Crash dieting can deprive your body (and hair) of required daily nutrients, such as protein, vitamins B12 and B6, iron, vitamins A, C, E, and necessary electrolytes. Without these important nutrients in your blood stream feeding the ravenous hair follicles, hair strands may become fragile, look lifeless, and even fall out.
The Process of Hair Loss
This type of hair loss associated with crash dieting is Telogen Effluvium. Your hair's growth cycle includes a prolonged growing phase, called anagen, and a much shorter resting phase named telogen. When the telogen phase of a follicle is completed, its hair strand falls out and a new one begins to grow.
As far as survival is concerned, hair is not a necessity. If your vital organs (liver, heart, kidneys) are deprived of nutrients, they do not think twice about borrowing energy from other tissues in your body, like hair follicles. If follicles lose energy their growth phase is interrupted, and too many hairs end up resting instead of growing. When the telogen stage hair falls out, as it is supposed to, the shocked follicle does not return to the anagen phase and replace what is lost.
Even when you return to eating normally, any damage done to the vital organs by the crash diet will be repaired by the body first. The hair follicles have to bide their time until that necessary work is done. This may prolong hair loss. It could take three months (or more) of good eating for the follicles to begin producing hair again.
Other Crash Issues
It is not just stopping food intake that can trigger follicle starvation. Using diet pills, depriving yourself of adequate sleep, and exercising in the extreme can also produce the right conditions for Telogen Effluvium. This is true for both men and women.
Your body also needs water and fat to create sebum, the oil that protects hair and scalp. Without sebum, hair strands become brittle, and their growth cycle may be disrupted. If a hair follicle is seriously compromised by dehydration, or prolonged inadequate nutrition, it may never produce hair again.
Your brain cells require twice the amount of energy, in the form of glucose, than the rest of your body. The brain also controls many body functions. If the brain does not get its daily requirement of glucose, it can turn off nonessential activities like oil production and hair growth, rerouting that energy as food for thought.
The Best Bet . . .
Telogen Effluvium usually results in thinning and shedding over the entire head, though it is possible to lose more hair on the top than sides and back. A person’s hairline usually does not recede. After the hair loss, it can take up to a year for hair to return to its original thickness.
The best bet is to avoid crash dieting. That includes diets that focus on one food, such as cabbage, or banana diets. Weight loss from crash dieting is seldom long lasting, anyway. It is best to plan ahead and choose a sensible diet. If you have only a few days to lose pounds for an event, you are better off wearing a suit or dress that already fits, than to shock your follicles into going on strike.