Mathematical Models of Adipose Tissue Dynamics - The Mechanobiology of Obesity and Related Diseases - page 28

Fig. 11 Comparison of lipid turnover (D) and lipogenesis/lipolysis (v m0 ) values in IRM and
ISM: Comparison of lipid turnover (diffusion, D) and lipogenesis/lipolysis (convective velocity,
vm0) values in Insulin Resistant Males (IRM) and Insulin Sensitive Males (ISM) at different
isocaloric diets. The lipid turnover for IRM and ISM are both negligible during weight gain and
are approximated at zero. Lipogenisis for IRM is 12 m/week (not shown on this scale) for all diets
\50 % carbohydrate. During weight loss (carbohydrate [ 50 %), ISM predict a greater
lipogenesis than IRM. ISM also predicts a greater diffusion coefficient while IRM displays a
transient curve
Though the IRM rate of lipogenesis was found to be 1 : 2 lm 2 /week for all diets
0-50 % carbohydrate, it may be that it exhibits a similar, albeit smaller decrease.
The differences in v m0 predict that insulin resistant individuals will more easily gain
weight while their insulin sensitive counterparts are slower to gain the same weight
[ 3 ]. In contrast, differences in lipolysis and turnover between ISM and IRM during
weight loss indicate that insulin resistant individuals will experience slower weight
loss compared to their insulin sensitive counterparts (Fig. 11 ). The three insulin
resistant groups exhibited narrow ranges for changes in D and v m0 during weight
gain and weight loss, consistent with previous conclusions that insulin resistant
adipocytes are less dynamic [ 36 ].
We used only the Gaussian component of the adipose cell size distribution but it
may be that the parameters could be determined with greater precision by using the
entire distribution. Note that the Gaussian approximation is best for the insulin
sensitive groups. The adipose tissue dynamics model will need to include cell
number changing processes for studies over longer time intervals [ 16 ]. Serial
biopsies in subjects over the course of weight gain or loss would be a definitive test
of the model comparison.