The best food group considered the source of complex carbohydrates is whole grains. Foods like brown rice, quinoa, oats, and whole grain bread provide sustained energy and essential nutrients. Complex carbohydrates digest more slowly than simple sugars, leading to gradual increases in blood sugar levels and long-lasting energy. They also contain fiber, which aids in digestion and promotes a feeling of fullness. Incorporating whole grains into a balanced diet can support long-term health and energy stability.