You need to edit BodyShop config file, just like in PC version; the difference, in Mac, is that you have to do it in the config file 
inside the BS application itself.
ctrl-click on the BodyShop icon, choose "Show Package Contents", then go to Contents/Resources/Config/.
Open Graphics Rules.sgr with a text editor, search for this part:
#############################################################################
#
# UI Options
log $logGroup $logLevelDebug "Begin parsing option definitions"
option MaterialDetail
   setting $Low
      boolProp bumpMapping false
      intProp  imageDataSizeReductionOnLoad 0
   setting $Medium
      boolProp bumpMapping false
      intProp  imageDataSizeReductionOnLoad 0
   setting $High
      boolProp bumpMapping true
      intProp  imageDataSizeReductionOnLoad 0
end
You should have "intProp  imageDataSizeReductionOnLoad" set to 1 or 2 in the first two entry; change them to 0, as shown.
Then, search for "option ScreenModeResolution" and change the values it like this:
option ScreenModeResolution
   setting $Low
      uintProp maxResWidth      2048
      uintProp maxResHeight     2048
      uintProp defaultResWidth  1024
      uintProp defaultResHeight 768
   setting $MediumButDefaultLow
      uintProp maxResWidth      2048
      uintProp maxResHeight     2048
      uintProp defaultResWidth  1024
      uintProp defaultResHeight 768
   setting $Medium
      uintProp maxResWidth      2048
      uintProp maxResHeight     2048
      uintProp defaultResWidth  1024
      uintProp defaultResHeight 768
   setting $High
      uintProp maxResWidth      2048
      uintProp maxResHeight     2048
      uintProp defaultResWidth  1024
      uintProp defaultResHeight 768
end
  In a nutshell, wherever you'll se defaultResWidth 800, change in 1024, and defaultResHeight 600 in 768.
Save as plain text (don't append .txt to the file!!), close the windows.
Last, but not least, hold down the command (apple) key while you launch BodyShop: it brings up a window in which you can enlarge the window size (default is 800x600) to at least 1024x768.
This should allow the best performance of BodyShop.