Scientists (Sort Of) Explain Why We Overeat

A new study may shed light on why obese people overeat, but, as Dr. David Kessler explains to Salon, most people struggle with overeating regardless of their size — and the problem may be more mental than physical.

The study showed that obese people salivated longer than the non-obese in response to a new taste. Study author Dr. Dale Bond explained the implications of this result:

Saliva production tends to decline in most people once they've gotten used to the taste of a certain food and had enough of it. The process, called habituation, is associated with a feeling of fullness.

Although more research is needed, it seems that people struggling with obesity may not be receiving mental cues — the feeling of being used to a new taste, and of being full — as quickly as people who aren't obese. Thus they may keep eating longer. This result is in line with the view of Dr. David Kessler, who believes overeating is a mental problem, similar to addiction. He tells Salon's Katharine Mieszkowski:

In people who have a hard time controlling their eating, their brain circuits remain elevated and activated until all the food is gone. Then the next time you get cued, you do it again. Every time you engage in this cycle you strengthen the neural circuits. The anticipation gets strengthened. It's in part because of ambivalence. Do you ever have an internal dialogue? "Boy, that would taste great. No, I shouldn't have it. I really want that. And I shouldn't do it."

That sort of ambivalence increases the reward value of the food.

While overeating is affected by factors like the amount of fat, sugar, and salt in food, and the number of chews per bite (the fewer chews, the more we overindulge), Kessler says its true cause is what's going on in our heads. The reason diets don't work, according to him, is not that the body returns to a certain set point — it's that the brain does. He says,

Sure, I can take you out of your environment. I can give you meal replacements, or you can white-knuckle it, and for 30 days, 60 days, 90 days, resist eating a lot of food, and you can lose weight, no question about that.

Now your diet's over. I put you back into your environment. You still have that old learning, that old circuitry. What's going to happen? You're going to get bombarded with the cues again and you're going to gain it back if you have not laid down new circuitry and new learning on top of that old circuitry.

But why is this circuitry a problem now, when it wasn't forty years ago (Kessler says that in the 1960s, people's weight remained stable throughout their adult lives)? Kessler's answer isn't totally satisfying:

We're eating in a disorganized and chaotic fashion. And we're being bombarded with the cues.

We make food into entertainment. We make it into a food carnival. Go into a modern American restaurant: the colors, the TVs, the monitors, the music. You do it with your friends. We've taken sugar and added all these multiple levels of stimuli. What do we end up with? Probably one of the great public health crises of our day.

Of course, we didn't have TVs in restaurants forty years ago. But food has been part of entertainment and celebration, and eating something people do with their friends, for a very long time. Looking for a "food carnival"? Try Carnival. So while Dr. Kessler's insights — and the findings about overeating and saliva — are interesting, its doubtful they're the whole story.

Why We Can't Eat Just One [Salon]
New Study Suggests Why Obese People Overeat [Diet Blog]