Unfortunately that's only an appareance.
The process UD.exe use few memory but it launch another one wich use approximately the same memory as BOINC. For example the "help defeat cancert" project use 265Mb on my PC. (as far as i'm concerned the name of the process is wcg_hdc_tma.exe in the task manager. But i think it's change depending on the project your computing)

ps: sorry if i made english mistake in this post. English is not my mother-tongue.