Year: 2016
Type: article
Abstract: We are writing in regards to the original article “Resting Metabolic Rate Varies by Race and by Sleep Deprivation” authored by Spaeth et al. (1). Our group found this work to be of high interest, and we commend Spaeth et al. for their detailed study design around a broadly applicable hypothesis on the relationship between sleep and metabolism. The article stimulated several thoughts particularly to the authors' conclusions about the association between resting metabolic rate (RMR) and race. Spaeth et al. reported significantly lower RMR for African Americans as compared with Caucasians, yet the observed difference may be explained by differences in lean mass between the two groups. If RMR is represented in terms of fat and fat-free masses (2), fat-free mass is the most significant contributor. In this study, mean fat-free mass in the African American sample is lower than that of the Caucasian sample. Although the fat-free mass is not significantly lower (P = 0.26, unpaired t-test), this result should be taken with caution since the probability of failing to detect a significant difference is β = 20.4% (α = 5%, note: beta typically 20%). The observed mean difference of 4.5 kg of fat-free mass between race groups implies a mean RMR difference of approximately 116 kcal according to the Nelson equation (2). This closely matches the ∼100 kcal difference observed between the race groups at baseline (Figure 3B), reported as significant at P = 0.043. In addition, the authors present concerns about the accuracy of their body composition measures assessed with bioelectrical impedance, a technique with limited accuracy (3, 4). In light of these considerations, we posit that the differences observed may be completely explained by lean mass considerations, not race. Another point that we would like to discuss is the baseline RMR for both the control and sleep-restricted groups. In Figure 3A, one can see a significant difference between the baseline RMR of the two groups and a noticeable, albeit nonsignificant, increase in RMR for control subjects over the course of the protocol. In addition, the control group had only half the number of participants as the sleep-restricted group such that the error bars on the control RMR values were larger than that of the sleep-restricted. Though follow-up RMR measurements are not significantly different between the groups, we would ask the authors to comment on why the baseline measurements are different and whether this difference may affect the conclusions. In short, given the lack of adjustment of lean mass, the differences in the baseline characteristics of the groups, and the low recruitment of the controls, we think it is difficult to draw a definitive conclusion based on race or sleep deprivation. We wish to thank the authors once again for this interesting article, and we look forward to hearing from them.
Source: Obesity
DOI: 10.1002/oby.21526
Authors: Jesus I. Avila, Bennett K. Ng, Lisa Kotowski, Benjamin J. Hinton, John Shepherd
Institution: University of California, San Francisco
Language: English
Subfield: Physiology
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
Funder: National Cancer Institute
Award: G3635643485
OpenAlex ID: W2345813162