There's no RAW, but I'd allow it.
RAW has no rules for modeling the humanoid metabolism. However, if we wanted to do something quick and off-the-cuff, then we can note that the lowest level an arcane caster could use this spell would be 7 (as a Wizard), meaning the material created by the spell lasts seven hours.
In humans, by this point the matter being eaten has already cleared both the stomach and the small intestine, and so some 95% of the nutrients have already been absorbed by the body. It is unlikely that any of it would have cleared the colon just yet, but in terms of nutrient absorption, the difference is quite small. For simplicity we will assume that other humanoid digestive systems work at a similar rate to humans.
At this point, the absorbed nutrients are part of the person, and I'd rule that this puts them beyond the reach of the spell's expiration. Maybe the stuff still in the colon would vanish, but this wouldn't have gotten you much more anyway.
So if you really want rules for something like this, here's something that balances simplicity with realism, while taking care to strike at that I suspect is the truly important question in your player's mind...
- If the matter lasts less than 6 hours, it cannot be used as food. This doesn't matter for wizards or sorcerers with minor creation, but psions get it sooner.
- If the matter lasts more than 16 hours, then it is essentially normal food. Waste will vanish when the spell expires, but by that point it's already made the full trip through your system.
- If the matter lasts between 6 and 16 hours, it can be used as food, though it is slightly less nutritious. You need a little more of it to avoid starvation: humans need a pound and a half every 24 hours, rather than a pound; halve or double for size as appropriate. On the other hand, you don't require a trip to the bathroom afterwards, because what's left over will vanish before that can happen.