Black tea has the most caffeine of all teas. (Photo by prakhar)
So far in my ongoing experiment to find ways to control hunger during fasting, I've been drinking quite a lot of black tea. According to the U.S. Department of Nutritional Services, 5 oz (about 1,5 dl) of black tea contains between 20 and 110 milligrams of caffeine, while coffee contains between 106 and 164 milligrams. Generally, black tea contains more caffeine than green tea and green tea contains more than white tea. The exact amount depends on the type of black tea and brewing time.
I usually make about half a liter (or 17 oz) of tea and drink it during the course of a half an hour or so. Drinking tea does seem to help a little with the hunger, and especially in the morning it's a good way to start the day if I'm fasting. The downside is that if I drink it in the evening, it'll keep me up at night. I suspect most of the appetite suppressing effect is due to the caffeine, but it is of course possible that there is something in black tea that helps with hunger.
The effect is quite minor, however, so black tea is most likely not the best drink choice if you're having trouble fasting. Also, I've noticed that if I drink black tea when I'm very hungry, I get a bit dizzy and don't feel very energetic. This may be due to the fact that black tea has been shown to lower blood sugar levels. Black tea seems to be a decent choice when you're feeling a little hungry but still have the energy to something besides sleep.
For more information on tea and fasting, see these posts:
Controlling Hunger During a Fast: Does Black Tea Help?
Controlling Hunger During a Fast: Does Decaffeinated Tea Help?
Controlling Hunger During a Fast: Does Coffee Help?
The Psychological Effects of Intermittent Fasting