Eating just the right thing before lifting weights or jumping on the elliptical trainer can keep you energized until the end. What you eat "depends on how hard and how long you're exercising," says Elizabeth Somer, RD, author of Nutrition for Women. Here are her surprisingly easy ways to fuel your muscles before different workouts and--pant, pant--help you recover after you've worked your butt off.

A solid aerobics session--30-60 minutes
BEFORE

"A small liquid snack 5 minutes before a run, step session, or power yoga class turns into fuel almost immediately," says Somer. Let these rules be your guide:

1. Keep it light (under 200 calories) for faster digestion.

2. The less time you have to eat before exercising, the less you eat. You don't want stuff sloshing about in your tummy as you move.

3. Skip juice blends or energy drinks that list high-fructose corn syrup or glucose gels on the label. Both heavy-hitter sweeteners can make blood sugar levels plummet mid-workout.

A few 200-calorie-and-under suggestions:

• A make-it-yourself 8 ounce fruit and low-fat yogurt smoothie or one of Dannon's Light & Fit ready-to-drink fruit smoothies
• Carnation No Sugar Added Instant Breakfast drink made with a cup of skim milk or light soymilk
• A 6 oz. glass of OJ and 2 graham crackers

AFTER

To re-hydrate and keep your blood sugar stable, have some water and:

• A low-fat granola or energy bar
• A cup of low-sodium chicken noodle soup
• A piece of fruit or a small bunch of grapes

Hit-the-wall aerobics--60 minutes or more
BEFORE

You want a snack that keeps muscles supplied with a steady flow of glucose. "Just as a car sputters to a stop when it runs out of gas, you 'hit the wall' or 'bonk' if your glucose supplies are drained. Once that happens, no snack will fuel you fast enough to finish the workout," warns Somer. Before you go all out, have some:

1. Water to ward off dehydration, especially when it's hot.

2. Easy-to-digest, high-quality carbs that leave your GI track quickly and supply enough glucose to fuel a long workout. 

3. Protein from yogurt, milk, soymilk, or nuts to offset a rapid drop in blood sugar from eating those carbs.

4. Foods that are light (again, 200 calories) and low-fat to avoid digestive problems. If your energy dips or your legs become shaky, eat more the next time until you hit on the right amount.

Good carb-protein combos:

• Half a 4 oz. whole-wheat bagel with 1 tbsp. low-fat cream cheese
• A small slice of last night's vegetarian pizza or 2/3 cup leftover spaghetti with marinara sauce
• 1 stick of low-fat string cheese, 1 medium pear, and 3 whole-grain crackers

AFTER

Recover with more water and a 100 calorie, all-carb snack, such as:

• 50 pretzel sticks
• 1/2 cup Breyer's Double Churn Fat-Free Caramel Swirl ice cream
• Half a baked potato topped with 2 tbsp. salsa

Up to 60 minutes of gentle yoga, stretching, or tai chi
BEFORE

A pre-workout snack isn't essential for low-sweat activities--say, an hour of yin yoga or a stretch class. But if you're hungry, try a banana for potassium and 2 graham crackers for carbs. Wash it down with some water.

AFTER

All you'll need is more water.

Semi-tough strength training--30-45 minutes
BEFORE

Carbs with a dash of protein is your fuel of choice. Only serious body builders and weight lifters who pump for more than 45 minutes at least three days a week need extra protein--"most people get plenty," says Somer.

If you're borderline hard-core, try these 200 to 250 calorie protein-laced snacks:

• Half a turkey sandwich on whole grain bread and a piece of fruit
• A handful of trail mix (nuts, dried fruit, and seeds)
• 3 whole-grain crackers with 1 Tbsp. peanut butter and 6 oz. of V8 juice

AFTER

Re-hydrate with water and have the other half of that turkey sandwich--the protein helps repair and build muscles.

For the average gym rat who does 30 minutes of weight training two or three times a week, just have a high-carb snack 10 minutes or so before you start:

• Plain, nonfat yogurt mixed with berries or applesauce
• 1 tbsp. nut butter and a sliced 1/2 banana on a 10" whole-wheat tortilla, all rolledup burrito-style
• 1 small (2 oz.) carrot-raisin muffin and a 6 oz. glass of OJ

An all-day hike, cross-country ski or snowshoe trek
BEFORE

To build your glycogen stores, plan ahead.
1. For a day or two prior to your outing, eat high-carb meals of whole-wheat pasta or brown rice dishes.
2. Drink ample fluids, too--at least 10 cups a day. Before setting out, have a substantial high-carb meal of pancakes or waffles with fruit.
3. In addition to lunch, pack a couple of energy bars, dried fruit-and-nut mix to nibble every 2 hours.
4. Regularly sip water or sports drinks; don't wait until you get thirsty.

AFTER

(Soak in the hot tub!) And keep drinking water. Have a high-carb snack such as a muffin, popcorn, pretzels, or hot cocoa and a graham cracker.

***

Not only will exercising regularly burn off all those snacks and more but it can make your RealAge as much as nine--yes, nine--years younger. And your body inches trimmer.

Nice.