title: Energy metabolism after 2 y of energy restriction: the biosphere 2 experiment.
abstract: BACKGROUND
  An adaptive decrease in energy expenditure (EE) in response to 6 mo of severely restricted energy intake was shown in a classic semistarvation study-the Minnesota experiment.
  
  
  OBJECTIVE
  Our objective was to examine whether such adaptation also occurs in response to less severe but sustained energy restriction.
  
  
  METHODS
  Body composition, 1-wk total EE (TEE), 24-h sedentary EE, and spontaneous physical activity were measured in 8 healthy subjects (4 men and 4 women) at the end of a 2-y confinement inside Biosphere 2. Unexpectedly, the food supply was markedly restricted during most of the confinement and all subjects experienced a marked, sustained weight loss (9.1 +/- 6.6 kg; P: < 0.001) from the low-energy (7000-11000 kJ/d), low-fat (9% of energy), but nutrient-dense, diet they consumed.
  
  
  RESULTS
  The TEE inside Biosphere 2, assessed 3 wk before exit, averaged 10700 +/- 560 kJ/d (n = 8). Within 1 wk after exit, the adjusted 24-h EE and spontaneous physical activity were lower in the biospherians (n = 5) than in 152 control subjects (6% and 45%, respectively; both P: < 0.01). Six months after exit and return to an ad libitum diet, body weight had increased to preentry levels; however, adjusted 24-h EE and spontaneous physical activity were still significantly lower than in control subjects.
  
  
  CONCLUSIONS
  In lean humans, an adaptive decrease in EE appears to occur not only in states of life-threatening undernutrition, but also in response to less severe energy restriction sustained over several years.
authors.affiliation: Clinical Diabetes and Nutrition Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, AZ 85106, USA. cweyer@phx.niddk.nih.gov
authors.forename: C
authors.initials: C
authors.lastname: Weyer
authors.forename: R L
authors.initials: RL
authors.lastname: Walford
authors.forename: I T
authors.initials: IT
authors.lastname: Harper
authors.forename: M
authors.initials: M
authors.lastname: Milner
authors.forename: T
authors.initials: T
authors.lastname: MacCallum
authors.forename: P A
authors.initials: PA
authors.lastname: Tataranni
authors.forename: E
authors.initials: E
authors.lastname: Ravussin
mesh_terms: D000328:Adult; D000368:Aged; D001481:Basal Metabolism; D001823:Body Composition; D002153:Calorimetry, Indirect; D004032:Diet; D018504:Ecological Systems, Closed; D002149:Energy Intake / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D010101:Oxygen Consumption; D011863:Radioimmunoassay; D012044:Regression Analysis; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D015431:Weight Loss
chemical_list: D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine