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Teen girls inspired by the web to become vegans are risking brittle bones, mood swings and poor brain function, experts have warned.

Doctors and nutritionists have called for youngsters to eat carefully and not attempt a vegan diet without seeking advice from their doctor.

“When someone cuts any type of food from their diet, unless they make sure they replace the nutrients of that food group, they’re at risk of nutritional deficiency,” dietician Sioned Quirke said.

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“The main concern with teenage girls is that they do have some quite specific requirements because they are still growing and need protein.

“They require higher levels of iron than boys and need a good balance of iron and minerals.”

Must replace nutrients

The National Diet and Nutrition Survey found last year that more than half of girls aged 11-18 lack magnesium. This can threaten their immune systems.

One in five lack vitamin B2, risking fatigue and anaemia, while iron levels are too low in 45% of girls.

Ms Quirke confirmed that issues such as brittle bones, mood swings and poor brain function can be risks to teenage girls when becoming vegan.

She said: “A vegan diet does tend to be relatively restrictive.

“If they go on a vegan diet, which is fine, they need to make sure they are 100% replacing all the nutrients.”

Parents must intervene

This can be difficult for a teen juggling school and a busy social life.

“It is difficult for an adult to do,” Ms Quirke said.

“They might not be 100% aware of the problems that can occur.

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“If they are still in school they might have a narrow choice of foods available at lunchtime unless they take food into school.

“The majority of teens still live at home so parents need to intervene to make sure they are OK.”

'Clean eating' is fashionable

Some doctors have treated teen vegans for vitamin B12 deficiency and anaemia.

Patients have walked into surgeries feeling unwell because they are surviving on pasta.

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Others have been left wiped out after catching infections because they have low trace elements – vital dietary components.

So called “clean eating” has proved fashionable with some teenagers.

'Not knocking vegans'

On Instagram more than 22 million pictures have been marked “#eatclean.”

But North Wales GP Dr White said: “You need to be selective about what you look at.”

He recommended people use websites like NHS Direct for advice.

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Dr White insisted he was “not knocking vegans.”

“But we were meant to eat a bit of meat,” he said.

“We are designed to have a mixed diet. All our immune systems are there for that.”

Seek guidance, says vegan Sophie

Financial administrator Sophie Tolputt, 36, became a vegetarian in her teens before becoming a vegan later.

“Seek proper nutritional advice,” she said.

“Try and find yourself a doctor who is open minded who can refer you to a nutritionist who is experienced and has expertise.

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“Always seek guidance. Thirteen-year-olds think they know everything. But they know very little in the grand scheme of things.

“They should not rely on search engines because there is a lot of misinformation out there about a lot of things.

“See if there are any cookery schools, or any local chefs, who hold cookery classes from their restaurants.

“The vegan ethos is a bit more user friendly than going to a Michelin starred restaurant. Vegans are a lot more down to earth, and if someone is interested in following that way of life, they are willing to help people get on board.”