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After a big workout, it's tempting to reward yourself with a sinful treat. But research shows that we grossly overestimate our calorie burn, which can stymie weight-loss efforts.
updated 9/15/2011 8:30:53 AM ET 2011-09-15T12:30:53

Maybe you've heard the recent downer reports that exercise won't make us thin because it makes us hungry, particularly for junk food. Or could be, you've noticed firsthand that you eat a lot more on gym days than on days off. Either way, it raises the question: If working outonly sets us up to blow our diet, what's the point?

For starters, some research suggests exercise doesn't always cause hunger but can curb it. "Exercise may lower levels of ghrelin, a hormone that stimulates appetite in the short term, while raising levels of peptide YY, a hormone that suppresses appetite," says study author David Stensel, Ph.D., reader in exercise metabolism at Loughborough University. That's only if the workout is intense (if you can chat, forget it), but the more intense it is, the longer the benefit seems to last. "It may be that your body needs to circulate more blood to prevent overheating," Stensel explains. Because eating would cause blood to flow to the stomach instead to aid digestion, your body dampens your appetite to prevent that.

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Like all good things, this satiating effect ends—about an hour later, when your body starts to crave the energy it used up. And unfortunately, the desire to refuel may hit women harder than it does men. "Physical activity may raise concentrations of longer-term appetite-stimulating hormones like insulin and leptin in women," says Barry Braun, Ph.D., associate professor of kinesiology at the University of Massachusetts in Amherst. What's up with the sexist hunger hormones? "It might be that women are wired to defend their body weight to preserve energy for pregnancy and lactation," Braun says.

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Here's where frequent exercise can save the day (and our waistline). "It appears to help restore sensitivity to brain neurons that control satiety," says Neil King, Ph.D., professor of human movement studies at Queensland University of Technology. In other words, the more you do it, the more in tune you become with your hunger signals, which may aid in offsetting them. More motivation to sweat regularly: It can lower heart disease risk, lift mood and up your odds of a longer life overall, whether you lose weight or not. Add to all that a bangin' bod, and a passing case of tummy growls is no biggie.

Beware the exercise halo

A great sweat session can make you feel like a health angel—for good reason, given its life-enhancing power. "But we can feel so virtuous that we reward ourselves with some not-so-healthy habits," warns Susan Bowerman, R.D., assistant director of the UCLA Center for Human Nutrition. Don't fall for these self-sabotaging thoughts:

My metabolismis higher after a workout, so this bite will burn right off.

Ah, the afterburn effect. That's when your body uses energy to return to a resting state. "It sounds great, but even very intense exercise lasting more than 45 minutes burns less than 100 extra calories," says Philip Clifford, Ph.D., professor of anesthesiology and physiology at the Medical College of Wisconsin in Milwaukee.

The bottom line Skip the cool-down nibble: Doing it five times a week saves you up to 500 calories—the equivalent of a Spin class you don't actually take!

I melted mega calories this morning. I can eat what I want today.

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Define mega. Research shows we grossly overestimate our sizzle. People who burned 200 calories by walking briskly thought they had burned 825 in a study at the University of Ottawa. "And they later overate by about 350 calories based on their miscalculations," says study author Eric Doucet, Ph.D.

The bottom line Don't just guess your calories burned; tally them in a reliable way using our calculator. For most women, a brisk walk zaps 5 calories per minute (225 in 45 minutes).

I kicked boot camp booty. I deserve a treat after my hard work.

True, but reward yourself with food and you're likely to stall your slim-down. "Run 40 minutes at a 9-minute-mile pace and you'll burn about 470 calories; grab a Starbucks Venti Caramel Frappucino afterward and you'll replace those calories plus an extra 20," Braun says.

The bottom line "It's incredibly easy to negate the weight loss effects of exercise with a single food item, so find other ways to indulge yourself," Braun says. Try inedible rewards such as a relaxing pedicure or new songs for your workout playlist.

Candy bar pre-workout? Why not! Those will be the first calories to go.

Step away from the junk food: Women who ate high-glycemic-index foods (candy, white bread, sugary cereal) before exercising burned 55 percent less fat than those who had low-GI foods (oatmeal, yogurt), a study in the Journal of Nutrition found.

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"High-GI foods raise insulin concentrations, suppressing the body's ability to burn fat; low-GI ones don't," says study author Emma Stevenson, Ph.D.

The bottom line Sweets are best in moderation—and not before the gym.

Fuel your fat burn

What—and when—you eat before you tackle that yoga mat or treadmill can push your calorie-blasting efficiency to a whole new level. Or it could totally set you back. Don't waste a perfectly good workout by downing the wrong nutrients. Check your schedule, then find the foods that can help you scorch calories at peak speed.

How long do you plan to exercise?

Less than 60 minutes, low intensity

I can carry on a convo without gasping. (walking, light strength training, yoga)

My workout is in less than an hour. You don't need to stock up for shorter bouts of low-intensity exercise; they don't deplete your energy supplies as much as more intensive exercise does, says Karen Reznik Dolins, Ed.D., registered sports dietitian at Columbia University. "But be sure you're not dehydrated or hungry, or you'll fatigue faster."

Best bite: A piece of fruit and a bottle of water provide a small boost without weighing you down.

My workout is in more than an hour. If you're hungry, you have time to digest a lowfat meal, Reznik Dolins says. A mix of low-glycemic foods offer a long charge.

Best bite: 8 ounces lowfat yogurt with 1/4 cup granola and a piece of fruit, or 3 slices of turkey on whole-wheat bread with fruit

Less than 60 minutes, high intensity

I'm working too hard to chitchat. (running, swimming, Spinning)

My workout is in less than an hour. "During high-intensity exercise, blood flow is diverted away from the gut to aid muscles, so digestion slows," Reznik Dolins says. If you have a meal shortly beforehand, sloshing undigested food could cause a stomachache. Haven't eaten recently? Enjoy a small snack with simple carbs for a speedy pick-me-up.

Best bite: One slice of white toast with jelly or a sports drink like Gatorade. Skip whole grains in this situation; they're harder to digest.

My workout is in more than an hour. Have a meal with low-GI foods to optimize fat burn. Carbs (muscles' main energy source) are key for tougher workouts.

Best bite: A whole-wheat wrap with veggies and eggs, or a PB&J on whole-wheat bread

60 minutes or more, low intensity

I can carry on a convo without gasping. (walking, light strength training, yoga)

My workout is in less than an hour. Digestion shouldn't be a problem during low-intensity exercise, but headstands on a full stomach? Not fun. A light snack of whole grains and protein offers extended energy, says registered dietitian Kristine Clark, Ph.D., director of sports nutrition at Penn State in University Park.

Best bite: A few whole-wheat crackers and 1 string cheese, or a Luna bar

My workout is in more than an hour. To fend off hunger and fatigue once you're past the hour mark, eat a meal beforehand that includes low-GI whole grains, healthy fats and lean protein, Kristine Clark suggests. The three digest at slow but varying rates, so you have more staying power.

Best bite: 1 cup whole-grain cereal with skim milk and blueberries and 1 hard-boiled egg

60 minutes or more, high intensity

I'm working too hard to chitchat. (running, swimming, Spinning)

My workout is in less than an hour. "The closer you get to a challenging workout like this one, the more you need simple carbs that can quickly convert to energy," Reznik Dolins says. Reach for something light (100 to 200 calories) to give your muscles pep, pronto.

Best bite: 1 cup dry cereal (not whole-grain) with raisins, or a few regular crackers with jam

My workout is in more than an hour. When you're huffing and puffing for a long period, carbs are a key source of fuel for muscles, Kristine Clark says. "Have a 400- to 600-calorie meal that contains at least 60 percent low-GI carbs, with the rest protein and healthy fats."

Best bite: 1 whole-wheat bagel with 1 tablespoon reduced-fat cream cheese and 2 slices turkey, or 1 cup cooked oatmeal with skim milk and a sliced banana or 1/3 cup raisins

Run, Done! Now What?

Your go-to workout could have a surprising effect on your appetite, eating habits and future fitness. Know what you're in for to one-up your biology.

Running or biking

If you went hard, you might not feel hungry for another hour. But because cardio uses up your glucose and glycogen, you should have a carb-rich snack, like whole-grain cereal or fruit, within 30 minutes to restock your supplies. "Muscles are most sensitive during this window; the sooner you eat, the more glycogen you'll store to improve stamina in your next workout," Bowerman says.

Swimming

Taking a dip really works up an appetite. "Immersing your body in cool water makes it lose heat, and this seems to prevent the release of hormones that suppress appetite," says Michael R. Bracko, Ed.D., director of Dr. Bracko's Fitness Consulting in Calgary, Alberta. Fortunately, you can offset post-pool munchies by warming up with a brisk walk or hot drink.

Strength training

Weight training has been shown to lower levels of ghrelin, a hunger-stimulating hormone, so you might not feel like eating right after you put away the dumbbells. But you should aim to have 10 to 15 grams of protein within an hour—it helps your body repair wear and tear on muscles, Kristine Clark says. Try an egg on whole-wheat toast or 1/2 cup lowfat cottage cheese.

Yoga

Yogis are more likely to eat mindfully and less likely to gain weight over a 10-year period than nonpractitioners are, research in the Journal of the American Dietetic Association shows. Learning to focus while in uncomfortable poses may increase your ability to stay present in other tough spots, such as when you are stressed and craving ice cream. Get your Down Dog on!

Do I need to eat while I work out?

If it's an intense, 90-minute-plus session, yes. "You need to replenish the blood sugar that feeds your brain and muscles," says Nancy Clark, R.D., author of Nancy Clark's Sports Nutrition Guidebook. Carbohydrates (sport drinks, a banana) are best because your body digests them quickly, replenishing energy. Aim for 100 to 250 calories per hour after the first hour.

I've heard A.M. workouts on an empty stomach burn more fat. True?

It's a long-held theory, but a recent review of research in Strength and Conditioning Journal found that the body burns roughly the same amount of fat regardless of whether you fast or eat before you work out. In fact, exercising on empty depletes glycogen (stored glucose you use for energy), which may cause you to lose muscle as you burn. Don't skip breakfast!

Do certain foods cause cramps?

Researchers aren't entirely sure what causes those annoying belly aches, but most evidence does point to pre-workout eating habits. "Greasy foods and those high in protein and fiber are especially hard to break down, so they can result in discomfort," Reznik Dolins says. "And high-impact exercise can jostle your stomach and its contents, so to avoid that upset, wait until any meal is fully digested, about two hours, before hitting the gym."

What can I eat to up my stamina?

Try sipping beetroot juice. We know, ewww. But it may help you exercise up to 20 percent longer, a study from the University of Exeter shows. Beets contain a compound that seems to aid oxygen supply to muscles, so you last longer.

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