Once the hair turns grey, I suppose there is no diet which can change the gray hair totally into black but prior to graying, it can be controlled to some extent with some of the foods.
Mainly intake of curry leaves are very good for hair - for hair loss and greying as well.
Similarly intake of coconut / coconut water is considered good for blackening the hair and for healthy hair.
before you follow any dieting method, I suggest you to consult a dietitian for proper guidance. Different people will have different type of skin and hence need different kind of nourishment.
Cucumber, curry leaves, water melon, papaya, all green leafy vegetables, and fruits.
Carrot plays an important role in maintaining good health and also gives more darker hairs.
If you have grey hair at early age, this is due to majorly cause of lack of food content.
I am also suffering due to that and I have come across Blackstrap mollasses. This is a thick syrup made of sugarcan extract and it has all important vitamins and minerals.
You may do more research on that as in some information I have found that many people have cured from unwanted greying of hair.
Once the pigmentation has changed it is very difficult to turn it gray hair to black, but sometimes in rare cases by gray hair turns black. But you can stop the further graying of hair by consuming almonds ,goose and message your hair with coconut oil.
Stop washing hair with shampoos and start using soap nuts or shikakai powder.
Grind bael leaves and apply it for two hours before you have your bath. Continue this process for a few weeks and see if it works.
1. You may use only coconut oil a few hours before shower.
2. You may use only one standard Shikakai or Soap or Shampoo for your hair.
3. Other vegetables and fruits too help it.
Although this condition is generic. Nobody can stop this. If anybody consume balanced diet forever and massage mustard oil once in a week then this can be beneficial.
I have a good remedy for healthy and black hairs. 60 grams of henna to be boiled in 250 ml of mustard oil until the color of henna turn to black. Then filter this oil and fill in bottle. Apply this oil at night and wash your hairs in early morning.
This is the effective remedy for black hairs.