In a talk my parents sent me a few years ago, the speaker (I believe a nurse) argued that you need at least ~20 calories to trigger a metabolic response. Hence,

In a talk my parents sent me a few years ago, the speaker (I believe a nurse) argued that you need at least ~20 calories to trigger a metabolic response. Hence, things like tea, coffee (even with a tiny bit of milk), fish oil, etc. should be fine.