Lipid droplets (LD) are spherical cellular inclusion devoted to lipids storage. 
It is well known that excessive accumulation of lipids leads to several human 
worldwide diseases like obesity, type 2 diabetes, hepatic steatosis and 
atherosclerosis. LDs' size range from fraction to one hundred of micrometers in 
adipocytes and is related to the lipid content, but their growth is still a 
puzzling question. It has been suggested that LDs can grow in size due to the 
fusion process by which a larger LD is obtained by the merging of two smaller 
LDs, but these events seems to be rare and difficult to be observed. Many other 
processes are thought to be involved in the number and growth of LDs, like the 
de novo formation and the growth through additional neutral lipid deposition in 
pre-existing droplets. Moreover the number and size of LDs are influenced by the 
catabolism and the absorption or interaction with other organelles. The 
comprehension of these processes could help in the confinement of the 
pathologies related to lipid accumulation. In this study the LDs' size 
distribution, number and the total volume of immature (n=12), mature (n=12, 
10-days differentiated) and lipolytic (n=12) 3T3-L1 adipocytes were considered. 
More than 11,000 LDs were measured in the 36 cells after Oil Red O staining. In 
a previous work Monte Carlo simulations were used to mimic the fusion process 
alone between LDs. We found that, considering the fusion as the only process 
acting on the LDs, the size distribution in mature adipocytes can be obtained 
with numerical simulation starting from the size distribution in immature cells 
provided a very high rate of fusion events. In this paper Monte Carlo 
simulations were developed to mimic the interaction between LDs taking into 
account many other processes in addition to fusion (de novo formation and the 
growth through additional neutral lipid deposition in pre-existing droplets) in 
order to reproduce the LDs growth and we also simulated the catabolism (fission 
and the decrease through neutral lipid exit from pre-existing droplets) to 
reproduce their size reduction observed in lipolytic conditions. The results 
suggest that each single process, considered alone, can not be considered the 
only responsible for the size variation observed, but more than one of them, 
playing together, can quite well reproduce the experimental data.