If drinking coffee can cause diarrhea, is that mean it may help losing weight?

Not really: If you get diarrhea after drinking coffee, your stomach may be sensitive to it. Any weight you lose with diarrhea is likely from fluid loss -- and can easily return once the stools stop. For healthy weight loss, you need to eat whole foods (no junk) and also exercise. Realize also that the composition of your body is more important than the number on the scale -- muscle is more firm than fat.

Unlikely: The diarrhea just means you get rid of your processed poo quickes.You may have some transient fluid loss, but will re-hydrate & cancel that effect during the day.It does nothingto eliminate the chub factor.