Letter regarding the article ‘Cold-activated brown adipose tissue in healthy men’ by Lichtenbelt et al.

LETTER TO THE EDITOR

Using integrated ¹⁸F-fluorodeoxyglucose positron emission tomography and computed tomography, Lichtenbelt et al [1] have demonstrated cold induced brown adipose tissue activity in lean and overweight healthy men. The authors also find a significant negative correlation between body mass index and brown adipose tissue activity.

In this study, body mass index (BMI) was used to classify subjects as lean (BMI < 25 kg/m²) or overweight/obese (BMI ³ 25 kg/m²). However, the percentage of body fat in overweight/obese subjects varied from 16.9 – 41.8%, the lower limit of this being much lower than that in ‘lean’ subjects, indicating that at least some of the subjects who were classified as obese were not ‘excessively fat’. Indeed, for body fat percentage values between 10 and 20% (n = 10 in this study), the authors also found a steep inverse relationship between body fat percentage and brown adipose tissue activity (Figure 3B in Ref. 1). Although what is a healthy body fat percentage remains to be established from prospective studies [2] and obesity is not currently defined on the basis of body fat percentage or fat mass index (i.e., fat mass in kg divided by square of the height expressed in meters; Ref. 3), we are interested in knowing how the volume of brown adipose tissue and resting metabolic rate compared if subjects in this study were dichotomized on the basis of an arbitrary body fat percentage (say 20%) or fat mass index rather than BMI.

Secondly, since waist circumference, an estimate of abdominal adiposity, has been demonstrated to independently predict mortality, [4] we wonder if this was measured in this study and if so how it correlated with brown adipose tissue activity.

Conflict of interests: none

E.S.Prakash and K.R.Sethuraman,

Faculty of Medicine, AIMST University, 08100 Semeling, Kedah, Malaysia

E-mail: dresprakash at gmail dot com

Acknowledgment:

E.S.Prakash is the Editor and Dr K.R.Sethuraman is a member of the Senior Advisory Board of Medical Physiology Online.

Editor for this Submission: This letter was reviewed and accepted for publication by Dr Roger Evans, Department of Physiology, Monash University, Melbourne, Australia. e-mail: roger dot evans at med dot monash dot edu dot au. Dr Evans is a member of the Senior Advisory Board for Medical Physiology Online.

Submitted 15 June 2009, revised 16 Jun 2009, accepted and published 17 Jun 2009.

References:

[1] van Marken Lichtenbelt WD, Vanhommerig JW, Smulders NM, et al. Cold-activated brown adipose tissue in healthy men. New England Journal of Medicine 2009; 360:1500-8 [Abstract]

[2] Gallagher D, Heymsfield SB, Heo M, Jebb SA, Murgatroyd PR, and Sakamoto Y. Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. American Journal of Clinical Nutrition 2000; 72: 694–701. [Full text]

[3] Schutz Y, Kyle UUG and Pichard C. Fat-free mass index and fat mass index percentiles in Caucasians aged 18 – 98 y. International Journal of Obesity 2002; 26: 953–960. [Abstract]

[4] Pischon T, Boeing H, Hoffmann K, et al. General and abdominal adiposity and risk of death in Europe. New England Journal of Medicine 2008; 359: 2105-2120. [Full text]

Please cite this letter as E.S.Prakash and K.R.Sethuraman. Letter regarding the article ‘Cold-activated brown adipose tissue in healthy men’ by Lichtenbelt et al. Medical Physiology Online 2009; available from http://www.medicalphysiologyonline.org

Some rights reserved © E.S.Prakash and K.R.Sethuraman, 2009. This is an open access article distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by-nc-sa/3.0/

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