According to a recent post on Healthbolt, coffee is...
...Not just good, but great! Reasonable amounts of coffee - no more than a few cups a day - promote all kinds of healthy side effects, from reduced risk of colon cancer, Parkinson’s, and type 2 diabetes to healthier liver function (aha!). And three cups of coffee have just as much fiber as an apple.
I had already heard most of this elsewhere, but not that "three cups of coffee have just as much fiber as an apple". How reliable is this assertion? I'm not qualified to say, and Healthbolt doesn't cite its sources, so I'll take it with a pinch of salt (but I may have to watch my blood pressure there).
Another thing I've read about coffee is that it isn't really an anti-diuretic. The Coffee Science Information Centre, for instance, says:
Q: Is coffee a diuretic?
A: The caffeine in coffee is a mild diuretic, but
moderate consumption of coffee has no greater effect than that seen with plain water. Decaffeinated coffee contains minimal amounts of caffeine and will therefore also have no greater effect on fluid loss than water.
Q: So will drinking coffee make me dehydrated?
A: No, coffee is an important source of fluid in the diet and moderate consumption, of 4-5 cups per day for the general population, will have no adverse effect on fluid levels in the body. In fact, experts in nutrition state that coffee can contribute significantly to daily fluid intake.
CoffeeScience (which appears to be a different organisation) confirms this and goes into more detail - an excerpt:
The diuretic effect of coffee was also evaluated in previous studies which Dr. Armstrong reviewed. The mild diuretic effect in coffee, tea and soda stems from their active agents, classified as methylxanthines. Dr. Armstrong explained, “The caffeine in coffee, tea, and soft drinks is 1,3,7-trimethylxanthine. Tea contains theophylline – 1,3-dimethylxanthine. Theobromine is found in tea, chocolate and cocoa as 3,7-dimethylxanthine. All three compounds are central nervous system and cardiac stimulants, as well as mild diuretics in some situations.
Both serious athletes and weekend athletes consume a number of beverages that, when taken in large volume, have a diuretic effect. It is interesting to note that researchers have shown that fluid-electrolyte replacement beverages have diuretic activity, and that even water is a diuretic. At less than 300 mg a day, the diuretic activity of caffeine is similar to that of water.
What I can tell you for sure is that drinking coffee is good exercise (but just how good depends on how far your desk is from the coffee machine).