While it's true that some foods may fight disease and help you live longer, many of us forget that just because a food is healthy doesn't mean it's calorie-free. In fact, eating too much of even a healthy food might cancel the very benefit it provides.

Here are a few foods, along with their health benefits and ways to keep them healthy.

AVOCADOS (AND GUACAMOLE)

The good: They're nutrient-dense and packed with antioxidants, and vitamins B6, C and E, as well as folate and potassium (60 percent more potassium per ounce than bananas), and they're a great source of monounsaturated fat, which studies have shown reduces serum cholesterol levels when used in place of saturated fats.

The bad: The calories add up. A 7-ounce avocado has about 360 calories. That's about 50 calories per 1-ounce slice or 110 calories in just 3 ounces of guacamole. Plus, guacamole doesn't keep very good company. Its best friends — cheese, chips and refried beans — can really pack on the pounds. Tortilla chips (seven to 10 chips): 140 calories, 6 g fat, 19 g carbs. Sour cream (2 tablespoons): 62 calories, 6 g fat, 1 g carbs.

Fit tip: Keep avocados and guacamole in your diet, but avoid the fried chips and other unhealthy foods that tag along. Serve guacamole in small dishes for portion control along with low-fat baked chips. Also, you can use avocado slices to replace other high-calorie foods that contain saturated fat, such as whole-fat cheese, which has 100 calories per ounce/slice.

FIGS

The good: Fresh or dried, high in antioxidants, figs are a top source of fiber, potassium, manganese and vitamin B6. They are fat-free, sodium-free and, like all plant foods, cholesterol-free. A 1/4-cup serving provides 244 mg of potassium (7 percent of the recommended daily value), 53 mg of calcium (6 percent of the DV) and 1.2 mg of iron (6 percent of the DV).

The bad: Ever look at the calories for one Fig Newton? 55 calories. The average fig has 40 to 50 calories. Most figs are dried, which makes it easy to eat many without thinking, and they're high in calories and carbs.

Fit tip: Chop some figs to scatter over oatmeal or cold cereal. Skip the sugar and enjoy the fig flavor and crunch. Sweeten up regular or sweet potatoes with chopped figs. The figs add a richness of their own, so you can skip the butter or margarine.

PRUNES

The good: Prunes, which are dried plums, are packed with important vitamins and minerals, such as potassium, vitamin A, magnesium and iron, as well as fiber, all of which help you stay healthy, balanced and energized. They are also high in disease-fighting, anti-aging antioxidants.

The bad: There are about 22 calories per prune. So if you want to get your daily dose you need to use them as a replacement for less-healthy foods (a bag of chips, for example). Another issue: If you eat too many, well, they have a laxative effect.

Fit tip: Combine one or two with a variety of lower-calorie fruits. Or chop the prunes and use them as topping on cereal and other foods.

YOGURT

The good: Yogurt's health benefits include improving digestion, preventing intestinal infection and reinforcing immune function. Yogurt is made by adding bacterial cultures to milk, which changes the milk's sugar, lactose, into lactic acid (a great way to get calcium if you're lactose intolerant). Yogurt is packed with vitamins and minerals, such as calcium, potassium, riboflavin, magnesium and phosphate, and it's low in fat.

The bad: Health claims aside, yogurt still has a lot of calories and added sugar. So eating too much of it may negate any potential benefits by increasing the health risk of being overweight. For instance, a 10-ounce container of Stonyfield Organic Lowfat Yogurt Smoothie has 250 calories, as well as added sugar. And then there's frozen yogurt, which is typically on a dieter's shopping list but is really closer to ice cream than yogurt. For instance, Haagen-Dazs Strawberry Nonfat Frozen Yogurt (1 cup): 280 calories. Or Ben & Jerry's Chocolate Fudge Brownie Low Fat Frozen Yogurt (1 cup): 380 calories. Also, keep an eye on yogurt-covered snacks; some are more like candies in disguise. One cup of yogurt-covered raisins: 750 calories. One cup of yogurt-covered pretzels: 391 calories.

Fit tip: Stick with the low-fat or no-fat yogurts, and try to find a brand with no added sugar. If you normally eat high-calorie foods like ice cream or cheese, it's great to replace them with low- or no-fat yogurt.

Charles Stuart Platkin is a nutrition and public-health advocate. Write to info@thedietdetective.com.