Starving yourself does reduce calories burned due to spontaneous fidgety behavior (are you really relaxed and holding still while you're at the computer?), as well as metabolic processes (even on a bodyweight-relative basis), by which I mean whatever energy is expended outside gross motion.

However, most people using this phenomena as an excuse are conveniently overestimating its magnitude (and/or underestimating their caloric intake). This helps them combat the stigma of moral weakness (often wrongly) associated with being fat.