Rolls has eaten about three quarters of her hummus, gruyere, sprout, lettuce and tomato sandwich, and she's bored with it. Sick of the texture and taste. Rolls has reached what she calls "sensory-specific satiety." In other words, her taste buds have maxed out and crave something different.

An associate professor in the department of psychiatry and behaviorial sciences at the Johns Hopkins University School of Medicine, Rolls is an appetite researcher. Through her experiments, she delves into what makes people feel full -- or what makes them want to eat more. Her findings have interesting implications for weight control and nutrition.

But right now, Rolls wants a piece of cake. So she gets back into the cafeteria line and grabs a piece of chocolate cheesecake.

In doing so, Rolls may personify her clinical results. Her findings suggest that when a food becomes monotonous -- in this case, the hummus sandwich -- appetites are revived simply by introducing a new one. That's why we always have room for chocolate truffles, even after an enormous French meal.

"Variety is a great stimulus," says Rolls.

It also means that if foods within a category are different enough in odor, appearance and texture, appetites may continue to be stimulated. After the chocolate truffles, you still may be tempted to try a floating island.

In one study of normal-weight individuals conducted by Rolls, people ate 15 percent more pasta during three successive courses when each course had a different-shaped pasta than when the three courses consisted of only one shape.

This doesn't mean that eating a boring diet ensures that you'll eat less. Weight loss crazes that focus on a few foods, such as grapefruit, may work in the short run, says Rolls. But ultimately, when faced again with variety, the weight is inevitably regained.

Variety isn't dangerous as long as the choices are nutritious ones. In fact, variety can help you stick to a healthful regime; if your diet gets too boring, you may be more tempted to abandon it and seek high-fat choices, Rolls says.

Aside from her interest in variety, Rolls has also conducted experiments in compensation to determine whether people who consume low-fat foods eventually make up for the calories.

In a collaborative study, Rolls and Richard Foltin, assistant professor of behavorial biology at Hopkins, offered subjects four different lunches for three days each. Two lunches contained approximately 800 calories, but one was high in carbohydrates and the other was high in fat. The other two lunches contained about 400 calories, but one was low in carbohydrates and other was low in fat. Subjects were free to choose what they ate during the rest of the day.

What the researchers found was that people ended up taking in the same number of calories every day of the study regardless of which lunch they selected. They didn't compensate for fat; when they preferred the high-fat lunch, they didn't eat less fat later in the day. As a result, even though they consumed the same number of calories over the course of the day, a higher percentage of their calories came from fat when they ate the high-fat lunch than the low-fat lunch.

This demonstrates, Rolls said, that low-fat foods may help decrease consumption of fat but may not necessarily minimize calories. Even so, if a smaller proportion of calories in the diet come from fat, weight loss can still occur, according to Rolls.

The moral: Don't narrow your choices to avoid temptation. Expand your list of acceptable items to include nutritious alternatives that are just as tasty.

Eating Right appears on alternate Tuesdays.