Tuesday, May 8, 2012

Unpacking the Neurobiology of Food Reward — and Why Your Brain Is a Cookie Monster

A researcher explains the science of food cravings and what teenage rats can teach us about healthy eating habits.

Chocolate-chip cookies
Creative Commons

If your sweet tooth feels stronger than a mere preference, if it feels like a biological impulse, neurobiologist Dianne F. Lattemann, PhD, can tell you why.

"The preference for sweet tastes is virtually hard-wired in quite a variety of animals," she says. "About as young as you can test an animal or human, we find a preference for sweet tastes.

"In humans, the brain is literally a cookie monster."

Dr. Lattemann, a researcher at the University of Washington and the VA Puget Sound Health Care System, gave a recent lecture at Bastyr University explaining her research into the neurobiology of food cravings. It's a familiar topic at Bastyr, where students study the intersection of food and the brain from a number of perspectives (especially in the Master of Science in Nutrition & Clinical Health Psychology program).

"Dr. Lattemann's work is relevant to understanding obesity," says Lynelle Golden, PhD, chair of Bastyr's Department of Basic Sciences. "We hope her talk will generate additional opportunities for collaboration."

Dr. Lattemann's team studies rats to better understand how brain chemicals respond to food. In the last year they have made progress pinpointing exactly when the desire for sweets is strongest. They've found that, in humans and rats alike, the early-adolescent or "tween" years are when sugar cravings are strongest.

In case you wondered, a tween rat is about 5 weeks old; by 8 weeks rats have completed adolescence. Dr. Lattemann and her research team observed confined rats that pressed a series of levers to release a reward — high-fructose corn syrup, other edibles or simply water. They studied rats that had already eaten their caloric needs for the day so they could investigate "recreational eating," or snacking.  Rats showed more interest in sweet sucrose than in fat emulsions or any other flavorings.

Says Dr. Lattemann: "The bottom line was extremely clear: Sucrose had the dominant effect on self-administration [pressing the levers]. Sugar is a major motivator for us to take in foods."

It's no wonder we've evolved this way, she says, since a jolt of quick energy from sugar can be crucial when food is scarce. But it becomes a problem when sweet foods are abundant. Dr. Lattemann called out the danger of processed foods that include "sneaky sugars." Even a savory food like SpaghettiOs with Meatballs contains 16 grams of sugar in a can, she says.

Middle-school-aged children often find themselves with spending money and new freedom to go out and buy snacks — what Dr. Lattemann calls the "convenience store effect."  (They're also targeted by junk-food marketers.)  Given all that, she says families and schools should do more than limit sodas from school vending machines, although that's a good start.

"I think our data suggest it's probably a good idea to get the high-fat snacks out of those machines as well," Dr. Lattemann told a full room at the April 26 talk.

She added that metabolic problems typically don't show up until later in life. But high-sugar diets are often high-fat diets too, and unhealthy habits developed in adolescence can be tough to break later, she says.

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