Hunger is the best spice

Ghrelin is a hormone produced in the stomach that
appears to stimulate appetite. A recent paper in Cell Metabolism shows that
giving ghrelin to volunteers made their brains respond more strongly to food
images, reward systems in the brain became more active and they rated their
level of hunger higher
. An immediate reaction in the blogosphere
was to consider the practical applications: Stomach hormone turns hungry people
into junkies
(New Scientist), Fast Food Joints Add
Hormone to Food That Makes You Want to Eat More
(Io9). Are we moving towards a future where
food will be literally addictive?

There is already a sizeable literature on
what influences how rewarding food is. We seem to have three
somewhat separate systems regulating food intake: a hunger system
controlled by the actual need to eat (as determined by the body and
hypothalamus), an appetite system dealing with the psychological
desire to eat (linked to how the food looks, expectations, habits, cultural
patterns and many other things), and satiety signals (such as a
full stomach) making us less willing to eat. We can have appetite for
dessert even if we are not hungry and feel rather full. Hunger may be
the reason we eat, but appetite tells us what to eat.

The rewards of eating also split into
actually wanting the food and liking it. As eating disorders and drug addiction
show, people can be driven by strong desires for things they do
not enjoy, or enjoy things they do not desire.

In psychology food is known to be a primary
reinforcer: if we are given food after an action, we are more
likely to do that action again in similar circumstances. However, the
strength of reinforcement depends on individual factors and

This means that delicious food is already
addictive to some extent. When we see it we feel desire for
it, and after having enjoyed it we are more likely to seek it out again.
Certain tastes are more rewarding than others: infants react very
positively to sweet tastes without knowing anything about what they
are, and quickly learn to do whatever it takes to get them

Umami, the fifth taste, is often signalled by glutamate (which can
be found in everything from soy to paramesan cheese to tomatoes). Glutamate is a flavor enhancer and can
improve appetite
, something which has been used to increase
eating among elderly people

Adding ghrelin straight to a meal is
unlikely to work both for biological and economical reasons: first,
ghrelin is destroyed in the stomach. Drugs that release ghrelin could
perhaps be devised, but would fall under drug  and food additive legislation. Second,
anybody selling food wants us hungry before we buy: additives that
makes us want to eat more will at most make us buy a bit more dessert at
the restaurant, but it will not help the fast food chain or convenience
store. Perhaps it could give return business, but the risk is that
the ghrelin kicks in when we are eating a competitors product and we
will remember that instead. Much safer to stick to sugar and
glutamate, as well as the classic trick of unit bias.

While hunger-manipulation is unlikely to be
a major marketing success it may still turn out to be important.
Interest in a ghrelin-antibody anti-obesity treatment is high, and the US military is
looking for ways of getting soldiers their food when it
suits military operations rather than the bodies. Food that could
manipulate hunger and satiety would sell well among the weight-conscious.

Being able to regulate our desires is in
many ways a good thing. But we want to make sure the higher-order
desires (what we want to want) are running the show, not the lower-order
desires (what we want). We cannot avoid wanting food, but we want to
avoid overeating and we want to want good food. It is relatively easy
for us to collectively decide that adding ghrelin-like substances to food
is against what we really want and that such additions should be
banned or must be clearly labelled.

Unfortunately that will not solve the
deeper problem: we will want the sweet, savoury and delicious food we now
can create. It is impossible to effectively ban good cooking and cheap
food. Appetite is something deeper and stronger than reason (which
after all was developed by evolution in order to make us better at
finding stuff to eat).

What we can do is to investigate ways of
enhancing our self-control and how to turn our appetite towards what
is good for us. Ironically, if we discover effective means to achieve
such control the discoveries are likely to be just as risky to us as
better ways of being overwhelmed by appetite: any tool that
controls motivation is a dangerous tool. Yet it would be so tempting
I doubt we could resist it.

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