Carb cycling diets involve changing the amount of carbohydrates you eat each day depending on your training schedule. On days when you have your hardest workouts, you eat a high amount of carbohydrates; on lower-intensity training days, you eat a medium amount of carbs; on your rest days, you eat the fewest carbs. Carb cycling can be very effective for losing fat or staying lean while building muscle. When choosing your carbohydrate sources, you should choose the ones best suited to what day you're on, and carbs high in nutrients. Get your doctor's approval for your diet and exercise regimen before beginning.

Grains

Grains include bread, pasta, rice and cereals and are very high in carbohydrates. This makes them ideal for your high- and moderate-carb days. When choosing your grains, look for whole grains over white or refined grains. This means swapping out white bread, pasta, rice and sugary cereals and adding in whole-wheat bread and pasta, brown or whole-grain rice and oats. According to MayoClinic.com, whole grains are a much better source of fiber and other nutrient, digest more slowly and have less of an effect on your blood sugar.

Vegetables

Fibrous vegetables, like spinach, broccoli, cauliflower, sprouts and kale, are all fairly low in carbohydrates, so are perfectly suited to your low-carb days. Starchy vegetables, such as yams, potatoes and squash, all contain more carbohydrates, so are better left for moderate and high days. Charles Poliquin, owner of the Poliquin Performance Center for elite athletes, recommends that when choosing vegetables, you look to include a variety of colors, as this will ensure you get a good range of vitamins, minerals and disease-fighting phytonutrients.

Fruits

Fruits vary greatly in the amount of carbohydrates they contain. Bananas, figs, cherries and dried fruits like raisins are all high in sugar, while apples, watermelon, peaches and all varieties of berries are much lower. Stick to low-sugar fruits on low-carb days and higher-sugar fruits on moderate and high days. Fruit is ideal after a workout, because the fast-digesting sugars help to deliver nutrients to your muscle cells and steady your blood sugar levels.

Beans and Legumes

Lentils, chickpeas, peas, and all types of beans — black, kidney, cannellini and pinto are just a few examples — all contain a moderate amount of carbohydrates — roughly the same as starchy vegetables. They can be consumed almost freely on high-carb days and in moderation on low-carb days. The added benefit that beans and legumes have is that they are good sources of protein, so can help keep your protein intake up if you don't eat meat or fish.