You may charge into the day full of energy. But by midafternoon a wave of sleepiness hits you. You find it hard to keep your eyes open, or you find yourself yawning. Many people have these late-in-the-day energy lags, but you can take steps to prevent them. Here are some tips for healthy ways to keep your energy flowing throughout the day.

The best way to keep your energy level at peak performance is to start the day with breakfast. Skipping any meal affects your ability to focus. This makes it harder to solve problems. Missed meals also mean you miss out on nutrients. Often, people who skip meals end up overeating later.

For a quick burst of fuel, choose foods high in complex carbohydrates. These are healthful sources of energy that digest the quickest. Go for whole-grain breads and cereals, fresh fruits, vegetables and vegetable sticks, pasta, beans, or brown rice. Even spring rolls or burritos can do the trick. To hold hunger at bay for longer, choose protein foods that take longer to digest. These include nuts, peanut butter, and cheese.

Instead of looking at snacks as extras, treat them as mini-meals that add to your overall nutrition for the day. Healthy snacks help provide fuel to keep your body going. Try fruits and vegetables to boost your intake of vitamins, minerals, and fiber. Choose plain nonfat yogurt or café lattes made with skim milk to get protein and calcium. When you snack, keep variety, moderation, and balance in mind.

Fat takes a long time to digest and makes the body feel sluggish. Most junk food is high in fat and sugar. Instead of buying chips or cookies from a vending machine at work, plan ahead and bring healthy foods for snacks.

Eating sugar causes your blood sugar to rise rapidly. This can result in an energy boost. But when sugar is introduced into the bloodstream, the body also makes insulin. This lowers blood sugar levels. Sometimes the body overadjusts itself, causing the blood sugar level to drop quickly. This explains the drop in energy some people have about 30 minutes after eating a sugary snack. Sugar in moderation, especially from fruit or 100% fruit juice, will give you energy without a lag.

Getting even 1 hour less of sleep can result in slower mental functioning the next day. Your reactions will be slowed and your memory may suffer. The average adult needs—but doesn't get—about 7 to 9 hours of sleep a night, according to the National Sleep Foundation. On average, a person over age 65 needs about 7 to 8 hours of sleep each night.

Your body needs a certain amount of water to function. When you don't have enough water, everything slows down and becomes less efficient. Water is best. But other liquids, like milk, juice, or the water in solid foods, will also work.

Caffeine is a stimulant, so it will give you a short-term energy boost. According to the FDA, as long as you keep your caffeine intake to about 400 mg per day—about the equivalent of 4 cups of coffee —caffeine typically isn't harmful to most healthy adults. But each person is different in how sensitive they are to caffeine and how fast they break it down. Remember, having too much caffeine can affect you for as long as 12 to 24 hours. Side effects can include:

• Trouble sleeping
• Jittery feeling
• Fast heart rate
• Anxiety
• Headaches
• Heartburn or an upset stomach

Exercise increases your endurance and makes your cardiovascular system more efficient. This gives you more energy for doing simple daily tasks. Exercise also helps you sleep better, improves your mood, eases stress, helps with weight control, strengthens bones and muscles, and lowers your risk for a host of diseases. Check with your doctor before starting an exercise program.

A good way to fight off tiredness during that midafternoon energy lag is to do some stretches. Or take a quick walk around the block. This will get the blood flowing. It also forces your senses to become sharper and more focused.