Eat 4-5 Walnuts a day: Walnut oil has often been added as an essential ingredient in several hair care products. This dry fruit has the potential of making the hair black and lustrous. It contains biotin, an essential nutrient, which makes your hair strong and voluminous. Since walnuts contain the goodness of protein, they help in strengthening the roots of the hair. Regular usage of walnut oil or consumption of walnuts will make the hair strong and beautiful.