What are the causes of hair loss?
A detailed answer is given in Hair loss causes. However to answer briefly, the interaction between the triad of, hereditary factors, male hormones, and age plays an important role in causing baldness in males. In females it is the change in the hormone levels at menopause, stress (both physical and mental), poor nutrition and ill health, which are responsible for hair loss. Damage to the follicles caused by injury, burns etc, certain medications can also lead to hair loss.

Is diet linked to hair loss?
Excess or deficiency of any kind will affect the system and thereby affect the hair follicle. Including fresh fruits, leafy vegetables, sprouts and cutting down oil and refined sugar will go a long way in tackling hair loss. Crash dieting is one of the major reasons for accelerated hair fall in females.

Eating a balanced diet is essential for maintaining good hair health and also your overall body health. According to nutritionists, people who have nutritional deficiencies in their diet have dull and stringy hair and can at times even suffer from a temporary case of hair loss. Hair loss caused due to dietary deficiencies is usually temporary and different from the pattern hair loss which is progressive and permanent.

A diet, which is very low in calories, can affect your hair. Eating too much of only certain food groups and eliminating others from your diet, can also cause hair loss. Studies have shown that a deficiency of Zinc can severely affect your hair and cause it to fall. Zinc is present in meat, seafood, and eggs; so you should try and incorporate these in your diet. For vegetarians, a zinc supplement may help.

Hair, to remain healthy, needs essential fatty acids. The omega-3 fatty acids provide the hair follicles with the nutrients necessary for good health and to keep the hair and scalp from drying up. If the hair follicle will not get its share of these fatty acids, it becomes weak and this results in hair loss and thinning of hair. Thus a diet, which all but eliminates fat, is not good for the hair. Omega-3 fatty acids are present in mackerel, salmon, flaxseed oil, macadamia nuts, and walnuts.

Another constituent of the Vitamin B complex, known as Biotin, is very essential for healthy hair. A deficiency of biotin is known to cause hair loss. Any foods which give you a good amount of protein such as meat, eggs etc, should take care of your biotin requirements for preventing temporary hair loss. Vegetarians can take milk products, cereals, cottage cheese, and tofu to increase their protein and biotin intake.

Hence, from all the above, it can be seen that people who have a poor diet or eating disorders such as anorexia and bulimia, are at an increased risk of temporary hair loss due to nutritional deficiencies that weaken their hair shafts and follicles. Thus it is important to have a proper diet. A healthy and balanced diet will definitely help in improving your hair condition as well as stop it from falling due to any diet related deficiency.

Nutritional deficiencies (or as you put it, restrictive diet) can cause hair loss. In addition, this may trigger a stress response and turn on a gene that may kick start your male pattern hair loss. Unfortunately, after the process has started it is difficult to stop the progression of hair loss.

Is there a link between smoking and hair loss?
Article in British Medical Journal BMJ says that there is a definite link between smoking and hair loss.

Which medications are responsible for hair loss?
The following is the list of drugs which may lead to hair loss usually with long-term use: