A cup of milk to make muffins, a little sour cream for the avocado dip, and ricotta cheese in your lasagna. You probably don't realize how often you eat dairy products. Used alone or combined with other ingredients, dairy products — such as milk, cheese and yogurt — are both versatile and nutritious.

Dairy products supply the richest source of calcium, although many other foods, such as green leafy vegetables, also contain calcium. Your body uses calcium to build strong teeth and bones. And your heart, muscles and nervous system need calcium to function properly. A calcium-rich diet may help lower the risk of a variety of diseases, including the bone-thinning disease osteoporosis.

Dairy products also provide protein, B vitamins and other minerals your body needs, such as selenium, zinc, phosphorus and magnesium. Most milk is fortified with vitamin D, which helps your small intestine absorb calcium. Low-fat and fat-free milk may also be fortified with vitamin A, which is lost in the removal of milk fat.

Whole-milk dairy products are high in fat — especially saturated fat — and calories. Fat-free and low-fat milk products provide the same nutritional benefits without the excess fat and calories.

Some dairy products also contain probiotics, sometimes referred to as good bacteria. Probiotic bacteria in cultured dairy products such as yogurt and buttermilk may help maintain a good bacterial balance in your intestinal tract. If you have trouble digesting lactose, cultured dairy products may be easier for your body to digest. These harmless bacteria may also play a role in the protection against cancer and high cholesterol.

Here are suggestions to help you select the highest quality dairy products when you're shopping, tips for storing them once you get home, and ways to safely prepare and serve these foods.

• Look for low-fat, fat-free or reduced-fat alternatives. Choose skim milk over whole milk, and low-fat or fat-free sour cream over full-fat sour cream. Read package labels carefully. Look for the grams of total fat and saturated fat per serving as you compare similar products.
• Don't buy food past the expiration date. Many products display a "sell by" or "use by" date on their containers. A sell-by date tells stores how long the product should remain on the shelves. A use-by date is the last date you should consume the product, to guarantee the best flavor and quality. Don't buy products past these recommended dates.
• Buy dairy products labeled 'keep refrigerated' only if they feel cold in the store. Most dairy products need refrigeration, so make sure these foods remain cold. Check that frozen products, such as ice cream, are solid. Some dairy products don't require refrigeration, such as unopened cans of milk (condensed milk, evaporated milk) or unopened jars of cheese spread and cheese foods.

• Refrigerate all dairy products within 2 hours of purchase and put ice cream and other frozen dairy products in your freezer as soon as possible. Pasteurization kills harmful bacteria. However, other bacteria naturally present in dairy products can grow quickly without proper cooling, affecting the quality of the product. Keep these foods refrigerated or frozen until served.
• Wrap cheese tightly in original package or in a sealed container after using a portion to prevent mold from growing. If you find mold on cheese, cut off and discard about one-half inch on all sides of the mold.
• Store dairy products for only the recommended amount of time. How long you can safely keep your dairy products varies. Here are common types of products and recommended safe storage times for opened containers. Remember that you can also use the date on the package as a guide.

Serving: Keep it safe

• Don't drink raw (unpasteurized) milk or eat foods made from it, such as unpasteurized cheese. Pasteurization — heating milk or milk products to a certain temperature for a specific amount of time — destroys harmful bacteria. Most milk and milk products available in stores are pasteurized, and are labeled as such.
• Keep dairy products cool — 40 F or below — while serving. If food needs to sit out for long periods of time in warmer temperatures, such as for a buffet or outdoor party, use a small tray of ice under the food to keep it cold. Replace the ice as it melts. Discard if the food sits at room temperature more than two hours.

Here are easy ways to incorporate low-fat dairy products into your diet.

• Choose skim milk, reduced-fat cheeses and lower-fat milk desserts, such as ice milk or frozen yogurt.

• Top your potatoes with fat-free or low-fat yogurt, sour cream or cottage cheese. Or top with shredded, fat-free hard cheese, such as cheddar cheese.

• Puree fat-free or low-fat cottage cheese and evaporated skim milk with lemon juice and rosemary to make a light pasta sauce.

• Substitute fat-free or low-fat yogurt for full-fat sour cream in your recipes. Or use buttermilk or pureed low-fat cottage cheese in recipes that call for sour cream.