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

Gender differences in body composition, dietary patterns, and physical activity: insights from a cross-sectional study

Introduction

This study investigates the interplay between body composition, dietary patterns, and physical activity across genders, focusing on gender-specific differences in food preferences and eating behaviors. Understanding these interactions is crucial for developing targeted nutritional and lifestyle interventions.

Methods

A cross-sectional study was conducted with 1,333 participants (58.7% female, 41.3% male), aged 18-65 years. Participants were categorized into tertiles based on their fat mass to fat-free mass (FM-to-FFM) ratio. Data on dietary choices, eating behaviors, and physical activity were collected and analyzed to identify gender-specific trends.

Results

Significant gender-specific differences were observed in food preferences and eating behaviors. Males experienced greater hunger in the late afternoon, while females felt more hunger in the morning. Males showed a preference for processed and red meats, whereas females preferred cooked vegetables. Eating behaviors such as meal skipping, uncontrolled eating, nocturnal eating, and taste preferences (sweet or salty) varied distinctly between FM-to-FFM tertiles and genders. Higher FM-to-FFM ratios correlated with lower physical activity levels, particularly in strength training and general sports engagement.

Discussion

These findings highlight the complex interactions between body composition, dietary habits, and lifestyle factors, emphasizing gender-specific differences. The results suggest that body composition and BMI significantly impact health-related behaviors, necessitating tailored interventions to address these differences and promote healthier lifestyles.

Modulation of synaptic inputs in magnocellular neurones in a rat model of cancer cachexia

In cancer cachexia, abnormal metabolism and neuroendocrine dysfunction cause anorexia, tissue damage and atrophy, which can in turn alter body fluid balance. Arginine vasopressin, which regulates fluid homeostasis, is secreted by magnocellular neurosecretory cells (MNCs) of the hypothalamic supraoptic nucleus. Arginine vasopressin secretion by MNCs is regulated by both excitatory and inhibitory synaptic activity, alterations in plasma osmolarity and various peptides, including angiotensin II. In the present study, we used whole-cell patch-clamp recordings of brain slices to determine whether hyperosmotic stimulation and/or angiotensin II potentiate excitatory synaptic input in a rat model of cancer cachexia, similar to their effects in normal (control) rats. Hyperosmotic (15 and 60 mmol L^-1   mannitol) stimulation and angiotensin II (0.1 μmol L^-1 ) increased the frequency, but not the amplitude, of miniature excitatory postsynaptic currents in normal rats; in model rats, both effects were significantly attenuated. These results suggest that cancer cachexia alters supraoptic MNC sensitivity to osmotic and angiotensin II stimulation.

Genetic and environmental influences on food preferences in adolescence

BACKGROUND

Food preferences vary substantially among adults and children. Twin studies have established that genes and aspects of the shared family environment both play important roles in shaping children's food preferences. The transition from childhood to adulthood is characterized by large gains in independence, but the relative influences of genes and the environment on food preferences in late adolescence are unknown.

OBJECTIVE

The aim of this study was to quantify the contribution of genetic and environmental influences on food preferences in older adolescents.

DESIGN

Participants were 2865 twins aged 18-19 y from the TEDS (Twins Early Development Study), a large population-based cohort of British twins born during 1994-1996. Food preferences were measured by using a self-report questionnaire of 62 individual foods. Food items were categorized into 6 food groups (fruit, vegetables, meat or fish, dairy, starch foods, and snacks) by using factor analysis. Maximum likelihood structural equation modeling established genetic and environmental contributions to variations in preferences for each food group.

RESULTS

Genetic factors influenced a significant and substantial proportion of the variation in preference scores of all 6 food groups: vegetables (0.54; 95% CI: 0.47, 0.59), fruit (0.49; 95% CI: 0.43, 0.55), starchy foods (0.32; 95% CI: 0.24, 0.39), meat or fish (0.44; 95% CI: 0.38, 0.51), dairy (0.44; 95% CI: 0.37, 0.50), and snacks (0.43; 95% CI: 0.36, 0.49). Aspects of the environment that are not shared by 2 twins in a family explained all of the remaining variance in food preferences.

CONCLUSIONS

Food preferences had a moderate genetic basis in late adolescence, in keeping with findings in children. However, by this older age, the influence of the shared family environment had disappeared, and only aspects of the environment unique to each individual twin influenced food preferences. This finding suggests that shared environmental experiences that influence food preferences in childhood may not have effects that persist into adulthood.

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.

Gender differences in food and energy intake among adult villagers in northwestern Bangladesh: a food frequency questionnaire survey

This study aimed to elucidate gender differences in dietary intake of rural Bangladeshi adults. A food frequency questionnaire (FFQ) survey using 15 food/dish items, together with anthropometric measurements, was conducted for 230 adults and adolescents (95 males and 135 females). To estimate the portion sizes of these foods/dishes, the samples consumed by 25 subjects were weighed. The FFQ revealed that rice was eaten two to three times (or more) per day by 98% of the subjects, providing nearly 60% of energy for both sexes. Puri (fried bread), meats, eggs, pulses, milk, fresh vegetables, fruits, tea with milk and sugar, and soft drinks were consumed more frequently by males. Males' larger portion sizes of rice, fish dish, potato dish, and vegetable dish resulted in larger daily energy intake per body weight in males (235 +/- 41 kJ/kg) than in females (161 +/- 28 kJ/kg). Despite males' larger energy intake, the proportion of chronically energy deficient persons (<18.5 kg/m2 in body mass index) was similar between males (35.8%) and females (37.8%), attributing to males' larger energy expenditure. Females' less-frequent consumption of nutritious foods and smaller energy intake were considered vulnerable to micronutrient deficiency.

Studies of twins indicate that genetics influence dietary intake

Habitual dietary intake is a complex behavior that may have both biological and nonbiological bases. We estimated the contribution of genetic and environmental influences on dietary intake in a large population-based sample of healthy twins. Data originated from a cross-sectional study of 600 male and female healthy twin pairs with self-reported food consumption frequency using a validated questionnaire with 247 foods and recipes. Estimates of relative proportion of additive genetic, nonadditive genetic, shared environmental, and unshared environmental effects on various aspects of dietary intake were obtained by quantitative genetic modeling of twin data based on linear structural equations. The analyses demonstrated genetic influence on total energy, macronutrient energy, and dietary fiber intakes, the glycemic index and the glycemic load of the foods consumed, and the dietary energy density, with significant heritability estimates ranging from 0.25 (0.11-0.38) to 0.47 (0.31-0.60) in men and 0.32 (0.12-0.48) to 0.49 (0.35-0.61) in women. When analyzing dietary intake as the intake of energy from 20 food groups, the genetic and environmental influences differed among food groups and between gender. For some food groups (fruit for both genders, poultry and eggs for men), no genetic influence was found, whereas nonadditive genetic effects were demonstrated for other food groups (juices and eggs for women). A number of food groups had shared environmental influences (potatoes, vegetables, fruits, poultry, fish, margarine, and candy). These results provide evidence for both genetic and shared environmental effects on dietary intake. Although the remaining nonshared environmental effects include measurement errors, there appears to be considerable potential for individually modifiable effects.

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.

Genetic and environmental contributions to food use patterns of young adult twins

The contribution of genetic factors to individual differences in food use was estimated in a large population-based twin cohort of young adults (22- to 27-year-old). Male and female twins (n=2009 complete twin pairs) evaluated use-frequencies of 24 food items using 5 categories (1=never-5=several times a day) in a postal questionnaire. Foods were categorized by factor analysis. Estimates of the relative proportions of additive genetic, shared environmental, and unshared environmental effects on the use-frequency of food items and factor scores were obtained by quantitative genetic modeling of twin data based on linear structural equations. Four factors of food use were identified: "healthy" foods, high-fat foods, sweet foods, and meats. The variance of the use-frequency of food items and food categories was explained by additive genetic and unshared environmental influences, whereas shared environmental factors did not contribute to food use. The average proportions of genetic effects on the total variance of the use-frequency of food items and food categories were 40% and 45%, respectively. Sex differences were observed in the magnitude of genetic influences for use-frequency of four food items (chocolate, other sweets, fried foods, and meat), and in genetic factors underlying the use of three (fresh vegetables, fruits, and cheeses) items. In conclusion, family environment does not appear to influence the food use of young adults and thus nutritional education should be targeted at this age group to support development of healthy eating patterns. In addition, the results illuminate the importance of the sex-specific genetic effects on food use.

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.

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.

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.

Twin study of genetic and environmental influences on glucose tolerance and indices of insulin sensitivity and secretion

AIMS/HYPOTHESIS

Family and twin studies have reported different estimates of the relative contribution of genetic and environmental factors to the quantitative traits glucose tolerance, insulin secretion, and insulin sensitivity. Our aims were to estimate these relative influences in a large sample of twins from the population and to assess the effect of age.

METHODS

In this population-based, cross-sectional study we gave an oral glucose tolerance test to 317 women and 290 men who were same-sex healthy twin pairs between 18 to 67 years of age. The genetic, common environmental and individual environmental variance components for fasting and 120-min glucose and for fasting and 30-min insulin as well as the linear effects of age on these components were estimated by multivariate analysis (using the software FISHER).

RESULTS

In women and men the heritability for fasting glucose was 12 and 38%, for 120-min glucose it was 38 and 43%, for fasting insulin it was 54 and 37%, and for 30-min insulin it was 57 and 47%, respectively. Under the assumption of no non-additive genetic effects (no intra- or inter-gene interaction) there was no strong evidence for common environmental effects, barring significant effects for fasting glucose in women. Heritability decreased with age for 120-min glucose in women and fasting insulin in men, whereas it increased for 120-min glucose in men.

CONCLUSION/INTERPRETATION

This study indicates a limited additive genetic influence on the result of an OGTT, possibly with sex-specific age effects, and generally little or no influence of the common environment. Accordingly, there is a considerable individual environmental variation.

Food intake in the real world: implications for nutrition and aging

Nutrient intakes are affected by two classes of factors, physiological and environmental. In the real world, environmental variables such as social factors, palatability, and the time of eating appear to have large influences on amounts ingested in the short-term. Physiological control mechanisms also operate to regulate intake, and they induce compensatory responses to deviations from the norm. These physiological influences only appear to have weak influences on short-term intake unless there are large deviations from the normal state, but over the long-term they act patiently and persistently to rectify the excesses produced by environmental fluctuations and thereby tend to maintain a relative balance between energy intake and expenditure. As individuals age there is a progressive decline in physiological function including the mechanisms that act to control intake in the young. This should not produce a problem in a healthy individual in a stable environment: however, if that situation should change due to illness or an environmental change such as the death of a spouse, which produces decline in intake, elderly individuals would not have the physiological mechanisms present to compensate. Thus, the deficit in energy intake would not be replaced, and the lower level of intake would be maintained as long as the new health condition or environment remains stable. Hence, the decline in the effectiveness of the physiological systems with age makes the elderly particularly vulnerable and unable to rebound from deficits. Although the elderly have difficulty compensating for deficits automatically by physiologically-induced adjustments, the studies of real world intake reviewed in this article suggest that compensation can be produced by adjustments to the environment. The elderly appear to be as responsive to environmental factors as younger individuals. In particular, they appear to increase intake in response to social facilitation, diurnal rhythms, the eating environment, and palatability to the same extent as their juniors. These data suggest that alterations in the social, temporal, environmental, or hedonic conditions of eating could induce desired alterations in the nutrient intakes of the elderly. The study of real world eating behavior has produced evidence that suggests that this strategy can work. It remains for future applied investigations to ascertain whether or not this strategy is effective in treating undernutrition in the elderly.

A general model of intake regulation

Previously proposed models of intake regulation focus on specific variables thought to influence overall intake, and include factors involved in negative feedback loops with intake as well as genetic influences on intake. Recent evidence, however, suggests that these models although informative, are incomplete. They cannot account for the observations of prolonged and increasing deviations from defended levels, weakness and transitoriness of compensatory responses, the presence of powerful factors that are not compensated, and behavioral genetic data suggesting that there are a wide variety of independent genetic influences on numerous factors that influence intake. As a result we propose a new general model of intake regulation in which intake is influenced by both a set of uncompensated factors that are not influenced by intake and by a set of compensated factors that are. The preferred levels of intake and both sets of factors are specified as influenced by heredity. Further, the model includes impact factors, weights, which specify the magnitude of the effect each factor has on intake. The weights are assumed to be different for different individuals and their values are determined by heredity. A computer simulation of the new model demonstrated that it maintains different levels depending upon the external and internal environments, that changes in these environments result in new levels, and that inherited individual differences in responsiveness to these factors can markedly influence the levels obtained. The proposed general model appears to fit existing knowledge and is parsimonious and widely applicable. Future work should be directed to testing the general model and further developing specific models within the conceptual framework employing known physiological systems and uncompensated stimuli.

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.

Age-related changes in the social, psychological, and temporal influences on food intake in free-living, healthy, adult humans

BACKGROUND

Elderly humans often have a reduction in intake that can produce malnutrition and impaired health. As a result, there is a need to investigate age-related changes in the eating behaviors of free-living humans.

METHODS

To address this issue, 7-day diet diary records that had been collected from 762 paid participants were reanalyzed, separating the participants into four age groups: 20-34 years, 35-49 years, 50-64 years, and 65 years and older.

RESULTS

The elderly ate with fewer other people present and earlier in the day than younger people. The elderly were found to be as responsive as younger groups to social facilitation of intake, palatability, cognitive restraint, time of day, day of week, and location, but showed blunted responses to self-reported hunger.

CONCLUSIONS

There does not appear to be a decline with age in the ability of nonphysiological factors to influence the nutrient intakes of the elderly, but they may not have as great an influence due to lower absolute levels. This suggests that the deficient intakes in the elderly might be corrected or ameliorated by manipulation of nonphysiological factors, such as the number of other people present at meals, the palatability of meals, and the time of day and location of meals.

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.

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.

Food intake and the regulation of body weight

This chapter reviews the recent literature on hormonal and neural signals critical to the regulation of individual meals and body fat. Rather than eating in response to acute energy deficits, animals eat when environmental conditions (social and learned factors, food availability, opportunity, etc.) are optimal. Hence, eating patterns are idiosyncratic. Energy homeostasis, the long-term matching of food intake to energy expenditure, is accomplished via controls over the size of meals. Individuals who have not eaten sufficient food to maintain their normal weight have lower levels of adiposity signals (leptin and insulin) in the blood and brain, and one consequence is that meal-generated signals (such as CCK) are less efficacious at reducing meal size. The converse is true if individuals are above their normal weight, when they tend to eat smaller meals. The final section reviews how these signals are received and integrated by the CNS, as well as the neural circuits and transmitters involved.

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.

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.