Three important nutrients for healthy hair are: Silica (helps the body absorb vitamins and minerals more effectively), zinc (helps form important hormones and enzymes) & biotin (for actual production fo healthy hair).
For silica: Eat cucumbers, celery, sprouts and bell peppers.
For zinc: Reduce intake of grains, legumes, & nuts (they contain phytic acids, which reduces zinc's effectiveness in the body). Adult males need 11 milligrams of Zinc each day, and adult females need 8 milligrams. Eat spinach, kidney beans, shrimp, flax seeds, pumpkin seeds, watermelon seeds, garlic, egg yolk etc.
For biotin: Almonds, carrot, yeast, grains, cold water fish etc.
You also need:
Collagen: A protein within hair that gives it volume and strength. Useful foods for collagen include bone broth and sulfur compounds found in onions, cruciferous veggies and mushrooms.
Anti-inflammatory Herbs: These contain anti-oxidants. Found in turmeric, oregano and ginger.
Low-sugar, nutrient dense fruit containing anti-oxidants: E.g. Lemon, lime, berries and apples.