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

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.

Prospective associations between appetitive traits and weight gain in infancy

BACKGROUND

Differences in appetitive traits such as food-cue or satiety responsiveness have been hypothesized to contribute to variability in weight gain. However, existing data were largely cross-sectional and could not exclude the possibility that differences in appetitive traits were consequences of differences in weight.

OBJECTIVE

We tested whether prospective associations between appetitive traits and subsequent weight were stronger than associations between weight and subsequent appetitive traits.

DESIGN

Data were from Gemini, which is a population-based cohort of 2402 families with twins. Parents completed a Baby Eating Behavior Questionnaire to assess 4 appetitive traits for each twin at ages 3 and 15 mo. We obtained infant weights at 3, 9, and 15 mo from records of health professionals. Weight SD scores were calculated by using UK 1990 reference data. A path analysis was used to examine prospective associations in each direction over sequential 6-mo intervals and over the same 12-mo period, with the significance of differences between the 2 paths established with bootstrapping.

RESULTS

Path analyses included 2213 infants. For each appetitive trait, the path to subsequent weight (standardized coefficients: 0.17-0.33) was significantly larger than the path from weight to subsequent appetite (coefficients: 0.07-0.13). Results were confirmed when both associations were analyzed by using changes from 3 to 15 mo.

CONCLUSION

Longitudinal analyses showed that associations between appetitive traits and subsequent weight were stronger than between weight and subsequent appetite, which supports the idea that differences in appetitive traits, in conjunction with environmental opportunities to overeat, influence weight gain in early childhood.

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.

Genes, the environment and the control of food intake

Genes are known to have independent influences on the height and weight of individuals, their overall levels of nutrient intakes and their meal sizes and frequencies. Recent evidence suggests that genes exert multiple and subtle influences on the controls of food intake. There are significant genetic influences on the level and responsiveness of the individual to physiological factors, such as the preprandial stomach contents of nutrients and subjective hunger, and also to environmental and psychological factors such as social facilitation of eating, diurnal rhythms of intake, palatability, cognitive restraint and dietary density. The general model of intake regulation provides an integrated and comprehensive account of how these physiological and environmental factors might fit together to produce the control of intake and body weight.

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.

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.

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.