Challenging Obesity

Source: Spalding et al. (2008). Dynamics of fat cell turnover in humans. Nature 453:783-787.

I loved this paper... I thought it was brilliant... First, a couple of known facts:

1. Obesity is a major issue. We might experience a decrease in life expectancy solely based on this factor.
   
2. Fat mass is a function of both the volume and the number of adipocytes.
3. The number of adipocytes, although different in individuals, stays the same throughout adulthood.
4. The number of adipocytes is set during childhood and adolescence.
5. While the number is constant, the turnover is not known.

This paper has tackled the last issue... The fact that the number of adipocytes doesn't change is not equivalent to the concept that these cells are immortal. We do know that these cells go through apoptosis and sometimes even necrosis in vitro but there are no data regarding this matter in living humans mainly due to the toxicity of the methods used for following cell progenies. In this paper, authors have used a modern and intersting method to estimate the rate of turnover in adipocytes. This method is based on the 14C level in the atmosphere. Following the nuclear bomb tests of the Cold War era, a rapid increase and notable increase in 14C level of the atmophere was reported. Upon the declaration of Test-Ban Treaty (1963), this level has decreased exponentially because 14C is assimilated by the plants as biomass which is then transferred to other ecological levels (including us). For example, someone who was 20 years old when those tests happened should have a pre-Cold War level of 14C if the adipocytes are immortal and don't regenerate. However, the measurements in this study prove otherwise. Integrating data from many samples followed by a mathematical modeling, the authors estimate an annual turnover rate of 10% for fat tissue.

The fact that 10% of the adipocytes are renewed annually is very important for developing drugs against obesity. If we can tackle the birth rate or increase the death rate then (theoretically) we should be able to control total body fat.