Nutritional deficiencies:

Inadequate Nutrition:  Nutritional deficiencies are almost never a cause of hair loss.  In situations where hair loss is in fact the result of a nutritional deficiency, many other far more serious symptoms are usually evident as well.  Nutritional treatments for hair loss are only effective in the rare situations where a nutritional deficiency actually exists.

Anorexia:  Severe malnutrition can cause Telogen effluvium, where a high proportion of hair follicles stop their growth cycle to conserve energy, and make a transition into the resting phase.  Three to four months later hair is shed by the resting follicles.  Severe malnutrition is usually quite evident in a person, and hair loss is usually not he main concern.  Severe "fad" diets, and eating disorders such as anorexia nervosa, can produce forms of malnutrition and can also trigger Telogen effluvium hair loss. Normal hair growth resumes with adequate nutrition.

Iron Deficiency:  A deficiency of iron in the diet results in a condition called anemia characterized by reduced amount of red blood cells, and can in some cases contribute to hair loss.  Anemic people generally appear pale and weak.  Women with heavy menstrual flows lose iron contained in their menses.  If their diets do not supply adequate iron to replace the iron lost each month, an iron deficiency and thinning hair can result.  Eating acidic foods cooked in cast iron cookware (such as tomato sauce prepared in a cast iron pot), increasing consumption of iron-containing nutritional supplements, usually restores normal hair growth in those suffering hair loss due to anemia.  Anemia is easily diagnosed with a laboratory blood test.