This short article, on HairstylesHowTo.com, list three foods to help thicken your hair. But you don’t eat them! Mix them with other foodstuff and use as a hair conditioner.
Coconut oil for thicker hair
This miracle oil works wonders on your skin and hair. Mix a tablespoon coconut oil with 1 tsp. castor oil and apply to hair. Rinse with shampoo after 10 minutes and allow your hair to air dry. Repeat this twice a week for up to a month.
See the suggestions for hair that is thinning or damaged on HairStylesHowTo.com
Image from the same article.