestaaten zwischen 20% bis 80% der Varianz des Körpergewichts auf erbliche Faktoren zurückgeführt werden kann. Die Entdeckung des Leptingens hat 1994 die Ära der molekularen Adipositasforschung eingeläutet. Bislang ist es beim Menschen gelungen, fünf monogene Formen der Adipositas zu identifizieren. Spezifische Mutationen im Melanocortin-4 Rezeptorgen bedingen eine autosomal dominante Form der Adipositas, die, unseren eigenen Befunden zufolge, bei circa 1% aller deutschen Kinder mit einer extremen Adipositas vorliegt. Die rezente molekulargenetische Forschung zeigt, daß insbesondere beim Vorliegen einer frühmanifesten und extremen Adipositas an eine erbliche Komponente (Hauptgeneffekt) gedacht werden sollte.