Sometimes the problem is lack of sleep, but just as frequently it’s diet. “You need calories and fluids to have energy and to feel good while you’re physically active,” says Kristine Clark, PhD, RD, director of sports nutrition for the Penn State University athletic department. So whether you’re walking 2 miles a day to lose weight, training for a 5-K, or trying to keep up with an active family, here are eight eating tips to help you stay energized and rarin’ to go.

1. Don’t Go Hungry

“That’s rule number one,” says Dan Benardot, PhD, RD, associate professor of nutrition and director of the Laboratory for Elite Athlete Performance at Georgia State University. “It’s extremely difficult to exercise when you haven’t eaten enough or at all, so to keep your blood sugar from getting low and to sustain your energy, you need to eat small amounts of carbohydrate-containing foods throughout the day.” He recommends having three moderate-size meals plus two snacks every day.  [sidebar]Pick complex carbs, “which will help sustain blood sugar levels,” thereby boosting energy, advises Clark. “Choose whole grain products, such as a small whole wheat pita or a bowl of oatmeal with fruit; the fiber in these foods helps the carbs stick with you.”

2. Never Go Thirsty

Dehydration is a real downer. If you haven’t had enough to drink, you can feel light-headed, headachy, dizzy, and confused and can have increased heart and breathing rates. “Any athlete who is ready to compete but isn’t holding a drink is not fully equipped,” says Benardot. That’s because “even a small amount of water loss can impair your ability to perform at your best and feel good about exercising,” says Christine Rosenbloom, PhD, RD, associate professor of nutrition at Georgia State University. When you exercise, don’t wait until you feel thirsty: Drink 6 to 8 ounces of liquid before and after you walk. And sip something every 15 minutes while you walk. (See these four tips to stay hydrated no matter what.) [pagebreak]

3. Save Sports Drinks for Special Occasions

Plain water is a fine hydrator, but if you fatigue quickly when you exercise or if you sweat a lot (you’re power walking, for instance, or it’s warm out), a sports drink may be just the ticket. Sports drinks contain glucose, the sugar your body needs for energy, as well as electrolytes such as sodium and potassium, which are lost when you perspire. Another reason to sip them: You’re taking a long walk or competing in a race and you don’t have access to a bathroom; the sodium-rich drinks help you hold on to your fluids.

4. Watch the Calories

“Unless you’ll be exercising for long periods of time, you don’t need to drink a quart of a sports drink or eat a 300-calorie energy bar beforehand,” says Rosenbloom. Energy snacks like these, especially the bars, are so high in calories they can cancel out the fat-burning benefit of your walk.  Instead, before you start, drink 6 to 8 ounces of fluid (such as water) and have an energizing snack of 100 to 200 calories if it’s been more than 2 hours since your last meal or snack. Can you have an energy bar? “If you’re planning to walk 40 minutes or longer after work and you haven’t eaten since lunch, an energy bar that contains protein as well as carbohydrates is a quick-energy option,” says Clark.  But keep an eye on calories. “I recommend to my clients that they eat half a bar. That way they can choose the one they want without overloading on calories,” she says.

5. Pick the Perfect Protein

Protein doesn’t give you the same burst of energy that you’ll get from an orange or a slice of whole wheat toast, but it does give you staying power, which could make the difference between going for a mile-long walk every morning or sticking it out for 3. “Protein helps to blunt the rise in blood sugar after a meal or snack, which aids in extending energy,” says Clark, who recommends combining protein and carbohydrates in every meal and snack. For most people following a walking plan, eating 0.5 to 0.75 g of protein per pound of body weight per day is enough. [pagebreak]For a 150-pound person, that adds up to 75 to 113 g of daily protein. Good sources include poultry, fish, lean meats, low-fat dairy products, legumes, nuts, and nut butters. Lean red meat and poultry can have up to 8 g of protein per ounce, while low-fat milk contains about 1 g per ounce. (You can get a day’s worth of protein from 1 cup of shredded wheat with a cup of fat-free milk, a small fast-food chili, a serving of chicken about the size of a deck of cards, 2 tablespoons of peanut butter, and ½ cup of cottage cheese.)  Bonus: Eating protein, particularly after exercise, can also help stimulate muscle building. And you know the rule: The more muscle you have, the more calories you burn.

6. Supplement

High energy comes from eating right every day. Since that’s not always possible, take a regular multivitamin/mineral supplement for added insurance. “Having enough iron in your diet is essential for energy, and for premenopausal women, taking a supplement that contains it is a good idea,” says Rosenbloom. “Check that your multi also contains zinc, which is involved in the functioning of more than 200 enzymes in the body. We tend not to do well in getting this mineral in our diets.” Both iron and zinc are most abundant in meat, poultry, and some types of fish. Other nutrients you may need to get the most out of your walk: calcium, vitamin D, and magnesium. While walking can strengthen bones, it only happens if you have adequate amounts of D and these minerals in your diet. Depending on your age, you need between 1,000 and 1,200 mg of calcium every day (those over 50 need the higher amount). You can get it from calcium-rich foods, such as dairy products, and a calcium supplement (take only 500 mg at a time so it will be absorbed). The best food source of D (you need 400 IU daily) is fortified milk; for magnesium (you need 400 mg daily), eat whole grain cereals, nuts, and spinach.

7. Eat Healthful Fish

Research suggests that antioxidants can help reduce the inflammation and stress that exercise puts on your body. To fully unlock their power, make sure you’re eating enough good fats. Aim for two weekly servings of fish rich in omega-3s, such as salmon, tuna, mackerel, and sardines. (Just make sure you don’t eat these 12 fish to always avoid.)[pagebreak]

8. Limit Fats

That’s good advice for many reasons, but if you’re eating for energy, fat (other than the omega-3s in fish) doesn’t really have a place at your training table. In fact, it’s likely to make you feel sluggish. “Fat is the last nutrient to leave the stomach, and it slows down digestion,” explains Rosenbloom.  When you eat anything, the act of digestion requires that your body increase circulation to your digestive tract. “You don’t want your body to increase its bloodflow to the stomach when you need it flowing to your muscles–this can drag you down,” she says. On the other hand, if you’re an endurance athlete or an avid hiker, a little fat can help; it powers longer-duration exercise and, like protein, it blunts the rise in blood sugar.  “The bottom line is to have a positive experience when you’re exercising,” says Rosenbloom. “If you’re eating right, you’ll feel good about what you’re doing—and you’ll want to do it again tomorrow.” That, after all, is the whole idea.

What’s the Fuel of Champions?

When it comes to giving you energy, carbs are the hands-down winner. The popularity of low-carb diets has given carbs a bad name, but there’s no refuting the science. Your muscles are fueled by glycogen, which is a form of glucose—another name for sugar.  Carbohydrates such as grains, fruits, and vegetables break down into sugar in your body, giving you nearly instant pep. But it’s a short burst: Ultimately, your blood sugar will drop, which can make you feel fatigued. For staying power, combine your carbs with protein, which keeps your blood sugar on an even keel—and you moving—longer. Good-to-Go Gorp What used to be “good old raisins and peanuts” has been dressed—and fattened—up with all kinds of dried fruits and chocolate (including M&M’s). You can make your own energy-blasting gorp that’s lower in fat and calories by combining ½ cup of Multi-Bran Chex with 2 tablespoons of dried cranberries and a dozen almonds (about ½ ounce). Makes 1 serving. Per serving: 229 cal, 5 g pro, 41 g carb, 8 g fat, 0.6 g sat fat, 0 mg chol, 6 g fiber, 196 mg sodium More from Prevention: 11 Fast Fixes For Instant Energy