It's that time of year again. With Thanksgiving just around the corner, the holiday season is about to begin, punctuated by Hanukkah, Christmas, Kwanzaa and the grand finale, New Year's Eve.

With so many opportunities to celebrate -- plus the stress and joy of travel and family gatherings -- it's no surprise that a National Institutes of Health study found the holiday season often makes unwanted contributions to your weight.

How much weight you gain seems to depend on your starting point. The 2000 study, published in the New England Journal of Medicine and written by Jack Yanovski and colleagues at the National Institute of Child Health and Human Development, showed that people at a healthy weight put on just under a pound between Thanksgiving and New Year's.

But it was a different story for those who were already overweight. (That's now two-thirds of adults; about half of those carrying too much weight are categorized as obese, according to the latest figures from the National Center for Health Statistics.)

The study found that the overweight and obese -- are you sitting down? Well, now get up -- add an average of five pounds during the holidays. What's more, the researchers discovered that this extra weight often isn't shed by spring. So it's five pounds this year, five more next. Do the math, and things get scary pretty fast.

With all that in mind, let the fourth annual Lean Plate Club Holiday Challenge begin.

The Holiday Challenge is not about dieting or trying to lose weight. This is a difficult time of year to make a vow to change your life and lose pounds.

The goal is simply to keep the bathroom scale stable through the holiday season, to make sure that what you weigh on Jan. 1 is no more than what you weigh today. If you can accomplish that, you'll have escaped unscathed from the part of the year most likely to add pounds to your frame. Beat the challenge, and you can decide whether to make more changes in your lifestyle and cut some weight in 2005.

As always, we'll be providing weekly tips and goals to help you stay the course. Look for charts, lists and other handy tools, which will be updated both in the Health section and at www.washingtonpost.com/leanplateclub.

Last year, Lean Plate Club member Amy Ginn, 30, a lawyer with the National Labor Relations Board, approached the holidays with some trepidation. Ginn had lost 12 pounds before Thanksgiving and worried that the holidays might bring them back.

"I did last year's Holiday Challenge and it helped a lot!" she wrote in an e-mail. "I really focused on the suggestions to be prepared for parties and events. I made lower-calorie, healthier dishes to take to any events that I attended. I limited my holiday baking (no kids to disappoint, so that helped). . . . The 12 pounds stayed gone and, beginning in January, I started a regular exercise routine, started counting calories, and lost another 24 pounds to put me solidly in a healthy weight range. Because I want to stay there, I'm looking forward to participating in this year's Holiday Challenge as well."

Before we get into the weekly routine it's important to prepare yourself, and your kitchen, for what lies ahead. So this week's goal is to get ready for the challenge. Here's what Lean Plate Club members -- and experts -- recommend.

Assemble your tool kit. During the challenge, you'll need to get yourself moving a little more and control what you eat. So gather up what you need to support that: Do you have comfortable walking shoes? Workout clothes? How about measuring cups and a kitchen scale? A player for listening to music or books while you walk, run or work out? And consider clearing a place to exercise in front of the TV. Or maybe dust off that exercise bike, rowing machine or other home equipment and make sure it's ready to use.

Check your starting weight -- or size. If you plan to maintain your weight, you'll obviously need to know your starting point. That means climbing on the bathroom scale, scary as it can be for some. Research from the National Weight Control Registry shows that those who track their weight are more likely to maintain it. There's a weight chart you can use to track your weight changes, provided on this page and also downloadable at www.washingtonpost.com/leanplateclub.

If you'd rather avoid dealing with the big numbers on the scale, measure your waistline and keep tabs on that throughout the holidays. Or you can even use a belt or a piece of clothing -- say, a skirt or pair of trousers -- to monitor your bodily changes (or lack thereof). If the clothing gets tighter, well, no need to spell out what that means.

Find your caloric balance. So far, scientists haven't discovered a way to circumvent the laws of thermodynamics. If you eat more calories than you burn, you'll gain weight. So, for the holiday season, you'll need to estimate how much is going in and how much is going out.

The first step is determining what calorie level is likely to keep your weight stable. (Another reason why you need to step on the bathroom scale.) The Dallas Dietetic Association offers a free online calorie calculator that applies to anyone age 19 or older at www.dallasdietitian.com/rd/calorie.htm. It will estimate how many calories you're likely to burn during a day, based on your weight, height, activity level and so on.

Or you can use this simple equation, drawn from "Nancy Clark's Sports Nutrition Guidebook" (Human Kinetics): Take your weight in pounds and multiply by 10. That equals your "baseline" calories. (For someone who weighs 150 pounds that would be 1,500 calories just for breathing, keeping your heart beating and other bodily basics.) Now add 20 to 40 percent more for the daily activities of a sedentary lifestyle, which the majority of us lead. That results in 1,800 to 2,100 calories per day, which is the average intake suggested for most adults.

Most people will need to keep their calorie intake toward the lower end of that range. But if you regularly log more than 7,000 steps daily -- or if you're in an active job that keeps you moving throughout the day -- then the higher end of the calorie scale may be fine. If you're really active in your daily job or your daily exercise rivals that of an Olympic contender, then you can add 40 to 80 percent more calories rather than 20 to 40 percent, depending on activity levels.

Track what you eat. Yes, it can be a chore, but it's the only way to be sure you're staying in caloric balance. You want to be able to enjoy some egg nog, don't you? You'll need to tally how much you've eaten during the day, or the week, to know how much holiday splurging you can do on potato latkes, buuche de Noel or other holiday treats.

So use the food form available at the holiday challenge Web site, or just use a notebook and pen to jot down what you eat and estimate the calories. You'll likely need to measure and weigh food, too, at least at the beginning, so get out those measuring spoons and cups now and put the kitchen scale out on the counter.

To determine how many calories are in that turkey sandwich or pecan pie, you'll need to get a source of calorie information. "The Doctor's Pocket Calorie, Fat and Carbohydrate Counter" (Family Health Publications; $6.99) is the one used by the University of Pennsylvania's Weight and Eating Disorders Program in Philadelphia.

There are some more high-tech ways to estimate calories, too. The U.S. Department of Agriculture (USDA) offers a free database for looking up the caloric content of thousands of foods at www.nal.usda.gov/fnic/foodcomp. You can use this tool online or download it for free to your computer or PDA.

Or you can use one of the growing number of electronic programs that track both calories in and calories out. Some, such as Nutridiary (www.nutridiary.com), Fitday (www.fitday.com) and Nutritiondata.com (www.nutritiondata.com), are free.

Healthetech (www.healthetech.com) offers for free a downloadable two-week trial of its Balancelog weight management program. Ditto for Calorie King (www.calorieking.com). Dietpower (www.dietpower.com) also offers a free, two-week trial for your computer. There's nothing to stop you from going from one free trial to another to compare systems.

Take stock of your pantry. And while you're at it, your fridge. What's lurking there may undermine your efforts, so now's the time to eliminate needless temptations. Swap high-calorie, high-fat, sugary food for great-tasting but healthy stuff. So toss, share or give away the cookies, chips, candy and other foods you'd rather not see in a moment of weakness. Replace them with such alternatives as: Popcorn and pretzels for savory snacks. Soups for late-afternoon pick-me-ups or high-volume meals that will help you feel full with fewer calories. Hot cocoa and (skim milk) puddings are other good alternatives. Make your own trail mix with dried fruit, whole grain unsweetened cereal and slivered nuts. Stock up on baby carrots, celery and bell peppers -- great for dipping into hummus, salsa or other low-impact dips.

Plan now how to fit in more physical activity. Enlist a partner for walks or trips to the gym. Whoever doesn't show has to buy the next round of (skim) lattes. Get these on the calendar now, before the pace gets too hectic. Or plan a holiday event such as ice skating, caroling or chopping down a Christmas tree. Even stringing lights burns a few calories.

Want to know how many? Check out www.caloriesperhour.com or www.nutritiondata.com. Then record your calories burned on the same sheet that tracks what you eat. Or simply jot it on your daily planner or calendar.

The free, Web-based Interactive Healthy Eating and Physical Activity Index, run by the U.S. Department of Agriculture, will store nearly three weeks of food records and activity logs. The more calories you burn, the more you can indulge. http://209.48.219.53.

Next week and each week until the new year, check back with the Lean Plate Club for specific eating and physical activity goals to help you navigate the season.

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Share Your Tips or ask questions about healthy nutrition and activity when Sally Squires hosts the Lean Plate Club online chat, from 1 p.m. to 2 p.m. today, on www.washingtonpost.com. Can't join live? E-mail leanplateclub@washpost.com anytime. To learn more, and subscribe to our free e-newsletter, visit www.washingtonpost.com/leanplateclub.

Last year's challenge helped Amy Ginn maintain her 12-pound weight loss.