There are many reasons your energy may flag throughout the day: medication side effects, pain that wears you out, depression, poor sleep from the night before and even inactivity. But you may be surprised to learn that some of your eating habits can sap your energy, too. Get on the right track with these smart eating tips for an energy boost.

Don't go hungry. The body needs energy to expend energy. That's why when you skip meals, or wait too long to eat, you can feel unfocused or lethargic.

"When you skip, you're simply not fueling your body enough," says Lona Sandon, assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center in Dallas. Plus, she adds, “when you're hungry, you get irritated and that can exacerbate fatigue."

Eat breakfast. People who eat breakfast tend to eat healthier. In one large study published in 2008 in the American Journal of Clinical Nutrition, researchers found that breakfast eaters tend to eat healthier meals and fewer calories over the course of a day. Women in the study who ate breakfast weighed less.

Pass on the sweet stuff. Sugary cereals, sweet pastries and high-calorie coffees will give you a quick jolt of energy, but at a cost. The sugar burns off quickly, leaving you lethargic, says Thomas Namey, MD, a rheumatologist and professor of medicine at the University of Tennessee in Knoxville.

"Simple carbohydrates can cause a tremendous up-shoot in serum insulin," Dr. Namey says. "The rapidly falling blood sugar contributes to a down swoop energy and burn out."