Brown adipose tissue and the regulation of nonshivering thermogenesis.

PURPOSE OF REVIEW: The recent rediscovery of functional cold activated brown adipose tissue (BAT) in adult humans fuelled an uprise in studies on this tissue. This review focuses on the contribution of human BAT to nonshivering thermogenesis and on factors other than cold that activate BAT. RECENT FINDINGS: Earlier studies revealed BAT activity using a glucose tracer for positron emission tomography/computed tomography (PET/CT) scanning. Several recent studies, using a mix of tracers and PET/CT dynamic scanning showed that human brown fat is metabolically active and related to the perfusion of the tissue. The actual contribution of BAT to nonshivering thermogenesis still needs to be explored.The last few years, several new factors that activate human BAT have been described. These studies also highlight the plasticity of brown and white adipose tissue. Some of these factors may have pharmacological significance. SUMMARY: New PET/CT studies provide information on oxidative human BAT metabolism in vivo. This new information in combination with the study on factors activating BAT are promising with respect to management of obesity and related disorders

Assessment of fat-mass loss during weight reduction in obese women.

Urho Kaleva Kekkonen Institute for Health Promotion Research, Tampere, Finland.Methods for assessing body fat mass (FM) loss were compared in 32 obese (body mass index [BMI], 29 to 41 kg/m2) premenopausal women before and after a weight loss of 13.0 +/- 3.4 kg (mean +/- SD). A four-component (4C) model was used as the criterion. The other methods were as follows: three-component models (body density with total body water [3W] or bone minerals [3M]), underwater weighing, dual-energy x-ray absorptiometry ([DXA] XR-26, software 2.5.2; Norland, Ft Atkinson, WI), bioelectric impedance analysis (BIA) with an obese-specific equation [Segal et al), skinfolds (Durnin and Womersley), and an equation with BMI (Deurenberg et al). The 3W model (bias +/- SD, 0.5 +/- 0.4 kg), XR-26 (0.6 +/- 2.1 kg), and BMI equation (-0.3 +/- 2.1 kg) gave practically unbiased mean estimations of fat loss. All other methods underestimated fat loss by at least 1.6 kg (range of bias, -2.7 to -1.6 kg). The small bias (0.7 +/- 1.0 kg) between underwater weighing and model 4C before weight reduction indicates that the two-component assumptions were valid in premenopausal, weight-stable obese women. However, particularly the water fraction of the fat-free body component (4C model) was increased after weight reduction (before, 72.9% +/- 1.4%; after, 75.7% +/- 2.2%), making both underwater weighing and the 3M model uncertain for assessment of body composition changes. A general tendency for overestimating FM was seen before and more clearly after weight reduction. However, most methods underestimated fat loss, apparently because of unexpected changes in hydration of the fat-free body component

Cold-induced heat production preceding shivering

Individual changes in heat production and body temperature were studied in response to cold exposure, prior to shivering. The subjects ten women (seven men) were of normal weight, had a mean age of 23 (SD 3) years and average BMI 22.2 (SD 1.6) Kg/m2. They were lying supine under thermoneutral conditions for 30 min and were subsequently exposed to air of 15 degrees C until shivering occurred. Heat production was measured with a ventilated hood. Body composition was measured with underwater weighing and 2H dilution. Body temperatures were measured with thermistors. Heat production during cold exposure prior to shivering increased and reached a plateau. Skin temperature decreased and did not reach a plateau during the test period. The non-shivering interval (NSI) ranged from 20 to 148 min, was not related to body composition and was not significantly different between women (81 (sd 15) min) and men (84 (sd 34) min). NSI was negatively related to skin temperature (r2 0.44, P=0.004), and skin temperature was related to heat production (r2 0.39, P=0.007). In conclusion, subjects with a relatively large heat production during cold exposure maintained a relatively high skin temperature but showed a short NSI, independent of differences in body composition

Effects of different cooling principles on thermal sensation and physiological responses

Applying low exergy cooling concepts in the built environment allows reduction of high quality energy sources. However, application of low exergy cooling systems can result in whole body and local discomfort of the occupants. Non-uniform thermal conditions, which may occur due to application of lowex systems, can be responsible for discomfort. However, in some cases combinations of local and general discomfort factors, for example draught under warm conditions, may not be uncomfortable. Two different cooling principles were studied: passive and active cooling. Active cooling occurred through either convection or radiation. Ten healthy male subjects (age: 20-29; BMI: 18-25) were exposed to four different experimental cases: (a) passive cooling through convection and (b) active cooling through convection, and active cooling by radiation via the (c) ceiling or (d) floor. Physiological and thermal sensation data indicate significant differences between the different cases