What is the best way to make a berry crisp healthy? Can you substitute the butter or sugar with something else?
I've used coconut oil instead of butter to make a crisp vegan, and it worked well. You could cut the sugar by a 1/4 to 1/3, and it would probably be just fine.
Or, substitute whatever fruit you are using for a sweeter fruit (white peaches over yellow, for instance) and use agave in lieu of sugar. Natural sugars will keep it more than sweet enough. I second the coconut oil suggestion as well. Or, treat it more like a "Betty" and don't use much fat in the topping -- just rustic bread crumbs or croutons!
I make a version on my blog with a topping toasted separately so you don't have to use much butter. Basically, toast (until it starts to brown) the topping of oats, flour, a little brown sugar, maybe some nuts for crunch. Sprinkle over the fruit in your baking dish and dot with some butter pieces. You don't need to use nearly as much butter. I also use honey instead of sugar if my fruit is not that sweet. The texture is not exactly the same, but I actually like it more.