What do a tennis ball, hockey puck and deck of playing cards have in common?

This unusual combination represents the equivalent serving sizes of some important food groups in your daily diet.

A portion of fruits or vegetables the size of a tennis ball is the equivalent of one serving, or about 20 percent of the "five a day" recommended servings. Half a bagel the size of a hockey puck represents one serving from the grain food group. Three ounces of protein is about the size of a deck of playing cards, according to Sandra Bastin, Extension food and nutrition specialist at the University of Kentucky College of Agriculture.

"It's important to choose the recommended serving sizes of the five major groups in the food guide pyramid to ensure a good balance of nutritional foods," she said. "The food groups -- bread, fruits, vegetables, meat and dairy -- in the pyramid collectively provide the nutrients essential for a healthful diet. It's easier to watch serving size than count calories."

Knowing the recommended servings for each pyramid food group makes it easier to maintain portion sizes, and thus reduce calories, at meals and snacks, according to Bastin.

General recommendations are six to 11 servings from the bread group, three to five servings of vegetables, two to four servings of fruits, and two to three servings from the milk group. From the meat group, five to seven ounces daily is recommended. Fats, oils and sweets should be used sparingly. Consume only 53 to 93 grams of total fat and just 6 to 18 teaspoons of total added sugars.

The higher numbers of servings total about 2,800 calories a day, which is a good diet for teenagers, active men and very active women. The lower numbers of servings provide about 1,600 calories a day, a maintenance diet for smaller or more inactive people. Pregnant and nursing women, children under two years old and some other groups have special nutritional needs beyond weight control.

Bastin gave these tips to help people manage food serving sizes.

* For a balanced meal, use the two-thirds, one-third rule. Vegetables, grains and fruits should occupy about two-thirds of the plate and meat, poultry or fish the remaining one-third.

* Measure servings at home with a food scale and measuring cups until you become comfortable estimating the sizes.

* Write down what and how much you eat. Research indicates people will stick to a diet if they make the effort.

* Use smaller-size plates.

* To help control the amount of food on the table, prepare standardized recipes, which make a known quantity.

*Read food labels, which list the number of servings. If the package contains more servings than you have people to eat the food, use the excess portions for leftovers.

* To curb impulse eating, plan menus in advance. And when eating out, it's good to pay attention to the foods and serving sizes in restaurants.

* Since restaurants often serve large portions, share a meal with a friend or ask for a "doggie bag."