Brown Fat in Humans: Turning up the Heat on Obesity

Abstract

The looming pandemic of obesity and overweight, driven by ready access to high-calorie food and an increasingly sedentary way of life, poses a severe threat to global public health. The pathological accumulation of excess dysfunctional adipose tissue that characterizes obesity is a major risk factor for many other diseases, including type 2 diabetes, cardiovascular disease, hypertension, stroke, arthritis, and various types of cancer (1). A basic, but often misunderstood, concept is that weight gain is caused by a fundamental energy imbalance, when energy intake from food chronically exceeds energy expended by physical activity and metabolic processes (Fig. 1). Humans have evolved efficient biological mechanisms to acquire and defend their energy stores. A therapy for weight loss must, therefore, involve a decrease in food intake and/or an increase in energy expenditure. FIG. 1. BAT contributes to energy expenditure. Weight gain and obesity are caused by chronic periods of positive energy balance. Energy intake comes from food consumption, whereas the major contributors to expenditure are exercise and basic metabolic processes. The studies reviewed here suggest that BAT activity could impact daily energy expenditure. BAT dissipates energy as heat and can thus counteract weight gain. Interindividual variability in the amount or function of this tissue may impact body weight. In addition, therapeutic expansion/activation of this tissue may prove to be an effective therapy for obesity. WAT, white adipose tissue. In addition to the better-known white adipose tissue that specializes in lipid storage and undergoes pathological expansion during obesity, mammals are also equipped with thermogenic brown adipose tissue (BAT). BAT evolved in mammals to dissipate large amounts …