Here’s the diet plan for 2007: You can eat anything you want — if you can control the portion size.

Most Americans have a distorted sense of portion size. We typically underestimate how much we eat by 50 percent. We eat a bran muffin and think we’re doing the right thing, but that muffin should be the size of a tennis ball, not a softball.

Twenty years ago, we were drinking 6\x-ounce bottles of soda (85 calories). Today the typical bottle is 20 ounces and a whopping 250 calories. A fast food cheeseburger in 1986 contained 333 calories. Today, it’s 590 calories, according to “Complete Food and Nutrition Guide” by Roberta Larson Duyff.

Statistics from the U.S. Department of Agriculture show that Americans’ total daily caloric intakes are 148 calories higher than they were in 1980. This amount leads to a weight gain of 15 pounds every year.

The experts credit that to “portion distortion.”

A proper portion is the serving size recommended by the U.S. Department of Agriculture, which also developed the food pyramid.

For instance, the food pyramid recommends six to 11 servings of whole grains daily. A recommended serving of whole grains would be one slice of bread or ½ cup of rice or pasta.

People often confuse the recommendations to mean portions with no regard to size, according to the Department of Health and Human Services’ National Institutes of Health. Larger portion sizes mean more calories. And more calories lead to weight gain, regardless of the source of the calories — fat, protein or carbohydrate.

Registered dietitian Fran Williams of Richmond, Ky., teaches portion sizes by explaining to her clients at Nutri-Style, a division of Dietary Consultants Inc., how to “eyeball” the correct serving size.

Williams uses common items such as dice, a box of dental floss, a shot glass, a deck of playing cards, a baseball, a softball, a tennis ball and a golf ball for visualizing portions.

Clients who want to lose weight often look to Williams for a diet plan.

“First of all, you shouldn’t follow a diet anyway. There’s more harm done losing weight, stopping the diet, and gaining back even more weight. It’s better to make gradual changes that result in long-term losses,” she said.

Williams teaches her clients that there are no bad foods. “We just have to make wiser choices and think of moderation, balance and variety — and exercise,” said Williams, who is also a personal trainer.

According to a survey conducted by the American Institute for Cancer Research, most Americans (78 percent) still think that the kind of food they eat is more important in managing their weight than the amount of food they eat.

Americans are concentrating too much on cutting fat, or relying on fad diets that restrict carbohydrates, sugar or some other nutrient. Studies reveal that these strategies fail to address the issue of total calories consumed, as well as overall good nutrition.

People can lose weight simply by learning portion control.

When we sit down to a meal, half of our plate should contain fruits and vegetables. One-fourth should have whole grains, and protein should take up the remaining one-fourth.

The portion of meat, poultry or fish should be about the size of a deck of playing cards, the palm of a woman’s hand or a computer mouse. One serving (Z\x cup) of fruit, vegetables, pasta or rice should be the size of half a baseball (not a softball).

On packaged foods, look at the serving size measurement on the nutrition label. If the serving size is 15 potato chips, that means one portion is 15 potato chips. When following a recipe, look for the number of servings the recipe makes. If the recipe says “serves four,” that means a serving is one-fourth of the total amount of food that results from following the ingredients’ measurements.

Years ago, dieters simply counted calories. Then we started following the trendy diets touted by celebrities. But the fact is, calories do count. To lose weight, you have to consume fewer calories than you burn each day. To eat more, you have to exercise more.

“Getting started in an exercise program starts with a mixture of cardiovascular training, weight training, as well as good sound nutritional habits,” said Josh Bowen, a personal trainer at Gold’s Gym in Lexington, Ky.

Bowen recommends three to five days of moderately intense exercise a week, with three of those being cardiovascular for 30 to 60 minutes and at least two days of strength training, hitting all major muscle groups in the process (upper and lower body).

Depending on the goal, some can walk, swim, bike or climb stairs. An out-of-shape person with some health issues should perform brisk walking three to five times a week to utilize the fat burning zone and incorporate exercise into his or her lifestyle, Bowen said. As one becomes more “trained,” a person can increase the intensity of the exercise.

• Fresh fruit or vegetables: 1 cup• Canned fruit or cooked vegetables: ½ cup• Starchy vegetables or dried beans: ½ cup• Bread: 1 slice• Dry cereal: ¾ cup• Cooked cereal: ½ cup• Rice or pasta: ⅓ cupDairy products: 1 cupLean meats, chicken and fish: 3 ouncesOil, margarine or butter: 1 teaspoonSOURCE: AMERICAN DIETETIC ASSOCIATION

These tips will help you control food portions.<B>At home</B>• Measure out single servings on your plates and bowls, and remember what they look like. Figure out how many servings should make up your personal portion, depending on whether you need to lose, gain or maintain weight.• Avoid serving food “family style.” Serve up plates with appropriate portions in the kitchen, and don’t go back for seconds.• Never eat out of the bag or carton.<B>In restaurants</B>• Ask for half or smaller portions. (Don’t worry if it doesn’t seem cost-effective; it’s worth it.)• Eyeball your appropriate portion, set the rest aside, and ask for a doggie bag right away.• If you order dessert, share it or choose a healthier option such as fruit.SOURCE: American Institute for Cancer Research