A lot of fruit is sweeter not because it contains more sugar per gram of fruit, but because they've bred out bitter compounds that compete with the sugar and make it seem less sweet. That is, they've bred out the very "phytonutrients" that we're supposed to benefit from if we take the advice to gorge ourselves on fruit.

The granny smith might have the same sugar as the honey crisp--but the tartness might have us eating less apple.

Wild blackberries are all over my lot. They don't taste all that sweet, even to this low carber. The ones in the store are like candy--but will never have as much flavour as when I add sweetener to the wild variety.