One blueberry muffin MUST be equal to one serving, right? But is this muffin the size of a small homemade muffin or one from a store? Many commercial muffins are the size of two to three homemade muffins. All those additional calories (from fat and sugar), add up to almost 400 calories.

So what is a serving size, anyway?

Confusion over serving sizes has contributed to the growing problem of obesity in the United States. It seems that serving sizes are getting bigger (think "supersized" meals) with our desire to eat them. We can consume a low-fat diet that is high in fruit, vegetables and whole grains and still gain weight unless we are knowledgeable and careful about serving sizes.

The easiest way to determine serving size is to read the nutrition facts on food labels. For example, one serving equals five Ritz crackers, 16 Wheat Thins or 55 Goldfish. If you like volume, choose the Goldfish. One cup of Raisin Bran, 2/3 cup of Great Grains granola-type cereal and 3/4 cup of Life are all one serving of cereal. Instead of pouring the same amount of cereal into your bowl regardless of type, measure your portion based on the serving size listed on the label. Most of the time, when we start to read labels for serving sizes and to consume appropriate amounts of food, we take in fewer total calories and lose weight.

For foods without labels, use these handy visual reminders:

• Three ounces of cooked meat, poultry or fish, the recommended amount at a meal, is about the size of a deck of cards or the palm of a small woman's hand.
• One cup of cooked rice, pasta or vegetables is about the size of a small fist; a large fist can be as much as two cups. Measure a cup of cooked rice at home, then compare it with your fist -- a "handy" reference.
• One ounce of cheese is about the size of four stacked dice.
• One teaspoon of mayonnaise, peanut butter or salad dressing is about the size of the tip of your thumb, from the end of the thumbnail to the first joint. Guidelines suggest limiting added fats such as margarine or mayonnaise to one teaspoon per meal (each teaspoon contains approximately 30 calories).
• One ounce of nuts or raisins is the amount you can hold in your cupped hand, if you have a small hand.