Boy, do I
love a fat slice of pizza or three. When that meaty, cheesy, tomatoey aroma
hits my nostrils and I see that greasy cardboard box open and reveal those
glistening triangular slices, I know I’m going to have a hard time controlling
myself. Put me in front of an unlimited supply and I might just eat myself into
a rather sorry state. At the same time, I know eating pizza isn’t healthy, and
the stakes couldn’t be higher: This is exactly the type of food that ends up
making us overweight, pushing us toward metabolic disease, sapping our vigor,
and ultimately shortening our lives. So why do I do it? Where does the siren
song of craving come from?
To
understand where cravings come from, first we have to understand what they are,
so I’ll start with a definition: A food craving is a state of heightened eating
motivation that is directed at a specific food. It’s not the same as hunger,
which is a nonspecific motivation for calorie-containing food in general.
Craving and hunger are distinct motivations that emerge from different brain
circuits in response to specific cues.
This
brings us to our next key question: Where does motivation come from? This might
sound like a metaphysical question, but in fact it is a concrete one that has
already been largely answered by science. The human brain is hard-wired to be
motivated by certain key goals that supported the survival and reproduction of
our ancestors. These are things like sex, water, social support, physical
comfort, and of course, food. Over the course of our lives, we learn how to
accomplish these goals in ever-more effective ways, and one of the key
mechanisms of that learning process is a powerful molecule called dopamine.
Here’s how
it works. When one of your behaviors accomplishes a hard-wired goal, your brain
releases dopamine in specific areas including the ventral striatum, and this
causes you to become more likely to execute the same behaviors the next time
you find yourself in the same situation.
In
technical terms, we say that your behavior has been reinforced. What you
experience is that the sensory cues of the situation, such as its appearance,
sounds, smells, tastes, and location, become motivational triggers that ignite
your desire to repeat your previous behavior. The larger the surge of dopamine,
the more motivated you will be the next time you encounter those cues. This is
well illustrated by highly addictive drugs like crack cocaine and
methamphetamine, which cause an immense release of dopamine that motivates
drug-seeking behaviors so strongly that they can supersede constructive
behaviors like eating, sleeping, holding a job, and maintaining personal
relationships. Addiction, at its core, is a very strong craving.
How does
this process work for food? At Brooklyn College, a researcher named Anthony
Sclafani has been quietly chipping away at this question for the last thirty
years, and along with other researchers in the field, he’s made considerable
progress. In 1988, Sclafani showed for the first time that starch infused
directly into the stomach of a rat can cause the rat to develop a preference
for an odor that it detects simultaneously in its nose. In other words, if you
give a rat cherry-flavored water while it gets an infusion of starch into its
stomach, it learns to prefer cherry-flavored water over other flavors of water
(recall that most “flavors” are actually odors). This suggested that starch in
the stomach produced a reinforcement signal in the brain.
Further
research showed that starch isn’t the only thing that reinforces behavior:
Sugar, fat, and protein were also effective. Follow-up studies by Sclafani and
others demonstrated that sensors in the mouth and small intestine detect the
glucose, fructose, fatty acids, and amino acids in starch, sugar, fat, and
protein and send a signal to the brain that releases dopamine. And the more
concentrated the nutrients, the greater the surge in dopamine. Although we may
like to believe that we have nothing in common with rats, research has shown
that the same process happens to us.
What this
tells us is that the brain isn’t simply wired to respond to food in
general—it’s wired to be motivated by specific food properties, and the more
concentrated they are, the higher the level of motivation. Presumably, these
instinctive drives evolved to guide our distant ancestors to the foods that
kept them alive and fertile in a challenging environment. This worked out well
when calorie-dense foods were hard to come by and required considerable effort
to obtain, but that’s not the world we live in today. In the modern world, we
still carry the powerful instinctive drives of our distant ancestors, but the
food properties they make us crave are far more abundant and easier to get than
ever before in human history.
And that
brings us back to pizza. I don’t remember the first time I ate pizza, but it
must have been as a young child, and I have a pretty good idea of how it went.
As the first slice traveled down my esophagus and into my stomach, then into my
small intestine, sensors began reporting back to my brain, and here’s what they
said: This food is an outstanding source of fat and carbohydrate, and a pretty
good source of protein. Dopamine began to surge, and my brain made careful note
of the meaty, cheesy, tomatoey aroma and flavor, the glistening, triangular
appearance of the slices, and the greasy cardboard box. These associations
strengthened over the course of my next few times eating it, until the smell or
sight of pizza alone was enough to get my saliva flowing. And that’s how I
react to this day.
This
doesn’t explain idiosyncratic cravings such as when a pregnant woman wants a
pickle with peanut butter on it and suddenly hates tomatoes—I’m not sure
science will ever understand that. But it does explain the cravings for
fattening, calorie-dense foods that are so common in our everyday lives and
affect many of us in profoundly negative ways. These are foods like chips,
fries, bacon, cookies, cake, ice cream, and chocolate, and the reason we crave
them is that they deliver exactly what our brains are instinctively looking
for: Concentrated starch, sugar, fat, salt, and protein.
Chocolate
is the most frequently craved food among women, and it’s also a common craving
for men. From the brain’s perspective, this isn’t hard to understand. Chocolate
is not only a highly concentrated source of fat and sugar, but it has another
trick up its sleeve that pushes its craveability into the stratosphere: A
habit-forming drug called theobromine. Like its cousin caffeine, theobromine is
a mild stimulant that acts on the same brain pathway as dopamine. This drug
accentuates fat and sugar’s natural ability to spike dopamine signaling, which
in many people results in powerful cravings, and in a few, addiction-like
behavior.
Understanding
cravings allows us to manage them more effectively. Since cravings are driven
by food-related sensory cues such as the sight and smell of tempting foods, the
most straightforward way to beat them is to avoid exposing yourself to those
cues. If tempting, unhealthy foods aren’t available in your personal
surroundings, not only will they be harder to eat, but you’ll be less likely to
crave them. That’s why pizza rarely crosses my mind, despite the fact that I
crave it when it’s around. I don’t put myself into situations that are likely
to trigger the craving: I rarely order it; I rarely go to restaurants that
serve it; and I rarely see TV ads that display images of it. Still, every now
and then I indulge myself— consequences be damned.
