Even the healthiest eaters have moments every now and then when they feel weak, shaky and a bit irritable thanks to what they did or did not eat. When you don't feed your body the right foods at the right time, it has to work really hard to regulate blood sugar. Whether it's releasing insulin to combat the heavy load of sugar brought on by a morning muffin, or breaking down energy stores to pump glucose into the bloodstream after you have worked out on an empty stomach, your body is sacrificing valuable energy to keep you going. Fortunately, the following simple dietary rules will help you blaze through your Pilates practice—and your day—with energy to burn.

Bed to Breakfast
Eating a breakfast of complex carbohydrates and lean protein, such as an egg white omelet with a slice of whole grain toast within a half hour of waking, will get your metabolism humming and set you up for a whole day of sustained energy, says Los Angeles-based nutritionist Derek Johnson. "If you wait too long to eat in the morning, your body will assume it is not going to be fed, and it will kick into preservation mode," he says. At that point, a rather taxing process of breaking down stored glycogen into usable fuel becomes your body's main priority, giving rise to bouts of low energy, loss of concentration and a voracious appetite come lunchtime.

Forgo Fast-Burning Carbs
Chances are when you're feeling a little sluggish, a cookie, bagel or soda sounds like just the thing to give you that burst of energy you need. However, such simple carbohydrates will ultimately drag you down. When you eat fast-burning carbs, your blood sugar shoots way up, giving you that quick jolt, but it is very short-lived. Your body then releases a hefty dose of insulin into the blood, sweeping all that sugar into cells and storage, leaving you once again lagging and in need of fuel. It is no surprise that sugar-filled sweets fall into this category, but the truth is white bread, white rice, potatoes, and fruit juices can be just as harmful to your body. Opt for whole-grain breads, grains such as millet and quinoa and yams instead.

Eat Frequently
It takes a lot of energy to run all the functions of your body. In fact, Johnson estimates your body needs 10 times your weight in calories just to sustain itself. In other words, if you weigh 135 pounds, you need to eat 1350 calories a day just to maintain. Now add in all the thinking, creating and running around you do, and what you are left with is a fuel-guzzling machine. Of course if you don't fill it up regularly, you are setting yourself up to conk out later, or more likely overeat. You should never go more than three or four hours without eating. Doing so brings on the combination of fatigue, irritability and weakness that most people refer to as "low blood sugar," but which is actually evidence that the body is working hard to prevent such a low from occurring. "Aim to distribute your total calories evenly throughout your day. The key is to include foods that the body absorbs more slowly, such as protein and healthy fats," says Johnson.

Eat protein at every meal
Including 1-2 ounces of lean protein with every meal keeps the body strong and delays the absorption of sugar into the blood—meaning a steady flow of energy for you. One way to think of it is to fill half your plate with vegetables, a quarter with a healthy starch and a quarter with protein. But not just any foods will do. Stick with lean protein sources such as fish and low-fat dairy products, and complex carbohydrates like brown rice, barley and winter squash. Snacks should include a combination of slow-burning, nutrients too.

Replenish before and after exercise
Pilates is a great way to strengthen your body, ease stress and stay trim, but when the endorphin rush is over, all those burned calories can leave you feeling less than energetic if you don't replenish your stores. First, to keep your energy high during your workout, consider eating half a banana or a couple of crackers 15 minutes before exercise—it is the one time of day when eating carbohydrates by themselves is useful. Then, rebuild your glycogen reserves by eating a combination of complex carbohydrates and protein within 45 minutes of working out. Good choices include half a turkey sandwich on whole wheat or a small yogurt sprinkled with a little low-fat granola. And don't forget the water. Drinking heartily before, during and after a workout will keep your muscles and organs hydrated and your energy high.