First off, true tea is made from the leaves of the tea plant. These leaves always contain caffeine in them. it doesn't matter if you drink them green (i.e. green tea) or black (i.e. regular tea). Green tea might have less caffeine, but it still contains it.
Other types of teas are in essence "herbal leaves and hot water" - for example chamomile tea. This is the herb chamomile dropped into hot water. It's sort of confusing to call these "teas" because they don't involve the tea leaf at all. Most of these types of teas do NOT contain caffeine
Most teas made from bags have only a tiny amount of carbs. An average amount per cup would be 0.3g per cup - i.e. 3 tenths of a gram. That's below registering for most people - you probably burn that up with the act of lifting and lowering the cup.
The thing to watch for is the caffeine. Caffeine has been shown in studies to raise blood pressure and to help your body become insulin resistant. Neither of these are good things. Herbal teas will not contain caffeine - but pretty much all regular teas (made from tea leaves) will.
You can get a decaffeinated tea, which is well worth it if you enjoy drinking tea. This will give you the flavors and warmth without the caffeine's negative effects on your body.
Here are some figures of caffeine content in an 8oz glass of the liquid. I realize some things aren't served in 8oz containers but this lets you compare them more easily.
Espresso - 410mg
Drip Coffee - 145mg
Instant Coffee - 57mg
Tea - 44mg
Diet Coke - 30mg
Green Tea - 25mg
Coca-Cola - 23mg
Lipton Iced Tea - 20mg
Hot Cocoa - 5mg
Decaf coffee - 2.5mg
Herbal tea - 0mg
As you can see, there are a wide range of caffeine figures for different drinks that "have caffeine" in them.
My research on the web seems to indicate that health professionals consider 300mg of caffeine to be the most someone should consume in a day, although many have lower numbers for people who have high blood pressure, stress in their lives already, who want to become pregnant, and so on. So you should always talk with your doctor to find out if your current level of caffeine ingestion is healthy for you.
Lisa Shea's Library of Low Carb Books
