Anchorage Daily News

A new research project involving hamsters brings some potential bad news for dieters. It appears that to lose weight you have to punish yourself twice: Not only should you eat less, but you should eat more of the same foods. In other words, if you wish to shed pounds, put limits on both quantity and variety in your diet.

On one level, this is a no-brainer. Waistlines seem to expand in direct proportion to our budgets. Being bored with a food item means you eat less of it. "In humans," says Gwen Lupfer-Johnson, an assistant professor of psychology at UAA, "changing the available food typically increases motivation to eat." That's why people stuffed with beef stew often find room for chocolate cake, she says.

But this link between a greater variety of food and increased appetite is also among the tentative conclusions to come from scientific studies of the eating habits of dwarf hamsters conducted by Lupfer-Johnson and a UAA colleague, Eric Murphy, and three undergraduate students at the university, Jennifer LaCasse, Linda Blackwell and Sarah Roberson.

Their studies focused on how flavor variety is related to one's motivation to eat.

In one experiment, for example, hamsters earned either chocolate- or bacon-flavored pellets in a chamber known as a "Skinner box." When receiving a single flavor, the hamsters decreased their rates of responding over the course of a session more quickly (and therefore earned fewer food rewards) than when the pellets they earned varied between bacon and chocolate.

Dwarf hamsters, an undomesticated species of hamster, turn out to be the ideal subject for research into eating habits because they hoard the food pellets they earn in their expansive cheek pouches rather than consume them on winning them. The hoarding rules out factors like satiety to explain decreased lever-pressing, since the hamsters haven't yet eaten their pellets by the time they're turning away from the levers.

A related project conducted with the dwarf hamsters, funded by the National Institute of Diabetes and Digestive and Kidney Disease, began last summer under the direction of Ian van Tets, also a UAA assistant professor of biology. In the summer project, instead of manipulating the variety of the reinforcing pellets that were earned in the Skinner boxes, Lupfer-Johnson and her diabetes institute student Emily Nosce altered the variety of the hamsters' regular diet, which was freely available to them in their home cages at all times, providing some hamsters four flavors and some just one flavor.

The flavored pellets were nutritionally identical. Results indicate that the hamsters gain weight faster when four flavors are available to them than if they have only one.

Lupfer-Johnson has been working with dwarf hamsters since she was a graduate student at Kansas State University, which she attended in 1998-2004.

There she conducted investigations of the social influences on their diets and found that the hamsters "develop preferences for foods found in other hamsters' hoards," she says.

For her graduate dissertation, she videotaped some of their feeding-related social behaviors, including a hamster smelling another's cheek pouches.

Lupfer-Johnson, Murphy, LaCasse, Blackwell, and Roberson will present their findings at the 35 th Annual Meeting of the Association for Behavior Analysis next May in Phoenix.

The data, Lupfer-Johnson said, will be used to evaluate dwarf hamsters as a model for human obesity.

Peter Porco is an editorial associate and writer at the University of Alaska Anchorage.

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