Day 1, my friend, and if it lasts 2-3 days, just imagine later on how little food matters.
The problem, as Guppy said, is that there aren't any consequences nor negatives at all. Rotten food takes away a bit of health. Big deal, pop a painkiller and live off of rotten food as well. There's no sense of satisfaction in filling the hunger bar if the threat of actually starving to death is non existent.
I can't speak for others, but I can speak for myself, and so far I have never spent a point in none of those skills. There's no need to, food is abundant. I'd rather save the points for when I reach the very expensive last levels of the int build.
If Iron Gut isn't really necessary now, with the vomiting mechanic, just imagine if there's no consequence of eating bad quality food anymore.