CHO intake alters obesity risk associated with Pro12Ala polymorphism of PPARgamma gene

A genomics perspective of personalized prevention and management of obesity

This review discusses the landscape of personalized prevention and management of obesity from a nutrigenetics perspective. Focusing on macronutrient tailoring, we discuss the impact of genetic variation on responses to carbohydrate, lipid, protein, and fiber consumption. Our bioinformatic analysis of genomic variants guiding macronutrient intake revealed enrichment of pathways associated with circadian rhythm, melatonin metabolism, cholesterol and lipoprotein remodeling and PPAR signaling as potential targets of macronutrients for the management of obesity in relevant genetic backgrounds. Notably, our data-based in silico predictions suggest the potential of repurposing the SYK inhibitor fostamatinib for obesity treatment in relevant genetic profiles. In addition to dietary considerations, we address genetic variations guiding lifestyle changes in weight management, including exercise and chrononutrition. Finally, we emphasize the need for a refined understanding and expanded research into the complex genetic landscape underlying obesity and its management.

A Personalized Diet Approach Study: Interaction between PPAR-γ Pro12Ala and Dietary Insulin Indices on Metabolic Markers in Diabetic Patients

BACKGROUND

The objectives were to investigate the effect of the interaction between peroxisome proliferator-activated receptor gamma (PPAR-γ) Pro12Ala polymorphisms and dietary insulin load and insulin index (DIL and DII) on Cardio-metabolic Markers among diabetic patients.

METHODS

This cross-sectional study was conducted on 393 diabetic patients. Food-frequency questionnaire (FFQ) was used for DIL and DII calculation. PPAR-γ Pro12Ala was genotyped by the PCR-RFLP method. Biochemical markers including TC, LDL, HDL, TG, SOD, CRP, TAC, PTX3, PGF2α. IL18, leptin and ghrelin were measured by standard protocol.

RESULT

Risk-allele carriers (CG, GG) had higher obesity indices WC (P _interaction =0.04), BMI (P _interaction =0.006) and, WC (P _interaction =0.04) compared with individuals with the CC genotype when they consumed a diet with higher DIL and DII respectively. Besides, carriers of the G allele who were in the highest tertile of DIL, had lower HDL (P _interaction =0.04) and higher PGF2α (P _interaction =0.03) and PTX3 (P _interaction =0.03). Moreover, the highest tertile of the DII, showed an increase in IL18 (P _interaction =0.01) and lower SOD (P _interaction =0.03) for risk allele carriers compared to those with CC homozygotes.

CONCLUSION

We revealed PPAR-γ Pro12Ala polymorphism was able to intensify the effect of DIL and DII on CVD risk factors; risk-allele carriers who consumed a diet with high DIL and DII score have more likely to be obese and have higher inflammatory markers. Also, protective factor against CVD risk factors were reduced significantly in this group compared to CC homozygotes. This article is protected by copyright. All rights reserved.

Type 2 Diabetes and Dietary Carbohydrate Intake of Adolescents and Young Adults: What Is the Impact of Different Choices?

Type 2 diabetes mellitus has a high prevalence worldwide, with a rapidly increasing incidence even in youth. Nutrition, dietary macronutrient composition, and in particular dietary carbohydrates play a major role in the development of type 2 diabetes. The aim of this narrative review is to discuss the current evidence on the role of dietary carbohydrates in the prevention and management of type 2 diabetes. The digestibility or availability of carbohydrates and their glycemic index (and glycemic load) markedly influence the glycemic response. High consumption of dietary fiber is beneficial for management of type 2 diabetes, whereas high consumption of both glycemic starch and sugars may have a harmful effect on glucose metabolism, thereby increasing the risk of developing type 2 diabetes in the presence of genetic predisposition or making its glycemic control more difficult to achieve in people with established T2D. Therefore, the same dietary macronutrient may have harmful or beneficial effects on type 2 diabetes mainly depending on the subtypes consumed. Some other factors are involved in glucose metabolism, such as meal composition, gut microbiota and genetics. For this reason, the glycemic response after carbohydrate consumption is not easy to predict in the single individual. Nutrition suggested to subjects with known type 2 diabetes should be always person-centered, considering the individual features of each subject.

Contribution of macronutrients to obesity: implications for precision nutrition

The specific metabolic contribution of consuming different energy-yielding macronutrients (namely, carbohydrates, protein and lipids) to obesity is a matter of active debate. In this Review, we summarize the current research concerning associations between the intake of different macronutrients and weight gain and adiposity. We discuss insights into possible differential mechanistic pathways where macronutrients might act on either appetite or adipogenesis to cause weight gain. We also explore the role of dietary macronutrient distribution on thermogenesis or energy expenditure for weight loss and maintenance. On the basis of the data discussed, we describe a novel way to manage excessive body weight; namely, prescribing personalized diets with different macronutrient compositions according to the individual's genotype and/or enterotype. In this context, the interplay of macronutrient consumption with obesity incidence involves mechanisms that affect appetite, thermogenesis and metabolism, and the outcomes of these mechanisms are altered by an individual's genotype and microbiota. Indeed, the interactions of the genetic make-up and/or microbiota features of a person with specific macronutrient intakes or dietary pattern consumption help to explain individualized responses to macronutrients and food patterns, which might represent key factors for comprehensive precision nutrition recommendations and personalized obesity management.

Food Consumption as a Modifier of the Association between LEPR Gene Variants and Excess Body Weight in Children and Adolescents: A Study of the SCAALA Cohort

No studies showing that food consumption is a modifier of the association of variants of the leptin receptor gene (LEPR) with body weight have involved a Brazilian population. The aim of this study was to evaluate the modifying effect of dietary intake on the association between the LEPR gene and excess weight. In this study, 1211 children and adolescents aged 4⁻11 years were assessed. Participants were genotyped for 112 single-nucleotide variants of the LEPR gene. Anthropometric measurements were performed, and dietary data were obtained. Logistic regressions were used to study the associations of interest. Of the participants, 13.4% were overweight/obese. The risk allele (G) of the rs1137100 variant was associated with excess weight in individuals with fat consumption below the median (odds ratio OR = 1.92; 95% confidence interval CI = 1.18⁻3.14), with daily frequency of consumption of drink/artificial juice (OR = 2.15; 95% CI = 1.26⁻3.68) and refined cereals (OR = 2.17; 95% CI = 1.31⁻3.62) above the median. The risk allele (G) of variant rs1177681 was also associated with excess weight (OR = 2.74; 95% CI = 1.65⁻4.57) in subjects with a daily frequency of refined cereal consumption above the median. The association between LEPR and excess weight can be modulated by the type and distribution of dietary fatty acids, sugary drinks, and refined cereals.

The importance of gene-environment interactions in human obesity

The worldwide obesity epidemic has been mainly attributed to lifestyle changes. However, who becomes obese in an obesity-prone environment is largely determined by genetic factors. In the last 20 years, important progress has been made in the elucidation of the genetic architecture of obesity. In parallel with successful gene identifications, the number of gene-environment interaction (GEI) studies has grown rapidly. This paper reviews the growing body of evidence supporting gene-environment interactions in the field of obesity. Heritability, monogenic and polygenic obesity studies provide converging evidence that obesity-predisposing genes interact with a variety of environmental, lifestyle and treatment exposures. However, some skepticism remains regarding the validity of these studies based on several issues, which include statistical modelling, confounding, low replication rate, underpowered analyses, biological assumptions and measurement precision. What follows in this review includes (1) an introduction to the study of GEI, (2) the evidence of GEI in the field of obesity, (3) an outline of the biological mechanisms that may explain these interaction effects, (4) methodological challenges associated with GEI studies and potential solutions, and (5) future directions of GEI research. Thus far, this growing body of evidence has provided a deeper understanding of GEI influencing obesity and may have tremendous applications in the emerging field of personalized medicine and individualized lifestyle recommendations.

Interaction between Pro12Ala polymorphism of PPARγ2 and diet on adiposity phenotypes

The aim of this report is to perform a systematic review and qualitative synthesis of the literature to address whether, and to what extent, diet modulates the effects of the Pro12Ala polymorphism of peroxisome proliferator-activated receptor gamma 2 (PPARγ2) on body weight and other measures of adiposity. A systematic search of the literature was conducted, wherein both observational and experimental studies of adults were reviewed. Overall, the results of the observational studies show little consistency. Methodological differences in their design, conduct and analysis may largely account for the apparently discrepant findings. This notwithstanding, the main picture that emerges is that the energy content and composition of the diet may affect BMI, body composition and metabolic parameters in Ala allele carriers more than in Pro/Pro homozygotes. In most studies, carriers of the Ala allele with an obesogenic lifestyle (i.e. high-energy, high-carbohydrate and, to some extent, high-fat diets) are more obese than Pro homozygotes. Well-designed intervention studies with a sufficiently large sample size consistently show that carriers of the Ala allele are more prone to weight loss when exposed to a healthy lifestyle; however, these individuals do not seem to retain these benefits when returning to a sedentary lifestyle and inadequate dieting behaviours. Some key questions in this area of research have emerged. Carefully designed and adequately powered studies are needed, particularly involving the development and validation of standardized tools for the assessment of dietary exposure, including the use of biomarkers, to move the field forward.

The genetics of childhood obesity and interaction with dietary macronutrients

The genes contributing to childhood obesity are categorized into three different types based on distinct genetic and phenotypic characteristics. These types of childhood obesity are represented by rare monogenic forms of syndromic or non-syndromic childhood obesity, and common polygenic childhood obesity. In some cases, genetic susceptibility to these forms of childhood obesity may result from different variations of the same gene. Although the prevalence for rare monogenic forms of childhood obesity has not increased in recent times, the prevalence of common childhood obesity has increased in the United States and developing countries throughout the world during the past few decades. A number of recent genome-wide association studies and mouse model studies have established the identification of susceptibility genes contributing to common childhood obesity. Accumulating evidence suggests that this type of childhood obesity represents a complex metabolic disease resulting from an interaction with environmental factors, including dietary macronutrients. The objective of this article is to provide a review on the origins, mechanisms, and health consequences of obesity susceptibility genes and interaction with dietary macronutrients that predispose to childhood obesity. It is proposed that increased knowledge of these obesity susceptibility genes and interaction with dietary macronutrients will provide valuable insight for individual, family, and community preventative lifestyle intervention, and eventually targeted nutritional and medicinal therapies.

Obesity and eating behaviour in children and adolescents: contribution of common gene polymorphisms

The prevalence of childhood obesity is increasing in many countries and confers risks for early type 2 diabetes, cardiovascular disease and metabolic syndrome. In the presence of potent 'obesogenic' environments not all children become obese, indicating the presence of susceptibility and resistance. Taking an energy balance approach, susceptibility could be mediated through a failure of appetite regulation leading to increased energy intake or via diminished energy expenditure. Evidence shows that heritability estimates for BMI and body fat are paralleled by similar coefficients for energy intake and preferences for dietary fat. Twin studies implicate weak satiety and enhanced food responsiveness as factors determining an increase in BMI. Single gene mutations, for example in the leptin receptor gene, that lead to extreme obesity appear to operate through appetite regulating mechanisms and the phenotypic response involves overconsumption and a failure to inhibit eating. Investigations of robustly characterized common gene variants of fat mass and obesity associated (FTO), peroxisome proliferator-activated receptor (PPARG) and melanocortin 4 receptor (MC4R) which contribute to variance in BMI also influence the variance in appetite factors such as measured energy intake, satiety responsiveness and the intake of palatable energy-dense food. A review of the evidence suggests that susceptibility to childhood obesity involving specific allelic variants of certain genes is mediated primarily through food consumption (appetite regulation) rather than through a decrease in activity-related energy expenditure. This conclusion has implications for early detection of susceptibility, and for prevention and management of childhood obesity.

Lifestyle factors modify obesity risk linked to PPARG2 and FTO variants in an elderly population: a cross-sectional analysis in the SUN Project

Genetic factors may interact with lifestyle factors to modify obesity risk. FTO and PPARG2 are relevant obesogenes. Our aim was to explore the effect of Pro12Ala (rs1801282) of PPARG2 and rs9939609 of FTO on obesity risk and to examine their interaction with lifestyle factors in an elderly population. Subjects (n = 978; aged 69 ± 6) were recruited from the SUN (Seguimiento Universidad de Navarra) Project. DNA was obtained from saliva, and lifestyle and dietary data were collected by validated self-reported questionnaires. Genotyping was assessed by RT-PCR plus allele discrimination. Subjects carrying the Ala allele of PPARG2 gene had a significantly increased obesity risk compared to non-carrier (Pro12Pro) subjects (OR, 1.66; 95  % CI, 1.01-2.74; p = 0.045). Greater obesity risk was also found in inactive or high carbohydrate intake subjects with the Ala12 allele of PPARG2 gene. Interestingly, subjects carrying the Ala allele of the PPARG2 gene and with a high CHO (>246 g/day) intake had an increased obesity risk compared to Pro12Pro subjects (OR, 2.67; 95 % CI, 1.3-5.46; p = 0.007; p for [CHO × PPARG2] interaction = 0.046). Moreover, in subjects with a high CHO intake, the co-presence of the Ala allele of PPARG2 gene and one minor A allele (rs9939609) of FTO gene did increase obesity risk (OR, 3.26; 95 % CI, 1.19-8.89; p = 0.021) when compared to non-carrier (Pro12Pro/TT) subjects. In conclusion, it appears that lifestyle factors may act as effect modifiers for obesity risk linked to Ala12 allele of the PPARG2 gene and the minor A allele of FTO gene in an elderly population.

Oxidative stress and inflammation interactions in human obesity

Obesity is often characterized by increased oxidative stress and exacerbated inflammatory outcomes accompanying infiltration of immune cells in adipocytes. The oxidative stress machinery and inflammatory signaling are not only interrelated, but their impairment can lead to an inhibition of insulin responses as well as a higher risk of cardiovascular diseases and associated features. Mitochondria, in addition to energy transformation, play a role in apoptosis, cellular proliferation, as well as in the cellular redox state control. Under certain circumstances, protons are able to re-enter the mitochondrial matrix via different uncoupling proteins, disturbing free radical production by mitochondria. Disorders of the mitochondrial electron transport chain, over-generation of reactive oxygen species, and lipoperoxides or alterations in antioxidant defenses have been reported in situations of obesity and type-2 diabetes. On the other hand, obesity has been linked to a low grade pro-inflammatory state, in which impairments in the oxidative stress and antioxidant mechanism could be involved. The current scientific evidence highlights the need of investigating the interplay between oxidative stress and inflammation with obesity/diabetes onset as well as the interactions of such factors either as a cause or consequence of obesity. The signaling mediated by the activation of inflammatory markers or nuclear factor kappa β and other transcription factors as central regulators of inflammation are key issues to understanding oxidative stress responses in obesity. This review aims at summarizing the main mechanisms and interplay factors between oxidative stress and inflammation in human obesity according to the last 10 years of research in the field.

Evidences on three relevant obesogenes: MC4R, FTO and PPARγ. Approaches for personalized nutrition

Obesity is a complex disease that results from the interaction between lifestyle (dietary patterns and sedentary habits) and genetic factors. The recognition of a genetic basis for human obesity has driven to identify putative causal genes to understand the pathways that control body mass and fat deposition in humans as well as to provide personalized treatments and prevention strategies to fight against obesity. More than 120 candidate genes have been associated with obesity-related traits. Genome-wide association study has so far identified over 20 novel loci convincingly associated with adiposity. This review is specifically focused on the study of the effects of melanocortin 4 receptor, Peroxisome proliferator-activated receptor γ and fat mass and obesity associated (FTO) gene variants and their interactions with dietary intake, physical activity or drug administration on body weight control. The advances in this field are expected to open new ways in genome-customized diets for obesity prevention and therapy following personalized approaches.

Gene-environment interaction and obesity

The epidemic of obesity has become a major public health problem. Common-form obesity is underpinned by both environmental and genetic factors. Epidemiological studies have documented that increased intakes of energy and reduced consumption of high-fiber foods, as well as sedentary lifestyle, were among the major driving forces for the epidemic of obesity. Recent genome-wide association studies have identified several genes convincingly related to obesity risk, including the fat mass and obesity associated gene and the melanocortin-4 receptor gene. Testing gene-environment interaction is a relatively new field. This article reviews recent advances in identifying the genetic and environmental risk factors (lifestyle and diet) for obesity. The evidence for gene-environment interaction, especially from observational studies and randomized intervention trials, is examined specifically. Knowledge about the interplay between genetic and environmental components may facilitate the choice of more effective and specific measures for obesity prevention based on the personalized genetic make-up.

Interaction between genes and lifestyle factors on obesity

Obesity originates from a failure of the body-weight control systems, which may be affected by changing environmental influences. Basically, the obesity risk depends on two important mutually-interacting factors: (1) genetic variants (single-nucleotide polymorphisms, haplotypes); (2) exposure to environmental risks (diet, physical activity etc.). Common single-nucleotide polymorphisms at candidate genes for obesity may act as effect modifiers for environmental factors. More than 127 candidate genes for obesity have been reported and there is evidence to support the role of twenty-two genes in at least five different populations. Gene-environment interactions imply that the synergy between genotype and environment deviates from either the additive or multiplicative effect (the underlying model needs to be specified to appraise the nature of the interaction). Unravelling the details of these interactions is a complex task. Emphasis should be placed on the accuracy of the assessment methods for both genotype and lifestyle factors. Appropriate study design (sample size) is crucial in avoiding false positives and ensuring that studies have enough power to detect significant interactions, the ideal design being a nested case-control study within a cohort. A growing number of studies are examining the influence of gene-environmental interactions on obesity in either epidemiological observational or intervention studies. Positive evidence has been obtained for genes involved in adiposity, lipid metabolism or energy regulation such as PPARgamma2 (Pro12Ala), beta-adrenoceptor 2 (Gln27Glu) or uncoupling proteins 1, 2 and 3. Variants on other genes relating to appetite regulation such as melanocortin and leptin receptors have also been investigated. Examples of some recently-identified interactions are discussed.

Effect of the Ala12 allele in the PPARgamma-2 gene on the relationship between birth weight and body composition in adolescents: the AVENA study

The intent of this study was to assess whether the effect of birth weight on later body composition is modified by Pro12Pro, Pro12Ala, and Ala12Ala genotypes of the peroxisome proliferator-activated receptor gamma-2 (PPARgamma-2) gene. The PPARgamma-2 gene polymorphism was genotyped in 273 adolescents aged 13-18.5 y, born at term and whose birth weight was known. They were selected from a cross-sectional multicenter study conducted in five Spanish cities in 2000-2002. Body mass index (BMI) was calculated from weight and height measurements, and body composition and fat distribution were estimated from skinfold thickness. A total of 229 subjects (111 males and 118 females) carried the Pro12Pro genotype and 44 (22 males and 22 females) the Pro12Ala and Ala12Ala PPARgamma-2 genotypes. In the Pro12Pro group, birth weight Z score was positively associated with both fat-free mass (FFM) (p < 0.05) and fat mass (FM) (p < 0.05), but these relationships disappeared after controlling for age, gestational age, socioeconomic status (SES), physical activity, Tanner stage, sex, and BMI. In the Ala12 group, birth weight Z score was positively associated with FFM (p < 0.01), and this relationship remained significant after controlling for confounding variables (p < 0.05). Small body weight at birth may program lower FFM in adolescents carrying the Ala12 allele in the PPARgamma-2 gene.

Genetics of obesity

Objective

The aim was to review and update advances in genetics of obesity.

Design

Analysis and interpretation of recent investigations about regulating the energy balance as well as about gene-nutrient interactions and current nutrigenomic research methods.

Background and main statements

Obesity results from a long-term positive energy balance. However, its rising prevalence in developed and developing societies must reflect lifestyle changes, since genetic susceptibility remains stable over many generations. Like most complex diseases, obesity derives from a failure of adequate homoeostasis within the physiological system controlling body weight. The identification of genes that are involved in syndromic, monogenic and polygenic obesity has seriously improved our knowledge of body weight regulation. This disorder may arise from a deregulation at the genetic level (e.g. gene transcription or altered protein function) or environmental exposure (e.g. diet, physical activity, etc.).

Conclusions

In practice, obesity involves the interaction between genetic and environmental factors.

Variants of the peroxisome proliferator-activated receptor gamma- and beta-adrenergic receptor genes are associated with measures of compensatory eating behaviors in young children

BACKGROUND

Young children can regulate energy precisely in the short term, showing the potential for an innate compensation mechanism of eating behavior. However, data suggest that precise compensation is attenuated as a function of increasing adiposity, parental feeding style, and age. Common variation in candidate obesity genes may account for some of the individual variation observed in short-term energy compensation. Polymorphisms in the peroxisome proliferator-activated receptor gamma (PPARG) and beta-adrenergic receptor (ADRB3) genes have been linked to increased body mass index (BMI; in kg/m(2)), obesity, and more recently dietary nutrients and preferences. In addition, common variation in ADRB3 interacts with PPARG to modulate adult body weight.

OBJECTIVE

This study investigated whether variants in these genes were associated with measurable effects on child eating behavior.

DESIGN

Children (n=84) aged 4-10 y were prospectively selected for variants of the PPARG locus (Pro12Ala, C1431T). Heights and weights were measured. Energy intake from a test meal was measured 90 min after ingestion of a no-energy (NE), low-energy (LE), or high-energy (HE) preload, and the compensation index (COMPX) was calculated.

RESULTS

BMI differed significantly by gene model, whereby Pro12Ala was associated with a lower BMI. Poor COMPX was associated with the PPARG T1431 allele (P=0.009). There was a significant interaction between COMPX and the ADRB3 Trp64Arg variant in modulating compensation (P=0.003), whereas the Arg64 allele was associated with good compensation (P=0.001).

CONCLUSIONS

This is the first study to suggest that a genetic interaction involving ADRB3 and PPARG variants influences eating behavior in children.

Weight regain after slimming induced by an energy-restricted diet depends on interleukin-6 and peroxisome-proliferator-activated-receptor-γ2 gene polymorphisms

Weight-loss maintenance after following an energy-restricted diet is a major problem that a number of studies are trying to characterise. The aim of the present study was to investigate the role of IL-6 -174G > C and PPAR-γ2 Pro12Ala variants on weight regulation in obese subjects receiving a low-energy diet and at 1 year after the acute slimming period. Sixty-seven volunteers (age 34·7 (sd 7·0) years; BMI 35·8 (sd 4·8) kg/m2) were enrolled in a 10-week dietary intervention and were contacted again 1 year after the end of this period. Body composition was measured at three times during the study. Also, PPAR-γ2 Pro12Ala and IL-6 -174G > C polymorphisms were analysed in the participants. No statistical differences were observed depending on the genetic variants at baseline for anthropometric variables, or after the intervention. However, the C allele of the -174G > C IL-6 gene polymorphism was more frequently observed (P=0·032) in subjects with successful weight maintenance (<10 % weight regain). In fact, the C allele partially protected against weight regain (odds ratio 0·24;P=0·049), while the conjoint presence of both gene variants (C+ and Ala+) further improved the ability for weight maintenance (odds ratio 0·19;P=0·043). The present study demonstrates that the C allele of the -174G > C polymorphism gives protection against regain of weight lost. Moreover, the presence of the Ala allele of the PPARγ-2 together with the C allele strengthens this protection. These findings support a role for these polymorphisms on weight regulation and suggest a synergetic effect of both variants on weight maintenance after following a diet to lose weight.

Genotype-by-nutrient interactions assessed in European obese women. A case-only study

BACKGROUND

The development of obesity is influenced by both genetic and environmental risk factors. Whereas changes in the environment appear to be responsible for the increasing prevalence of obesity, genetic factors interacting with environmental factors would contribute to explain obesity onset and severity.

AIM

To explore epidemiologic genotype-by-nutrient interactions in obesity.

METHODS

A total of 42 polymorphisms of 26 candidate genes for obesity were genotyped in 549 adult obese women recruited from eight European centres in a case-only study. The nutritional variables assessed in this study were the dietary fibre intake (grams per day), the ratio of dietary polyunsaturated fat to saturated fat (P:S ratio) and the percentage of energy derived from fat in the diet as calculated from a weighed three-day food record (%E). Under the assumption of genotype-nutrient independence in the population, the odds ratio calculated in a sample of obese women would indicate the existence of genotype-by-nutrient interactions, measured as deviations from the multiplicative effects of the genetic and the nutrient factors separately.

RESULTS

No new but confirmaty evidences for genotype-by-nutrient interactions in obesity were detected in this case-only study. The test of interaction between fibre intake and the -514 C > T polymorphism of the hepatic lipase gene (LIPC) yielded P-values of 0.01 across different statistical models. Likewise, the -11377G > C polymorphism of the adiponectin gene (ADIPOQ) and the -681 C > G polymorphism of the PPARG3 gene might interact with the percentage of energy derived from fat in the diet for the development of obesity (P-values in the range of 0.01-0.05 across different statistical models). The P-values were not adjusted for multiple testing, so these results should be considered with caution.

CONCLUSIONS

Although the use of obese-only samples is theoretically a useful approach to detect interactions, few genotype-by-nutrient interactions have been suggested in obese European women after the analysis of candidate polymorphisms and the selected nutrient variables. The most remarkable multiplicative interaction found in this study refers to the combination of the hepatic lipase gene polymorphism -514 C > T and fibre intake.

Energy balance and food intake: the role of PPARgamma gene polymorphisms

Mechanisms regulating energy balance involve complex interactions between genetic, environmental and behavioural (learnt and intrinsic) factors. Genotype may drive the partitioning of energy metabolism and predispose to site-specific adiposity, culminating in a state of energy imbalance. One candidate gene with a direct link to adiposity is the peroxisome proliferator-activated receptor gamma (PPARG) gene. PPARG is a cell nuclear receptor expressed almost exclusively in adipose tissue that regulates adipocyte differentiation, lipid metabolism and insulin sensitivity. PPARgamma appears to be a key regulator of energy balance, with polymorphisms on the PPARG gene linked to obesity and effects on body composition. Our research has confirmed an association between the pro12ala allele and reduced incidence of obesity in pre-pubertal children and there are strong associations between genetic variation at the PPARG locus and percentage body fat. Moreover, our evidence suggests that PPARG C-681G and pro12ala polymorphisms display opposing effects in terms of growth phenotype, with pro12Ala associated with deficient energy utilisation, leading to reduced growth and the G-681 variant associated with accelerated growth compared with wildtypes. Common differences in this gene have also been associated with variations in body weight in response to dietary macronutrients. Preliminary evidence suggests that PPARG variants may even be involved in the control of short term energy compensation. Taken together these data suggest that the role of PPARG is varied and complex, influencing fat deposition and growth velocity early in life, with potential impact in the control of energy intake and appetite regulation, and could provide a key target for future research and anti-obesity agents.

The Pro12Ala and C-681G variants of the PPARG locus are associated with opposing growth phenotypes in young schoolchildren

AIMS/HYPOTHESIS

Peroxisome proliferator-activated receptor gamma is an important regulator of adiposity in mouse and man, and common variation in the PPARG gene has been associated with birthweight, adult obesity, insulin sensitivity and type 2 diabetes. We hypothesised that these variants may be associated with childhood obesity.

METHODS

Height and weight were recorded for 2454 prepubertal children aged between 4 and 10 years, who were then genotyped for three common variants of the PPARG locus: C-681G, Pro12Ala and C1431T.

RESULTS

No single variant of PPARG was significantly associated with height, weight or BMI. However, when modelling the variants together we detected an opposing interaction between the -681G and the Ala12 variants in height and weight, but not BMI (p=0.018, 0.013 and 0.119 respectively). The data were consistent with the Ala12 carriers being deficient in energy storage/utilisation, leading to reduced growth. In contrast, the -681G variant, which has been associated with increased adult height, was associated with accelerated growth. The two variants were in strong linkage disequilibrium. However, rare individuals bearing the isolated variants demonstrated the greatest variation from the mean, the most contrasting genotypes being associated with a variation of 7 kg in weight and 6 cm in height, standardised to 7.4-year-olds (p=0.006 and p=0.02 respectively).

CONCLUSIONS/INTERPRETATION

This study demonstrates that quantitative trait analysis of energy balance/growth and the PPARG locus is complex and requires the use of multiple genetic markers.

Gene-gene interaction between PPAR gamma 2 and ADR beta 3 increases obesity risk in children and adolescents

AIMS

Multiple genes are likely to be involved in obesity and these genes may interact with environmental factors to influence obesity risk. Our aim was to explore the synergistic contribution of the two polymorphisms: Pro12Ala of the PPAR gamma 2 gene and Trp64Arg of the ADR beta 3 gene to obesity risk in a Spanish children and adolescent population.

METHODS

We designed a sex- and age-matched case-control study. Participants were 185 obese and 185 control children (aged 5-18 y) from the Navarra region, recruited through Departments of Pediatrics (Hospital Virgen del Camino, Navarra University Clinic and several Primary Health Centers). The obesity criterion (case definition) was BMI above the 97th percentile according to Spanish BMI reference data for age and gender. Anthropometric parameters were measured by standard protocols. The genotype was assessed by PCR-RFLP after digestion with BstUI for PPAR gamma 2 mutation and BstNI for ADR beta 3 variants. Face-to-face interviews were conducted to assess the physical activity. Using a validated physical activity questionnaire, we computed an activity metabolic equivalent index (METs h/week), which represents the physical exercise during the week for each participant. Statistical analysis was performed by conditional logistic regression, taking into account the matching between cases and controls.

RESULTS

Carriers of the polymorphism Pro12Ala of the PPAR gamma 2 gene had a significantly higher obesity risk than noncarriers (odds ratio (OR)=2.18, 95% CI=1.09-4.36) when we adjusted for sex, age and physical activity. Moreover, the risk of obesity was higher (OR=2.59, 95% CI=1.17-5.34) when family history of obesity was also taken into account in the model. The OR for obesity linked to both polymorphisms (PPAR gamma 2 and ADR beta 3) was 5.30 (95% CI=1.08-25.97) when we adjusted for sex, age and physical activity. After adjustment for family history of obesity, the OR for carriers of both polymorphisms was 19.5 (95% CI=2.43-146.8).

CONCLUSIONS

A synergistic effect between polymorphism Pro12Ala of the PPAR gamma 2 gene and Trp64Arg of the ADR beta 3 gene for obesity risk was found in a case-control study including children and adolescents.

Genes, lifestyles and obesity

OBJECTIVE

To review the role of genes and lifestyle factors, particularly dietary habits and physical activity patterns, in obesity risk as well as their potential interactions.

DESIGN AND MEASUREMENTS

A descriptive report of a number of genes definitely ascribed or potentially implicated in excessive fat accumulation leading to obesity as assessed by different research approaches (Mendelian transmission, genetic animal models, epidemiological association/linkage studies and genome-wide scans). Also, the involvement of macronutrient intake and composition (fat/carbohydrate) as well as the role of activity-linked energy expenditure in obesity onset is reviewed.

RESULTS

Examples of the role of the genotype as well as of the dietary macronutrient composition/intake and sedentary/low energy cost of physical activities in obesity prevalence are reported.

CONCLUSIONS

Both genes and everyday life environmental factors such as cultural and social mediated food intake and reduced domestic and living work activities are involved in the obesity pandemia. The occurrence of gene x gene and gene x environmental factors interactions makes it more difficult to interpret the specific roles of genetics and lifestyle in obesity risk.

Estudios sobre la obesidad en genes candidatos

There are more than 430 chromosomic regions with gene variants involved in body weight regulation and obesity development. Polymorphisms in genes related to energy expenditure--uncoupling proteins (UCPs), related to adipogenesis and insulin resistance--hormone-sensitive lipase (HLS), peroxisome proliferator-activated receptor gamma (PPAR gamma), beta adrenergic receptors (ADRB2,3), and alfa tumor necrosis factor (TNF-alpha), and related to food intake--ghrelin (GHRL)--appear to be associated with obesity phenotypes. Obesity risk depends on two factors: a) genetic variants in candidate genes, and b) biographical exposure to environmental risk factors. It is necessary to perform new studies, with appropriate control groups and designs, in order to reach relevant conclusions with regard to gene/environmental (diet, lifestyle) interactions.