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School of Exercise and Nutrition Sciences
Deakin University
221 Burwood Highway
Burwood, Victoria 3125
Australia
E-mail: boyd.swinburn{at}deakin.edu.au
Monash Institute of Health Services Research
Monash University
Melbourne
Australia
School of Human Movement and Sports Sciences
University of Ballarat
Ballarat
Australia
National Institute of Diabetes and Digestive and Kidney Diseases
National Institutes of Health
Phoenix, AZ
Pennington Biomedical Research Center
Baton Rouge, LA
We thank Bosy-Westphal and Müller for their commentary on our prediction equation for estimating the body weight change in children in response to energy imbalance (1) and for providing additional information on the issue. They have found, as we did, a positive relation between energy expenditure and body weight, although they have used resting energy expenditure (REE) rather than total energy expenditure (TEE). They also extended these findings to adults and added some helpful explanatory analyses about the independent contributions of height and sex. However, we are not convinced that the use of REE has any practical advantages over that of TEE for the purposes of predicting changes in weight for given changes in energy intake or expenditure.
Bosy-Westphal and Müller also speculate on 2 additional matters. The first is that, under conditions of positive energy balance, weight gain will be correlated positively with total energy intake (TEI) and negatively with TEE. We believe that such a correlation would be very difficult to show, because the daily energy imbalance during weight gain is tiny in comparison with the absolute levels of TEE or TEI (2). Thus, if, for example, heavier people are more likely than are leaner people to gain weight (3, 4), weight gain will be positively related to both absolute TEE and absolute TEI. The second matter has to do with their graph (see Figure 1 in the letter of Bosy-Westphal and Müller), which is problematic because "overweight children" are defined by their weight rather than by their body composition. If the 2 populations shown in the graph were defined as "lean children" and "fat children" (ie, the description was based on body composition), then, at any given weight, leaner children would certainly have a higher TEE. In reality, however, the leaner children will also be lighter (after adjustment for age, sex, and height), and thus they would be clustered closer to the origin in the graph, and the fatter, heavier children would be clustered in the top right corner.
In summary, Bosy-Westphal and Müller have confirmed our findings with some further valuable explanations and have hypothesized about 2 additional aspects that we challenge but that should be tested with real data. They also say that they dispute one of our key conclusions—that it is predominantly a high TEI rather than a low TEE (due to low physical activity) that explains a high body weight in children. This question is an excellent topic for debate, and if there are any data or arguments that may contradict our conclusions, we look forward to those discussions.
ACKNOWLEDGMENTS
The authors had no personal or financial conflict of interest.
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