(WCCO)

Just last year, Annick Alexander was 100 pounds heavier. As she thinned out, so did her hair.

"Every time I was taking a shower or brushing my hair, I would pay close attention to if I would lose any hair," Alexander said.

It's a little known secret, but experts say dieting can cause hair loss. Dermatologists say they're seeing more and more dieters with thinning tresses, whether they've lost 9 pounds or 90.

Dr. Michael Reed, a dermatologist, says it's a problem that's hard for people to digest.

"I see patients all day long, quite hysterical, who suddenly notice or gradually notice that too much hair is coming out," Reed said.

Someone can lose 300 to 400 hairs a day if he or she isn't careful, and that adds up over time.

"It can cause half the hair to be lost on the head," Reed said.

It can happen with all kinds of diets -- whether it's a fad diet or a vegetarian diet; whether someone restricts carbs or loads up on them.

"It can even happen when people lose weight gradually," Reed said.

It can also happen when someone loses weight rapidly, such as Annick Alexander. She was warned her gastric bypass would cause hair loss, but said it was still scary to see.

"At one point a friend approached me and said, 'Your hair's thinning out,' and I was like, 'Oh my God, other people are noticing it, too!'" Alexander said.

Reed said so many dieters are losing their locks because hair is sensitive and needs nutrients such as protein and iron.

"Hair also needs essential B vitamins," Reed said. "It also needs essential fatty acids, and it also needs adequate minerals in order to grow properly."

"Hair will be shocked" if someone doesn't eat a balanced diet and exercise daily, Reed said. "It will go into a resting phase, and it will come out prematurely."

Elisa Zied, a nutritionist with the American Dietetic Association, said a healthy weight loss plan is the key to happy hair.

"One that incorporates small portions of all the key food groups," Zied said. "We're talking about whole grains, fruits, vegetables, lean protein sources."

Fish is also important. Zied said it's a great source of omega-3 fats and protein.

"Those are two nutrients that are very important for hair health," Zied said.

A basic multivitamin is also recommended. Reed said he likes to add one more supplement.

"We sometimes recommend biotin, which is a B vitamin that hair really likes," Reed said.

It may also help to jumpstart hair growth, but Reed says it will take at least six months to see results.

Annick Alexander had to cut her hair short and make some major diet changes. One year later, she says her hair is longer and stronger.

"Now I notice I take a shower, there's no hair in the sink or anything," Alexander said.

Exercise is also key to healthy hair, as it increases the flow of oxygen and nutrients to the skin.