WHY do people overeat?

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From the Journal " Obesity surgery " :

Study Offers Clues to Why People Overeat

Published: June 10, 2009

People usually gain weight because they overeat, but what makes them overeat? A

new study suggests that obese people have a different physiological response to

food: they continue to salivate longer in response to a new taste than do people

of normal weight.

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, said Dale S. Bond, a

study author and assistant professor of research at The Miriam Hospital in

Providence, R.I.

But among very obese people in the new study, all of whom were candidates for

bariatric surgery, the decline in saliva in response to a stimulus — in this

case, lemon juice — was slight and occurred much more gradually than among those

who were of normal weight, researchers said.

The study was published online in the journal Obesity Surgery.

" This is basically saying that there is a difference in how we respond to food

physiologically depending on our weight status, " Dr. Bond said. " It suggests

that this habituation process is impaired in people who are obese. "

" They're not as sensitive to those feelings of fullness, and as a result, they

continue to eat longer, " he added.

In the study, researchers recruited 34 obese patients who were candidates for

bariatric surgery and 18 people of normal weight for comparison. The scientists

placed cotton rolls on each side of the mouth and under the tongue of each

participant.

Then, after measuring the baseline levels of saliva by placing a small amount of

water on the volunteers' tongues, they conducted 10 lemon juice tastings at

regular intervals and measured the salivary changes that occurred.

Although the groups did not differ in their baseline responses to the water

stimulus or in their initial responses to the lemon juice, the normal-weight

participants experienced a greater decrease in salivation over time in response

to the lemon juice, while the responses of the bariatric surgery candidates did

not decrease significantly.

" It's going to be longer before they stop eating, " Dr. Bond said of the

protracted salivary response.

But he noted it is not clear whether the slower habituation response is a cause

of obesity or a feature of it.

" What we don't know is whether obese people show this different level of

responding before they become obese, or if it is something that happens as you

gain weight, and whether it changes with weight loss, " he added.