Brown adipose tissue and the cold war against obesity.

Abstract

Obesity is one of the most burdensome health issues of our time. According to a 2012 World Health Organization report, there are more than 1.4 billion overweight adults worldwide, of whom ∼500 million are obese (1). Strikingly, 40 million children under the age of 5 are currently overweight or obese (1). These statistics are especially alarming because of the long list of obesity-associated conditions. These include insulin resistance, type 2 diabetes, dyslipidemia, cardiovascular disease, and several cancers (2). Among the consequences of the obesity epidemic are an expanding population of chronically ill people, escalating health care expenses, and the prediction that, for the first time in human history, the current generation will have a shorter life span than the previous one (3). Accumulation of fat results from a prolonged imbalance between energy intake and energy expenditure. One might think that reducing fat mass in obese individuals could be achieved relatively simply by either decreasing food consumption or increasing energy expenditure, thereby attaining a sustained negative energy balance. Unfortunately, this task is not easy to achieve, in large part because of the combination of sedentary lifestyle and the availability of calorie-dense, inexpensive food. With the exception of bariatric surgery (4), most antiobesity interventions that target energy intake result in moderate, and often temporary, weight loss. Sadly, pharmacological strategies aimed at increasing energy expenditure have not delivered on the promise of efficacy or safety when translated from animal models to humans. For instance, supraphysiologic doses of thyroid …