If the discussion in the following hair loss article is accurate, the author credits the "highly bioavailable protein" and biotin in eggs as beneficial for hair.
The ancient source we have been studying (in the form of the Medical Medium books) tell us that most Leafy Greens are the best source of protein. (And that surprisingly other, harder to digest and use sources of protein. cause many ills.)
Life Changing Foods, Leafy Greens, pg. 146
If you worry about getting enough protein, fret no more. Leafy greens have the most bio-available and assimilable proteins you can find, readily available for your body to take up. Leafy greens help reverse all protein-related diseases, such as gout, kidney disease, kidney stones and gall stones, gallbladder disease and hepatitis C, lymphedma, convective tissue damage, osteopenia, osteoporosis, osteoarthritis, and heart disease, which all arise from protein sources that are not breaking down or assimilating and are instead causing deterioration of the body.
Leafy greens.. such as lettuce, spinach, Swiss chard, mache, and watercress... also kale, collard greens, mustard greens, arugula, radish greens, dandelion greens, parsley and cilantro...
https://food.ndtv.com/food-drinks/5-foods-to-prevent-hair-fall-and-help-with-growth-and-thickness-3334650