According to drive reduction theory, the body constantly attempts to keep the state of equilibrium, and when the equilibrium is broken, the body creates drives to restore it. Hunger is an example of such a drive. When one’s stomach is empty, the hormone of ghrelin is created in the stomach and hypothalamus, resulting in the feeling of hunger, which drives one to eat. When one’s stomach is not empty, however, the production of ghrelin stops; the hormone of leptin is created, which suppresses the feeling of hunger, resulting in satiation (Lloyd, 2010, p. 64).
As for the obesity epidemic, there are three main evolutionary explanations for it (Speakman, 2013):
- Excess body weight is adaptive; it allowed for better survivability/fecundity during the periods of hunger; thus, individuals with “thrifty genes” allowing for better energy storage in fat tissues gained an advantage;
- Excess body weight is not adaptive, but it is favored nowadays as a maladaptive by-product of adaptive genetic selection on some different trait;
- Genetic mutations giving predisposition to excess body weight are neutral, “drifty” genes.
Social and environmental factors that may contribute to the obesity epidemic in the First World include the increased access to food; the use of artificial chemical compounds for enhancing the taste properties of food; the use of hormones or other compounds (which accumulate in meat) to increase meat production in farms; the commercial popularization of foods containing carbohydrates; the consumption of unhealthy fats; the way of life which involves little physical activity (e.g., office jobs), etc.
To change one’s lifestyle to attain/maintain a healthy BMI, it is possible to introduce regular physical activity in one’s life, change one’s diet to a healthier one, and maintain a proper regime of sleep/rest and activity. For instance, one could create a schedule including running in the early morning, healthy food intake at the same times during the day, and daily sleep of 8 hours.
References
Lloyd, R. V. (Ed.). (2010). Endocrine pathology: Differential diagnosis and molecular advances (2nd ed.). New York, NY: Springer.
Speakman, J. R. (2013). Evolutionary perspectives on the obesity epidemic: Adaptive, maladaptive, and neutral viewpoints. Annual Review of Nutrition 33, 289-317. Web.