Some months ago, I did a fair bit of research into the caffeine/ketosis/insulin question ... and posted it in the Health forum ..
http://forum.lowcarber.org/showthre...=&threadid=3347 .. Basically what I found is that unless you are sensitive to caffeine, or very insulin-resistant, its effect on your weight loss effort is likely to be minimal. I have read that the original studies on which Atkins based the no-caffeine rule were conducted in the late 1980's (his New Diet Rev. was publ. in '92) ... using diet cola ... and it was later determined that the citric acid in the cola was the culprit, not caffeine.
BUT, I've since read some articles on the stimulating effects of caffeine on serum cortisols. This might trigger increased insulin production, and so is something to consider. Note that watching the Super Bowl or listening to your screaming kids will also raise serum cortisol levels
The FAQ's at the official Atkins website
http://atkinscenter.com/faq/search.asp?type=condition state that "Excess caffeine stimulates insulin production, which will drop blood sugar levels and leave you hungry for sweets." (Sorry, I have to rant here ... this admonition is next to their ads for maltitol and glycerine sweetened bars, ice creams, candies, cakes and syrups ..
)
Once again, it boils down to YMMV
However, there is a cautionary note to coffee, not specifically caffeine. And that is ...
coffee has carbs .. whether it's caffeinated or not. A small 6 fl. oz cup of coffee has 0.8g carbs in it. The average mug holds 10 fl oz, which would be 1.2g carbs. Those carbs add up pretty quick when you only have 20 or 30 grams to play with, especially if you also use cream and/or the packets of artificial sweetener.
Moderation is still the key.
Doreen