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Psychologist Deirdre Leigh Barrett | Meeting the Minds

The instinct to become overweight

Deirdre Leigh Barrett explores obesity and fitness from an evolutionary standpoint. Deirdre Leigh Barrett explores obesity and fitness from an evolutionary standpoint. (PAT GREENHOUSE/GLOBE STAFF)

Deirdre Leigh Barrett has one piece of advice for people struggling with their weight: Don't listen to your instincts.

Humans are hard-wired to prefer the kinds of foods that were scarce on the savannas where we evolved, says Barrett, 53, a psychologist with Cambridge Health Alliance. But now that those foods are readily available, if we listen to our instincts, we'll all be obese.

"Most psychological advice about how to diet is out of synch," said Barrett, who published her ideas this summer in a book titled "Waistland: A (R)Evolutionary View of Our Weight and Fitness Crisis." "There's a huge disconnect between our modern environment and what our instincts are telling us."

Instead of listening to those urges, she argues, we need to exert an unnatural effort to reject the call of the cheeseburger. And that means dropping refined foods cold turkey, she argues, rather than rewarding yourself with regular treats.

"Too many bad psychology books tell you to give yourself food rewards - a small order of fries," Barrett said. "You wouldn't tell a heroin addict to cut back or only do it on weekends."

It's harder to eat half an order of fries, she said, than to give them up entirely - at least after the first few days.

Barrett, also an assistant clinical professor at Harvard Medical School, hatched the idea for her book from her clinical work, which has increasingly involved patients hoping to lose weight and those struggling with eating disorders.

"When I was doing health psychology, the most common referral from physicians used to be smoking cessation," she said. A veteran of Harvard's Behavioral Medicine program, she spent years studying the efficacy of hypnosis in medical treatment, and has authored several books on the subject.

But in the past few years, there's been a dropoff in requests for help quitting smoking and "a huge increase in people coming in because they need to lose weight," she said.

While weight loss programs like the Atkins Diet are pointing people towards a diet more in tune with our hunter-gatherer past, Barrett thinks diets can't be successful without understanding our psychological predisposition to junk food. Regardless of culture, she said, people across the planet respond to the same stimuli of sugar, salt, and fat. Desserts, for example, catch on very quickly between people from different societies. So do McDonald's products, which, while taking on local forms, like flatbread instead of hamburger buns, are more or less the same around the world.

"There's something very appealing about fats and carbohydrates," she said.

Of course, there are lots of competing - and possibly complementary - explanations for the current epidemic of obesity.

"I would say the issue of calorie intake and environment is complex," said Alice H. Lichtenstein, professor of Nutrition Science and Policy at Tufts University. Just as important as the ready availability of junk food, "are all the technological advances that have decreased our need to expend calories - from not having to get up to change a TV channel or run after an animal to kill, butcher, and cook it to not having to chop wood to stay warm."

Still, Barrett's nutrition advice ends up looking a lot like Lichtenstein's and others': Eat lots of fruits, vegetables, whole grains, fish, and lean meat and avoid trans fats, white flour, and processed sugar. Of course, exercising as much as a hunter-gatherer doesn't hurt, either.

Hometown: Cambridge.

Family: Her mother in Tennessee. Barrett grew up in the town of Oak Ridge, a community of physicists working on the atomic bomb project. "It perhaps made me think scientifically, but it put me off the formal, natural sciences. I had a little too much exposure to them."

Hobbies: "Psychology and writing interest me so much that I don't have a strong need to be doing something 'fun.' " Otherwise, she's a movie buff.

On being hypnotized: "I'm moderately susceptible [to hypnosis]. I can have an interesting experience with it, but it's not a profound, radical state."

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