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