Energy intake or energy expenditure?

Institut für Humanernährung und Lebensmittelkunde
Christian-Albrechts-Universitet
Kiel
Germany
E-mail: abosyw{at}nutrfoodsc.uni-kiel.de

Dear Sir,

Swinburn et al (1) recently published in the Journal the prediction equation they developed for body weight in children by using cross-sectional data for total energy expenditure (TEE), height, age, and sex. This approach has a high value in predicting mean weight changes in a population as an outcome in response to interventions targeting total energy intake (TEI) or TEE. Swinburn et al assumed that the population was in energy balance, and therefore TEE = TEI = energy flux (EnFlux). They argue that a higher TEI, rather than low physical activity and a low TEE, was the main determinant of high body weight in children. This argument was based on the positive relation of EnFlux with weight after adjustment for height, age, and sex.

We are not sure whether this conclusion is justified. At a positive energy balance, weight gain has a positive relation with TEI and a negative relation with TEE. However, at a zero energy balance, TEI resembles TEE, and energy intake and energy expenditure above the basal requirement (ie, resting energy expenditure; REE) correspond to each other. The variance in body weight should thus be measured by using REE, which is mainly a function of fat-free mass and age.

Using data for 103 children and adolescents (49 boys and 54 girls aged 4–18 y) and 253 adults (94 men and 159 women aged 28–84 y), we predicted lnWeight from lnREE, height, sex, and age:

children, and

In children, the model explained 85% of the variance in lnWeight (SEE = 0.15 kg) and is thus similar to the 86% variance in lnWeight explained by lnTEE, height, age, and sex that was obtained by Swinburn et al (1). The mass of a body, in both children and adults, can thus be described by its basal energy expenditure. The independent contribution of height and sex to the mathematical model for lnWeight prediction in children is explained by a child's maturity status, which influences the relation between REE and body mass (ie, a higher REE/body mass in younger children). Standardized coefficients (0.71 for height, 0.32 for lnREE, and 0.14 for sex) showed that height was the main predictor of lnWeight in our group of children.

Because lean persons are likely to have a higher TEE per kg body weight (because of a higher REE that results from a higher fat-free mass), the slope of the regression line between TEE and body weight should be steeper in overweight than in normal-weight children (Figure 1). However, under the condition of energy balance, both TEI and TEE should be positively related to body weight in both groups. Alternatively, in obese children, the regression line between weight and TEE may be flatter because a higher specific REE has been found in obese children (2) as well as in obese adults (3-5), possibly as a result of obesity-associated metabolic disturbances such as insulin resistance and elevated sympathetic tone.

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FIGURE 1.. Hypothetical relations between body weight and total energy expenditure (TEE) in lean and overweight children.

ACKNOWLEDGMENTS

Neither of the authors had a personal or financial conflict of interest with respect to the study by Swinburn et al.

REFERENCES