depends on the type of fiber and your body's natural microbiome.... some types like soluble fibers can be broken down to yield roughly 1.5 calories per gram or something... idk cuz nobody usually calculates that specifically... but using the estimates you probably do (do you lick the plate clean, measure every gram of food, oil, regulate your sleep cycle and calculate rates for body metabolic rate increase on days after exercise, the ~20 calories in your day won't make a difference