Here's some info:

Hair Loss

Some people may experience temporary hair loss while on any dieting and weight loss program. There are a variety of reasons.
Lack of protein and vitamin supplements can be the cause. The amount of supplements needed varies for each person. Most find that taking an essential fatty acid supplement or using at least 1 tsp of olive oil each day helps. There are many brands of essential fatty acid supplements on the market.

It's important to drink enough water each day and keep your body hydrated.

Stress and hormonal changes can trigger temporary hair loss. Your body could be showing signs of stress because it has been using food as a coping mechanism. Your body is learning how to deal with new habits and lifestyle changes and has triggered a normal response. There is also a small amount of estrogen produced in fatty tissue, some people experience hormonal changes with weight loss which can lead to hair loss. Both of these problems are temporary and will stop once your body has adjusted.

Getting enough sleep (but not too much) is important not only for your state of mind but for your body. A well rested body will react better to the stress of dieting.

It's normal to "shed" hair at certain times of the year. If you are also dieting during this time it can become quite noticable.

If you're still concerned, or experience any other symptoms besides the hair loss, please consult your physician.

Also, since hair cycles on and off, a shock like losing a lot of weight can make all the hair go into "lose it" mode at once. With more protein and fat in your diet, your hair should settle down and create new hair that's better (that's why it got rid of the old stuff.)