Oxford dictionary defines a theory as a set of principles based on generalizations that have been crystallized through a series of observations. It is a supposition that aims to explain an abstract concept wherein those generalizations made are independent of a particular thing that is being explained. In a scientific perspective, a theory serves as a skeleton in explaining observations and assumptions from a series of hypotheses that can be tested. An individual is referred as a theorist when he or she develops theories. Charles Darwin's Theory of Evolution is one classic example. To date, there are also various emerging theories that may explain the probable cause or existence of obesity and overweight in the entire human race. Obesity and overweight are sometimes used interchangeably. However, what sets obesity apart from overweight is the concept of body mass index.
Obesity and overweight along with their related disorders are among the primary causes of death throughout the world. Based on the statistical projections of the World Health Organization, an estimated 1.2 billion people all over the world are overweight. Of the total number of overweight people, at least a quarter of the total estimate (i.e.300 million people) suffer from obesity. In the United States alone, 300,000 people die every year because of complications and other disorders related to obesity. Similarly 15-20% of the total population in Europe are obese. A recent estimate of the the prevalence of obesity in Europe shows that the rate is as high as 22% for children alone and as high as 26% and 31% in men and women respectively. In the Asia-Pacific Region type 2 diabetes and other obesity-related illnesses have also been increasing according to some scientific studies. In fact, many Asian races are likely to develop abdominal obesity (Wilborn et al., 2005).
While obesity has been linked with diseases such as hypertension, diabetes and hypercholesterolemia to name a few, more recent studies noted that the disease is also influenced by genetic, physiological and behavioral factors. Obesity is not just a mere case of an imbalance between energy intake and energy use.
There are two main theories that were drafted in the attempt to establish the link between obesity and behavioral patterns of an individual. These include the Externality Hypothesis and the Restrained Eater Hypothesis. The Externality Hypothesis has been proposed by Stanley Schachter. Schachter, an American psychologist, suggested that an obese's food consumption is mainly controlled by external stimuli in the immediate environment. His experiment along with other colleagues indicate that food intake of individuals having normal weight is affected by internal physiological factors (Meyers, Stunkard and Coll, 1980). Schachter also postulated that overweight individuals do not respond to internal hunger stimuli and that they only eat in response to sight, taste and other factors related to food. That is; an individual tends to overeat when given a highly palatable food (Wong, 2000). External factors may also affect individuals of normal weight in the state of physiological hunger (Conger et al., 1980). Although according to Rodin, both external stimuli and internal stimuli can be found in lean and obese individuals and that externality is not exclusively associated to the state of overweight. This is because both external stimuli and internal states of the body can affect motivational states (Wong, 2000). Several test have been made to prove the relevance of externality. And Schachter's students failed to produce the same result that could support the External Hypothesis. The External Hypothesis has been continuously challenged until it disappeared in the 1980s (Pool, 2001). Such disappearance implies that it is very difficult to determine a consistent behavioral pattern that will explain the difference between obese and individuals of normal weight. This result also suggests that while behavior may have an influence in the eating habits of an individual, it is not a potent measure to define the differences of an obese from a normal individual.
The Restrained Eater Hypothesis on the other hand is a revised idea of Richard E. Nisbett's supposition that the preferential weight of an adult is determined by the number of fat cells during childhood or adolescence. And the hypothalamus operates in the weight maintenance of the body. The lesions observed in the hypothalamus of rats indicate hunger and promote rats and other animals to eat voraciously. It is that constant hunger in animals that causes behavioral changes in animals may it be human or rat (Pool, 2001). Peter Herman refined Nisbett's idea and argued that it is not constant hunger that drives to eat more but the restraint set by an individual to eat less than what is required by his or her body. Herman referred to this term as disinhibition. He further argued that what Schachter thought about changes inceating behavior as a response to external stimuli is more of a resultof disinhibition. Anxiety lowers one's appetite, and once anxiety in the form of restraint is removed people tend to eat more.
Several theories have emerged from Herman's Restrained Eating Hypothesis that served as a basis to develop more theories and challenge existing theories on obesity. These theories include the Ironic Process Theory of Daniel Wegner and Boundary Model of Peter Herman and Janet Polivy. The Ironic Process Theory proposes that the cognitive capacity of human plays an important role in maintaining mental control in times of limiting capacity. The occurence of an opposite phenomenon from what is intended to be achieved is a result of a limited capacity. There are two m ain processes involved in mental control--intentional operating process and ironic monitoring process. The intentional process is associated with objects that are consistent to the desires of the mind. The process demands the high effort of the cognitive capacity for control. The monitoring process on the other hand is linked to the objects that are inconsistent to the desires of the mind and thus indicate a failure in mental control. The monitoring process mediates the initiation or the inhibition of the internal operating process. Thus, while eaters aim to restrict food intake during the operating process, the monitors look for inconsistencies with food restriction. As thecognitive capacity is subjected to distractions the monitor continues to find failures that may result to the inhibition of the operating process making it difficult for restrained eaters to disallow themselves to eat (Boon et al., 2002).
The Boundary Model suggests that restrained eaters develop eating patterns that results to restraint and overindulgence. That is; any disinhibihition such as anxiety promotes the "deprivation-motivated eating behavior. Eating patterns are determined by factors such as physiological factors of hunger and satiety and the conscious effort to resist the desire to eat (Adesso et al., 1994). Boon and colleagues also developed the Limited Capacity Hypothesis based on Wegner's Ironic Process Theory and Herman and Polivy's Boundary Model. The Limited Capacity Hypothesis suggests that overeating is a result of cognitive capacity limitations of restrained eaters. Such impairment of cognitive capacity leads to overeating among restrained eaters. The difference in eating habits is associated with food perceived to be high in calories.
There are many other theories that are also associated to the psychosocial aspects of obesity. But these aforementioned theories have contributed greatly to the further understanding of obesity and overweight. However, there are gaps that are still needed to be filled.
Adesso, V. A., Reddy, D. M. and Fleming, R. (Editors). (1994). Psychological Perspectives On Women's Health. Washington, DC: Taylor and Francis.
Boon, B., Stroebe, W., Schut, H. and R. IJntema. (2000). Ironic Processes in the Eating Behaviour Of Restrained Eaters. British Journal of Health Psychology, 7:1–10.
Conger, J. C., Conger, A. J., Costanzo, P. R., Wright, K. L. and Matter, J. A. (1980). The Effect of Social Cues on the Eating Behavior of Obese and Normal Subjects. Journal of Personality, 48(2):258-271.
Meyers, A. W., Stunkard, A. J. and Coll, M. (1980). Food Accessibility and Food Choice:A Test of Schachter's Externality Hypothesis. Archives of General Psychiatry, 37:1133-1135.
Pool, R. (2001). Fat : Fighting the Obesity Epidemic: Fighting the Obesity Epidemic. New York, NY: Oxford University Press, Inc.
Wilborn, C., Beckham, J., Campbell, B., Harvey, T., Galbreath, M. et al. (2005). Obesity: Prevalence, Theories, Medical Consequences, Management, and Research Directions. Journal of the International Society of Sports Nutrition, 2(2): 4-31.
Wong, R. (2000). Motivation: A Biobehavioural Approach. Cambridge, UK: Cambridge University Press. Obesity and Overweight:Theory and Theorists