"* No calories are to be ingested during the fasted phase, though coffee, calorie free sweeteners, diet soda and sugar free gum are ok (even though they might contain trace amount of calories). A tiny splash of milk in your coffee wont affect anything either (½-1 teaspoon of milk per cup at the most - use sparingly and sensibly if you drink a lot of coffee). Neither will sugar free gum in moderation (~20 g)."
A little half and half should be fine.. Martin suggests keeping it under ~50kcals to stay "fasted"
Also from the website
"The fasted state is not an on/off switch
I often encounter questions that goes a little something like this
"...can I use milk/cream in my coffee during the fast?"
"...will I break the fat if I have a 1/2 cucumber during the fast?"
"...I accidentally drank a mouthful of regular Pepsi during the fast, is this considered a fast breaker?"
A: The fasted state is not an on/off switch that immediately gets turned off once you have a tiny amount of calories, like a lot of people seem to believe. The research is not clear on exactly what it is with fasting that causes the positive effects seen in the clinical trials, but some of the hypotheses revolve around
a) letting insulin levels drop below a certain threshold, rather than a semi-elevated state (which would be the case with a higher meal frequency approach)
b) creating an acute energy deficit (which you enter during the fast)
Note that I'm really dumbing this down to get my point across.
So, it's a question of a dose-response effect. Can you have some milk in your coffee? Sure, I wouldn't worry about it and I have it myself. Life would just be too damn boring with only black coffee, especially if you're used to having some milk with it. How much milk/cream? I would put the limit at 50 kcal total used throughout the fast. That's about 1 deciliter or 1/2 cup 2% milk."