Although some types of hair loss are due to dietary issues, such as consuming too much vitamin A or not enough iron or protein, most are due to age, medications or health conditions. While onions can be a healthy part of your diet, they aren't likely to help you minimize hair loss or regrow lost hair.
Onions in Diet
Eating onions isn't likely to increase your hair growth or minimize hair loss. A medium onion does contain 14 percent of the daily value for vitamin C, which is important for forming the sebum and collagen that help keep your hair strong and moisturized, however.
Some people try a mix of onion juice and honey applied to their head in an effort to minimize hair loss. This was a treatment used in the Middle Ages for this purpose, but there isn't a lot of scientific evidence to back it up. A small study published in the Journal of Dermatology in June 2002 found that spreading onion juice on patchy areas caused by the autoimmune disease alopecia areata helped increase the regrowth of lost hair. Further research is necessary to verify this benefit and determine whether it would help with any other types of hair loss.