A twin study of genetic and environmental influences on the intake of fluids and beverages

Healthy beverage index is associated with metabolic syndrome: insights from the Ravansar non-communicable disease (RaNCD) cohort study

BACKGROUND

Dietary patterns play a crucial role in the development and management of metabolic syndrome (MetS). The Healthy Beverage Index (HBI) is a novel tool that assesses the quality of beverage choices in the diet and provides insights into their potential impact on metabolic health. The aim of this study was to investigate the association between the HBI and the MetS.

METHODS

This cross-sectional study was conducted using data collected at baseline from the Ravansar Noncommunicable Disease Cohort Study. A total of 9,025 participants aged 35 to 65 years were included in the analysis. HBI was calculated using food items from the Food Frequency Questionnaire (FFQ). MetS status was defined according to established criteria, and logistic regression analysis was performed to assess the association between HBI scores and MetS, adjusting for potential confounding variables.

RESULTS

In our study, 41.13% of the population was found to have MetS, with a significant association between MetS and tertiles of HBI. Furthermore, the logistic regression model showed a significant inverse association between HBI scores and the odds of developing a MetS (OR = 0.90; 95% CI: 0.86, 0.94), even after adjusting for confounding factors, emphasizing the potential protective effect of higher HBI scores.

CONCLUSION

Increased HBI scores were associated with lower risk of MetS, emphasizing the importance of choosing health-promoting beverages in controlling MetS. These findings support the association between dietary habits and metabolic health and provide practical guidance for individuals and public health initiatives aimed at improving metabolic outcomes.

Rare variants in the sodium-dependent phosphate transporter gene SLC34A3 explain missing heritability of urinary stone disease

Urinary stone disease (USD) is a major health burden affecting over 10% of the United Kingdom population. While stone disease is associated with lifestyle, genetic factors also strongly contribute. Common genetic variants at multiple loci from genome-wide association studies account for 5% of the estimated 45% heritability of the disorder. Here, we investigated the extent to which rare genetic variation contributes to the unexplained heritability of USD. Among participants of the United Kingdom 100,000-genome project, 374 unrelated individuals were identified and assigned diagnostic codes indicative of USD. Whole genome gene-based rare variant testing and polygenic risk scoring against a control population of 24,930 ancestry-matched controls was performed. We observed (and replicated in an independent dataset) exome-wide significant enrichment of monoallelic rare, predicted damaging variants in the SLC34A3 gene for a sodium-dependent phosphate transporter that were present in 5% cases compared with 1.6% of controls. This gene was previously associated with autosomal recessive disease. The effect on USD risk of having a qualifying SLC34A3 variant was greater than that of a standard deviation increase in polygenic risk derived from GWAS. Addition of the rare qualifying variants in SLC34A3 to a linear model including polygenic score increased the liability-adjusted heritability from 5.1% to 14.2% in the discovery cohort. We conclude that rare variants in SLC34A3 represent an important genetic risk factor for USD, with effect size intermediate between the fully penetrant rare variants linked with Mendelian disorders and common variants associated with USD. Thus, our findings explain some of the heritability unexplained by prior common variant genome-wide association studies.

The Association Between Healthy Beverage Index (HBI) With Metabolic Risk Factors Among Apparently Metabolically Healthy Overweight and Obese Individuals

Recent studies have evaluated the association between specific beverage intake and metabolic risks in adults. However, more evidence is needed to examine the association between the Healthy Beverage Index (HBI) and metabolic factors. Therefore, this study investigated the relationship between HBI and metabolic factors in adults. In this cross-sectional study, 338 overweight and obese individuals living in Tabriz, Iran were selected. Data on beverage consumption, demographics, physical activity, and anthropometric characteristics were evaluated using validated standard protocols. The predefined HBI was calculated based on previous studies. The mean value of HBI index among all of the participants was 59.76 ± 6.51. Those at the higher HBI scores had significantly lower waist circumference, waist-to-hip ratio, fat mass, and weight (p < 0.05). HBI and triglyceride scores also had a significant relationship. It has been shown that at higher HBI scores compared to lower scores, high-density lipoprotein cholesterol levels increase while homeostatic model assessment for insulin resistance, low-density lipoprotein cholesterol, total cholesterol, and blood pressure decrease. HBI scores higher among Iranian adults were associated with a better chance of losing weight and weight loss and a better lipid profile, and lower blood pressure. Therefore, HBI can be a useful and helpful tool for assessing the overall quality of beverages adults consume. However, further studies are warranted to confirm the possible health effects of healthy beverage index.

The genetics of kidney stone disease and nephrocalcinosis

Kidney stones (also known as urinary stones or nephrolithiasis) are highly prevalent, affecting approximately 10% of adults worldwide, and the incidence of stone disease is increasing. Kidney stone formation results from an imbalance of inhibitors and promoters of crystallization, and calcium-containing calculi account for over 80% of stones. In most patients, the underlying aetiology is thought to be multifactorial, with environmental, dietary, hormonal and genetic components. The advent of high-throughput sequencing techniques has enabled a monogenic cause of kidney stones to be identified in up to 30% of children and 10% of adults who form stones, with ~35 different genes implicated. In addition, genome-wide association studies have implicated a series of genes involved in renal tubular handling of lithogenic substrates and of inhibitors of crystallization in stone disease in the general population. Such findings will likely lead to the identification of additional treatment targets involving underlying enzymatic or protein defects, including but not limited to those that alter urinary biochemistry.

The association between Healthy Beverage Index and anthropometric measures among children: a cross-sectional study

PURPOSE

Several studies evaluated the associations between specific beverages and cardio-metabolic risks among children. However, the evidence on the association between patterns of the beverage consumption and children's anthropometric indices is rare. Therefore, this study was conducted to examine the association between Healthy Beverage Index (HBI) and anthropometric measures among 6-year-old girl children.

METHODS

In this cross-sectional study, 788 children selected from health centers in Tehran, Iran. Data on beverage intake, socio-demographic, physical activity, and anthropometric characteristics were evaluated using reliable and validated standard protocols. The predefined HBI was calculated based on the previous research.

RESULTS

After controlling for several confounders [mother age, mother body mass index, mother physical activity, socioeconomic status, children physical activity and energy intake, total oils (all kinds of oils like animal and plant oils), and total sweet foods (sweet foods except sweetened beverages)], being in the third compared to the first tertile of HBI among children was associated with increased odds of wasting (OR: 5.16; 95% CI 1.5-17.79) and underweight/wasting (OR: 1.81; 95% CI 1.07-3.07). Among the HBI components, just being in the third compared to the first tertile of high-fat milk was inversely associated with decreased odds of wasting (OR: 0.18; 95% CI 0.04-0.73).

CONCLUSIONS

The HBI among children was associated with higher odds of wasting and underweight/wasting. In addition, high-fat milk consumption decreased the odds of wasting among children. Further prospective studies need to confirm these results.

LEVEL OF EVIDENCE

Level V, descriptive cross-sectional study.

Genetic and Environmental Influences of Dietary Indices in a UK Female Twin Cohort

A healthy diet is associated with the improvement or maintenance of health parameters, and several indices have been proposed to assess diet quality comprehensively. Twin studies have found that some specific foods, nutrients and food patterns have a heritable component; however, the heritability of overall dietary intake has not yet been estimated. Here, we compute heritability estimates of the nine most common dietary indices utilized in nutritional epidemiology. We analyzed 2590 female twins from TwinsUK (653 monozygotic [MZ] and 642 dizygotic [DZ] pairs) who completed a 131-item food frequency questionnaire (FFQ). Heritability estimates were computed using structural equation models (SEM) adjusting for body mass index (BMI), smoking status, Index of Multiple Deprivation (IMD), physical activity, menopausal status, energy and alcohol intake. The AE model was the best-fitting model for most of the analyzed dietary scores (seven out of nine), with heritability estimates ranging from 10.1% (95% CI [.02, .18]) for the Dietary Reference Values (DRV) to 42.7% (95% CI [.36, .49]) for the Alternative Healthy Eating Index (A-HEI). The ACE model was the best-fitting model for the Healthy Diet Indicator (HDI) and Healthy Eating Index 2010 (HEI-2010) with heritability estimates of 5.4% (95% CI [-.17, .28]) and 25.4% (95% CI [.05, .46]), respectively. Here, we find that all analyzed dietary indices have a heritable component, suggesting that there is a genetic predisposition regulating what you eat. Future studies should explore genes underlying dietary indices to further understand the genetic disposition toward diet-related health parameters.

Genetic determinants of beverage consumption: Implications for nutrition and health

Beverages make important contributions to nutritional intake and their role in health has received much attention. This review focuses on the genetic determinants of common beverage consumption and how research in this field is contributing insight to what and how much we consume and why this genetic knowledge matters from a research and public health perspective. The earliest efforts in gene-beverage behavior mapping involved genetic linkage and candidate gene analysis but these approaches have been largely replaced by genome-wide association studies (GWAS). GWAS have identified biologically plausible loci underlying alcohol and coffee drinking behavior. No GWAS has identified variants specifically associated with consumption of tea, juice, soda, wine, beer, milk or any other common beverage. Thus far, GWAS highlight an important behavior-reward component (as opposed to taste) to beverage consumption which may serve as a potential barrier to dietary interventions. Loci identified have been used in Mendelian randomization and gene×beverage interaction analysis of disease but results have been mixed. This research is necessary as it informs the clinical relevance of SNP-beverage associations and thus genotype-based personalized nutrition, which is gaining interest in the commercial and public health sectors.

Heritability of dietary traits that contribute to nephrolithiasis in a cohort of adult sibships

BACKGROUND

Kidney stones and their risk factors aggregate in families, yet few studies have estimated the heritability of known risk factors.

OBJECTIVE

Estimate the heritability of dietary risk factors for kidney stones.

METHODS

Dietary intakes were assessed using the Viocare Food Frequency Questionnaire in sibships enrolled in the Rochester, MN cohort of the Genetic Epidemiology Network of Arteriopathy. Measures of urinary supersaturation were determined using 24 h urine samples. Heritabilities and genetic correlations were estimated using variance components methods.

RESULTS

Samples were available from 620 individuals (262 men, 358 women, mean (SD) age 65 (9) years). Dietary intakes of protein, sucrose, and calcium had strong evidence for heritability (p < 0.01) after adjustment for age, sex, height and weight. Among the significantly heritable dietary intakes (p < 0.05), genetic factors explained 22-50 % of the inter-individual variation. Significant genetic correlations were observed among dietary protein, dietary sucrose, and dietary calcium intakes (p < 0.001).

CONCLUSIONS

Evidence from this relatively large cohort suggests a strong heritable component to dietary intakes of protein, sucrose and calcium that contributes to nephrolithiasis risk. Further efforts to understand the interplay of genetic and environmental risk factors in kidney stone pathogenesis are warranted.

Twin studies advance the understanding of gene–environment interplay in human nutrigenomics

Investigations into the genetic architecture of diet–disease relationships are particularly relevant today with the global epidemic of obesity and chronic disease. Twin studies have demonstrated that genetic makeup plays a significant role in a multitude of dietary phenotypes such as energy and macronutrient intakes, dietary patterns, and specific food group intakes. Besides estimating heritability of dietary assessment, twins provide a naturally unique, case–control experiment. Due to their shared upbringing, matched genes and sex (in the case of monozygotic (MZ) twin pairs), and age, twins provide many advantages over classic epidemiological approaches. Future genetic epidemiological studies could benefit from the twin approach particularly where defining what is ‘normal’ is problematic due to the high inter-individual variability underlying metabolism. Here, we discuss the use of twins to generate heritability estimates of food intake phenotypes. We then highlight the value of discordant MZ pairs to further nutrition research through discovery and validation of biomarkers of intake and health status in collaboration with cutting-edge omics technologies.

Overweight and obese humans overeat away from home

The built environment has been implicated in the development of the epidemic of obesity. We investigated the differences in the meal patterns of normal weight vs. overweight/obese individuals occurring at home vs. other locations. The location of meals and their size in free-living participants were continuously recorded for 7 consecutive days. Study 1: 81 males and 84 females recorded their intake in 7-day diet diaries and wore a belt that contained a GPS Logger to record their location continuously for 7 consecutive days. Study 2: 388 males and 621 females recorded their intake in diet diaries for 7 consecutive days. In both studies, compared to eating at home, overweight/obese participants ate larger meals away from home in both restaurants and other locations than normal weight participants. Overweight/obese individuals appear to be more responsive to environmental cues for eating away from home. This suggests that the influence of the built environment on the intake of overweight/obese individuals may contribute to the obesity epidemic.

Cerebellar lingula size and experiential risk factors associated with high levels of alcohol and drug use in young adults

Previous studies have reported cerebellar abnormalities or static ataxia associated with risk for chronic use of alcohol and drugs. Adverse childhood experience is another strong risk factor for later substance abuse. We therefore sought to ascertain the relationship between morphological phenotypes of the lingula (lobule I) of the anterior cerebellar vermis, and exposure to emotional (EM) versus physical (PM) maltreatment, on the degree of ongoing alcohol or drug use. The study design consisted of a cross-sectional in vivo neuroimaging study, utilizing retrospective assessment of maltreatment history and self-reports of alcohol and substance use. Study participants were 153 subjects (54 M/99F, 21.9 +/- 2.2 years) selected for imaging from a database of 1,402 community participants 18-25 years of age, who completed a detailed online screening instrument and met rigorous inclusion/exclusion criteria. Subjects were exposed to only physical abuse or harsh corporal punishment (HCP; PM group, n = 37) and parental verbal abuse and/or witnessing domestic violence (EM group, n = 58) or had no history of maltreatment or axis I disorders (n = 58). The main outcome measures consisted of the gray matter volume of lobule I as measured by manual tracing, number and type of alcoholic beverages consumed during a drinking session, number of sessions per month, and monthly drug use, along with family history of drug and alcohol abuse. Lingula thickness was not attenuated by alcohol use or maltreatment history. However, increased lingula thickness was associated with greater consumption of drugs and hard liquor, particularly in physically maltreated subjects who consumed 2.5- and 2.7-fold more alcohol and used drugs 6.1- and 7.8-fold more frequently than controls or EM subjects, respectively. In conclusion, physical maltreatment was observed to interact with cerebellar morphology resulting in a strong association with alcohol and substance use. Lingula thickness may represent a novel, experientially sensitive, phenotypic risk factor for enhanced alcohol and drug use that perhaps modulates sensitivity to these agents.

The control of food intake of free-living humans: putting the pieces back together

The control of food intake has been studied using reductionism; by separately investigating environmental, physiological, and genetic variables. The general model of intake regulation attempts to reassemble the pieces into an organized whole. It postulates that intake is influenced by sets of both physiological factors which have negative feedback loops to intake and environmental factors which do not. Data and behavioral genetic analysis on a number of environmental, psychological, dietary, and social variables demonstrate that they have large impacts on the intake of free-living humans in their everyday environments and their magnitude and impact on intake are influenced by heredity. Recent evidence of built environment influences on activity and intake further indicate the profound influence of environmental circumstances on both intake and expenditure. A computer simulation of the general model of intake regulation demonstrates that the model predicts different maintained levels of intake and body weight depending upon the external environment and that change in the environment can produce new sustained levels. It is suggested that eating is influenced by a myriad of physiological and non-physiological factors and that total intake results from the integral of their influences. It is concluded that recombining the components broken down in the reductionistic process results in a functional whole that can well describe human behavior in natural environments. The paper represents an invited review by a symposium, award winner or keynote speaker at the Society for the Study of Ingestive Behavior [SSIB] Annual Meeting in Portland, July 2009.

Sex differences in the effects of inherited bitter thiourea sensitivity on body weight in 4-6-year-old children

Previous studies have shown that inherited taste blindness to bitter compounds like 6-n-propylthiouracil (PROP) may be a risk factor for obesity, but this literature has been highly controversial. The objectives of this study were (i) to confirm findings that show an interaction between PROP status and sex on BMI z-score, and (ii) to determine if sex also interacts with variations in TAS2R38 (phenylthiocarbamide (PTC) genotype) to influence weight status in 4-6 year olds. Also, we tested whether nontaster children consumed more fat and total energy at laboratory-based meals. Seventy-two ethnically diverse children who ranged in weight status were classified as tasters (N = 52) or nontasters (N = 20) using a standard PROP screening solution. Anthropometric measures were taken, and at the end of each visit, children ate ad libitum from test meals intended for exploratory purposes. Genomic DNA was extracted from saliva and alleles at TAS2R38 were genotyped for A49P polymorphisms. In 75.8% of children, PTC genotype predicted PROP phenotype, whereas in 24.4%, genotype did not predict phenotype. PROP nontaster males had higher BMI z-scores than taster-males and females in both groups (P < 0.05), but due to a three-way interaction between PROP phenotype, TAS2R38 genotype, and sex, this relationship was only true for children who were homozygous for the bitter-insensitive allele (P < 0.0005). There were no differences in test-meal intake as a function of PROP phenotype or TAS2R38 genotype. These results suggest that the TAS2R38 variation, PROP phenotype, and sex interact to impact obesity risk in children. Future studies should be done to determine how this trait influences energy balance.

When, how much and what foods are eaten are related to total daily food intake

Intake in the morning is associated with a reduction in the total intake for the day, while intake at night is associated with greater overall daily intake. These associations are macronutrient specific, with morning carbohydrate intake associated with reduced daily carbohydrate intake, morning fat intake associated with reduced daily fat intake and morning protein intake associated with reduced daily protein intake. Since different types of foods contain differing proportions of macronutrients, the present study investigated the associations of different types of foods ingested at various times of day with total daily and macronutrient intakes. The intakes of 388 male and 621 female free-living individuals reported in 7 d diet diaries were reanalysed. The intakes of twenty-four different types of foods and seven different drinks occurring during the morning (04.00-10.29 hours), afternoon (10.30-16.59 hours) and evening (17.00-02.00 hours) were identified and related to overall daily intakes. Dairy foods, ice cream, beef, other meats, potatoes, pastry, nuts, chips and snacks, condiments, alcohol and soda were significantly associated with higher total intake over the day, while fruit, soup, breakfast cereal, pasta, pizza, water, coffee/tea and diet soda were either not associated or were associated with lower overall intake. Dietary energy density appeared to mediate the associations between particular foods and beverages and overall energy intake. This suggests that eating low-density foods in the morning and avoiding high-density foods at night might aid in reducing overall intake and may be useful in dietary interventions for overweight and obesity.

A genetic analysis of coffee consumption in a sample of Dutch twins

Caffeine is by far the most commonly used psychoactive substance. Caffeine is consumed regularly as an ingredient of coffee. Coffee consumption and coffee preference was explored in a sample of 4,495 twins (including 1,231 pairs) registered with the Netherlands Twin Registry. Twin resemblance was assessed by tetrachoric correlations and the influence of both genetic and environmental factors was explored with model fitting analysis in MX. Results showed moderate genetic influences (39%) on coffee consumption. The remaining variance was explained by shared environmental factors (21%) and unique environmental factors (40%). The variance in coffee preference (defined as the proportion of coffee consumption relative to the consumption of coffee and tea in total) was explained by genetic factors (62%) and unique environmental factors (38%).

Beverage consumption patterns of children born at different risk of obesity

BACKGROUND

Increased intake of sugar-sweetened beverages and fruit juice has been associated with overweight in children.

OBJECTIVE

This study prospectively assessed beverage consumption patterns and their relationship with weight status in a cohort of children born at different risk for obesity.

METHODS AND PROCEDURES

Participants were children born at low risk (n = 27) or high risk (n = 22) for obesity based on maternal prepregnancy BMI (kg/m(2)). Daily beverage consumption was generated from 3-day food records from children aged 3-6 years and coded into seven beverage categories (milk, fruit juice, fruit drinks, caloric and non-caloric soda, soft drinks including and excluding fruit juice). Child anthropometric measures were assessed yearly.

RESULTS

High-risk children consumed a greater percentage of daily calories from beverages at age 3, more fruit juice at ages 3 and 4, more soft drinks (including fruit juice) at ages 3-5, and more soda at age 6 compared to low-risk children. Longitudinal analyses showed that a greater 3-year increase in soda intake was associated with an increased change in waist circumference, whereas a greater increase in milk intake was associated with a reduced change in waist circumference. There was no significant association between change in intake from any of the beverage categories and change in BMI z-score across analyses.

DISCUSSION

Children's familial predisposition to obesity may differentially affect their beverage consumption patterns. Future research should examine the extent to which dietary factors may play a role in pediatric body fat deposition over time.

Genetic and shared environmental influences on children's 24-h food and beverage intake: sex differences at age 7 y

BACKGROUND

The genetics of habitual food and beverage intake in early childhood is poorly understood.

OBJECTIVE

The objective was to test the magnitude of genetic and environmental influences on 24-h food and beverage intake in 7-y-old children. The association between intake of specific food-beverage categories and child body mass index (BMI; in kg/m(2)) was also tested.

DESIGN

A classic twin design was conducted, using the MacArthur Longitudinal Study of Twins. There were 792 children, including 396 boys from 102 monozygotic and 96 dizygotic twin pairs and 396 girls from 112 monozygotic and 86 dizygotic twin pairs; Children's 24-h dietary intake was estimated by parental recall, from which 9 composite food-beverage categories were derived. Height and weight were converted to BMI. Biometrical analyses of children's daily intake of food-beverage categories and BMI were conducted.

RESULTS

There was consistent evidence of genetic influences on children's 24-h intake of food and beverages (servings/d), especially among boys. Seven categories showed significant heritability estimates among boys, ranging from 12% (fish and lemon) to 79% (peanut butter and jelly). Only 3 categories showed significant heritability estimates among girls, ranging from 20% (bread and butter) to 56% (fish and lemon). BMI showed a genetic correlation only with bread and butter intake in girls.

CONCLUSION

The magnitude of genetic and environmental influences on children's 24-h food and beverage intake differed for boys and girls, which suggests sex differences in the development of eating patterns. Heritability estimates were generally large, although other eating phenotypes may be necessary for identifying genetic correlations with adiposity.

Heritability of BMD of femoral neck and lumbar spine: a multivariate twin study of Finnish men

Of the 80% variation in BMD among male twins that is caused by genetics, part was explained by genetic influences on lifting strength and lean body mass/height. Lifting strength was significant in both the femoral and spine BMD and body weight only for lumbar BMD.

INTRODUCTION

The dominant role of heritability in BMD has been shown in twin studies among women. However, the mechanisms of genetic influences are poorly understood. BMD is associated with lean body mass and muscle strength, which both have a genetic component, but the relative effects of muscle strength and lean body mass/height on the total genetic and environmental variations influencing BMD of men are unclear.

MATERIALS AND METHODS

Measurements of BMD from a DXA scanner on a representative sample of 147 monozygotic and 153 dizygotic male twin pairs (age, 35-70 yr) were related to a variety of anthropometric and behavioral covariates and interview data. Data were analyzed with univariate modeling of genetic characteristics, bivariate modeling of covariates that were significant in univariate models, and multivariate modeling of the simultaneous effects of significant covariates from the bivariate models.

RESULTS

Heritability influences were estimated to account for 75% of the variance in femoral BMD and 83% in lumbar BMD. Univariate and bivariate modeling showed that, of the factors studied, only lifting force and lean body mass/height had statistically significant influences. Of the total genetic variation in femoral BMD, lifting force explained 9%, and lean body mass/height 18%; the proportions for lumbar BMD were 9% and 11%, respectively. Of the total environmental variation, the correlation with isokinetic lifting force explained 9% for femoral BMD and 10% for lumbar BMD. The genetic correlations between lifting force and femoral and lumbar BMD were approximately 0.3, as were the environmental correlations of isokinetic lifting force and femoral and lumbar BMD and of lean body mass/height and femoral BMD. The environmental correlation of lean body mass/height and femoral BMD was not significant.

CONCLUSIONS

Lifting force had effects on both femoral and lumbar BMD. Body weight was important, but only for lumbar BMD. Muscle strength may have the best potential for modification among behavioral factors to increase both femoral and lumbar BMD.

Heritability of hyperphagic eating behavior and appetite-related hormones among Hispanic children

OBJECTIVE

Eating in the absence of hunger (EAH) may be a genetically influenced phenotype of overweight children, but evidence is limited. This research evaluated the heritability (h(2)) of EAH and its association with overweight among Hispanic children 5 to 18 years old. Genetic and environmental associations of EAH with overweight, fat mass, and key hormonal regulators of food intake were also evaluated.

RESEARCH METHODS AND PROCEDURES

A family design was used to study 801 children from 300 Hispanic families. Weighed food intakes were used to measure EAH after an ad libitum dinner providing 50% of estimated energy needs. Fasting ghrelin, amylin, insulin, and leptin were measured by immunoassays. Measured heights, weights, and fat mass (using DXA) were obtained. Total energy expenditure (TEE) was measured by room respiration calorimetry.

RESULTS

On average, children consumed 41% of TEE at the dinner meal, followed by an additional 19% of TEE in the absence of hunger. Overweight children consumed 6.5% more energy at dinner (p < 0.001) and 14% more energy in the absence of hunger (p < 0.001) than non-overweight children. Significant heritabilities were seen for EAH (h(2) = 0.51) and dinner intake (h(2) = 0.52) and for fasting levels of ghrelin (h(2) = 0.67), amylin (h(2) = 0.37), insulin (h(2) = 0.37), and leptin (h(2) = 0.34). Genetic correlations were seen between eating behavior and fasting hormones, suggesting common underlying genes affecting their expression.

DISCUSSION

This research provides new evidence that overweight Hispanic children exhibit elevated levels of hyperphagic eating behaviors that are influenced by genetic endowment.

The time of day and the proportions of macronutrients eaten are related to total daily food intake

Intake in the morning is particularly satiating and associated with lower total amounts ingested for the day while intake at night is associated with greater overall daily intake. But, the influence of carbohydrates, fats or proteins ingested at various times of the day is unknown. The intakes of 375 male and 492 female free-living individuals that were acquired with 7 d diet-diary reports were reanalysed. The intakes of carbohydrates, fats and proteins, and the density of intake occurring during three 6 h periods (06.00 to 11.59 hours (morning), 12.00 to 17.59 hours (afternoon) and 18.00 to 23.59 hours (evening)) were identified and related to overall daily and meal intakes. Energy density of intake during all periods was found to be positively related to overall intake. When the proportion of daily carbohydrate ingested in the morning was high, less total food energy and carbohydrate were ingested over the entire day. When the proportion of daily fat ingested in the morning was high, less total food energy and carbohydrate and fat were ingested over the entire day. When the proportion of daily protein ingested in the morning was high, less protein was ingested over the entire day. Conversely, when intake was relatively high in the evening of either total food energy, carbohydrate or fat, then overall daily energy intakes tended to be higher. The results suggest that the morning intake association with reduced total intake is macronutrient specific, with morning carbohydrate, fat and protein intake associated with reduced daily carbohydrate, fat and protein intake, respectively.

Genetics of food intake and eating behavior phenotypes in humans

This review summarizes the research advances of the past decade regarding the role of human genetic differences in energy and nutrient intake as well as in eating behavior phenotypes and selected eating disorders. The evidence for familial aggregation and heritability based on twin and nuclear family study designs is summarized. Genome-wide linkage scans and quantitative trait loci identified to date are discussed. DNA sequence variants in candidate genes are reviewed. Single genes associated with classical eating disorders are also incorporated. Epigenetic events will need to be incorporated in future studies designed to investigate the effects of DNA variants on dietary phenotypes. Understanding the relative contribution of global genetic variation and of DNA sequence variants in specific genes is important in the effort to influence dietary habits in a healthier direction.

Genetic and Other Contributions to Alcohol Intake in Rhesus Macaques (Macaca mulatta)

BACKGROUND

The etiology of alcoholism and alcohol abuse, like many other complex diseases, is heterogeneous and multifactorial. Numerous studies demonstrate a genetic contribution to variation in the expression of alcohol-related disorders in humans. Over the past decade, nonhuman primates have emerged as a valuable model for some aspects of human alcohol abuse because of their phylogenetic proximity to humans. Long-term, longitudinal studies of rhesus macaques (Macaca mulatta) have provided much insight into environmental influences, especially early life experiences, on alcohol consumption and behavior patterns that characterize alcohol intake later in life. It is not known, however, whether there is a genetic component as well to the variation seen in alcohol consumption in rhesus macaques. A significant genetic component to variation in alcohol consumption in rhesus macaques would show for the first time that like humans, for nonhuman primates additive genetic influences are important. Moreover, their use as a model for alcohol-related disorders in humans would have even greater relevance and utility for designing experiments incorporating the expanding molecular genetics field, and allow researchers to investigate the interaction among the known environmental influences and various genotypes.

METHODS

In this study, we investigate factors contributing to variation in alcohol consumption of 156 rhesus macaques collected over 10 years when subjects were adolescent in age, belonging to a single extended pedigree, with each cohort receiving identical early rearing backgrounds and subsequent treatments. To measure alcohol consumption each animal was provided unfettered simultaneous access both to an aspartame-sweetened 8.4% (v/v) alcohol-water solution, the aspartame-sweetened vehicle, and to water for 1 hour each day during the early afternoon between 13:00 and 15:00 in their home cages for a period of 5 to 7 weeks. We use multiple regression to identify factors that significantly affect alcohol consumption among these animals and a maximum likelihood program (ASReml) that, controlling for the significant factors, estimates the genetic contribution to the variance in alcohol consumption.

RESULTS

Multiple regression analysis identified test cohort and rearing environment as contributing to 57 and 2%, respectively, of the total variance in alcohol consumption. Of the remaining 41% of the variance about half (19.8%) was attributable to additive genetic effects using a maximum likelihood program.

CONCLUSION

This study demonstrates that, as in humans, there are additive genetic factors that contribute to variation in alcohol consumption in rhesus macaques, with other nongenetic factors accounting for substantial portions of the variance in alcohol consumption, Our findings show the presence of an additive genetic component and suggest the potential utility of the nonhuman primate as a molecular genetics tool for understanding alcohol abuse and alcoholism.

Influence of heredity on dietary restraint, disinhibition, and perceived hunger in humans

OBJECTIVE

Dietary restraint, disinhibition, and perceived hunger have been shown to affect food intake and body weight and are thought to be risk factors for eating disorders, but little is known about their origins. We investigated the influence of heredity, shared (familial) environment, and individual environment on dietary restraint disinhibition, perceived hunger and their relation to body size and food intake.

METHODS

Scores on the Three Factor Eating Questionnaire and the Restraint Scale in addition to height, weight, body mass index, and 7-d diary reported nutrient intakes were obtained from 39 identical, 60 fraternal same-sex, and 50 fraternal opposite-sex adult twin pairs who were living independently. Linear structural modeling was applied to investigate the nature and degree of genetic and environmental influences.

RESULTS

Analysis showed significant genetic and individual environmental, but not shared (familial) environmental, influences on cognitive restraint, perceived hunger, and Restraint Scale scores, with genes accounting for 44%, 24%, and 58% of the variance, respectively. In contrast, disinhibition was found to be significantly influenced by the shared (familial) environment, accounting for 40% of the variance. Further analysis showed that cognitive restraint and perceived hunger heritabilities could not be accounted for by significant heritabilities of body weight, height, or body mass index. In contrast, the heritability of Restraint Scale scores was found to be related to body size. Cognitive restraint was negatively correlated with nutrient intake, and differences in cognitive restraint were found to be related to differences in the body sizes of identical twin pairs.

CONCLUSIONS

Dietary restraint appears to be another component in a package of genetically determined physiologic, sociocultural, and psychological processes that regulate energy balance, whereas dietary disinhibition may be the intermediary between upbringing and the development of overweight and/or eating disorders.

Stomach filling may mediate the influence of dietary energy density on the food intake of free-living humans

The energy density of the diet has been demonstrated to be a significant influence on the daily intakes of humans which has led to the hypothesis that intake control is based upon the weight and volume of food and not its energy content. The study explored the roles of the components used in the calculation of energy density and stomach filling in dietary energy density effects upon intake. Dietary energy density relationships with intake and body size were studied in 264 male and 406 female free-living adult humans who provided a detailed record of their eating and drinking in 7-day diaries. High energy density was associated with larger amounts of food energy and larger amounts of solids, but lower total weight of meals, daily intakes, and weekly intakes. The lower total weight occurred due to lower fluid intake in drinks. Multiple regression analysis revealed that overall dietary energy density was more important than the energy density of particular nutrients. Intake of fluids in drinks did not contribute to the relationship of dietary energy density with intake. The estimated weight of the contents of the stomach following the meals was relatively constant regardless of the energy density of the meals, daily, or weekly intakes. Energy density was not significantly related with body size, height, weight, or BMI. The findings support the notion that short-term intake is controlled on the basis of its weight and volume as opposed to its food energy content.

Role of parents in the determination of the food preferences of children and the development of obesity

The role of parental behaviour in the development of food preferences is considered. Food preferences develop from genetically determined predispositions to like sweet and salty flavours and to dislike bitter and sour tastes. Particularly towards the second year of life, there is a tendency to avoid novel foods (neophobia). Food aversions can be learnt in one trial if consumption is followed by discomfort. There is a predisposition to learn to like foods with high-energy density. However, from birth genetic predispositions are modified by experience and in this context during the early years parents play a particularly important role. Parental style is a critical factor in the development of food preferences. Children are more likely to eat in emotionally positive atmospheres. Siblings, peers and parents can act as role models to encourage the tasting of novel foods. Repeated exposure to initially disliked foods can breakdown resistance. The offering of low-energy-dense foods allows the child to balance energy intake. Restricting access to particular foods increases rather than decreases preference. Forcing a child to eat a food will decrease the liking for that food. Traditionally, educational strategies have typically involved attempts to impart basic nutritional information. Given the limited ability of information to induce changes in behaviour, an alternative strategy would be to teach parents about child development in the hope that an understanding of the characteristic innate tendencies and developmental stages can be used to teach healthy food preferences.

When identical twins differ: an analysis of intrapair differences in the spontaneous eating behavior and attitudes of free-living monozygotic twins

Heredity has been shown to have major influences on the body size and ingestive behaviors of humans. However, environment is also important as evidenced by the fact that even identical twins can differ in body size and nutrient intake. To investigate the relative influence of heredity and environment, differences between the body size and food intake of 110 identical adult twin pairs who were living independently were studied with a 7-day diet diary technique. Differences within twin pairs (intrapair differences) in diet density were related to differences in daily intakes, but not with body size differences. On the other hand, cognitive restraint and disinhibition were related to intrapair differences in body size, but not intake. The fact that there are important environmental and psychological factors that influence intake and body size, even in individuals who have identical genotypes, supports the recently proposed general model of intake regulation [de Castro JM, Plunkett S. A general model of intake regulation. Neurosci. Biobehav. Rev. 26 (5) (2002) 581-595].

The time of day of food intake influences overall intake in humans

Circadian and diurnal rhythms affect food intake, and earlier research has suggested that meal sizes increase, whereas the after-meal intervals and satiety ratios decrease over the day. We hypothesized that the time of day of food intake would be related to total intake such that intake early in the day would tend to reduce overall intake, whereas intake later in the day would tend to increase intake over the entire day. The intakes of 375 male and 492 female free-living individuals, previously obtained via 7-d diet diaries, were reanalyzed. The total and meal intakes of food energy, the amounts of the macronutrients ingested and the density of intake occurring during five 4-h periods (0600-0959, 1000-1359, 1400-1759, 1800-2159 and 2200-0159 h) were identified and related to overall and meal intakes during the entire day. The proportion of intake in the morning was negatively correlated with overall intake (r=-0.13, P<0.01), whereas the proportion ingested late in the evening was positively correlated with overall intake (r=0.14, P<0.01). The energy densities of intake during all periods of the day were positively related to overall intake (range, r=0.13-0.23, P<0.01). The results suggest that low energy density intake during any portion of the day can reduce overall intake, that intake in the morning is particularly satiating and can reduce the total amount ingested for the day, and that intake in the late night lacks satiating value and can result in greater overall daily intake.

The influence of heredity on self-reported sleep patterns in free-living humans

The heritability of self-reported sleep patterns was investigated with 86 identical and 78 fraternal same-sex and 51 fraternal mixed-gender adult twin pairs who were paid to maintain 7-day diaries. Linear structural modeling was applied to investigate the nature and degree of genetic and environmental influences and revealed significant genetic influences on the time that individuals went to sleep and woke up, how often the individual woke up during the night, the duration of sleep and wakefulness, and how alert the individual felt upon waking and over the day, accounting for 21% to 41% of the variance. These influences of heredity were present for sleep-wake behavior over the entire week and also when the sleep-wake pattern was analyzed separately for weekdays and weekends. Further, it was demonstrated that there were multiple independent influences of heredity on sleep-wake behavior. The results suggest that sleep-wake patterns are not learned but result in part from multiple heritable influences.

Twin studies in behavioral research: a skeptical view

We review in detail two major ongoing research projects that employ samples of twins reared apart (and in one case, twins reared together). The studies attempt, via model fitting, to estimate proportions of genetic and environmental variance for many human traits. We discuss problems concerning the representativeness of samples, the accuracy and reliability of the data, the extent of contact of nominally separated twins, the measurement of selective placement effects, and the particular model-fitting procedures. The two studies agree in their conclusions, but we do not find the conclusions to be convincing. We suggest that no scientific purpose is served by the flood of heritability estimates generated by these studies.

Independence of heritable influences on the food intake of free-living humans

OBJECTIVE

The time of day of meal ingestion, the number of people present at the meal, the subjective state of hunger, and the estimated before-meal contents in the stomach have been established as influences on the amount eaten in a meal and these influences have been shown to be heritable. Because these factors intercorrelate, the calculated heritabilities for some of these variables might result indirectly from their covariation with one of the other heritable variables. The independence of the heritability of the influence of these four factors was investigated with 110 identical and 102 fraternal same-sex and 53 fraternal mixed-sex adult twin pairs who were paid to maintain 7-d food-intake diaries.

METHODS

From the diary reports, the meal sizes were calculated and subjected to multiple regression analysis using the estimated before-meal stomach contents, the reported number of other people present, the subjective hunger ratings, and the time of day of the meal as predictors. Linear structural modeling was applied to the beta-coefficients from the multiple regression to investigate whether the heritability of the influences of these four variables was independent.

RESULTS

Significant genetic effects were found for the beta-coefficients for all four variables, indicating that the heritability of their relationship with intake is to some extent independent and heritable.

CONCLUSIONS

This suggests that influences of multiple factors on intake are influenced by the genes and become part of the total package of genetically determined physiologic, sociocultural, and psychological processes that regulate energy balance.

The roles of adulthood behavioural factors and familial influences in bone density among men

BACKGROUND

A primary strategy in osteoporosis prevention is advice on exercise, smoking, and calcium intake, although its practical value is unclear.

AIM

To investigate the roles of such factors on bone density (BMD) after considering the influences of familial aggregation (combined effects of genetics and familial influences) in Finnish men 35-69 years old.

METHODS

We selected 105 male monozygotic twin pairs, with discordance in suspected determinants.

RESULTS

Dietary calcium was associated with BMD of the femoral neck; and body weight and lifetime frequency of endurance and ball game sport activities were associated with both femoral neck and lumbar BMD. Occupational loading and smoking were associated with neither. However, age and familial aggregation explained 73% of the variance of BMD in both the femoral neck and lumbar spine; calcium intake explained 1% in femoral neck and lifetime exercise 1% in lumbar spine.

CONCLUSIONS

The effects of dietary calcium and physical activity that are not 'embedded' in the familial influences had very modest effects on the variance of BMD. Thus our chances of influencing BMD in later adulthood by targeting behavioural habits are likely to be limited. Interventions focused on childhood and the family unit may achieve more beneficial long-term results.

Heritability of diurnal changes in food intake in free-living humans

OBJECTIVES

The time of day of meal ingestion, the number of people present at the meal, the subjective state of hunger, and the estimated before-meal contents in the stomach have been established as influences on the amount eaten in a meal, and this influence has been shown to be heritable. Because these factors intercorrelate, the possibility that the calculated heritabilities for some of these variables could result indirectly from their convariation with one of the other heritable variables was assessed.

METHODS

The independence of the heritability of the influence of these four factors was investigated with 110 identical and 102 fraternal same-sex and 53 fraternal mixed-sex adult twin pairs who were paid to maintain 7-d food intake diaries. From the diary reports, the meal sizes were calculated and subjected to multiple regression analysis using the estimated before-meal stomach contents, the reported number of other people present, the subjective hunger ratings, and the time of day of the meal as predictors. Linear structural modeling was applied to the beta coefficients from the multiple regression to investigate whether the heritability of the influences of these four variables was independent.

RESULTS

Significant genetic effects were found for the beta coefficients for all four variables, indicating that the heritability of their relationship with intake is to some extent heritable.

CONCLUSIONS

These results suggest that the influences of multiple factors on intake are influenced by the genes and become part of the total package of genetically determined physiologic, sociocultural, and psychological processes that regulate energy balance.

Palatability and intake relationships in free-living humans: the influence of heredity

The heritability of the before and after meal self-ratings of palatability and their relationship to food intake was investigated with 86 identical and 78 fraternal same-sex and 51 fraternal mixed gender adult twin pairs who were paid to maintain 7-day food intake diaries. From the diary reports, the total and meal intakes of food energy and the amounts of the macronutrients ingested were estimated. Participants rated the meals for palatability on a 7-point (Bad - Good) scale both before and after eating. Linear structural modeling was applied to investigate the nature and degree of genetic and environmental influences and revealed significant genetic influences on subjective palatability both before and after the meals. In addition, the relationship between palatability and intake was influenced by the genes. Significant dominance genetic effects were found for the change in meal size between low-moderate and high palatability meals, indicating that palatability and it's relationship with intake are to some extent heritable. This suggests that the level of subjective experience and the individuals responses to them are influenced by the genes and become part of the total package of genetically determined physiological, socio/cultural, and psychological processes that regulate energy balance.

Eating behavior: lessons from the real world of humans

Food intake by normal humans has been investigated both in the laboratory and under free-living conditions in the natural environment. For measurement of real-world intake, the diet-diary technique is imperfect and tends to underestimate actual intakes but it appears to be sensitive, can detect subtle influences on eating behavior, and produces reliable and valid measures. Research studies in the real world show the multivariate richness of the natural environment, which allows investigation of the complexities of intake regulation, and even causation can be investigated. Real-world research can overcome some of the weaknesses of laboratory studies, where constraints on eating are often removed or missing, facilitatory influences on eating are often controlled or eliminated, the importance of variables can be overestimated, and important influences can be missed because of the short durations of the studies. Real-world studies have shown a wide array of physiologic, psychological, and social variables that can have potent and immediate effects on intake. Compensatory mechanisms, including some that operate with a 2- to 3-d delay, adjust for prior excesses. Heredity affects all aspect of food-intake regulation, from the determination of body size to the subtleties of the individual preferences and social proclivities and the extent to which environmental factors affect the individual. Hence, real-world research teaches valuable lessons, and much more is needed to complement laboratory studies.

What are the major correlates of macronutrient selection in Western populations?

In order to better understand the factors that may influence and regulate the intake of the macronutrients carbohydrate, fat and protein a 7 d diet diary technique was employed to study eating behaviour in the natural environment of free-living human subjects. In general, factors that promote energy intake tend to promote fat and protein intake to a greater extent than carbohydrate intake. This increased intake occurs as the result of: environmental factors such as social facilitation and the time of day, week or lunar phase; subjective factors such as hunger and elation; individual difference factors such as obesity, restraint and ageing. There are indications that the intake of macronutrients is regulated by negative feedback systems. In the short term, the amount of protein remaining in the stomach at the onset of a meal appears to have a restraining effect on intake, especially protein intake. Over several days, macronutrient intake appears to be affected by a nutrient-specific delayed negative feedback. Protein intake during 1 d is negatively associated with protein intake 2 and 3 d later, while carbohydrate intake is negatively related to later carbohydrate intake, and fat intake to later fat intake; both peaking after a 2 d delay. Studies of the intakes of twins suggested that many aspects of the control of macronutrient intake are influenced by inheritance; these factors include the overall amounts ingested, the before-meal stomach contents and the responsiveness of the subject to the negative impact of the stomach contents. The results indicate that macronutrient intakes are regulated by multiple persistent processes that are to a large extent inherited.

Heritability of hunger relationships with food intake in free-living humans

The heritability of the before and after meal self-ratings of hunger and thirst and their relationship to food intake was investigated with 110 identical and 102 fraternal same-sex and 53 fraternal mixed-gender adult twin pairs who were paid to maintain 7-day food intake diaries. From the diary reports, the total and meal intakes of food energy and the amounts of the macronutrients ingested were estimated. Subjects rated their subjective levels of hunger on a seven-point scale both before and after eating. Linear structural modeling was applied to investigate the nature and degree of genetic and environmental influences and revealed significant genetic influences on the self-rated levels of hunger both before and after the meals and the change in hunger over the meal. In addition, the relationship between hunger and intake was influenced by the genes. Significant heritabilities were found for the correlations, and the slopes of the regression lines relating before-meal hunger to meal size and also the change in hunger over the meal to intake. This indicates that hunger's effect on intake and, in turn, intake's effects on hunger are to some extent heritable. This suggests that the level of subjective experience and the individuals responses to them are influenced by the genes and become part of the total package of genetically determined physiological, socio/cultural, and psychological processes that regulate energy balance.

Food choice and intake: the human factor

Human perceptions and selection of food are derived from the prevailing and momentary food, agro-economic and cultural environment, cognitive and biological characteristics of individuals, and the real and perceived intrinsic and extrinsic attributes of foods themselves. The range of items typically chosen and consumed within a given population is largely determined by interaction of the external environmental context with guiding sets of implicit and explicit social and psychobiological 'rules'. Within the rather broad limits of biology, individual food choices and intake behaviours relate to and reflect aspects of food availability, existing habitual behaviours, learning mechanisms, and individual beliefs and expectations. Many of the relevant features of these variables are uniquely human, together determining what is 'food', when, how, by and with whom it is chosen and eaten, and in what quantities. They also provide the opportunities for individuals to establish and maintain a relatively stable set of culturally and biologically determined affective responses ('likes') and intake behaviours. Understanding of the potential contribution of these influences under different conditions can serve to explain many of the observed characteristics of human eating, and highlight potential avenues for intervention.

Behavioral genetics of food intake regulation in free-living humans

It has been established that the genes influence body size. Recently, it has become clear that food intake is also influenced by heredity. Surprisingly, the genetic effect on intake was found to occur independent of body size. Taking height and body weight into consideration, strong influences of heredity were found on the total amounts of food energy, macronutrients, and fluids ingested. Also, genetic influences were found related to the microstructure of intake, affecting the number, timing, and composition of meals. Since overall intake is determined by the size and frequency of meals, this was not surprising. However, these heritable factors were shown to influence meal size and frequency even when overall daily intake was considered in the model. Recently, we have shown that there are even heritable factors that influence the choice of the environmental conditions at the meals; the time, degree of hunger, stomach fullness, and the number and type of people at the meal. Also the degree to which these conditions affect intake appears to be heritable. These findings suggest that there are important heritable factors that influence body size, overall daily intake independent of body size, meal intake independent of overall daily intake, and the selection of and responsivity to the environmental conditions surrounding eating.

Inheritance of premeal stomach content influences on food intake in free living humans

The heritability of the before-meal stomach content effects on food intake was investigated with 110 identical and 102 fraternal same-sex and 53 fraternal mixed-gender adult twin pairs who were paid to maintain 7-day food intake diaries. From the diary reports, the total and meal intakes of food energy and the amounts of the macronutrients ingested were estimated. A simple computer model of stomach emptying was used to estimate the contents of the stomach at the beginning and end of the meals. Linear structural modeling was applied to investigate the nature and degree of genetic and environmental influences and revealed significant genetic influences on the amount of food energy and macronutrients estimated to be present in the stomach at the beginning and end of meals. However, these influences were found to be secondary to genetic influences on overall intake and meal size such that when these were considered in the model the heritabilities for stomach contents vanished. The genes were also found to affect the magnitude of the negative correlations between the before meal stomach contents and the amounts of nutrients ingested, and the magnitude of the negative slope of the best-fitting regression line between before meal stomach contents and meal size. These results suggest that although the amount in the stomach found at meal time is only affected indirectly by the genes, the impact of the content of the stomach on the amount ingested is to some extent inherited. This suggests that responses to internal stimuli are influenced by the genes and become part of the total package of genetically determined physiological and psychological processes that regulate energy balance.

Genetic and environmental influences on self-reported diet: a reared-apart twin study

A sample of 66 monozyogtic twins reared apart (MZA) and 51 dizygotic twins reared apart (DZA), and 101 nontwin individuals (mostly spouses of the twins) who participated in the Minnesota Study of Twins Reared Apart (MISTRA) from 1979 to 1995 completed a self-report food frequency questionnaire. Intraclass-correlations and model-fitting analyses indicated that approximately 30% of the variance in the self-report of diet was attributable to genetic factors, with random environmental factors and measurement error responsible for the remaining variance. Spouse correlations were moderate. To investigate the effects of living together during marriage, the absolute differences between husband and wife on the dietary variables with years of marriage were correlated. None of the correlations were significant. Hierarchical multiple regression analyses also indicated that no convergence occurred during marriage. These results suggest that sharing a current family environment exerts minimal influence on individual differences in self-reported diet.

Genes and environment have gender-independent influences on the eating and drinking of free-living humans

Males and females differ in the amounts of food and fluids they ingest. Previous studies suggest that this may be due to differences in genetic influences on intake. Gender differences in the heritability of food and fluid intake were investigated with 110 identical and 102 fraternal same-sex and 53 fraternal mixed-gender adult twin pairs who were paid to maintain 7-day food intake diaries. Linear structural modeling revealed significant genetic influences on the overall and meal intakes of foods and fluids and specific beverage and food types. No gender differences were found in the genes that influence intake or, for the most part, in the magnitude of the genetic influences on intake. However, gender differences were found for the between-meal intakes of fluids, being influenced by heredity for males but by common, familial, environment for females. The data suggest that intakes are equivalently influenced by inheritance and individual environment for both males and females and that most gender differences are due to a simple multiplicative difference between intakes possibly due to body size and/or caloric expenditure differences.

Socio-cultural determinants of meal size and frequency

Total energy intake and the frequency and size of meals are profoundly influenced by the socio-cultural context in which it occurs. Simply eating with one other person increases the average amount ingested in meals by 44% and with more people present the average meal size grows even larger. The impact of social facilitation of energy intake on the individual appears to result from genetic effects both on the individuals' sensitivity to the presence of other people and also on the number of other people an individual tends to eat with. Culture markedly affects the choice of foods in the diet and the pattern of meals over the day. However, many of the social, psychological and physical variables that influence intake are similar across cultures.