The genetic epidemiology of obesity: a case study

The energy balance hypothesis of obesity: do the laws of thermodynamics explain excessive adiposity?

In this work, we reflect upon the energy balance hypothesis of obesity. International organizations, the general population and many scientists hold the belief that obesity is indisputably caused by an imbalance between energy intake and energy expenditure. Most of them argue that the laws of thermodynamics support this view. We identify and review the main arguments used to support this belief, and we explain the reasoning mistakes those arguments harbor. We show that the laws of thermodynamics do not support the idea that obesity is an energy problem nor an energy balance problem more than they do in the growth of any other tissue in the human body. We argue that the validity of the energy balance paradigm for obesity must be questioned. Although correction of a wrong belief is laudable per se, in this particular case harm may arise by influencing the way in which obesity prevention is tackled and obese patients are treated.

Dynamic profile and adipogenic role of growth differentiation factor 5 (GDF5) in the differentiation of 3T3-L1 preadipocytes

Adipocyte differentiation is key to determining the number of adipocytes during the development of obesity. Recent studies have shown that growth differentiation factor-5 (GDF5) promotes brown adipogenesis, however its role in white adipogenesis is still uncertain. The aim of the present study was to investigate the effect of GDF5 on white adipogenesis using 3T3-L1 preadipocyte model. In the present study, GDF5 was found to be differentially regulated during adipocyte differentiation. GDF5 protein increased the differentiation of 3T3-L1 preadipocytes, especially when these cells were exposed to hormone cocktails without insulin. During adipogenesis, GDF5 enhanced the expression of genes related to adipocyte differentiation and caused cells to enter the S phase. Short-hairpin-RNA knockdown of GDF5 in 3T3-L1 cells was found to prevent adipogenesis induced by a standard hormone cocktail and to downregulate the expression of adipocyte genes and proteins, this impairment could be partly rescued by GDF5 protein. Collectively, these results suggest that GDF5 can promote progression of the cell-cycle and increase numbers of cells in S phase, GDF5 might play a critical role in 3T3-L1 preadipocyte differentiation.

Intragastric balloon for the treatment of obesity: evaluation of pulmonary function over a 3-month period

BACKGROUND

Obesity has become a global epidemic in the 21st century, and the placement of an intragastric balloon (IB) is a therapeutic modality used to treat it. Our objectives for this study were to evaluate changes in lung function resulting from IB use and to correlate the pattern of body fat distribution with changes in lung function.

METHODS

This was an interventional study with 30 overweight and obese patients with metabolic syndrome. All of the subjects underwent anthropometric measurements, assessment of their body fat distribution pattern by dual-energy X-ray absorptiometry, and pulmonary function testing before implantation of the IB.

RESULTS

During the initial evaluations, the main pulmonary function abnormalities observed were decreased expiratory reserve volume (ERV), decreased total lung capacity (TLC), and increased diffusing capacity of carbon monoxide (DL(CO)), which occurred in 56.7, 40, and 23.3 % of patients, respectively. We observed a statistically significant positive correlation between the DL(CO) and the percentage of trunk fat mass (ρ = 0.42; p < 0.01). Three months after placement of the IB, there was a significant reduction in the body mass index (p < 0.0001) and the maximal inspiratory pressure (p < 0.009). We also observed a significant increase in the forced vital capacity (p < 0.0001), TLC (p < 0.001), and ERV (p < 0.0001).

CONCLUSIONS

Weight loss as a result of IB causes increased static lung volumes and decreased inspiratory muscle strength. Additionally, being overweight and obese is related to increased DL(CO), especially in individuals with truncal obesity.