STEP AWAY FROM THE COOKIES.

We know, it's tough. Barely into the new year, you're already losing your resolutionary zeal. The next few months stretch before you like a dark and icy abyss. And there you are, holed up in the house, which -- dangerously -- also contains cookies. They call to you, softly but urgently, offering to wrap you in their sweet, comforting embrace. What's the harm of just one, you think. OK fine, just three. Or, well ... chompchompchompchompchomp ... just nine. Oops.

Doctors know that cravings for sweets and starches, high-carbohydrate foods, are a classic symptom of seasonal affective disorder (SAD), or its milder cousin "winter blues." It's less clear what causes them.

Is your body trying to tell you something? Do the cravings signal some sort of biological need for carbs, the way thirst signals the need for hydration? In "The Serotonin Solution," author Judith J. Wurtman, founder of a Harvard University hospital weight-loss facility, argues that eating carbohydrates boosts the brain's supply of the feel-good neurochemical serotonin. The cravings reflect the body's need to replenish its serotonin supply; obey by consuming moderate amounts of carbs and you'll boost the brain chemical, feeling cheerier and, ultimately, healthier.

Other experts disagree, including psychologist Larry Christensen of the University of South Alabama in Mobile, who has studied food-craving triggers and the relationship between foods and mood.

"It's a nice explanation, but it doesn't hold up under scrutiny," Christensen said. A high-carb snack can provide a quick lift, but it quickly wears off, "so you go back and do it again." Like a craving for an addictive drug, carb cravings may simply reflect the "reinforcing effect" of that short-term boost, not the key to sustained depression relief.

In fact Christensen's own research has suggested that sugar, at least, can have just the opposite effect.

"For some people I've found that you take away the added sugar from the diet, their depression goes away," he said. (Others in his studies responded similarly to eliminating caffeine.) Note the all-important "some people." Whether an individual is a "sugar responder" is tied to personal body chemistry; Christensen likens it to different people suffering from different allergies -- in other words, your mileage may vary. But "for the people that are sensitive to it, you can get some very dramatic changes in mood."

He recalled one sugar responder whose depression was so severe that she had quit her job, and lacked energy even to perform ordinary household tasks.

"After one week on a no-sugar diet, she chuckled for the first time at dinner," Christensen said. Improvement in mood may not be noticeable for a few days or a week, and "if you don't see a change in two weeks if you're totally eliminating sugar, you're not a responder."

His research focused on sugar specifically, not starchy carbs like potatoes or grains that people also crave. But his sugar prohibition was strict: He asked his subjects not only to avoid sweet snacks (save for a piece of fruit here and there), but to restrict all foods containing added sugar, such as ketchup. "What I have them do is read labels."

Because his research was conducted in the Sun Belt, where winter mood problems such as seasonal affective disorder are relatively rare, he focused on depression in general. But SAD sufferers may benefit from eschewing sugar as well, he said. In any case, it can't hurt -- sugar is unhealthy for a host of reasons in addition to its potential tie to depression. "Sugar is not our friend," Christensen said. "That's the bottom line."

Katy Read • 612-673-4583