Physiology of the Weight-Reduced State: A Report from a National Institute of Diabetes and Digestive and Kidney Diseases Workshop

Peripheral thyroid hormone deiodination: Entry points to elucidate mechanisms of metabolic adaptation during weight regain

The concept of dual-adaptive thermogenesis underlying metabolic adaptation to prolonged energy deficit posits that there are two control systems that govern energy sparing: a rapid-reacting system to energy deficit and a slow-reacting system to fat store depletion. The latter control system, referred to as the "adipose-specific" control of thermogenesis, contributes to accelerating fat store replenishment (catch-up fat) during weight regain. The case is put forward here that, whereas adaptive thermogenesis during weight loss results primarily from central suppression of the sympathetic nervous system and hypothalamic-pituitary-thyroid axis, during weight regain it operates primarily through peripheral tissue resistance to the actions of this neurohormonal network. Emerging evidence that altered deiodination of thyroid hormones within the skeletal muscle and liver is a key determinant of such peripheral resistance therefore offers entry points toward elucidating the molecular mechanisms that underlie the adipose-specific control of thermogenesis and unraveling tissue-specific targets to counter obesity recidivism.

Drugs for Treating Obesity

Older medications approved for chronic weight management (orlistat, naltrexone/bupropion, liraglutide 3 mg and, in the USA, phentermine/topiramate) have not been widely adopted by health care providers. Those medications produce only modest additional weight loss when used to augment lifestyle intervention. However, semaglutide 2.4 mg weekly has recently emerged and produces much more weight loss - on average 15% weight loss at 1 year. Semaglutide's enhanced efficacy and that its class (GLP-1 receptor analogs) is well-known may result in more clinicians adopting pharmacotherapy. Furthermore, the first dedicated cardiovascular outcome trial powered for superiority testing an anti-obesity medication (SELECT) is underway with semaglutide 2.4 mg. A positive outcome will further promote the concept that weight management should be a primary target for cardiometabolic disease control. In phase 3, tirzepatide and cagrilintide/semaglutide combination are showing promise for even greater weight loss efficacy. Another recently approved medication takes a personalized medicine approach; setmelanotide is approved as a therapy for those with some of the ultra-rare genetic diseases characterized by severe, early onset obesity. This chapter reviews the currently available and anticipated medications for chronic weight management as well as those approved for the genetic and syndromic obesities.