David A. Levitsky

The freshman weight gain: a model for the study of the epidemic of obesity.

OBJECTIVE: The objective of this study was to quantify the weight gain of freshmen during their first 12 weeks at Cornell University. In addition, students completed questionnaires that revealed particular behaviors and activities that were associated with weight gain.DESIGN: Serial, correlational study.SUBJECTS: A total of 68 freshmen from Cornell University.MEASUREMENT: A total of 60 students were weighed during the first week of the semester, then again 12 weeks later. They were also given a questionnaire to complete concerning their behavior during the previous 12 weeks.RESULTS: After adjusting for clothing weights, the mean weight gain of the freshmen was 1.9±2.4 kg, a value significantly different from 0. Two regression models generated from the questionnaire were fitted to the weight gain. The first linear regression model (Model 1) accounted for 58% of the variance and indicated that eating in the ‘all-you-can-eat’ dining halls accounted for 20% of the variance in weight gain. Snacking and eating high-fat ‘junk food’ accounted for anther 20%. When initial weight was used as a covariate (Model 2), the consumption of junk foods, meal frequency and number of snacks accounted for 47% of the variance.CONCLUSION: The study clearly demonstrated that significant weight gain during first semester college is a real phenomenon and can be attributed to tangible environmental stimuli. The weight gain is considerably greater than that observed in the population and may be useful as a model to test various techniques that may reduce or reverse the ‘epidemic’ of obesity observed in the general population.

Malnutrition and the Brain: Changing Concepts, Changing Concerns

Our conceptions of how malnutrition endured early in life affects brain development have evolved considerably since the mid-1960s. At that time, it was feared that malnutrition endured during certain sensitive periods in early development would produce irreversible brain damage possibly resulting in mental retardation and an impairment in brain function. We now know that most of the alterations in the growth of various brain structures eventually recover (to some extent), although permanent alterations in the hippocampus and cerebellum remain. However, recent neuropharmacological research has revealed long-lasting, if not permanent, changes in brain neural receptor function resulting from an early episode of malnutrition. These more recent findings indicate that the kinds of behaviors and cognitive functions impaired by malnutrition may be more related to emotional responses to stressful events than to cognitive deficits per se, the age range of vulnerability to these long-term effects of malnutrition may be much greater than we had suspected and the minimal amount of malnutrition (hunger) necessary to produce these long-term alterations is unknown.

Feeding patterns of rats in response to fasts and changes in environmental conditions.

Abstract The feeding patterns of male albino rats were observed following either a 24 hr or 48 hr fast, during and following water restriction, during and following the addition of quinine to the food supply, and when given access to an activity wheel. Following any reduction of food intake imposed either by the experimenter or as a result of water restriction or the consumption of an unpalatable diet, food intake was adjusted almost entirely by increasing meal size. Meal frequency was not affected by the previous deprivations but was significantly reduced by the addition of the running wheel. During water restriction neither meal frequency nor the distribution of meals during the 24 hr period was affected. The addition of quinine sulfate to the food resulted in smaller but more frequent meals.

Set points, settling points and some alternative models: Theoretical options to understand how genes and environments combine to regulate body adiposity

The close correspondence between energy intake and expenditure over prolonged time periods, coupled with an apparent protection of the level of body adiposity in the face of perturbations of energy balance, has led to the idea that body fatness is regulated via mechanisms that control intake and energy expenditure. Two models have dominated the discussion of how this regulation might take place. The set point model is rooted in physiology, genetics and molecular biology, and suggests that there is an active feedback mechanism linking adipose tissue (stored energy) to intake and expenditure via a set point, presumably encoded in the brain. This model is consistent with many of the biological aspects of energy balance, but struggles to explain the many significant environmental and social influences on obesity, food intake and physical activity. More importantly, the set point model does not effectively explain the ‘obesity epidemic’ – the large increase in body weight and adiposity of a large proportion of individuals in many countries since the 1980s. An alternative model, called the settling point model, is based on the idea that there is passive feedback between the size of the body stores and aspects of expenditure. This model accommodates many of the social and environmental characteristics of energy balance, but struggles to explain some of the biological and genetic aspects. The shortcomings of these two models reflect their failure to address the gene-by-environment interactions that dominate the regulation of body weight. We discuss two additional models – the general intake model and the dual intervention point model – that address this issue and might offer better ways to understand how body fatness is controlled.

Monitoring weight daily blocks the freshman weight gain: a model for combating the epidemic of obesity

Background:The Tissue Monitoring System (TMS) is an algorithm that estimates changes in body tissue from a series of daily weight measures. It is intended to provide people with a feedback of changes in their tissue weight so they may have a basis for estimating how much they would have to change their intake or expenditure to maintain their weight at a prescribed level. We tested the effectiveness of the TMS to prevent freshmen from gaining weight during their first semester in college.Methods:In two similar but independent studies (Fall 2002, 2003), female freshmen college students were given analog bathroom scales and instructed to weigh themselves each morning immediately after rising from bed, then e-mail their weight to our staff. After 7 days, a linear function was performed on the most recent 7 days of the weight-day function for each participant. In the first study, the slope of this function was e-mailed back to the participants. In the second study, the difference between last point and the original weight was determined, using linear regression techniques, converted to calories, and the information was e-mailed back to the participants. Control participants in both studies were weighed at the beginning and the end of the semester.Results:The untreated controls gained 3.1±0.51 kg and 2.0±0.65 kg, respectively (P<0.01 for both studies), whereas weight gain of the experimental groups was 0.1±0.99 kg and −0.82±0.56 kg, values that were not significantly different than zero.Conclusions:The TMS appears to be an effective technique to help female college freshmen resist gaining weight in an environment that is conducive to weight gain. These results suggest that the TMS may be a useful method to help curb the slow increase in the prevalence of overweight and obesity that is characteristic of all industrialized societies.

Enduring Cognitive Effects of Early Malnutrition: A Theoretical Reappraisal

This article presents a reappraisal of the literature on the enduring cognitive effects of early malnutrition. In addition to summarizing the existing empirical literature, we present a theoretical framework for determining whether the processes likely to be most vulnerable to early malnutrition were adequately assessed. The two types of information used to make this determination are clinical and experimental behavioral data as well as reported neural changes. One point of clear consensus is that animals exposed to early malnutrition exhibit lasting changes in the realm of emotionality, motivation, and/or anxiety. Because these alterations profoundly affect all aspects of behavioral functioning, including cognition, it is suggested that future research focus on these changes, rather than control for them as many past studies have done. The functional integrity of specific cognitive processes is less clear. The only cognitive processes for which enduring cognitive changes were demonstrated in rehabilitated animals--outside of effects mediated by these affective changes--are cognitive flexibility and, possibly, susceptibility to proactive interference. However, the inference that these are the only processes affected does not appear to be warranted on the basis of the evidence that several cognitive processes likely to be affected have not been fully assessed. Examples include executive functions linked to the prefrontal cortex (for example, attention), transfer of learning, procedural learning and long-term memory. Future research focusing on these specific cognitive functions as well as on these unequivocal affective changes should allow a more definitive conclusion regarding the enduring functional consequences of early malnutrition.

Feeding conditions and intermeal relationships

Abstract The free feeding pattern of rats was examined as a function of decreasing the accessibility of the meal. Meal frequency decreased and meal size increased proportionally resulting in a constant food intake per unit time. Various characteristics of the feeding pattern were dramatically affected by these procedures. A diurnal variation in meal size and meal frequency was observed when food was most accessible, but the variation in meal size and meal frequency disappeared when accessibility was slightly hampered. Moreover, no correlation between meal size and postmeal interval was observed in the free feeding situation, but did occur when mean accessibility was decreased. Finally, a regular periodic feeding pattern emerged when accessibility was maximally hindered. A second experiment showed that these changes in the characteristics of the meal eating pattern produced in Experiment 1 were more related to the increase in meal size than to the particular feeding situation. The data also suggested that a minimum calorie intake at a meal of approximately seven calories was necessary to obtain a significant meal size-postmeal interval correlation for dry diets and a minimum intermeal interval of four hours was necessary to obtain a meal size-premeal interval relationship.

Schedule-induced wheel running

Abstract Rats reinforced for bar pressing on a variable interval schedule were allowed access to a running wheel. Wheel running displayed many of the characteristics of schedule-induced drinking. These data call into question the explanations of schedule-induced drinking based entirely upon thirst motivation, and suggest that it is only one of a number of post-reinforcement behaviors affected on an intermittent reinforcement schedule.

Prenatal cocaine exposure impairs selective attention: Evidence from serial reversal and extradimensional shift tasks

This study assessed the effects of prenatal cocaine exposure on cognitive functioning, using an intravenous (IV) rodent model that closely mimics the pharmacokinetics seen in humans after smoking or IV injection and that avoids maternal stress and undernutrition. Cocaine-exposed males were significantly impaired on a 3-choice, but not 2-choice, olfactory serial reversal learning task. Both male and female cocaine-exposed rats were significantly impaired on extradimensional shift tasks that required shifting from olfactory to spatial cues; however, they showed no impairment when required to shift from spatial to olfactory cues. In-depth analyses of discrete learning phases implicated deficient selective attention as the basis of impairment in both tasks. These data provide clear evidence that prenatal cocaine exposure produces long-lasting cognitive dysfunction, but they also underscore the specificity of the impairment.

Tolerance to anorectic drugs: Pharmacological or artifactual ☆

Abstract The results of three studies are presented which demonstrate that the anorexia produced by amphetamine and fenfluramine is secondary to a direct weight suppressing effect of these drugs. Furthermore, these data strongly suggest that the decreasing weight loss and the return to normal appetite that occurs with repeated drug usage is not due to pharmacological tolerance, but rather reflects a successful physiological and behavioral adjustment to a lowered level of body weight.