Q. Should I eat a doughnut at morning work meetings, or have nothing at all?

A. Doughnuts are the better choice, but just marginally. "Not only are they excessively high in fat, but doughnuts are also made with sugar and white flour, carbohydrates that are quickly absorbed into your bloodstream," says Farrell. "You may feel satisfied during your meeting, but you'll probably start feeling hungry shortly thereafter." Over time, these breakfasts may lead to weight gain: A Saint Louis University study found that women who chose carb-rich meals over higher-protein ones ate about 400 more calories and had stronger cravings over the next 36 hours.

The next time your boss calls an impromptu brainstorming session, go for a French cruller (169 calories, 8 grams of fat) or a glazed doughnut (190 calories, 10 grams of fat) and skip the cream-filled (307 calories, 21 grams of fat) and cake versions (303 calories, 17 grams of fat). And while muffins may seem like a healthier bet, keep in mind that some pack nearly 700 calories and 33 fat grams!

If you expect things to wrap up within an hour or so, eat breakfast after the meeting. Keep an emergency stash of options, like whole-grain cereal and high-fiber energy bars, at your desk.

Q. Will blotting my pizza cut down on calories?

A. It won't soak up all of the fat and calories in your lunch, but it can make a dent. "If you're eating a medium slice of cheese pizza, swabbing it first with a napkin can remove up to 45 calories and 5 grams of fat," says Farrell.

But all the mopping in the world won't help if you're ordering the wrong kind of pie. A report from the Center for Science in the Public Interest in Washington, D.C., found that stuffed-crust and meat-lovers varieties, which can clock in at 800 calories per slice, contain more than a day's worth of fat and sodium.

If you really want to improve the nutritional profile of your pizza, skip the meat toppings and order your pie with extra veggies—like mushrooms, spinach, or broccoli—and half the cheese (which saves about 80 calories and 6 grams of fat per slice). Switching from deep-dish to thin-crust can also slash up to 200 calories and 6 grams of fat.

Q. Does exercising on an empty stomach burn more fat?

A. Yes, but you might not be able to work out as hard as you would if you'd eaten first. Researchers at the University of Ottawa in Canada asked two groups of people to hit the treadmill in the morning until they'd blasted 400 calories. The joggers who skipped breakfast burned 58 percent more fat than those who had eaten a meal before their run. But pre-workout fasting won't necessarily translate into weight loss. "People incorrectly assume that if you're using fat for fuel, it equates to losing body fat," says Nancy Clark, R.D., a sports nutritionist in West Newton, Massachusetts. "But what affects weight loss most is how many calories you've depleted during your workout and if you've sustained a deficit by the day's end."

It may sound counterintuitive, but having a 150- to 200-calorie snack at least 30 minutes before your sweat session could help you get slimmer in the long run. A study from Pennsylvania State University found that women who had a mini-meal before their workout were able to exercise up to 16 percent longer than those who drank only water beforehand. Plus, says Clark, women who exercise on empty become so ravenous after they finish that they often end up making poor food choices. Eating a banana or a granola bar before lacing up your sneakers can give you the energy you need to crank up the intensity.

Q. Can foods like cabbage soup and grapefruit help me flush fat?

A. Despite long-standing rumors to the contrary, "there's no science proving that any particular food can burn, melt, or flush away fat," says Donald Hensrud, M.D., an associate professor of preventive medicine and nutrition at the Mayo Clinic. "If a woman loses weight on a grapefruit or cabbage soup plan, it's likely because she has cut calories by restricting her intake to a handful of foods."

Hensrud's colleagues at the Mayo Clinic (which is often incorrectly credited with creating both the cabbage soup and grapefruit diets) estimated that people who follow either plan faithfully eat 1,000 to 1,200 calories a day. "You'd almost certainly lose weight eating 1,000 calories of anything, whether it's bananas or potato chips," he says. "But it will be pretty tough to keep the pounds from returning once you return to your normal diet."