Hair is mostly composed of protein and also needs vitamins and minerals to grow. These nutrients are taken directly from the food that you eat.
If your diet is deficient in any minerals and vitamins it's your hair (and nails) that will suffer.
How does that work?
Well, your body has to prioritise where its resources go. Hair (and nails) come very low down in your body's list of priorities. Your body will give the nutrients and minerals available to the organs first (liver, kidney etc.) and to vital body functions like maintaining a heart beat, digestion and so on before hair and nails get a look in. I think that makes sense...
What should your diet be rich in to encourage healthy hair growth?
Proteins plus the vitamins and minerals that go into making protein, this includes:
- Vitamin E
- Vitamin D
- Vitamin B and
- Relatively smaller amounts of selenium, copper, zinc and magnesium
Can you just take a supplement to make up for a poor diet?
Supplements will not make up for an atrocious diet. That said, if you have a healthy diet and decided to take a vitamin supplement to make up for possible deficiencies, e.g. inadequate vitamin D from the sun in winter then a supplement will help.
It's very hard to have dietary deficiencies if you live in a developed country but companies that make vitamins will prey on any insecurity you might have and encourage you to buy them. Keep that in mind.
Personally, I do take vitamins sometimes but I don't take them religiously because I usually forget to.
Any other notes?
Yes - if you're on a diet and shed a lot of weight over a short period of time you may incur increased rates of hair loss. When your weight stabilizes this hair should grow back. Keep this in mind next time you want to take drastic measures to lose weight.
If you will be dieting it's important to choose the most nutritious foods within your calorie allowance to ensure you're getting the vitamins you need. 100 calories of raw, fresh carrots will do your hair a lot more good than 100 calories of chocolate.