That is not correct. If you listen to his talk Lustig said something to the effect of "wherever god put the poison, he also put the anitdote." Thus, anywhere in nature where fructose appears there is also fiber. And fiber if it is processed at the same time and similar quantities as fructose allows the liver to process fructose properly.
So there should not be anything in its natural state that is problematic. The only exception to that may be honey.
> wherever god put the poison, he also put the anitdote
This should be taken as a tendency, not an absolute rule.
The tendency is, of course, caused by the fact that if it's plausible for any species to have evolved digestive mechanisms that allow them to make good use of a food source that's significantly available over a long period of time, then it probably happened, and become widespread.
But you have to consider implementation complexity (why aren't we immune to ALL poisons and disease that have been around for long enough? why don't we all have lifelong 20/5 vision?) vs. time vs. benefit. That, and a lot of things that could have evolved, haven't yet.
he said fruit is okay because it has more fiber content. also to go along with this: he said we don't know enough about artificial sweeteners to conclude whether they're a healthy alternative yet.
