Roughly speaking, the stop comes when the amount of pleasure equals the amount of displeasure (the latter coming from the taste itself and/or from the effort in searching for food). In fact, experiments show that the natural tendency is to stop slightly after the "zero point": if the temperature is gradually decreased during a pleasant video game, the player usually stops a few minutes *after* the discomfort due to the temperature exceeds the pleasure due to the game, because, the decision to stop demands some effort. Maybe that phenomenon is not a problem in nutrition, if the instinct takes it into account (i.e., if the taste change comes when the aliment is still beneficial to the body). But maybe our instinct is adapted to natural conditions only (we have to store enough nutrients, that will be consumed when searching food later). Under natural conditions, I think both factors (taste change and fatigue) can be important, depending on the food. The instinctive stop can come rather quickly (for me: potatoes, onions, garlic...), or later than "fatigue" (wild strawberries are very small and scarce). It happens that the same food is available in large quantities: it may take several days for chimps to eat all the fruits on a tree; a sole individual can eat a young baboon almost entirely; using a stick as a tool to dip it into a comb doesn't require much more effort than eating jarred honey with a teaspoon. I also suspect that picking fruits is not really a problem for chimps which are much more agile and strong than us. Cracking nuts is not really deterring either (I can easily overeat in-shell nuts; cracking them with my teeth is quasi-automatic, and requires less effort than deciding to stop). The only differences I see when trying to use our instinct in the modern world is that searching for food is too easy for us, except if we eat on the spot, and *one food at a time* (but we have other things to worry about than continuously going to the market or the grocery...) Maybe the facts of hunting, climbing on the tree, produce a conditioned appetence, as with Pavlov's dog [the mere fact of hearing the sound of a bell really makes it *hungry*, it is not simply a reflex of salivation]. Best wishes, Jean-Louis