Some of our primate relatives live off fruit, but a) wild fruit is generally way less sugary than whatever we produce now, b) they are fairly far from us in many other regards (lifespan, anatomy, the ability to swing in the trees), so we cannot really derive relevant lessons on human metabolism from them.
Our closest living relatives are chimps, who can eat tree bark and some leaves that we are unable to digest (they do not prefer them, but can eat them without ill consequences). Even at this relatively short evolutionary distance, our food requirements diverged.
Some of our primate relatives live off fruit, but a) wild fruit is generally way less sugary than whatever we produce now, b) they are fairly far from us in many other regards (lifespan, anatomy, the ability to swing in the trees), so we cannot really derive relevant lessons on human metabolism from them.
Our closest living relatives are chimps, who can eat tree bark and some leaves that we are unable to digest (they do not prefer them, but can eat them without ill consequences). Even at this relatively short evolutionary distance, our food requirements diverged.