In 1985, bagels were about 3 inches in diameter and had about 140 calories. Today's bagels are twice as big and pack an additional 210 calories.

Pepperoni pizza? Two slices are big enough to account for nearly half a day's worth of calories at 850. That's 350 more calories than slices 20 years ago, according to the National Heart, Lung and Blood Institute, one of the National Institutes of Health.

Even popcorn isn't safe from the so-called portion distortion of the 21st century. In 1985, a 5-cup bag had 270 calories, compared to today's 630-calorie tub.

"As a country, we've really lost sight of what a normal portion is," says Katherine Beals, director of the University of Utah's Nutrition Clinic. "Normal to us is supersize anywhere else."

Those extra calories add up to extra pounds.

The potential to overdo it is even greater during the holidays, when research shows we're most likely to gain weight with such an abundance of high-calorie, high-fat food available.

So in our Sugarplum Challenge to maintain weight through the new year, this week's goal is to pay attention to portion size at home and when dining out.

This builds on last week's goal (keeping food and exercise journals), which you should keep doing.

Successful weight loss and weight management depends on three key ingredients: food quantity, food quality and physical activity, says Steven Aldana, a professor of exercise science at Brigham Young University.

"I would say food quantity and quality are the bigger of the three, and that's coming from the exercise guy," he says.

Clara Reyes, 72, discovered the importance of food quality and quantity two years ago when she attended Salt Lake County-offered classes on dining out. They covered everything from portion size to cooking strategies. The knowledge has made Reyes a smarter eater.

"I'm more conscious of what I should be eating and how much," the Murray resident says. "I'm trying so hard because I'm trying to control my diabetes."

For our goal, we're talking about more than measuring a 3-ounce filet of salmon for dinner or a half-cup or raisins for your afternoon snack. Like it or not, we tend to eat for volume. Put a plate of pasta in front of us, and we pick away at it well beyond the point of feeling full. It may be more effective, then, to pay attention to portions based on the types of foods we eat, according to researchers at Penn State University.

Several of their studies show people who eat low-calorie foods have better results at losing and maintaining weight than people who eat the same amount of calories but in high-calorie foods.

The difference is volume. We can eat more of the low-calorie foods.

In one study, more people lost weight by eating low-calorie food than people who were advised to reduce fat intake and portion sizes.

A study published in the journal Obesity Research this year showed that obese people who ate one or two servings of low-calorie soup lost 50 percent more weight than did obese people who ate the same amount of calories in high-calorie snacks. Because the snacks were high in calories, they tended to be smaller in volume, leaving subjects hungry.

So apply that concept during the holidays. Eat a salad before dinner and you'll eat less of the higher-calorie main course. Eat yogurt with fruit and nuts for a midmorning snack, and you'll eat less at lunch.

Low-calorie foods with high water content - fruit and vegetables are at the top of the list - seem to do the best job of filling us up because we can eat more of them and still feel satisfied.

That's a good thing where weight loss and maintenance is concerned.

"We're fatter now than any other time in recorded history and we have more diabetes now than anytime in state history," Aldana says. "This is what we have become."

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If you're trying to maintain your weight during the holidays and are willing to share your triumphs and struggles,contact Ronnie Lynn at rlynn@sltrib.com or 801-257-8722.

Tribune's Sugarplum Challenge: Week 3

Nutrition goal: Watch your portion sizes at every meal and snack. You don't have to eat everything in front of you, especially at restaurants. Eat a salad before the main course, and you'll feel full faster. Save half of the meal for another time.

Fitness goal: Add five minutes of physical activity to your day. If you've been sticking to the past two weeks' goals (getting at least 30 minutes of physical activity on most days of the week), you've been burning calories and creating a fitness base you'll build on from here on out.

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The Tribune's Sugarplum Challenge aims to help readers avoid weight gain during the holidays by offering weekly nutrition and exercise goals. Read previous stories at http://www.sltrib.

com/health.