You'll need less food to maintain weight...so yes you probably need to cut down on the fat calories....which is a good thing considering now you spend less time eating, still keep the same muscle, burn fat...and oxidize less food creating less free radical damage and slowing down the aging process. Not a bad deal if you ask me!
I'm not sure if the fasting really slows down the metabolism per say. The lowered body temp could be in response to doing less digestion all day long or built in survival mechanism when on a more reduced calorie diet (as seen below from PubMed, which is more on CR but same can be said for IF I am sure)
Indirect calorimetry showed that 24-hr energy expenditure was reduced by approximately 24% during short-term CR. The temporal association between reduced body temperature and energy expenditure suggests that reductions in body temperature relate to the induction of an energy conservation mechanism during CR. These reductions in body temperature and energy expenditure are consistent with findings in rodent studies in which aging rate was retarded by CR, now strengthening the possibility that CR may exert beneficial effects in primates analogous to those observed in rodents.
You also use your food more efficiently so you can assimulate more protein from less grams per day than you are used to. Your themogenesis digestive part of your metabolism is dropping, I think there have been studies to show the T3 levels do not until you start fasting over 2+ days.
Again...all good problems to have considering the health and longevity benefits gained.