As @SlowBurnMary posted on a previous thread -
"Jason Fung MD, Mary Dan Eades MD, Stephen Phinney MD, Michael Eades MD, Megan Ramos and others educate on how it’s protein and carbs not fat calories that takes one out of the fasted state. The only thing that matters is carbs up to a point. (This may however not apply to sedentary non-fasters who take a heavy fat morning coffee along with a huge breakfast, followed by two other big meals - at some point, caloric excess can become a prob without physical activity).
That being the case, a coffee with 2-4 tblsp of fat (some of it HWC) to feed the brain all day is not only great for brainz, it in turn supports the metabolism and extends happy fasting.
In my own experience, inch-dropping and metabolic power have been unhindered by abundant fat in my coffee while doing IF 4:3 or 5:2. In fact, being an under 55 year old female I use a little half n half to get 1-2 carbs to help my body not lurch into the female mammalian starvation response of fat storage - which not only works according to my results, but also is tasty.
Plus, black coffee on its own is very hard on the stomach lining as well as tooth enamel, being quite acidic. Alkalinizing it with dairy (or salt, as some do) makes it all better tho apparently."
I am of the same mindset about fasting and will continue to use creamed coffee during my fasts. 