One of the things folk often struggle with at first doing BD is cramming 'enough' calories into a smallish volume of BD. I think a lot of that comes down to the, er, interesting ways doctors and dietitians have of making statistical analyses of needs and averages, in combination with the incredibly high calorie count per volume of commercial formula. Which is mostly sugar, in its various guises.
It's very common to find that when you move to BD, a much larger volume is able to be ingested (I really don't like the word 'tolerated') compared with commercial formula, meaning you can make it less calorically dense for the same value. You will probably find that the body absorbs nutrition far better from food than from formula too, although it can take some time in transition. There are, of course, lots of variables.
Anyway, I thought I'd do a list of the commonly used calorie fortifiers: please send me your own favourites too and I'll add them to the list.
MCT oil (generally a blend of coconut and palm oils, these are absorbed in the intestine rather than actually digested)
Various other vegetable oils
Half-and-half (an American thing; half milk, half cream)
CARBS/SUGARS (watch the GI of some of these, but they're mostly lower GI than usual sugars)
Hemp seed powders
Tree nuts (too many kinds to list, really)
Meats of all kinds
Legumes (again, too many to list)
These are just short lists of things especially high in certain types of calories. Many of them could easily be in another category too - sardines have great oils, as do most nuts, and avocado and the dairy products have good proteins. There are tons more you can add, these are just the ones I recall seeing over and over on the forums and lists. You can help by sending me yours to share too! Leave a comment or mail me HERE.