Obesity and Set-Point Theory

Excerpt

Obesity is a chronic condition affected by complex factors and is now considered a global epidemic. Worldwide obesity prevalence has nearly tripled in 30 years (1975-2016). In the United States between 1999-2000 and 2017-2018, the obesity prevalence increased from 30.5 to 42.4%, and severe obesity prevalence increased from 4.7 to 9.2%. By 2030, 78% of American adults may be overweight or obese. Obesity is associated with an increased risk of several comorbidities such as cancer, sleep apnea, stroke, osteoarthritis, nonalcoholic-steatohepatitis (NASH), cardiovascular disease, diabetes, and hypertension that may contribute to economic and healthcare-system burdens.

The set-point theory is related to homeostasis. The theory posits that the human body has a predetermined weight or fat mass set-point range. Various compensatory physiological mechanisms maintain that set point and resist deviation from it. Feedback systems are vital in driving the body weight back toward the set point. In 1953, Kennedy proposed that body fat storage is regulated. In 1982, nutritional researchers William Bennett and Joel Gurin expanded on Kennedy's concept when they developed the set-point theory.

Notably, the rate at which one regains weight following weight loss is considerably high, with over 80% of individuals eventually regaining the weight they lost. The set-point theory may explain the high incidence of regained weight. Garvey WT stated, "Obesity protects obesity." When an individual loses weight, the body triggers increased appetite through modulation of satiety hormones, altered food preferences through behavioral changes, and overcompensated reduction in metabolism to drive the body weight back toward the set-point range. On the other hand, weight gain also triggers compensatory mechanisms, but these are weaker than those protecting weight loss. This asymmetry could be due to the evolutionary advantage of storing fat for survival during prolonged caloric restriction periods.

The set-point theory remains a theory since all the molecular mechanisms involved in set-point regulation are unclear, and some researchers may consider this theory to be oversimplistic. The theory also suggests that a person's weight set point is established early in life and remains relatively stable unless altered by specific conditions. However, factors such as childbirth, menopause, aging, obesogenic environment, and diseases can change the set points throughout one's life. Most individuals do not have one, but several, set points throughout their lives.