Fitness, Fatness, and Metformin

Dear Editor-in-Chief: In a recent study, Rynders et al. (4). came to a potentially significant conclusion that the antidiabetic drug metformin provides no added benefit to 6 months of lifestyle modifications among obese adolescents. The authors reported improvements in body composition, inflammatory factors, and cardiorespiratory fitness (CRF) in a group of obese adolescents, whether or not they used metformin. This conclusion certainly strengthens the importance of and promotes proper nutrition and physical activity in that population. The authors further observed that the improvements in body composition and inflammatory factors were much more pronounced in those participants who had demonstrated an improvement in CRF, as reflected by increased maximal oxygen consumption (V˙O2max). They thus concluded that future intervention programs should be designed to increase V˙O2max. Although we generally agree with such recommendations, the authors’ conclusion is not borne out by their reported data. V˙O2 and V˙O2max are measured in absolute terms of liters of O2 per minute. When training effects are assessed in adults, these absolute values are the yardsticks for changes in CRF. In such individuals, body weight–normalized values may reflect weight loss or gain due to training, diet, or other factors. However, when children or adolescents are assessed, increases in absolute V˙O2max may reflect growth-related gains in muscle mass (2). To take into account both the training and growth factors, one should normalize V˙O2max to fat-free mass rather than to total body mass. When a 4.1 mL O2·kg−1·min−1 improvement in V˙O2max is observed in conjunction with a 4.3-kg weight loss, as was reported in the present study, one should be hard pressed to assign the improvement to fitness gain rather than to weight loss. We suggest that the observed V˙O2max increase reflects weight reduction rather than increased CRF. The authors note that “these favorable changes occurred with an average of only one supervised exercise setting per week” (4, p. 790). Indeed, the 12.5% V˙O2max improvement after a single weekly session contradicts previous findings in youths (1,3). Although the data provided in the article do not allow us to examine the effect of weight reduction on V˙O2max, the data in Table 2 (4) can easily be interpreted to mean that favorable changes in inflammatory factors and CRF were more pronounced in participants with greater reductions in body weight and fat percentage. The authors have the data (absolute V˙O2max, body mass, and fat percentage) and may be interested in verifying our suggestion. Moreover, the reported maximal test values (heart rates <160 beats·min−1, low RERs that diminished posttraining, and V˙O2max <21 mL O2·kg−1·min−1) suggest that the incremental test performed by the participants resulted in peak rather than maximal V˙O2max values. We propose that the observed postintervention augmentation of cardiovascular values could also reflect the participants’ habituation to the testing environment. Thus, the study certainly supports the importance of lifestyle modifications in obese adolescents. It also demonstrates an association between weight reduction and improvement in V˙O2max. However, it neither proves nor disproves the significance of exercise training in improving cardiorespiratory fitness. The training load was simply insufficient. Bareket Falk, PhD Department of Kinesiology Brock University, St. Catharines, ON, Canada Raffy Dotan, MSc Faculty of Applied Health Sciences Brock University, St. Catharines, ON, Canada The authors declare no conflicts of interest.

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