If you're feeling sluggish and lacking in energy, you may not be eating enough of the right types of carbohydrates. Your brain prefers carbohydrates as a source of energy, so aim to get the recommended 45 to 65 percent of your calories from these nutrients. Although all carbohydrates provide energy, some provide longer-lasting energy than others. Choose healthier carbohydrates over less nutritious and highly processed carbohydrates that contain lots of added sugars. Complex carbohydrates with a low glycemic index will provide you with the longest-lasting energy.

Simple vs. Complex

Simple carbohydrates are those that are quickly digested and absorbed by your body, such as sugar. Although they provide you with a quick burst of energy, this is soon followed by a crash as your body deals with the sudden rush of sugars into your bloodstream. Some starchy foods containing refined grains, like white flour and white rice, are quickly digested as well. Complex carbohydrates containing starches and fiber, including foods such as whole grains, fruits, vegetables and legumes, are more slowly digested. These foods give you a longer and steadier stream of energy and also keep you feeling full for longer.

Glycemic Index

The glycemic index measures how much a particular food will increase your blood sugar. Foods with a high glycemic index of 76 and above can cause spikes in your blood sugar levels, while those with a low glycemic index below 55 don't greatly increase your blood sugar levels. Low glycemic index foods help increase endurance and lasting energy during long bouts of strenuous exercise if you eat them before you start your workout, according to an article on the Food and Agriculture Organization of the United Nations website. Healthy carbohydrates that are low on the glycemic index include nonstarchy vegetables, carrots, parsnips, yams, peas, whole-grain spaghetti, chickpeas, lentils, black beans, apples, grapefruit, oranges, peaches, pears, quinoa and brown rice.

Processed vs. Unprocessed

The more processed a food is, the higher the glycemic index is likely to be. Likewise, long cooking times can increase the glycemic index. If you do eat a more processed food, eat it along with a food with a low glycemic index or along with a source of protein or fat since this will lower the overall glycemic index of your meal or snack and minimize the effect on your blood sugar.

Fiber Considerations

Although fiber itself isn't digested and doesn't provide you with much energy, it slows down the digestion of the other carbohydrates in your food, which helps lower the glycemic index and spread out the release of sugars into your bloodstream so your food provides longer-lasting energy. For each 1,000 calories you eat, you should get at least 14 grams of fiber in your diet.