I have a couple of cups of coffee a morning, each with 20g of double cream (which gives just under 10g fat per coffee).
My (completely unsubstantiated and grossly over-simplified) reasoning is as follows:
* if my BMR is approx 2200kcal per day, then in an average hour my body uses 90 odd calories (2200kcal/24h)
* in all likelihood a 'waking' hour probably uses more than that (more activity than when asleep)
* 10g fat is roughly 90kcal
* consuming the fat maintains/primes my body to prioritise fat metabolism (my body needs energy, fat's around = use it)
* at most I'm causing my body to reduce the amount of body fat it's burning (because it's burning the ingested fat) for 1 hour per coffee
* so assuming a 7am wake-up and a 1pm lunch that's 2 hours reduced body-fat burning and 4 hours 'primed' body-fat burning until lunch
* net effect = more body fat burnt, lower likelihood of muscle catabolism (to utilise the protein for energy needs)
In an ideal world I would be using coconut oil rather than double cream for the insta-available MCTs that it contains.