Diets, especially "crash" or "fad" diets, can lead to hair loss.

If you have been on a diet that does not include enough protein, iron, and other dietary requirements, your hair loss may be from poor nutrition. If you are eating a balanced diet, it is less likely that you have a nutritional deficiency.

In some situations, a nutritional deficiency is more likely. For example, the body needs only a very small amount of biotin. This is widely available in many foods. It is also produced by the natural bacteria in your intestine.

But there are foods and medicines that can keep biotin from doing its job. This can result in a deficiency. Raw eggs contain a substance called avidin. This makes biotin unavailable to the body. So any diet that includes eating raw eggs can lead to a biotin deficiency.

Antibiotics can destroy the healthy bacteria in your intestines that produce biotin. A very long treatment of antibiotics can decrease the body's supply of biotin, leading to a deficiency. And taking certain anticonvulsant drugs can increase the breakdown of biotin.

A more likely cause of hair loss with weight loss is "telogen effluvium." The stress to one's system from sudden or excessive weight loss can throw hair follicles into their resting phase. This is when many hairs are shed. Other stressors -- high fevers, childbirth, surgery -- can lead to telogen effluvium. This resting phase usually lasts two or three months. Hair growth returns to normal after that.

Because there are many causes of hair loss, it is important to see your doctor. The right treatment depends upon the correct diagnosis. If your doctor suspects a nutritional deficiency, tests can determine what you need to become balanced again.