When it comes to convenience and low cost, fast food is king. But before you order your next meal, chew on this: In a large study by the National Heart, Lung, and Blood Institute, young adults who ate fast food at least twice a week doubled their insulin resistance--a risk factor for diabetes--and gained ten more pounds over time than those who indulged infrequently.

The problem with most fast food is twofold. Mindy Hermann, a Mount Kisco, New York, registered dietitian, says, "The Calories add up quickly, and unless you choose a high-fiber food such chili, it isn't filling. So you end up eating lots of calories and you're still not satisfied."

Sodium levels also tend to be very high--a serious concern because of our runaway rates of high blood pressure. "It's almost impossible to keep your sodium intake down at a fast-food restaurant," Hermann notes.

According to the USDA's 2005 Dietary Guidelines, those at risk for high blood pressure should limit their sodium intake to 1,500 milligrams a day, and everyone should cap their daily fat consumption at 65 grams. Keeping these numbers in mind--along with nutritional value, portion size and what you're likely to order--we studied the nutrition facts of five popular chains to find the best options.

McDONALD'S

BEST BURGER: Quarter Pounder

Serving size: 171 grams

Calories: 420 Total fat: 18 g

Sodium: 730 milligrams

Why we chose it: Compared with other large burgers like the Big Mac and the Double Cheeseburger, a Quarter Pounder has the least amount of fat and a relatively low amount of sodium.

For best results: If the burger alone doesn't fill you up, get the 15-calorie, zero-fat Side Salad instead of the fries, which, at minimum, will cost you 230 calories and 11 grams fat.

BEST CHICKEN: 6-piece Chicken McNuggets

Serving size: 96 g

Calories: 250 g Total fat: 15 g

Sodium: 670 mg

Why we chose it: Six McNuggets are the best chicken option. Most of Micky D's chicken sandwiches contain more than 900 milligrams sodium, as do the three piece Chicken Selects.

For best results: if you can't bear to eat naked McNuggets, ask for honey, which is fat- and sodium-free. The other dipping sauces--from Sweet 'N Sour to Spicy Buffalo--contain between 160 and 9100 milligrams of salt per serving.

BEST BIG SALAD: Caesar With Grilled Chicken

Serving size: 301 g

Calories: 210 Total fat: 6 g

Sodium: 830 mg