Poor diet can contribute immensely to your energy levels, as junk foods are mostly void of the important vitamins and minerals found in fresh whole foods.
A good rule of thumb is to fill half your plate with vegetables, a quarter with grains or starchy vegetables, and the other quarter with lean protein sources like fish, chicken or red meat, eggs or tofu, lentils, and beans.
Make good use of healthy fats as well, using olive oil, nuts, seeds, and avocado.