title: Adaptive thermogenesis with weight loss in humans.
abstract: Adaptive thermogenesis (AT) with weight loss refers to underfeeding-associated fall in resting and non-resting energy expenditure (REE, non-REE); this is independent of body weight and body composition. In humans, the existence of AT was inconsistently shown and its clinical significance has been questioned.
  
  
  OBJECTIVE
  Discrepant findings are mainly due to different definitions of AT, the use of various and nonstandardized study protocols, and the limits of accuracy of methods to assess energy expenditure. With controlled underfeeding, AT takes more than 2 wk to develop. AT accounts to an average of 0.5 MJ (or 120 kcal) with a considerable between subject variance.
  
  
  METHODS
  Low-sympathetic nervous system activity, 3,5,3'-tri-iodothyronine (T3) and leptin are likely to add to AT; however, the kinetic changes of their plasma levels with underfeeding differ from the time course of AT and controlled intervention studies substituting and titrating these hormones are rare in humans. AT in response to underfeeding is independent of thermogenesis in response to either diet or cold. Although fat-free mass (FFM) and, thus, liver, and skeletal muscle are considered as major sites of AT, cold-induced nonshivering thermogenesis relates to the metabolism of brown adipose tissue (BAT). In humans, diet-induced thermogenesis is related to postprandial substrate metabolism of FFM with a questionable role of BAT. Obviously, the REE component of AT differs from and its non-REE component with respect to organ contribution as well as mechanisms. Thus, AT cannot be considered as unique.
  
  
  CONCLUSIONS
  AT should be characterized based on individual components of daily energy expenditure, detailed body composition analyses, and mathematical modeling. The biological basis of AT as well as the influences of age, sex, obesity, stress, and inflammation remain to be established in humans.
authors: Institut für Humanernährung und Lebensmittelkunde, Christian-Albrechts-Universität zu Kiel, Düsternbrooker Weg 17, 24105 Kiel, Germany. mmueller@nutrfoodsc.uni-kiel.de
authors: M J
authors: MJ
authors: Müller
authors: A
authors: A
authors: Bosy-Westphal
mesh_terms: D002001:Adipose Tissue, Brown / Q000378:metabolism; D001823:Body Composition; D001835:Body Weight; D004032:Diet; D002149:Energy Intake; D004734:Energy Metabolism / Q000502:physiology; D006801:Humans; D020738:Leptin / Q000097:blood; D012146:Rest / Q000502:physiology; D013564:Sympathetic Nervous System / Q000378:metabolism; D022722:Thermogenesis; D015431:Weight Loss / Q000502:physiology*
chemical_list: D020738:Leptin