Coffee (specifically caffeine) affects everyone differently. I can barely drink a large cup without getting super jittery, so personally I stick to tea. Coffee is, technically, a natural diuretic (so yes, it will decrease your water content but its relatively minimal). Appetite thing is also dependent on the person. For me, caffeine suppresses my appetite. Cofee itself isn't healthy or unhealthy. It's just flavored water. It get's bad when you add in the cream, the sugar, the syrups, etc. So since you drink black coffee, it seems like there's nothing wrong. How does coffee make YOU feel? Do you feel like you should drink more water? Maybe alternate those 3-4 cups of coffee with a glass of water between each. How does it affect your own appetite? Do you drink coffee on an empty stomach? I can't tolerate that, my stomach gets real upset. If your goal is to lose weight (and here I'd prefer to say, 'lose fat'), then your goal is to create a calorie deficit. Black coffee is great because it's around 5 calories for an 8 ounce serving. So, while the caffeine may increase your TDEE every so slightly (I'm talking like, maybe you burn an extra 20 calories a day because of coffee), it's really not something to focus on.